It’s no secret to milling specialists how to use a dividing head, but many people don’t even know what it is. It is a horizontal machine tool that is used on jig boring and milling machines. Its main purpose is to periodically rotate the workpiece, during which division into equal parts occurs. This operation is relevant when cutting teeth, milling, cutting grooves, and so on. With its help you can make gear teeth. This product is often used in tool and machine shops, where it helps to significantly expand the operating range of the machine. The workpiece is secured directly in the chuck, and if it turns out to be too long, then in a steady rest with emphasis on the tailstock.

Types of work performed

The UDG device allows you to provide:

• Precise milling of sprockets, even if the number of teeth and individual sections is several dozen;
• It is also used to produce bolts, nuts and other parts with edges;
• Milling of polyhedra;
• Grooving the depressions located between the teeth of the wheels;
• Grooving of cutting and drilling tools (for which continuous rotation is used to obtain a spiral groove);
• Processing the ends of multifaceted products.

Methods of performing work

The operation of the dividing head can be done in several ways, depending on the specific situation and what operation is being performed on what specific workpiece. Here it is worth highlighting the main ones that are most often used:

• Direct. This method carried out by rotating the dividing disk, which controls the movement of the workpiece. The intermediate mechanism is not involved. This method is relevant when using such types of dividing tools as optical and simplified. Universal dividing heads are used only with a frontal disk.
• Simple. With this method, counting is carried out from a stationary dividing disk. The division is created using a control handle, which is connected through a worm gear to the spindle on the device. With this method, those universal heads are used on which a dividing side disk is installed.
• Combined. The essence of this method is manifested in the fact that the rotation of the head itself is a kind of sum of the rotation of its handle, which rotates relative to the dividing disk, located motionless, and the disk, which rotates with the handle. This disk moves relative to the pin, which is located on the rear clamp of the dividing head.
• Differential. With this method, the spindle rotation appears as the sum of two rotations. The first refers to the handle rotating relative to the index disk. The second is the rotation of the disk itself, which is carried out forcibly from the spindle through the entire system gear wheels. For this method, universal dividing heads are used, which have a set of replaceable gears.
• Continuous. This method is relevant when milling spiral and helical grooves. It is produced on optical heads, which have a kinematic connection between the spindle and the feed screw to the milling machine, and universal ones.

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Design and principle of operation of the dividing head

To understand how the dividing head works, you need to know what it consists of. It is based on housing No. 4, which is fixed on the machine table. It also has a spindle No. 11, which is mounted on bearings No. 13, No. 10 and head No. 3. Worm #12 drives worm wheel #8. It is connected to flywheel No. 1. Handle No. 2 serves to secure the spindle, and therefore the worm wheel. It is connected to pressure washer No. 9. The worm wheel and worm can only rotate the spindle, and the error in their operation does not affect the overall accuracy.

One of the ends of the roller is seated in the eccentric bushing, which allows them to be lowered down together. If you disengage the spindle wheel and the worm, you can rotate the spindle head. Inside the case there is a glass disk No. 7, which is rigidly fixed to the spindle No. 11. The disk is lined with a 360 degree scale. Eyepiece No. 5 is located on top of the head. To turn the spindle the required number of degrees and minutes, a handwheel is used.

Work order

When the operation is performed directly, the worm gear is first disengaged from the hook, for which it is enough just to turn the control handle to the appropriate stop. After this, you should release the latch that stops the dial. The spindle is rotated from the chuck or from the part being processed, which allows you to place the device at the desired angle. The angle of rotation is determined using a vernier, which is located on the dial. The operation is completed by securing the spindle using a clamp.

When the operation is performed in a simple way, here you first need to fix the dividing disk in one position. Basic operations are performed using the locking handle. The rotation is calculated according to the holes made on the dividing disk. There is a special rod to fix the structure.

When the operation is performed in a differential manner, the first thing you need to do is check the smooth rotation of the gears that are installed on the head itself. After this, you should disable the disk stopper. The setup procedure here completely coincides with the setup order when in a simple way. Basic work operations are performed only with the spindle in a horizontal position.

Division table for dividing head

Number of division parts	Number of handle turns	Number of holes counted	Total holes
2	20
3	13	11	33
4	13	9	39
5	13	13	39
6	19
7	8
8	6	22	33
9	6	20	30
10	6	26	39
11	5	35	49
12	5	15	21
13	5
14	4	24	54
15	4
16	3	10	30
17	3	3	39
18	2	42	49
19	2	18	21
20	2	22	33
21	2	20	30
22	2	28	39

Calculation of the dividing head

The division into UDG is carried out not only according to tables, but also according to a special calculation that you can do yourself. This is not so difficult to do, since only a few data are used in the calculation. Here you need to multiply the diameter of the workpiece by a special factor. It is calculated by dividing 360 degrees by the number of division parts. Then you need to take the sine from this angle, which will be the coefficient that needs to be multiplied by the diameter to obtain the calculation.

UDG.Cutting gear teeth: Video

Cutting cylindrical gears on a milling machine using a universal dividing head (UDG)

1. Basic provisions

Table 1. Set of eight disc modular cutters

The profile of each cutter of the set is made according to the smallest number of teeth in the interval (for example, for cutter No. 2 at Z = 14), therefore, the greatest error is obtained when manufacturing wheels with the highest a large number teeth of each interval. In addition to the error associated with the inaccuracy of the instrument, there is always an error in the operation of the dividing head.

The copying method is used only in individual and sometimes small-scale production.

2. Setting up the machine

The gear blank is secured to the mandrel with a nut. The mandrel is clamped in a three-jaw chuck, which is screwed onto the spindle of the dividing head. The second end of the mandrel is supported by the tailstock (Fig. 2).

The corresponding modular disk cutter is mounted on the machine spindle mandrel and installed in the center of the workpiece. To do this, raise the table until the center of the workpiece mandrel is flush with the bottom of the cutter. Then the table is moved in the transverse direction until the center of the workpiece mandrel coincides with the top of the cutter tooth. After this, the table is lowered and the workpiece is brought under the cutter (longitudinal feed) so that a sheet of thin paper placed between them is bitten. After this, the workpiece is moved away from the cutter, giving the table a longitudinal feed, and the table is raised to the milling depth, counting along the dial.

Before you start cutting teeth, you need to check the setup and adjustment of the machine. Cutting modes – cutting speed and feed are found in tables for processing a given material.

The cutting depth is equal to the tooth height t = h.

3. Universal dividing heads

Dividing heads are important accessories for cantilever milling machines, especially universal ones, and are used when it is necessary to mill edges, grooves, splines, wheel teeth and tools located at a certain angle relative to each other. They can be used for simple and differential division.

To calculate the required angle of rotation of the spindle 1 of the dividing head (Fig. 4), and therefore the mandrel 7 with the workpiece 6 fixed on it, a dividing disk (dial) 4 is used, which has several rows of holes on both sides, located on concentric circles. The holes on the disk are intended for fixing handle A in certain positions using the locking rod 5.

Rice. 4. Kinematic diagram of the universal dividing head (UDG)

Transmission from the handle to the spindle of the dividing head is carried out via two kinematic chains.

During differential division, stopper 8 is released, securing the dial to the body of the dividing head, the worm pair 2, 3 is turned off, and when the handle with the dial is rotated, transmission to the spindle is carried out via the chain:

Where i cm is the gear ratio of the replaceable gears.

With simple division, the replaceable gears are disabled, the dial is stationary, the locking rod is recessed in the handle, when rotated, movement is transmitted to the spindle through a chain:

The characteristic of the dividing head N is the reciprocal of the gear ratio of the worm pair (usually N = 40).

3.1. Setting the dividing head for simple division

When setting the dividing head for simple division, the replaceable gears are removed and the equation of the kinematic adjustment chain has the following form:

,
where Z 0 is the number of divisions that need to be performed;

a – the number of holes on the concentric circle of dividing disk 4 corresponding to the calculation;
c – the number of holes to which handle A moves;
Z chk – number of teeth of the worm wheel;
K – number of worm passes.

From the equation it follows:

,

Where Z chk = 40; K = 1; Z 1 = Z 2, from here:

Attached to the dividing head (UDGD-160) is a dividing disk having seven concentric circles with holes on each side.

Number of dividing disk holes:

On one side - 16, 19, 23, 30, 33, 39 and 49;

On the other side - 17, 21, 29, 31, 37, 41 and 54.

The maximum diameter of the workpiece is 160 mm.

Setting example

Set up the dividing head for processing gear Z 0 =34:

.

Therefore, to implement this division it is necessary to make one full revolution of the handle and on a circle with the number of holes 17, turn the handle at an angle corresponding to 3+1 holes and fix it in this position.

To install the handle with a lock on the required circle of the dividing disk (Fig. 5), you need to loosen the clamping nut, turn the handle so that the lock rod falls into the hole in the circle, and re-fasten the nut.

To count divisions, use a sliding sector, consisting of two rulers 1 and 5, a clamping screw 3 for fastening them at the required angle, and a spring washer that keeps the sector from arbitrary rotation.

After determining the required circle on the dividing disk and the estimated number of holes to which the latch should be moved, the sector is set so that the number of holes between the rulers is one more than the number obtained by counting (positions 2 and 4), and it is turned immediately after moving the latch . The sector should remain in this position until the next division, and it should be brought to the hole smoothly and carefully so that the latch removed from the fuse enters the hole under the action of a spring.

If the handle is moved beyond the required hole, it is pulled back a quarter or half a turn and brought back to the corresponding hole. For accurate division, the handle with the lock should always be rotated in the same direction.

The number of turns of the handle for simple division is given in the appendix. 1, for differential division - in adj. 2.

3.2. Tooth size control

Having cut the first tooth, you need to measure its thickness with a caliper or caliper and the height of the tooth with a depth gauge.

Tooth thickness S = m a,

Where m is the gear module in mm;

A – correction factor (Table 2).

Table 2. Dependence of the correction factor on the number of teeth

This material is based on lectures from the Department of Materials Technology (MTM)

(Fig. 92) is the most common processing method, carried out on gear hobbing machines and provides 8...10 degrees of accuracy.

The support, with the cutter, has a translational movement along the axis of the workpiece from top to bottom (S prod) and rotational movement around its axis (V fr). The workpiece is mounted on the machine table and has a rotational movement (circular feed, S circle), as well as movement along with the table to set the cutter to the tooth depth. For one revolution of the cutter, the workpiece is rotated by a number of teeth equal to the number of passes of the hob cutter (i=1...3).

Rice. 92. Scheme for cutting a gear with a hob cutter

Single pass hobs are used for finishing processing of straight and helical teeth cylindrical wheels, complete cutting of wheels of small modules, rough milling for subsequent shaving, as well as for milling spur gears with a small number of teeth and large depth of cut.

Multi-pass hobs are used to increase productivity during rough gear hobbing, because they reduce processing accuracy.

When choosing a number cutter entries are guided by the following rule:

for an even number of workpiece teeth, a cutter with an odd number of passes is selected and vice versa,

those. the number of cuts of the cutter and the number of teeth of the ring gear should not be multiples. This is caused by the need to avoid copying the cutter error onto the ring gear.

After teeth milling multi-pass cutter, depending on the required accuracy and the presence of heat treatment, Cleaning recommended gear hobbing with a single pass cutter, gear shaving or gear grinding.

When milling multi-pass hob cutters performance does not increase in proportion to the number of cuts of the cutter.

While angular velocity the workpiece increases in proportion to the number of cuts of the cutter, then longitudinal feed two- and three-thread cutters are reduced, compared to milling with a single-thread cutter, by 30...40%.

When slicing cylindrical gear wheels with straight tooth In this way, the cutter is fixed in the machine support, which is rotated at an angle a equal to the helix angle of the cutter.

Rice. 157. Installation of a hob cutter when gear cutting cylindrical gears with an oblique tooth:

1 – right-hand cutter; 2 – blank of a right-hand gear; 3 – left-hand wheel blank

When slicing helical gear wheels, the angle of inclination of the cutter () depends on the angle of inclination of the teeth of the wheel being cut (Fig. 157):

If the direction of the helical lines on the wheel and the cutter coincide, then the angle () is equal to

= α – β , Where

β. - angle of inclination of the helix of the gear wheel on the pitch circle;

If the direction of the helical lines is different, then

= α + β.

When hobbing gears with tooth angle more than Hobs with a fence cone are used. The conical part of the cutter, the length of which is determined experimentally, is used for roughing, the cylindrical part, approximately 1.5 steps long, is used for the final formation of the tooth profile.

The main time when cutting spur teeth of cylindrical gears with a modular hob cutter is determined by the formula

l o – tooth length, mm;

m – number of simultaneously cut gears, pcs;

l вр – cutter penetration length, mm;

l per – cutter overrun length (2…3 mm);

z z.k – number of gear teeth;

i – number of moves (passes);

S pr.fr – longitudinal feed of the cutter per revolution of the gear wheel, mm/rev;

n fr – cutter rotation speed, rpm;

q – number of hob cutter passes.

Number of moves(passes) has a certain impact on the performance of the machining process and is set depending on the gear module.

At module less than 2.5 the gear wheel is cut in one stroke (pass), with a modulus more than 2.5 – in 2…3 moves(passage).

The amount of cutter penetration during gear cutting is determined by the formula

l time = (1.1…1.2), Where

t – depth of the cut cavity between the teeth, mm.

When using hob cutters plunging length (l r) can be significant, especially when using large diameter cutters.

Reduction in value penetration can be achieved by replacing the conventional, axial, cutter penetration with a radial one (Fig. 158).

Rice. 158. Insertion of a hob cutter: a – axial; b - radial

However with radial feed sharply the load on the teeth of the hob increases and therefore the radial infeed is taken to be significantly less than the axial one, namely

S glad ( ) S pr.fr. ,

and consequently, if double tooth height longer than the length of the axial plunge, then using radial feed is impractical.

To increase the accuracy of the gear cutting process, reduce the roughness of the machined tooth surface and increase the durability of the hob cutter, diagonal gear hobbing is used.

The essence of the process is that the hob cutter is moved along its axis during the cutting process at the rate of 0.2 microns per revolution.

Axial movement milling can be carried out:

After cutting a certain number of gears;

After each gear hobbing cycle during workpiece change;

Continuously during the operation of the cutter.

For this purpose, modern gear hobbing machines have special devices.

Duration period hob cutter by 10...30% can be increased by using down milling.

The feasibility of using up or down milling during gear processing is determined experimentally. For example, when processing workpieces made of cast iron, down milling has no advantages, but when milling workpieces from “sticky” materials, it allows reducing surface roughness. For gear processing with a module greater than 12, counter milling is preferable.

The following cutters are used for gear hobbing:

With unground profile, provide 9th degree of accuracy

With ground profile, provide 8th degree of accuracy

Backed, regrinding is carried out along the front surface and

Sharpened hob cutters, differing from the previous ones in a large number of teeth and regrinding along the back surface.

Gear processing modes:

V fr = 25…40 (150…200) m/min;

S pr.fr = 1…2 mm/ob.z.k (during roughing);

S pr.fr = 0.6…1.3 mm/ob.z.k (during finishing processing).

The minute feed of the cutter during gear hobbing is determined by the formula

S min =, mm/min

S tooth.fr - feed per cutter tooth, mm/tooth;

z fr - number of cutter teeth.

Relative performance various methods gear machining compared to gear hobbing with single-thread hobs made of high speed steel standard design is given in table. eleven.

If the size of this arc is taken as many times as there are teeth on the wheel, i.e. z times, then we also obtain the length of the initial circle; hence,

Π d = t z
from here
d = (t/Π)z

Step ratio t of a link to a number Π is called the module of the link, which is denoted by the letter m, i.e.

t / Π = m

The module is expressed in millimeters. Substituting this notation into the formula for d, we get.

d = mz
where
m = d/z

Therefore, the module can be called the length corresponding to the diameter of the initial circle per one tooth of the wheel. The diameter of the protrusions is equal to the diameter of the initial circle plus two heights of the tooth head (Fig. 517, b) i.e.

D e = d + 2h"

The height h" of the tooth head is taken equal to the module, i.e. h" = m.
Let's express it in terms of module right side formulas:

D e = mz + 2m = m (z + 2)
hence
m = D e: (z +2)

From fig. 517, b it is also clear that the diameter of the circle of the depressions is equal to the diameter of the initial circle minus two heights of the tooth stem, i.e.

D i= d - 2h"

The height h" of the tooth leg for cylindrical gears is taken equal to 1.25 modules: h" = 1.25m. Expressing the right-hand side of the formula for D in terms of the modulus i we get

D i= mz - 2 × 1.25m = mz - 2.5m
or
Di = m (z - 2.5m)

The entire tooth height h = h" + h" i.e.

h = 1m + 1.25m = 2.25m

Consequently, the height of the tooth head is related to the height of the tooth stem as 1: 1.25 or as 4: 5.

The tooth thickness s for unprocessed cast teeth is taken to be approximately equal to 1.53m, and for machined teeth (for example, milled) - equal to approximately half the pitch t engagement, i.e. 1.57m. Knowing that step t engagement is equal to the thickness s of the tooth plus the width s in the cavity (t = s + s in ) (step size t determined by the formula t/ Π = m or t = Πm), we conclude that the width of the cavity for wheels with cast raw teeth.

s in = 3.14m - 1.53m = 1.61m
A for wheels with machined teeth.
s in = 3.14m - 1.57m = 1.57m

The design of the rest of the wheel depends on the forces that the wheel experiences during operation, on the shape of the parts in contact with this wheel, etc. Detailed calculations of the dimensions of all elements of the gear wheel are given in the course “Machine Parts”. To perform a graphic representation of gears, the following approximate relationships between their elements can be accepted:

Rim thicknesse = t/2
Shaft hole diameter D in ≈ 1 / in D e
Hub diameter D cm = 2D in
Tooth length (i.e. thickness of the wheel ring gear) b = (2 ÷ 3) t
Disc thickness K = 1/3b
Hub length L=1.5D in: 2.5D in

The dimensions t 1 and b of the keyway are taken from table No. 26. After determining the numerical values ​​of the engagement module and the diameter of the hole for the shaft, it is necessary to coordinate the resulting dimensions with GOST 9563-60 (see table No. 42) for modules and for normal linear dimensions in accordance with GOST 6636-60 (table No. 43).

To cut the teeth of bevel gears with 7-8 degrees of accuracy (GOST 1.758-72), special gear cutting machines are required; if they are not available, bevel gears with straight and oblique teeth can be cut on a universal milling machine using a dividing head with disk modular cutters ; Of course, accuracy. processing with this method is lower (9-10th degree).

Blank 1 bevel gear is mounted on a mandrel in the spindle of the dividing head 2 (Fig. 9, A), which is rotated in a vertical plane until the forming cavity between the two teeth occupies horizontal position. The teeth are usually cut in three strokes and only in two strokes with small modules. During the first move, a cavity between teeth with a width of 2 (Fig. 9, b); the shape of the cutter corresponds to the shape of the cavity at its narrow end; the second pass is made modular

Rice. 9. Bevel gear hobbing:

c - installation of the workpiece on the mandrel; b - diagram of milling the cavity between

wubs; V - three workpieces at the same time; g - one workpiece with two disk

cutters; d- three workpieces with a special disk cutter

a cutter whose profile corresponds to the outer profile of the tooth, while turning the table with the dividing head at an angle:

Where b 1- the width of the cavity between the teeth at its wide end in mm;- the width of the cavity between the teeth at its narrow end in mm;- length of the depression in mm.

In this position, all left sides of the teeth are milled (platform 1 - Fig. 9, b). During the third stroke, all the right sides of the teeth are milled (platform 2), for which the dividing head is turned at the same angle, but in the opposite direction.

This method of cutting teeth is low-productive, and the processing accuracy corresponds to approximately 10th degree.

To cut straight teeth of precise bevel gears in serial and mass production, more productive machines are used - gear planing machines, on which the teeth are processed by the rolling-in method. When processing teeth with a modulus of more than 2.5, they are pre-cut with profile disk cutters using the dividing method; Thus, complex gear planing machines are not loaded with rough pre-cutting and are therefore better used for fine cutting.

In Fig. 9, V shows the preliminary milling of the teeth of three bevel gears simultaneously on a special or specialized machine used in large-scale and mass production. The machine is equipped with a device for automatic division and simultaneous rotation of all processed workpieces.

In large-scale and mass production, gear cutting machines are used to pre-cut the teeth of small bevel gears to simultaneously mill three workpieces with automatic division, stop, approach and retraction. In Fig. 9, d shows a diagram of the arrangement of spindles of a 3-spindle high-performance machine for simultaneous milling of teeth on three workpieces located around a special disk cutter.

The machine operator one by one places the workpieces on the mandrels of the working heads, moves the head all the way and turns on the self-propelled gun. All other movements are performed automatically: working feed, withdrawal of the cutting wheel and turning it by one tooth, the next approach, switching off when the other two heads continue to work.

The final finishing cutting of teeth with approximately 8th degree of accuracy is carried out by planing on gear planing machines (Fig. 10).

. These machines operate using the rolling method : two planing cutters (1 and 2) perform rectilinear reciprocating movements along the teeth of the workpiece being processed; during the reverse stroke, the cutters are slightly retracted from the surface being processed to reduce unnecessary wear of the cutting edge. Mutual rolling of the workpiece and cutters ensures an involute profile. The tooth cutting time, depending on the material, module, roughing allowance and other factors, ranges from 3.5 to 30 sec..