In this process, cutting is carried out with a multi-cutting rotating tool in the shape of a disk - a circular saw. In circular saws, the saw can be in an upper or lower position relative to the workpiece (Fig. 24).
The cutting diameter D = 2R, mm (it is also the main characteristic of the tool - the diameter of the saw), in the process analysis is assumed to be the same for all teeth. The saw rotation speed p, min -1, is considered constant. Then the speed of the main movement v, m/s:
On average, the speed v when sawing with circular saws on machines is 40...80 (maximum 100...120) m/s.
The feed movement is usually applied to the workpiece. The mechanical feed speed v s in machine tools reaches 100 m/min or more.
Feed per saw revolution S 0 and per tooth S z mm, determined by the formulas
where z = πD/t 3 - number of saw teeth; t 3 - tooth pitch, mm.
A distinction is made between sawing with counter feed, when the projection of the speed vector of the main movement v on the direction of feed and the vector of the feed speed of the workpiece v s are directed towards each other, and with sawing along the way, when they coincide in direction.
When longitudinal sawing, passing feed is rarely used, since it can drag the wood into the saw, which leads to uneven feed speed, overloading the motors of the main movement and feed mechanisms, i.e. to an emergency situation. Climb feed is common when crosscutting with a stationary workpiece. In Fig. 24, a, b shows sawing with counter feed. Changing the direction of the vector v will correspond to the sawing pattern with a passing feed.
The trajectory of the main movement - rotation of the saw around an axis - is a circle of radius R on which the tops of the teeth are located. The trajectory of the feed movement of the workpiece (or the axis of rotation of the saw, if it is given a feed movement) is a straight line. The trajectory of the cutting movement - the movement of the top of the saw tooth relative to the wood being cut - is obtained as a result of the addition of two simultaneously occurring movements: the main and feed.
In all modern circular saws, the speed of the main movement v is many times higher than the feed speed v s, so the cutting speed vector v e differs little in magnitude and direction from the speed of the main movement. In calculations they are usually assumed to be equal, allowing for a slight error. The layer (see Fig. 24, b) is cut along the arc AB, which is called the arc of tooth contact with wood. Point A is the entry point, point B is the exit point of the tooth from the wood. Midpoint C bisects the arc of contact. The marked points correspond to the entry angle φin, exit angle φout and average angle φ avg, which are counted from the normal to the feed direction. Angle values φin And φout determined by distance h, saw radius R and cutting height t(Table 11).
Table 11. Calculation ratios φin And φout
The angle corresponding to the cutting arc or the length of the cut layer is called the contact angle φ contact:
Current angle φ , which determines the position of the tooth on the cutting arc, increases evenly, in proportion to time; therefore we can talk about the average angle φ avg, characterizing the sawing mode:
When longitudinal sawing, the angle φ avg will correspond to the average angle of meeting of the main cutting edge of the tooth with the wood fibers:
The length of the cut layer / is calculated as the length of the arc of contact
Where φ contact measured in degrees.
During the feeding process, two adjacent teeth form different surfaces of the bottom of the cut: one tooth - a surface with a trace of 1- 1 ", the second is a surface with a 2-2" trace. The distance between these surfaces in the feed direction is equal to S z. The normal distance - the kinematic thickness of the layer a - is different (Fig. 24, c). The current value of the kinematic thickness of the cut layer is calculated using the formula
Partial layer thickness values:
at the entry point
at the exit point
in the middle of the cutting arc (mid-thickness)
The average thickness is calculated by dividing the lateral surface area of the layer f c b for length:
Formulas (109), (110) give slightly different results, however, with sufficient accuracy for practice, we can equate the average chip thickness over the length of the cutting arc and the average chip thickness over the lateral surface area:
In a section passing through the axis of rotation of the saw (transverse), the geometry of the cut layer, as noted earlier, depends on the methods of widening the cut: the average thickness of the layer along the cross section in the middle of the contact arc
The width of the layer also depends on the method of widening the cut:
When longitudinal sawing, the main (short) cutting edge of the tooth cuts the wood fibers and forms the bottom of the cut, and the side cutting edges participate in the formation of the walls of the cut. This distribution of functions predetermines the requirements for the geometry of the saw teeth for longitudinal sawing: the short cutting edge must be moved forward in the direction of rotation relative to the front surface due to a positive angle γ . This will cut the fibers before they begin to separate at the front surface, thereby preventing unorganized fiber pullout.
With increased requirements for the quality of the cut surface, a positive rake angle must be created at the side cutting edges due to oblique sharpening along the front edge (γ side = φ 1). Since the teeth form two walls of the cut, oblique sharpening must be done through the tooth: even teeth - in one direction, odd teeth - in the other.
The kinematics of the sawing process determines the presence of systematic irregularities on the cut surface - marks left by the teeth (see Fig. 24, d). You can calculate the height of kinematic irregularities y, for example for a saw with set teeth. From the geometric relationships it follows that = 2a tan λ р, where a is the thickness of the cut layer; λ р - angle of separation.
Can be measured directly on the saw tgλ p = b 1 /h p ; b 1 иh p = 0.5h 3 .
To assess surface roughness using the R m max parameter, it is necessary to calculate the largest value of kinematic irregularities ymax:
Calculations of R m max using formula (114) give an underestimated result (sometimes by several times). This is explained by the fact that when sawing on a machine, the roughness of the cut surface is additionally influenced by inaccuracies in the widening of the teeth, contact with the teeth of the non-working zone of the saw, elastic recovery of wood fibers and elastic bending of the teeth, blunting of the cutting edges and tips of the teeth, friction of chips against the walls of the cut, runout saw blade in the radial and transverse directions, vibration of the saw, displacement of the workpiece during sawing and many other reasons.
A fairly accurate forecast of the expected roughness of the cut surface can be obtained on the basis of experimental data, in which the height of the roughness R m max is related to the most important initial cutting conditions: the greatest thickness of the cut layer (through the parameters S z and φout) and the method of widening the cut.
In table 12 and 13 show the permissible feeds per tooth, ensuring the specified surface roughness .
Table 12. Maximum feed per tooth, mm, at different specified cut surface roughness for rip sawing with circular saws
| Height of unevenness Rmm ah, um, no more | Set teeth | Flattened teeth | Radial undercut teeth (planing) | ||||
| at exit angle φout, ° | |||||||
| 20 ...50 | 60...70 | 20 ...50 | 60...70 | 20...50 | 60... 70 | ||
| 1,2 | 1,2 | 1,8 | 1,5 | - | - | ||
| 1,0 | 0,8 | 1,5 | 1,2 | - | - | ||
| 0,8 | 0,5 | 1,2 | 0,75 | - | - | ||
| 0,3 | 0,1 | 0,45 | 0,15 | - | - | ||
| 0,1 | 0,1 | 0,15 | 0,15 | - | 0,3 | ||
| od | - | 0,15 | - | 0,3 | 0,15 | ||
| - | - | - | - | 0,15 | 0,07 | ||
| - | - | - | - | 0,07 | - | ||
Table 13. Maximum feed per tooth, mm, at different specified cut surface roughness for cross-cutting with circular saws
Note: Average production cutting conditions, sharp teeth.
When cross-cutting (Fig. 25), the working conditions of the cutting edges are different than during longitudinal sawing: the side edge cuts the fibers and forms the cut wall, and the short cutting edge and the front surface chop off the cut fibers, forming the bottom of the cut.
This determines the following requirements for tooth geometry. The side edge must cut the fibers before the front surface comes into contact with them. To do this, it must be moved forward along the saw blade relative to the short edge due to a negative (or zero) contour rake angle ( γ ≤ 0°) and have a positive rake angle γ side due to oblique sharpening. Typically, oblique sharpening is performed along the front and back surfaces of the tooth.
As a rule, to place chips in the tooth cavities, there is no need to limit the feed rate, calculated from the condition of ensuring the required roughness (see Table 13). For rip sawing, the groove tension coefficient σ = 2... 3, and for transverse σ = 20... 30 due to low feeds per tooth. This means that the conditions for placing chips in the cavities and transporting chips from the cut remain normal.
In practical calculations of energy consumption for the sawing process when designing the drive of circular saws, determining the force effects on the tool and machine elements, the average cyclic tangential force is calculated.
The average cyclic tangential force is a conditional constant tangential force F x c, which, acting on a path equal to the circumference of the saw 2 πR (one revolution is the cycle of the main movement), does the same work as the average tangential force on the tooth F xcp for one revolution of the saw:
where z is the number of saw teeth (for one revolution of the saw, each tooth will pass through the cut, doing work equal to F xcp l).
From the equality it follows
Where z r e f- the number of simultaneously cutting teeth (weighted average value, not rounded to whole units).
The average tangential force on a tooth F xcp is a conditional constant tangential force, which, acting along a path equal to the length of the cut layer l, does the same work as the actual variable tangential force along a path equal to the actual arc of contact of the cutter with the wood.
The force F xcp is related to the midpoint of the contact arc C (see Fig. 24, b), the position of which determines the angle φ avg. Its value is calculated using the formula
where F xT is the tabulated value of the tangential force for the process of longitudinal sawing with a circular saw, taken for the thickness of the cut layer a cf at the midpoint of the contact arc, N/mm (Table 14); b - width of the cut layer, mm; and popr- general correction factor, taking into account the difference between the calculated cutting conditions and the tabulated ones.
Table 14. Tabular shear force F xT and specific work K t for rip sawing with a circular saw
| A avg, mm | F x t, N/mm | K t, J/cm 3 | A avg, mm | FxT, N/mm | K t, J/cm 3 |
| 0,10 | 9,5 | 0,50 | 23,8 | 47,5 | |
| 0,15 | 12,0 | 0,60 | 26,4 | 44,0 | |
| 0,20 | 14,2 | 0,80 | 31,2 | 39,0 | |
| 0,25 | 16,0 | 1,00 | 36,0 | 36,0 | |
| 0,30 | 18,0 | 1,20 | 40,8 | 34,0 | |
| 0,35 | 19,3 | 1,40 | 44,8 | 32,0 | |
| 0,40 | 21,0 | 52,5 | 1,60 | 48,8 | 30,5 |
| 0,45 | 22,5 | 50,0 | 2,00 | 56,0 | 28,0 |
Note: Pine, W = 10... 15%; t = 50 mm, φ in = 60°; V = 40 m/s; the teeth are sharp; δ = 60°.
Maximum tangential force
where a tah = aout is the maximum layer thickness (near the exit point); and cf is the average layer thickness.
Maximum normal force
Using the average cyclic force, the cutting power P p, W is calculated:
Cutting power can also be calculated using the volumetric formula
where K T is the tabulated value of the specific work of longitudinal sawing with a circular saw (see Table 14), J/cm 3 ; and popr- general correction factor, taking into account the difference between the calculated conditions and the tabulated ones.
Highest feed speed v s (р) , permissible under the condition of full use of the given cutting power P r, is calculated using the converted volumetric formula
According to the table 14 find the value of the average thickness of the cut layer a cf, corresponding to the calculated tabulated force F XT. Then, using a cf sequentially in accordance with formulas (112), (111), (101), determine and middle, S z. v s.
When transverse cutting, the calculation of cutting forces is more difficult. The average punitive force on the tooth F xcp is calculated through the tabulated tangential force F XT (Table 15), related to the unit of cut width, and not the actual cut layer, and selected depending on the kinematic, and not the cross-sectional average thickness of the chip in the middle of the contact arc:
The same table shows tabulated values of the specific work of cross-cutting K T.
Table 15. Tabular shear force F T and specific work KT for cross-cutting wood with a circular saw
| A middle = S z sin j avg mm | F xT , N/mm, for cutting width B etc, mm | K t, J/cm 3, for cutting width B etc, mm | ||||||
| 1,5 | 2,5 | 3,5 | 5,0 | 1,5 | 2,5 | 3,5 | 5,0 | |
| 0,01 | 1,25 | 1,05 | 0,90 | 0,75 | ||||
| 0,02 | 2,14 | 1,84 | 1,56 | 1,24 | ||||
| 0,03 | 2,94 | 2,52 | 2,10 | 1,65 | ||||
| 0,04 | 3,76 | 3,16 | 2,60 | 1,96 | ||||
| 0,05 | 4,50 | 3,75 | 3,05 | 2,25 | ||||
| 0,075 | 6,45 | 5,25 | 4,15 | 2,85 | ||||
| 0,10 | 8,30 | 6,70 | 5,20 | 3,50 | ||||
| 0,15 | 12,30 | 9,60 | 7,50 | 4,95 | ||||
| 0,20 | 16,20 | 12,20 | 9,80 | 6,40 |
Note: Pine, W = 15%, sharp teeth.
Features of sawing wood materials. For sawing chipboards, the general nature of the dependence of the tangential and normal cutting forces and the roughness of the processed surface on the average thickness of the cut layer remains the same as for sawing wood. In table 16 shows approximate data for sawing chipboard with a circular saw.
Table 16. Table tangential force F xr and specific work K T for sawing chipboard with a circular saw
| a Wed, mm | Fxr, N/mm, with slab density, kg/m 3 | K T, J/cm 3, at slab density, kg/m 3 | ||||
| 0,2 | 1,6 | 2,5 | 3,3 | 78,6 | 123,0 | 167,0 |
| 0,4 | 2,2 | 3,4 | 4,7 | 54,4 | 85,0 | 117,0 |
| 0,6 | 2,6 | 4,1 | 5,6 | 43,5 | 68,0 | 92,5 |
| 0,8 | 3,0 | 4,6 | 6,3 | 37,1 | 58,0 | 78,9 |
| 1,0 | 3,4 | 5,3 | 7,2 | 33,9 | 53,0 | 72,0 |
| 1,2 | 3,9 | 6,1 | 8,3 | 32,7 | 51,0 | 69,4 |
| 1,4 | 4,5 | 7,1 | 9,6 | 32,4 | 50,6 | 68,9 |
| 1,6 | 5,2 | 8,1 | 11,0 | 32,2 | 50,4 | 68,5 |
| 1,8 | 5,8 | 9,0 | 12,3 | 32,1 | 50,2 | 68,2 |
| 2,0 | 6,4 | 10,0 | 13,6 | 32,0 | 50,0 | 68,0 |
| 2,2 | 7,0 | 11,0 | 14,9 | 31,9 | 49,8 | 67,8 |
Note: The amount of binder is 8%, the teeth are sharp, v = 40 m/s, V = 3 mm, V = 1.7 mm, φ av = 35 0.
The quality of sawing chipboard is characterized by the size of chips on the edge (measured along the face of the slab in the direction perpendicular to the plane of the cut) and the roughness of the cut surface (mainly the size of the fracture irregularities and hairiness).
Chips are a consequence of the detachment of the surface particles of the slab under the force of the teeth at the entrance to the material or at the exit from it. The amount of chipping can be minimized by correctly choosing the geometry of the saw teeth (the rake angle and the angle of the bevel sharpening), ensuring proper support along the face of the slab near the edge of the cut, and eliminating the possibility of working with a dull tool. The roughness of the cut surface largely depends on the average thickness of the cut layer (feed to the cutter). At the same time, the roughness indicators deteriorate with a decrease in the density of the slabs and the binder content.
To obtain satisfactory quality of the cut surface, the following feeds per saw tooth are recommended: 0.03... 0.05 mm for slabs with a density of 700 kg/m 3 and with a binder content of less than 8%; 0.05...0.1 mm for slabs with a density of 900 kg/m 3 and with a binder content of 8... 12%; 0.15...0.25 mm for slabs with a density of over 900 kg/m 3 and with a binder content of over 12%.
When sawing chipboards lined with decorative plastic, increased demands are placed on chipping along the cladding surface. The conditions for finishing sawing have been determined under which the length of the chips does not exceed 50 microns: a saw of minimum diameter with
teeth equipped with carbide plates, γ
= -10°, α
= 15°, β
= 70°, φ side < 13 мкм, v=
= 40... 50 m/s, S z< 0,03 мм. ДСтП, облицованные шпоном, можно распиливать поперек волокон облицовки теми же пилами при несколько большей подаче на зуб: S z ≤ 0,05 мм.
Wood laminated plastic chipboard-B is most often processed by sawing, in which every 1...2 parallel layers of veneer one layer is located at an angle of 90° to them.
The structure of the plastic (Fig. 26) predetermines the use of the following types of sawing: across the fibers 5 and along the fibers in the pressing direction 3, perpendicular to the pressing direction 1, parallel to the adhesive layers 4 and along the fibers with cutting them to the end 2. The amount of specific work and recommended cutting parameters Chipboards using a circular saw are given in table. 17 and 18.
Table 17 Specific work of sawing chipboard with a circular saw
Based on the type of side surfaces of the saw blade (cross-sectional shape), flat, conical and planing (with undercut side surfaces) circular saws are distinguished.
Flat saws. The design characteristics of saws are regulated by GOST 980 - 80 “Round flat saws for sawing wood” and GOST 9769-79 “Wood-cutting circular saws with hard alloy blades”.
Saws for sawing wood (Fig. 27) are made from 9HF steel of two types: A - for longitudinal sawing, B - for transverse sawing. When using saws in various woodworking industries, a wide variety of standard sizes is required. The diameter of the saws ranges from 125... 1600 mm, the thickness of the disc is 1.0... 5.5 mm, the number of teeth is 24... 72 for type A saws and 60... 120 for type B saws. The angles of the teeth are set taking into account the operating conditions of the main (short) and side tooth blades during longitudinal and transverse sawing.
Type A saws (see Fig. 27, b) for longitudinal sawing are available in two versions: version 1 - with a broken-linear back surface of the teeth and version 2 - with a straight back surface of the teeth. Type A saws, version 2, with a diameter of 125...250 mm with an increased number of teeth, are used mainly in electrified hand tools, on household woodworking and milling machines.
Type B saws (see Fig. 27, b) for cross-cutting also have two versions: version 3 - with a rake angle equal to zero, and version 4 - with a negative rake angle. Saws of version 3 are used on circular saws with a lower spindle position, and version 4 - on machines with an upper spindle position relative to the material being cut.
Angles of teeth of circular flat saws, °
Normal stable operation of a circular saw is possible only if the diameter and thickness of the disk, as well as the diameter of the washer securing the saw to the machine spindle, are selected correctly. The smallest diameter D min , mm, of the saw blade is determined by the thickness of the material being cut and the diameter of the flange for securing the saw to the spindle of the machine (for saws with the spindle located above and below the material being cut, respectively) according to the relations
where t is the cutting height, mm; d f - diameter of the clamping flange, mm; h 3 - the smallest exit of the saw from the cut, approximately equal to the height of the saw tooth, mm; h - the shortest distance from the saw axis to the machine table, mm.
Initial disk diameter D = D min + 2Δ, Where Δ - radius margin for wear, mm (Δ ≈ 25 mm).
The thickness of the saw blade, mm, is selected depending on the diameter:
Other dimensions of the tooth profiles are calculated using the formulas: tooth pitch t 3, mm, with disk thickness b, mm:
tooth height h 3, mm:
Number of teeth z, pcs.:
Vulture radius r, mm:
Circular saws are manufactured from alloy tool steel 9ХФ, HRC 3 40... 45 in accordance with the requirements of the standard according to approved technical documentation.
Flat saws with carbide blades. These saws (Fig. 28) are used for sawing wood materials (chipboard, fiberboard, laminated wood), as well as solid wood (GOST 9769-79).
The cutting plates of the saw teeth are made of a ceramic-metal alloy of tungsten carbide and cobalt VK6, VK15, and the saw body is made of tool alloy steel 50KhFA or 9KhF, HRC 3 40...45. According to their technological purpose, saws are divided into three types (Table 19).
Table 19. Dimensions and angles of teeth of circular flat saws with carbide inserts (see Fig. 28)
| Saw parameters | Types of saws | ||
| 1 - for cutting chipboard, plywood, fiberboard, sheet plastic and laminated wood | 2 - for longitudinal sawing of solid and laminated wood | 3 - for sawing lined panels across the grain | |
| Diameter D, mm Nominal cutting width IN pr, mm | 160...400 2,8...4,1 | 160...450 2,8...4,3 | 320...400 3,0...4,5 |
| Bore diameter | |||
| holes d, mm | 32...50 | 32... 80 | |
| Number of teeth z Angle, °: | 24...72 | 16...56 | 56...96 |
| front γ | 10; 5; 0 | 20; 10 | 20; 10 |
| sharpening β | 65; 70; 75 | 55; 65 | 55; 65 |
| rear α | |||
| cutting δ | 80; 85; 90 | 70; 80 | 70; 80 |
| oblique sharpening φ |
Circular (circular) conical saws. Conical saws (Fig. 29, a) are used for edge sawing of lumber into thin planks in order to reduce wood waste into sawdust (the width of the cut is almost half that when sawing with flat saws). The thickness of the sawn boards should not exceed 12... 18 mm, otherwise the saw will not be able to bend them to the side and it will jam in the cut. For asymmetrical sawing, one-sided conical saws (left- and right-conical) are used, for symmetrical sawing - double-sided.
Dimensions of one-sided bevel saws: diameter 500... 800 mm, thickness of the central part of the disk 3.4... 4.4 mm, thickness of teeth 1.0... 1.4 mm, number of teeth 100; diameter of the mounting hole is 50 mm. The saw teeth have a rake angle of 25° and a sharpening angle of 40°. Saw material - steel 9HF, HRC 3 41...46.
Circular (circular) planing saws. In planing saws, the side surfaces have an undercut from the periphery to the center at an angle of 0°15’ ... 0°45", as a result of which there is no need to widen the cutting rim by spreading or flattening the teeth.
The lateral cutting edges of the planing saw teeth, forming the cutting surfaces, are located in the same plane. A saw blade with an undercut is stable in operation, therefore the quality of sawing is characterized by small values of kinematic and vibration irregularities. The roughness of the cut surfaces is close to planed (hence the name of the saws).
Planing saws are used for finishing sawing dry wood with a moisture content of no more than 20% in any direction relative to the grain. Saw sizes and tooth profiles are standardized (GOST 18479-73). According to the cross-sectional shape, saws are distinguished between single-cone 4 and double-cone saws 5 (Fig. 29, b). The latter are provided for longitudinal and transverse 7 sawing.
In a planing saw, the mass of metal grows towards the periphery of the disk; with significant disk diameters and high rotation speeds, dangerous bursting stresses from centrifugal forces can arise in the disk. Therefore, the diameters of these saws do not exceed 400 mm (160...400 mm). Saw material - steel 9ХФ or 9Х5ВФ, HRC 3 51... 55.
Circular saws
TO category:
Woodworking machinery
Circular saws
Circular saws with a diameter of up to 800 mm and a thickness of up to 2.5 mm are used on circular saws. On formatting machines, in addition to saws, cutters are installed.
Depending on the profile, circular saws are divided into flat (Fig. 1, a, b), in which the thickness of the disk is the same throughout the entire cross-section, and into “undercut” saws, i.e., with a thickened peripheral part of the disk (Fig. 1, V). Saws with undercuts are called planing saws. Saws are also used, on the tips of the teeth of which hard alloy plates are soldered (Fig. 1, d).
Saws with hard alloy blades are widely used in the woodworking industry for processing furniture blanks, cutting and filing slabs, plywood, veneered panels, and for sawing solid and laminated wood. The durability of the teeth of such saws is 30 - 40 times higher than the durability of the teeth of saws made of alloy steel. The diameter of saws from resharpening decreases slightly. The width of the cut when sawing with a tool with carbide blades is slightly greater than the width of the cut obtained when sawing with conventional saws, but this (especially when cutting sheet materials) is not of great importance, in addition, the appropriate preparation of saws with carbide blades (grinding the side edges plates after soldering) allows you to obtain a high-quality cutting surface, which compensates for the loss of wood to sawdust.
Rice. 1. Circular saws: a - general view, b - profile of a flat saw, c - profile of a planing saw, d - saw tooth with a hard alloy plate
The outer diameter D of circular saws is the diameter of the circle drawn along the tops of the teeth. Each circular saw has an internal hole for mounting it on the saw shaft. The diameter of this hole is the internal diameter d of the saw blade and must match the diameter of the saw shaft. A gap of no more than 0.1 - 0.2 mm is allowed between the saw shaft and the hole.
The machine operator selects a saw depending on the material being processed. For example, when cutting particle boards and fibreboards, saws with carbide plates or fine teeth are used. For longitudinal cutting, saws with tooth profile I and II are used (Fig. 2, a), for transverse sawing, with profile III and IV (Fig. 2, b). The diameter of the circular saws is selected depending on the thickness of the material, and the profile - on the required roughness of the cut. So, if the surface is intended for gluing (for example, onto a smooth fugue), planing saws are used.
Rice. 2. Profiles of saw teeth a - for longitudinal sawing, b - for pepper sawing
Rice. 3. Checking the forging of circular saws: 1 - saw, 2 - ruler
You should use saws of the smallest diameter for these cutting conditions, as this allows you to reduce power consumption, reduce the width of the cut and the tooth set. Saws of small diameters are more stable in operation, provide better quality of the cut surface, their teeth are easier to sharpen, and saws are easier to edit.
The requirements that circular saws must meet are as follows:
1. The saw blade must be forged, that is, its central part must be somewhat weakened by hitting it with a hammer on both sides of a blade placed on an anvil. Flat saws with a diameter of 250 mm or more need to be forged. The correctness of forging is determined by using a straight edge, placing it on the disk in the direction of the radii (Fig. 3). There should be a gap between the ruler and the saw blade in its central part, which is the same for any position of the ruler. In case of poor forging, in one position of the ruler there is a gap between it and the disk, in another there is no gap or a bulge appears.
The amount of clearance characterizes the concavity of the saw and depends on its diameter and thickness.
The need to forge saws is explained by their working conditions. During the sawing process, the saw teeth, in contact with the wood, heat up and, if the middle of the saw is not weakened by forging, the saw blade becomes bent. If the curvature is significant (exceeds the boundaries of elastic deformations), then the shape of the disk is not restored even when it is cooled. With proper forging, the crown of a circular saw, when heated, slightly increases its size due to the weakened middle. This saw is stable in operation.
2. The teeth of a flat saw must be set apart, that is, their tips must be bent alternately: one tooth to the right, the neighboring one to the left. The amount of spread on one side is 0.3 - 0.5 mm. Saws designed for longitudinal sawing of dry wood and hardwood have a smaller offset; saws for sawing freshly cut coniferous and soft hardwood have a larger offset.
Setting the teeth can be replaced by flattening them. When flattening, the width of the teeth, which are shaped like a spatula, increases. Flattened teeth are more stable and less dull than set teeth; energy consumption when using them is reduced by 12-15%.
3. Saw teeth must be sharpened. Large burrs and tip curls are not allowed. The teeth of a crosscut saw should be beveled at an angle of 40° for soft wood, 60° for hard wood, and their tips should be at the same distance from each other and from the center of the blade.
4. Saws that have at least one broken tooth or cracks on the peripheral part of the blade are considered defective; install them on. the machine is prohibited.
Before installing the saw blade, thoroughly clean the washers and shaft journal with a rag or ends and check the supporting surfaces of the washers. If even minor protrusions are detected on the supporting surface, the washers are replaced.
If the diameter of the internal hole of the saw exceeds the diameter of the saw shaft by more than 0.1 - 0.2 mm, insert bushings should be used for precise installation of the saws. The saw is secured to the shaft using a washer and nut.
Round flat saws for cross-cutting with teeth set (Fig. 1, a, b) are used for preliminary trimming of parts, since high quality cutting is not required here. To secure it to the spindle, the saw has a mounting hole, the diameter d of which depends on the diameter of the disk D and the thickness of the saw b. The number of saw teeth should be 48, 60 or 72. The profile of the teeth for cross-cutting is shown in Fig. 1, b. The teeth must have a lateral oblique sharpening along the front and rear edges, as well as a negative front contour angle equal to minus 25°.
Rice. 4. Circular saws: a - general view, b, c - for cross cutting
In this case, the angle of sharpening of the side cutting edges of the tooth, measured in the normal section to the edges, should be 45° when sawing softwood and 55° when sawing hardwood. Circular saws with carbide inserts are used for cross cutting. Saw teeth are made with an inclined back surface, as shown in Fig. 4, f. Depending on the inclination, if you look at the tooth from the front, saws are distinguished, left-handed, right-handed, or with a symmetrical alternating inclination.
Solid steel rip saws are shown in Fig. 4, d. and with hard alloy plates - in Fig. 4, e. Circular saws for mixed sawing must have teeth whose front contour angle is 0° (Fig. 4, e).
If high cutting quality is required, planer saws with a negative rake angle are used (Fig. 4, g), as well as carbide saws with an alternating symmetrical inclination of the rear surface of the teeth.
Preparing round flat saws for work includes straightening, sharpening and setting the teeth. Saws after preparation for work must meet the following requirements. The number of teeth and their profile must correspond to the type of sawing. The saw blade must be flat. Deviation from flatness (warping, bulging, etc.) on each side of a disk with a diameter of up to 450 mm should be no more than 0.1 mm. The flatness of the saw is checked using a straight edge or a special device.
The required angular parameters of the teeth and the sharpness of the cutting edges must be ensured by sharpening. The sharpened teeth should not have shine at the corners formed by the intersection of the working edges of the cutter. Shine indicates that during sharpening an insufficient layer of metal was removed from the tooth. The difference in the size of the front angles and the sharpening angles is allowed no more than ±2°.
The roughness of the end surfaces of the saws and the surfaces of the mounting hole should be microns. The cutting teeth of a sharpened saw must be free of burrs, breaks and twists. Burrs from the side faces of the teeth are removed with a fine-grained grinding stone. The quality of saw sharpening is checked with a universal goniometer or a template for checking the angular elements of the teeth. The tops of the teeth should be located on the same circle with a deviation of no more than 0.15 mm. To align the gear rim in height and width, the saw teeth are planed, i.e. grind off the material from the tips of the most protruding teeth while rotating the saw at operating frequency.
After sharpening, the teeth of steel saws are set apart. In this case, the tips of adjacent teeth are bent in different directions by 1/3 of their height (counting from the top). The amount of bending of each tooth (set to one side) is set depending on the cutting mode and wood species. For cross-cutting with saws with a diameter of 500 mm, the side spread should be 0.3 mm for dry wood and 0.4 mm for wood with a moisture content of over 30%. The accuracy of the teeth set is controlled by an indicator gauge or a template. Permissible deviation ±0.05 mm.
Preparing for use of circular saws with carbide plates involves soldering the plates, sharpening and finishing the teeth. In addition, they must be balanced. Unbalanced discs due to their uneven thickness can cause loss of stability of the saw blade during operation, severe spindle runout and unsatisfactory cutting quality.
The strength of the soldering is checked by testing the saws by rotation at a peripheral speed of the teeth of at least 100 m/s. Sharpening and finishing of saws equipped with hard alloy plates is carried out on semi-automatic machines of increased accuracy and rigidity. Pre-sharpening is done with abrasive (carborundum) wheels, and finishing sharpening and finishing is done with diamond wheels.
Static balancing of saws is carried out using a special device. Disc imbalance is characterized by residual imbalance, which is equal to the product of the unbalanced mass and the amount of its displacement relative to the axis of rotation (eccentricity). The amount of residual imbalance depends on the diameter of the saw blade.
Types and sizes of saws.
The shape of the teeth of circular saws depends on the cutting direction and the hardness of the wood being cut. For longitudinal sawing, oblique teeth with a straight, broken (wolf tooth) and convex back are used; for cross cutting - isosceles (symmetrical), asymmetrical and rectangular.
Teeth with a broken and convex back are more stable than with a straight one, so saws with such teeth are used for sawing hardwood. Softwood and soft hardwood can be cut with saws that have straight-backed teeth. In Fig. Figure 31 shows a method for determining the tooth angles of a circular saw.
Rice. 5. Profiles of circular saw teeth: a - for longitudinal sawing; b - for cross cutting
When setting, the tops of the teeth are bent by 0.3-0.5 of their height. A break in the back of the wolf tooth is made from the top at a distance equal to 0.4 step sizes. Sharpening saw teeth for rip saws
sawing - straight continuous, for saws for cross-cutting - oblique through the tooth at an angle of 65 - 80° to the plane of the saw.
Planing saws are a special type of circular saws. They are used to obtain a clean cut that does not require planing.
The thickness of the planing circular saw from the toothed rim to the center along 2/3 of the radius gradually decreases at an angle of 8 - 15°. Therefore, the saw teeth do not move apart; The cutting edges of the teeth are the short front and side ones. The teeth of planing saws are grouped, or, as they say, cut with “scallops”. Each group (comb) has a large “working” tooth with a pointed angle of 45°. This tooth cuts wood. Behind the working tooth there are from 3 to 10 small teeth with a sharpening angle of 40°. The shape of the teeth on planer saws for longitudinal and transverse sawing is different.
Rice. 6. Determining the tooth angles of a circular saw
The industry produces planing saws with a diameter of 100 to 650 mm, and a tooth thickness of 1.7 to 3.8 mm. Planing saws for last years are becoming more and more widely used.
Rice. 7. Planing saws
Installation and fastening of circular saws. The circular saw is mounted on the working shaft using two clamping washers (flanges), one of which is usually machined together with the shaft; its clamping plane is strictly perpendicular to the shaft. The second washer is tightened with a nut in the direction opposite to the rotation of the saw, to prevent it from unscrewing during operation.
The washers should not protrude above the surface of the work table.
The nut must be fully tightened. A saw installed in the machine should produce a clear, ringing sound when lightly tapped.
The height of the cut when working with a circular saw is approximately equal to 1/3 of the diameter of the saw.
When choosing a saw, depending on the thickness of the material to be cut, you can be guided by the following ratios (dimensions in mm):
material thickness: 60 80 100 120 140 160 200 220 240 260 saw diameter: 200 250 300 350 400 450 500 600 650 700
Such ratios of the thickness of the material being cut and the diameter of the saw are correct when the material is pushed straight onto the saw or saws onto the material. If the saw is pushed onto the material in an arc, as, for example, in a pendulum saw, the diameter of the saw should be larger.
Requirements for circular saws and their care.
The saw blade must be well ground and free from cracks, bulges and burns. The teeth must be sharpened and evenly spaced; Burrs and burns are not allowed on them. The teeth of machine saws for longitudinal cutting are often riveted or flattened instead of being set, that is, their ends (tops) are widened by blows or pressure. For this purpose, special riveters and conditioners are used. Riveting and flattening of teeth is most often done with large round and wide band saws.
When working with a well-polished disc, the friction between the disc and the sawdust falling into the cut is reduced, so the disc heats up less.
If the disc becomes too hot, it may warp. Bulges form on it, which will quickly heat up, resulting in local tempering of the steel, causing so-called burns. These burns can be identified by their darker color, by applying a ruler to the saw, or by touch.
A saw with burns is not suitable for work; it must be straightened by forging.
Forging a circular saw is done on both sides on an anvil using a hand hammer. The parts of the disc surrounding the burn (bulge) are forged, not the burn itself. Forging begins from the areas most distant from the burn, gradually approaching it and gradually reducing the force of the blows. The straightened disc should be completely flat.
A circular saw often experiences stretching along the teeth, causing the stretched areas to become loose. Such a saw does not make a straight cut; it, as they say, “cuts.”
Stretching is eliminated by straightening, i.e., forging the saw in the middle annular part in the direction from the washers to the gear rim. This achieves some elongation of the middle annular part of the saw. The straightening is repeated from time to time. Straightening is done on a planed cast iron plate with a handbrake, selected by weight at the rate of 1 kg per 300 mm saw diameter.
If the saw has only one small crack, then in cases where it is impossible to replace it with a completely serviceable saw, a small hole is drilled at the end of the crack; This prevents the crack from increasing in length - you can continue working with such a saw. However, such a measure is always forced, temporary, and cannot be resorted to constantly.
The industry produces circular saws with balanced rotating parts. The saws are also balanced. However, in the future, the balance may be disturbed due to grinding of saws, due to the replacement of some machine parts (working shaft, washers, nuts).
The balance of the saws is checked on parallel horizontal balancing knives. The working shaft laid on the knives with the saw blade mounted on it is rotated by hand around the axis of rotation, stopping it in various positions around the circumference. If the shaft with the disk remains motionless in its given position during all such stops, then it is considered balanced. If the shaft makes some additional rotational movement, then this indicates that it is not sufficiently balanced.
Circular saws are multi-cutting tools that have the shape of a disk, sphere or cylinder. Sawing is carried out by the rotational movement of the tool during the translational movement of the material being processed or the saw together with its drive. Rotational motion is characterized by peripheral speed, which is conventionally called cutting speed, and translational motion is characterized by feed speed. The cutting speed in circular saws is always several times more speed submissions. The sawing process is only possible if both movements are present.
In order for circular saws to withstand the effects of cutting forces, inertia, heat and others that arise during sawing, they are made from high-quality alloy steels. The dimensions of the saw blade and teeth are given in GOSTs and technical specifications.
The cutting part of circular saws consists of teeth arranged around a circle. The shape of the teeth and their profile are determined by the cutting angles and the outlines of the rear and front edges between the tooth cavity.
Depending on the purpose of the saws, the profile of the teeth and their angular values vary. According to the type of sawing, circular saws are divided into saws for longitudinal, transverse and mixed sawing of wood and wood materials. They differ from each other in the profile of the teeth, cutting angles and the method of sharpening the teeth. The classification of circular saws is given in the diagram (Fig. 1.1).
Circular saws differ in the size of the saw blade (outer diameter, shape, profile of its cross-section, diameter of the center hole and thickness of the disk), size, number and profile of teeth. The cross sections and designs of various saws are shown in Fig. 1.2.
In production practice, saws with a flat disk having the same thickness over the entire cross-section, a conical disk, with an undercut, spherical and cylindrical are used. Some foreign companies produce conical saws with different sections of the saw blade (Fig. 1.2, b).
Attempts were made to use saws with a different saw blade design: three-layer, with an unhardened layer of metal in the middle, and on the outer surfaces layers of high-hardness alloy steel (54 - 56 HRC), as well as with a noise-absorbing layer, which was located in a small recess along the entire plane saw blade. Due to the complexity of operation, they have not received industrial distribution.
In recent years, the outer surfaces of circular saws began to be coated with a thin layer of anti-friction material - Teflon, which has a reduced coefficient of friction. The saw blade heats up less, which improves its stability in operation, however, the presence of this layer complicates the preparation of saw blades, and they are also not widely used.
The rake angle y is the angle between the radius of the saw and the front edge of the tooth; sharpening angle (3 - the angle between the front and rear edges of the tooth; rear angle a - the angle between the rear edge of the tooth and the tangent to the circle of rotation of the saw drawn from the top of the tooth (the tangent is perpendicular to the radius of the saw). Cutting angle 8 is formed by the front edge of the tooth and the tangent to the circle of rotation of the saw drawn from the top of the tooth.The cutting angle is equal to the sum of the tip angle and the relief angle:
The sum of all cutting angles (rake, back and tip angle) is always equal to 90°:
γ + β + α = 90°
For saws for longitudinal sawing of wood, the rake angle has a positive value and the cutting angle is less than 90° (Fig. 1.3, a-c), and for saws for cross-cutting, the rake angle can be zero and have a negative value.
Each saw tooth has two side (1 -2 and 1′-2′) and one short 1 -1′ cutting edges (Fig. 1.3, II). The short cutting edge is formed by the intersection of the front and rear surfaces of the tooth and is enclosed between the side planes of the saw; lateral - by the intersection of the front surface (1’, 2’, 2’, 1’) with the side planes of the saw.
The industry produces circular saws with a flat disk (steel, with hard alloy plates), with undercut (planing), conical, spherical, cylindrical. Steel saws are manufactured in accordance with the requirements of GOST 980-80 “Flat round saws for sawing wood. Technical conditions". It has 232 standard sizes of circular saws, of which 119 are for longitudinal and 113 for cross-cutting wood. The values of the stress state of saw blades are normalized. In GOST 980-63, 980-69, these values were linked to the most rational sawing modes of 40 - 60 m/s, which provide the lowest energy consumption for longitudinal sawing of wood and are most widely used in circular saws. GOST 980-80 does not have this link, which is its significant drawback.
Saws with hard alloy blades are manufactured in accordance with GOST 9769-79 “Circular saws with hard alloy blades for processing wood materials. Specifications" GOST establishes 115 standard sizes of saws for various purposes.
We produce circular saws: with flat discs in accordance with the requirements of GOST 980-80 from steel 9ХФ (according to GOST 5950-73); planing according to GOST 1 8479-73 from steel 9ХФ or 9Х5ВФ, with plates made of hard alloy according to GOST 9769-79 from steel 50ХФA (according to GOST 1 4959-79) or 9ХФ. The tensile strength of these steels is 1350 - 1500 N/mm 2.
Cutting saws (Fig. 1.4), in addition to sawing saws (7), have two rows of crusher teeth (8, 9), which crush the sawn edge. Each row has 12 teeth. The cutting teeth of the saw and the grinding teeth of the crusher are mounted in a special housing (10), secured to it with screws and a cover. The permissible imbalance is no more than 50 g x mm. Saws are preliminarily tested for strength at a rotation speed of at least 9000 rpm; permissible operating speed no more than 6000 min -1.
The design of a scoring saw is similar to that of a cutting saw, but the scoring saw does not have the grinding teeth of a crusher (Fig. 1.5). In this saw, 24 sawing teeth are mounted in the body, secured in it with screws (8) and a cover (1). The tips of the teeth are equipped with artificial diamonds. The design of the teeth of both saws is the same. The tooth body has a complex shape, made of 40X steel, and its tip has a widening, to which a cutting element made of artificial diamond is soldered with silver solder PSR-40 (GOST 19738-74).
Tests of saws have shown their high wear resistance. If in scoring and cutting operations a saw with blades made of hard alloy VK15 is operational for 2 – 3 weeks, then these saws are operational for up to 3 months. Due to the lack of saw blades, straightening and forging are not required. To ensure quality performance, these saws require careful installation of all cutting teeth and balancing once assembly is complete. When sharpening, the teeth are removed and sharpened in a special device with diamond wheels.
N. Yakunin
professor, candidate of technical sciences,
Honored Worker of the Forestry Industry,
Honorary Academician of the Russian Academy of Natural Sciences.
Flat blade saws are the most common and are widely used on most circular saws. The industry produces several types of circular saws for circular saws, which is explained by their different technological purposes. A circular saw (Fig. 98) consists of a body (thin disk) and a cutting part (gear). According to the shape of the disc in cross section, circular saws are divided into saws with a flat disc, conical and discs with a recess (undercut).
The steel used for the saw must have ductility that allows stamping and setting of teeth. The teeth of flat blade circular saws can be equipped with carbide inserts or overlays.
Rice. 98. Designs of circular saws:
a - general view; b - with a flat bottom; c - left-conical; g - right-conical; d - double-sided conical; e - planer with double-cone undercut; g - planer with single-cone undercut
The main design parameters of circular saws are: outer diameter D, bore diameter d, thickness b, number of teeth z.
The geometry of the cutting teeth of circular saws is characterized by linear and angular parameters. Linear parameters include: pitch and height of the teeth, rounding radius of the cavity, length of the rear edge.
Tooth pitch tз is the distance between the vertices of two adjacent teeth. Tooth height hz is the distance between the top and bottom of the tooth cavity, measured along the radius of the saw.
Depending on the type of sawing, the position of the saw and the direction of rotation, the profile of the teeth of the circular saws is selected.
Round flat saws for sawing wood are made of two types: 1 - for longitudinal sawing, 2 - for transverse sawing. Flat saws of type 1, execution 1 (Fig. 99 a) are used for longitudinal sawing of wood in circular saws with mechanized feed, and saws of execution 2 (Fig. 99 b) are used mainly for machines with manual feed and in electrified hand tools.
Rice. 99. Circular flat saws for sawing wood:
a, b - steel for longitudinal sawing; c, d - steel for cross cutting; d, f, g - with hard alloy plates for sawing wood materials;
Saws of type 2, version 1 (Fig. 99 c) are used for cross-cutting wood in machines with a lower saw shaft, and saws of execution 2 (Fig. 99 d) are used in machines with an upper saw shaft.
The industry produces a wide variety of standard sizes of cool saws. Their diameter ranges from 125 to 1500 mm, thickness from 1 to 5.5 mm, the number of teeth for type 1 saws can be 24, 36, 48, 60, 72; for type 2 saws - 36, 60, 72, 96 and 120. The diameter of the mounting hole is 32, 50 and 80 mm.
Normal stable operation of a circular saw is possible only with the correct choice of the diameter and thickness of the disk, as well as the diameter of the flange securing the saw to the machine spindle. The smallest diameter (mm) of the saw blade is calculated using the formulas:
for saws with overhead spindle
D = 2(H + 0.5d + h);
for saws with bottom spindle
D = 2(H + g + H)
where H is the height of the cut (mm), d is the diameter of the clamping flange (mm), g is the shortest distance from the saw axis to the surface of the machine table (mm), h is the smallest exit of the saw from the cut, approximately equal to the height of the saw tooth (mm).
Cool saws are made from 9XF tool steel.
The average durability of round flat saws between resharpenings is at least 90 minutes. when sawing coniferous and soft deciduous wood and 60 minutes when sawing hard deciduous wood.
Deviations for saws with a thickness of 1.2 to 3.4 mm are limited to ±0.07 mm, and for saws with a thickness of 3.8 mm or more - ±0.13 mm. The permissible difference in thickness for saws with a thickness from 1.2 mm to 3.4 mm is no more than 0.1 mm, and for saws with a thickness of 3.8 mm and above - no more than 0.15 mm. The centers of the saw and the hole for the shaft must coincide (eccentricity is permissible no more than 0.05 mm).
Flat circular (circular) saws with carbide plates are used primarily for sawing sheet and tile wood materials, lined slabs and panels, plywood, glued plywood, etc. solid wood.
The cutting plates of the saw teeth are made of a metal-ceramic alloy of tungsten carbide and cobalt VK 6, VK15, and the saw body is made of steel 50HFA or 9XF.
Saws with carbide plates are produced with a diameter of D = 100 - 450 mm; bore diameter d = 32, 50, 80 or 130 mm; number of teeth Z = 24, 36, 48, 56, 72. Thickness of the saw body B = 2 - 2.8 mm, thickness including hard alloy plates B = 2.8 - 4.1 mm.
Saws are made of two types: 1 - with an inclined rear surface; 2 - without tilt (see Fig. 99)
Circular (circular) planing saws - used for finishing cutting of dry wood (humidity no more than 20%) in any direction relative to the fibers. In planing saws, the side surfaces have an undercut from the periphery to the center, as a result of which there is no need to widen the cutting rim by spreading or flattening the teeth.
The lateral cutting edges of the planing saw teeth, forming the cutting surfaces, are located in the same plane.
Round (circular) conical saws - used for edge sawing of lumber into thin planks in order to reduce wood waste into sawdust (the cutting width of such saws is 1.7 - 2.7 mm, which is almost half as much as when sawing with flat saws). The thickness of the sawn boards should not exceed 12-18 mm, otherwise the disk will not be able to bend them to the side and the saw will jam in the cut.
It is not without reason that some people call a hole saw for wood an end mill - the material is processed in almost the same way, and the tools are similar in appearance. The equipment in question, although it leaves a lot of chips, allows, using a conventional power tool, to create clean through holes in the wood.
Hole saw for wood
The saw blade of such a saw is a cutting crown, the number and profile of the teeth of which depends on the strength and relative humidity of the wood. Most manufacturers of wood hole saws produce hole saws in sets, which allows you to use the tool for processing drywall and even metal.
The saw blade itself consists of two sections: the cutting head and the shank. For the manufacture of bimetallic cutting heads, which are intended for working on wood, high-quality tool steel type 11ХФ, ХГС or 9ХВГ is used, while the cutting bit for working on metal can also be made of carbide. The shank is made of hardened structural steel such as 45 or 40X steel, and is soldered to the cutting part with a high-resistant brass alloy. On the opposite side, the shank is equipped with a seat for an electric drill chuck. For conventional locking tools, the end part of the shank is hexagonal, and in new models it is integrated under the keyless chuck.
Since the process of processing wood with a hole saw produces a significant amount of chips, the design of the tool includes a spring, with the help of which the chips stuck between the teeth are removed out.
The technological parameters of the wood hole saw are:
- The height of the working part of the crown, which determines the depth of the volume of wood removed by the saw in one pass. By default it is standard and equal to 40 mm. Depending on the hardness and fiber of the wood, this makes it possible to obtain cavities up to 35...38 mm deep.
- The outer diameter of the cutting part of the crown. The sets include crowns ranging in size from 30 mm to 150 mm. Installation possibilities are determined by the engine power and the ability to regulate the speed: for hole saws for wood with a diameter of more than 110 mm, the speed of the drill must be reduced to a minimum, or a special stand must be used.
- The tooth profile, which depends on the material being processed and the operating principle of the nozzle. There are reversible saws that allow you to change the direction of their rotation. Such saws are more convenient for the master, since they make it possible to hold the drill while working with both the left and right hand. However, when working for a long time, they heat up more, and as a result, they begin not to cut the wood, but to tear off the surface layer from it, deteriorating the quality of the processing. The tooth profile of such saws has the shape of a triangle in plan, widening towards the base.
Features of operation
Due to the high area of contact between the saw and the wood, the tool becomes very hot during operation. Therefore, long-term non-stop operation of a drill with a hole saw on wood is impossible (unless, of course, you adapt an air or water cooling system).
Hole saws are often called stackable saws, which is explained by the composite design of the tool. For such equipment, the method of connecting the shank to the cutting part is very important. Possible options:
- Flat soldering. In this case, the wood hole saw will withstand the minimum possible shear loads, and it should be used for a short time, removing a minimum amount of material per pass. The diameter of the nozzles usually does not exceed 30 mm.
- Soldering with fitting of the shank into the seating part of the crown. The reliability of fixation increases, so such saws are produced with an increased diameter - up to 127 mm, and they can work longer.
- The same as in the previous case, but the shank additionally rests on the collar in the upper part of the bit. This option is implemented in the designs of hole saws with sizes ranging from 150 mm or more (saws with a diameter of up to 210 mm are known), since the thermal expansion of the material during operation of the saw will not cause deformation of the typesetting tool.
In practice, hole saws for wood are installed in special revolving-type cups, which, when rotated in a chuck, place a crown of the required diameter on the processing line. To ensure fixation, a union nut is used, and to center the hole being drilled, a drill, which is included in any kit, is used. The drill protrudes beyond the working surface of the teeth, and this guarantees the required alignment for obtaining a blind hole. However, this design requires changing the number of revolutions of the drill shaft: at the initial stage, when working with a drill, the required torque is small, so it is more rational to increase the number of revolutions. Then, when the teeth of a circular saw on wood come into action, the load increases sharply, so the number of revolutions of the drill is reduced.
- for pre-drilling – 1750…2000 min -1 ;
- to obtain a blind hole – 750…1000 min -1 ;
- for finishing the generatrix of the resulting hole, countersinking it and other similar operations - 1000...1500 min -1.
How to choose the right hole saw for wood?
Since significant shearing forces constantly arise when working with the tool in question, preference should be given to hole saws, the design of which includes solutions that ensure the necessary accuracy of work. Thus, the presence of centering pins made of hardened steel on the supporting surface of the shank provides additional centering of the crown. In this case, the height of the pin must be at least twice its diameter.
It is desirable that the kit includes an ejector spring, which facilitates the work when it is necessary to make blind holes in fibrous wood (ash, pear, hornbeam).
If in practice wood hole saws are intended to be used to produce blind holes with a diameter of more than 70...75 mm, additional threaded attachments that are secured with screws to the bottom of a glass with a set of crowns will be useful. The number of screws must be at least three, and it should be noted that the nozzles should be chosen from the same manufacturer. The diameter of the nozzle should not be too large (more than 45 mm), since in this case the inertia of the set as a whole increases, and the power of the drill may not be enough.
By the way, about power. Despite the fact that the material being processed is wood, the presence of chips and increased friction of the teeth against the walls of the hole create additional braking torque for the electric motor. This negatively affects the operating time and durability of the drive. Therefore, the minimum power of a drill for working with a hole saw on wood should not be less than 1000 W.