Why are gear disc milling cutters numbered in sections? How are they sectioned numbered?

Because the tooth shape curve of a gear is determined by the size of its base circle, and the base circle size is related to the gear's modulus, number of teeth, and tooth shape angle. Therefore, gears with the same modulus and tooth shape angle but different numbers of teeth should have different milling cutters. This would require the production of numerous cutters with different tooth shapes, which is not economical. To address this, the disc milling cutters for gears with the same modulus and tooth shape angle are segmented and numbered according to the number of teeth of the gears being machined. The tooth shape error produced by the same-numbered gear cutter for processing gears within the segment is permissible for gears that do not require high precision. This approach is more economical and practical, hence the necessity to differentiate disc milling cutters by number.

There are two methods for segmentally numbering standard gear disc milling cutters. When m equals 1 to 8mm, there are 8 cutters per set, numbered 1 to 8. When m equals 9 to 16mm, there are 15 cutters per set, numbered 1, 1.5, 2, 2.5, ..., up to 8.

2. The operation process of hobbing straight-cut cylindrical gears

The general operation process for cutting straight-crowned cylindrical gears is as follows:

Inspect the tooth blank's top circle size according to the pattern requirements.

(2) Install the indexing head, fixture, and align the workpiece. After performing the indexing calculation, adjust the indexing handle and indexing fork.

(3) Select and install milling cutters.

(4) Sharpen the blade using notching or scoring methods.

(5) Adjust machine tool cutting parameters and inspect the operation of the cutting fluid and cooling system.

(6) Mill very shallow grooves every 3 to 5 teeth on the blank, and check if the indexing calculation and adjustment are correct.

(7) Adjust the milling depth. Generally, the total tooth depth should be cut in two stages: rough and finish milling. After milling two tooth slots, measure the tooth thickness.

After all the gear slots have been milled, measure the gear thickness again, and then disassemble the workpiece for inspection.

What are the common measurement methods used after hobbing straight teeth cylindrical gears?

Three common measurement methods for cutting straight cylindrical gears are commonly used:

Measure the pitch circle chordal tooth thickness and pitch circle chordal tooth height of the gear using a gear caliper.

(2) Measure the fixed chord tooth thickness and fixed chord tooth height of the gear using a gear caliper.

(3) Measure the addendum length of the gear using a micrometer for the addendum length.

4. Comparison of characteristics of three commonly used measurement methods after hobbing straight-cut spur gears

Answer: (1) Measure the chordal thickness and chordal height of the pitch circle teeth. The characteristic is that when measuring the chordal thickness of the pitch circle teeth, the tooth tip circle should be used as the measurement reference. However, the accuracy requirement for the tooth tip circle during actual gear operation is not high, so the design and processing accuracy of the tooth tip circle is generally low, which affects the measurement accuracy of the chordal thickness.

(2) The measurement of fixed chord thickness and fixed chord height is characterized by the fact that the calculated values are only related to the modulus and tooth shape angle of the gear being measured, and not its number of teeth. Additionally, since the modulus and tooth shape angle of standard gears are standardized, the calculation process is quite convenient. However, when measuring the fixed chord thickness, the tooth top circle should also be used as the measurement reference, which can affect the measurement accuracy.

(3) The measurement of the addendum length is characterized by its simple measuring tools, ease of measurement, accuracy, and the manufacturing error of the addendum circle has no effect on the measured value of the addendum length.

In practical production, the latter two measurement methods are employed.

What are the main reasons for producing scrap when cutting straight-cut cylindrical gears?

The primary reasons for producing scrap during the hobbing of straight-cut cylindrical gears include:

(1) The issue of incorrect number of teeth and pattern is due to: not carefully examining the pattern; incorrect pitch calculation or incorrect adjustment of the pitch head.

(2) Unequal gear thickness or excessive pitch error is caused by: improper operation of the indexing head, where the indexing handle is rotated multiple times before returning to correct, without eliminating the indexing head worm gear clearance; and the workpiece is not properly aligned, resulting in excessive radial circular跳动.

(3) Incorrect tooth height and thickness are caused by: incorrect adjustment of milling depth, incorrect selection of milling cutter modulus, or incorrect selection of cutter number.

(4) The cause of misaligned gear teeth is: the milling cutter is not centered.

(5) The surface of the gear teeth is rough, primarily due to: dull milling cutters or excessive cutting depth; excessive runout after the cutter is mounted; poor workpiece clamping, with the machine tool and indexing head not properly tightened, resulting in vibration during cutting.

What is the equivalent number of teeth for an oblique cylindrical gear?

In response: Based on geometric principles, it can be determined that the intersection line between the normal plane at a certain point on the helical gear's tooth line and the pitch cylinder surface forms an ellipse. Using the major curvature radius of this ellipse as the pitch radius of an imaginary straight-sided cylindrical gear, and applying the normal module and normal tooth form angle of the helical gear as the module and tooth form angle of the imaginary straight-sided cylindrical gear, this imaginary gear is referred to as the equivalent gear of the said helical gear. The term "equivalent teeth of the helical gear" refers to the number of teeth on the equivalent gear of the helical gear.

Why Choose the Appropriate Tool Number Based on Equivalent齿 Numbers When Machining Helical Bevel Gear Teeth?

In the case of helical bevel gears, where the teeth have a spiral slot, when using a gear disk milling cutter, the worktable must be tilted at a helical angle to align the cutter's spiral plane with the direction of the gear's slot. This means the cutter's tooth shape should match the gear's normal tooth shape, which is equivalent to the tooth shape of the helical bevel gear's equivalent gear. Therefore, when machining helical bevel gears, the cutter number should be selected based on the number of teeth of the equivalent gear.

What are the two common methods for tool setting when machining helical cylindrical gears on a universal horizontal milling machine?

There are two common methods for tool setting. The first method is to set the tool before adjusting the worktable angle. This is typically done using the scribing or scoring technique. The second method is to set the tool after adjusting the worktable angle. Generally, the scoring technique is used to ensure the milling cutter's contour symmetry line is correctly aligned with the shaft center of the blank.

How to verify if the indexing wheel and worktable angle are correctly adjusted during the hobbing of helical cylindrical gears?

The inspection method involves lightly cutting on the gear blank after the tool has been checked, observing whether the width of the cutting mark matches the width of the milling cutter's blade edge. If the cutting mark is straight and the same width as the blade edge, it indicates that the indexing and worktable rotation angles are correct. Otherwise, it suggests that the indexing or worktable rotation angles are incorrect, and a recheck and correction are necessary.

Why can the 8-inch gear disc milling cutter with the same module be borrowed when cutting straight racks? Which method, the longitudinal displacement method or the lateral displacement method, is suitable for which occasions?

Because the teeth of the rack have a linear profile, which is similar to the tooth profile of a spur cylinder gear when the number of teeth approaches infinity, the profiles of the 8mm end mills are manufactured according to the linear profile. Therefore, an 8mm gear milling cutter of the same modulus can be used to mill straight racks.

Vertical displacement method is generally used for milling long racks, while horizontal displacement method is typically used for milling short racks.

When machining helical rack gears, what are the two methods of workpiece clamping to ensure the helix angle β? What are the applications of each method? Are there any differences in the displacement dimensions during machining using these two clamping methods?

An approach involves tilting the workpiece for clamping. After clamping, the workpiece's datum side forms an angle with the table's displacement direction, with the angle size being equal to the workpiece's helix angle β. Each displacement of the table should be equal to the normal pitch of the helical rack, pn. This method is suitable only for milling helical racks with small helix angles.

The second method involves clamping the workpiece's reference side parallel to the direction of the worktable's movement. Then, rotate the worktable to allow it to turn the workpiece together by a helical angle. When using this rotating worktable method to mill helical gears, the feed distance should be equal to the face pitch of the helical gear, pt, and is suitable for milling longer helical gears on a universal milling machine.