Shaving cutterDesign, Selection and Troubleshooting

A shaving cutter is a helical-gear-shaped finishing tool whose tooth flanks carry many serrations (grooves) that serve as cutting edges. It is meshed with a gear cut by a hob or pinion cutter at a crossed-axes angle, and the relative sliding along the helix direction removes a very thin layer from the tooth flank. In a short time it improves the accuracy and flank roughness of mass-produced gears before heat treatment, and applies profile modifications such as crowning.

Illustration: Shaving cutter — Illustration (not an exact drawing)

✎How to Design and Select

Conventional and diagonal shaving allow the cutter to be narrower than the gear; underpass and plunge cut need a cutter wider than the gear and serrations arranged in a staggered pattern (differential serrations). Machining time ratio, with plunge cut as 1: conventional 3, diagonal 2, underpass 2 (Mitsubishi Materials). Crossed-axes angle and traverse angle are drawn schematically.

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How it cuts (crossed-axes angle and sliding)

When the gear being cut and the shaving cutter are meshed at a fixed crossed-axes angle with no backlash and rotated, the serration edges cut the tooth flank through relative sliding along the helix direction. With a crossed-axes angle of 0, no cutting occurs^[1][2][3]
Each serration cutting edge crosses the gear tooth flank, with points on the cutter from root (a) to the meshing circle (b) to tip (c) tracing trochoid curves^[1]One source / reference
The cutter is driven by a motor and the workpiece (gear being cut) is driven along by meshing with the cutter. There is no mechanism to transmit rotation positively, so the workpiece profile is affected by fluctuation in meshing^[1][4][2]
Shaving can correct indexing (pitch), helix angle, profile and eccentricity errors. It removes 65–80% of the errors from hobbing or gear shaping, but the quality of the result depends greatly on the quality of the teeth from the previous operation (a process that makes good gears better)^[2][3]One source / reference
Features: short machining time and high productivity / large improvement in accuracy / low tool cost per gear / profile modification possible / easy crowning in the helix direction / no skill required^[1]One source / reference
For good shaving results, gear hardness should not exceed 30–32 Rc (finishing before heat treatment)^[2]One source / reference
Part names: outside diameter, pitch circle diameter, diameter of the relief hole centers, hub diameter, relief (recess) width, width, bore diameter, keyway. For the serrations on the tooth flank: serration depth, serration pitch, serration land width; the tooth root has drilled holes (relief holes)^[1]One source / reference
The serration grooves run the full tooth depth and open into relief holes (clearance) at the tooth root. The relief holes serve as a passage for cutting oil to flow and chips to leave, and also allow the serrations to be cut to a uniform depth^[2][5][1]

Choosing the crossed-axes angle (cutter helix angle)

Make the cutter's normal module and normal pressure angle the same as those of the gear being cut^[1][5]
The crossed-axes angle is roughly the difference between the helix angles of the cutter and the gear being cut. Choose the cutter helix angle so that the crossed-axes angle is most suitable^[1][5]
A larger crossed-axes angle improves cutting action but reduces the tooth contact area and lowers guidance (risk of helix error). A smaller angle increases the contact area and improves guidance, but lowers cutting action (the finished surface is burnished)^[1][2][3]
Suitable crossed-axes angle ranges (Mitsubishi Materials Table 2): spur and helical gears (other than cast iron) 12°–15° / spur and helical gears (cast iron) 15°–20° / stepped gears 4° and up (take the maximum that does not interfere with the stepped section) / large-diameter gears (outside diameter 500 or more) 6°–10° / internal gears 6°–10°^[1]One source / reference
In National Broach's explanation, the crossed-axes angle is usually 10°–15° (or roughly equal to the difference in helix angles), and the desirable range in cutter design is 5–15°^[2][5]One source / reference
Crossing the axes produces a nearly uniform oblique sliding from tip to root, which compensates for the uneven sliding peculiar to gears meshing on parallel axes while providing the shearing action needed for cutting^[2][3]One source / reference

Deciding the number of cutter teeth and nominal size

Decide the cutter's nominal size from the specifications of the shaving machine to be used and the dimensions of the gear being cut, then, considering the helix angle and module, choose the number of teeth so that the pitch circle diameter is close to the nominal size^[1][5]
The number of teeth of a shaving cutter should in principle be a prime number (Mitsubishi Materials). National Broach also says that the hunting tooth condition (a combination sharing no common divisor with the number of teeth of the gear being cut) and machine capacity are important factors in choosing the number of teeth^[1][5]
Commonly used numbers of cutter teeth: 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 113, 127, 131, 137, 149, 151, 157, 173, 179, 197 (of these, 71, 83, 101, 131, 151 and 173 are not included in JIS B4357)^[1]One source / reference
Standard dimensions of round shaving cutters (JIS B4357) are nominal sizes 175, 200, 225 and 300. Modules are 1.25–4 for size 175, 1.5–6 for size 200, 2–8 for size 225 and 4–12 for size 300. The pitch circle diameter is close to the nominal size, and widths are 19.05, 25.4 and 31.75^[1]One source / reference
Examples from the standard dimension table: size 175 m2 is z89, size 200 m3 is z67, size 225 m4 is z53, size 300 m6 is z47 (for the same nominal size, the larger the module, the fewer the teeth)^[1]One source / reference

Meshing pressure angle and contact ratio

With a gear having a low contact ratio, meshing fluctuation is large and the profile becomes unstable. Mitsubishi Materials calculates the expected profile from the balance of left and right flank cutting, fillet interference of the gear being cut, and cutting balance across the face width from the length of the contact line, and selects the optimum meshing pressure angle^[1]One source / reference
When the contact ratio is greater than 1 and less than 2, the contact point changes from 2 points to 1 point to 2 points as the gears rotate, and the profile changes easily with cutting conditions. When there is no phase shift between the contact points on the left and right flanks, the contact pressure is constant and, in theory, the profile has no waviness (optimum meshing condition)^[6][1]
The optimum meshing condition can be obtained at only one point in the progress of regrinding, so each company sets the optimum meshing near the new-cutter condition. In Yamaha Motor's case, the contact ratio was set to 2 or more, where the profile changes little, the degree of change in meshing pressure angle was kept below 0.3 (empirically), and the meshing pressure angle of a new cutter was set to the boundary value + 1.5° with tool life in mind^[6]One source / reference
The larger the module, the longer the cutting length and the greater the cutting load. The fewer the teeth, the shorter the contact length and the greater the meshing fluctuation. Both lead to vibration, and gear accuracy defects occurred in the region of large module and few teeth^[4]One source / reference

Cutter width

Cutter width for conventional shaving (Mitsubishi Materials Table 3): 19.05 for m ≤ 1.75, 25.4 for 1.75 < m ≤ 6, 31.75 for 6 < m^[1]One source / reference
Diagonal cutters are designed individually from the diagonal angle (formula (1)); underpass and plunge cut cutters are designed considering the face width of the gear being cut and the crossed-axes angle (formula (2)). Common cutter widths are 19.05, 22.225, 25.4, 31.75, 38.1, 44.45 and 50.8^[1]One source / reference
For underpass and plunge cut, make the cutter width wider than the face width of the gear being cut^[1][5]

Choosing a shaving method

The method is determined by the relative feed direction of the cutter and the gear being cut, and there are four: conventional, diagonal, underpass and plunge cut. Choose by the shape, size and production volume of the gear being cut^[1][5]
Conventional (axial): feeds in the gear axis direction, with a feed length about equal to the face width. The most common method, suited to gears with wide face widths and large gears. Cutting pressure is low, so it also suits shaft-type gears that deflect easily. Its drawback is the long machining time^[1][5][6]
For conventional, make the feed length about 1/16" longer than the workpiece face width to minimize overtravel at both ends (National Broach)^[5]One source / reference
Diagonal: feeds at an angle to the gear axis, with a feed length shorter than the face width. Suited to mass production of gears slightly wider than the cutter. The crossing point moves along the cutter width, so wear is spread out and life is longer, and machining time is up to 50% shorter than conventional^[1][5][2]
The diagonal traverse angle is often 30°–60°. The sum of traverse angle and crossed-axes angle should be up to about 55° unless differential serrations are used (beyond that the serrations track). With a wide-faced workpiece and a narrow cutter, the traverse angle has to be made small^[5]One source / reference
Underpass (tangential): feeds perpendicular to the gear axis, with a feed length shorter than the two methods above. Suited to stepped gears (gears with a shoulder). Requires differential serrations and a cutter wider than the workpiece^[1][5]
Plunge cut: no traverse; the cutter is only fed into the gear radially. Suited to high-efficiency machining of mass-produced gears. Requires differential serrations and a cutter wider than the workpiece. Cutting pressure is high, so profile accuracy is hard to achieve on low-rigidity workpieces^[1][5][6]
Machining time ratio (plunge cut = 1): conventional 3, diagonal 2, underpass 2, plunge cut 1^[1]One source / reference
Serration arrangement: conventional and diagonal use normal serrations; underpass and plunge cut use differential serrations (the serration cutting edges are staggered in the order of the teeth that mesh with one tooth of the gear being cut). Even with diagonal, differential is needed when the traverse angle exceeds 55°^[1][5][4]
Features of plunge cut (Mitsubishi Materials): no traverse, so machining time is about 1/2; a special serration arrangement improves flank roughness to 1/2 of the conventional; the cutting amount of each serration edge becomes uniform, which improves life. Because the feed marks fall midway between the previous ones, flank roughness improves (with conventional and diagonal, roughness does not change even if the number of finishing passes is increased)^[1]One source / reference
Plunge cut cycle: rapid traverse to the switching point → approach in forward rotation → plunge feed → infeed complete → dwell for T1 (removes irregularities in the finished surface) → reverse rotation and dwell for T2 → cutter retracts (back movement, retraction 0–0.05 mm) → dwell for T3 (removes distortion due to elastic deformation) → rapid return^[1]One source / reference

Shaving stock and pre-machining (shaving hob, protuberance)

Keep the accuracy of pre-machining (gear cutting) within 2–3 grades of the JIS gear accuracy standard relative to the accuracy wanted after shaving^[1]One source / reference
Recommended shaving stock (stock at the tooth thickness, Mitsubishi Materials Table 5): 0.05–0.08 for mn ≤ 2.25, 0.06–0.10 for 2.25 < mn ≤ 3.5, 0.08–0.12 for 3.5 < mn ≤ 5, 0.10–0.15 for 5 < mn ≤ 12^[1]One source / reference
The larger the feed of the pre-cutting hob (per workpiece revolution), the deeper the feed marks, so the optimum shaving stock is also larger (Fig. 15: modules 1–8, feed from 2 or less to 8 mm/work rev, 0.01–0.10 mm)^[1]One source / reference
The stock must be enough to remove the errors from pre-machining, but too much shortens cutter life and lowers finishing accuracy. Excess stock causes tooth flank damage, flank roughness and cutter breakage^[3][1]
National Broach's recommended shaving stock (per tooth side, inches): normal DP 2-4 is 0.0015-0.0020, 5-6 is 0.0012-0.0018, 7-10 is 0.0010-0.0015, 11-14 is 0.0008-0.0013, 16-18 is 0.0005-0.0010, 20-48 is 0.0003-0.0008, 52-72 is 0.0001-0.0003^[3]One source / reference
The pre-machining tool (pre-shave tool) should have a high addendum of 1.35 module or more. Select it so that there is a clearance of 0.15 module or more between the shaving cutter tip and the root of the gear being cut, and the cutter tip does not interfere with the root fillet of the gear being cut^[1]One source / reference
If the cutter tip hits the root fillet formed in pre-machining, the cutter wears abnormally and the accuracy of the involute profile also suffers. The fillet height must not exceed the lowest contact point between the cutter and the workpiece^[3][1]
Before shaving, a slight undercut (relief) is often put in the tooth root with a hob or pinion cutter that has a protuberance. This smooths the transition between the shaved profile and the unshaved root and also reduces wear on the cutter tip. Match the undercut amount to the thinner side of the tooth, and make the top of the undercut join the involute below the contact diameter^[3]One source / reference
National Broach's recommended undercut (total per tooth side, inches): DP 2-4 is 0.0025-0.0030, 5-6 is 0.0023-0.0028, 7-10 is 0.0015-0.0020, 11-14 is 0.0012-0.0017^[3]One source / reference
Remove completely any burrs left on the end faces of the gear being cut during pre-cutting. Burrs that jam in the serration grooves cause cutter breakage^[1][6]

Shaving diameter (cutter outside diameter) and trochoid diagram

Criteria for setting the shaving diameter: (1) smaller than the minimum meshing circle diameter with the mating gear (or involute start diameter: TIF diameter), and (2) larger than the fillet start diameter so as not to interfere with the root fillet of the pre-cut profile. Because (1) takes priority, (2) may not always be satisfied^[1][5]
The margins for (1) and (2) are judged from a trochoid diagram showing the trochoids (paths) of the shaving cutter and the tip of the mating gear. Drawing it requires the pre-machining tool shape, the shaving stock, and the number of teeth and outside diameter of the mating gear and the center distance to the gear being cut^[1]One source / reference
Regrinding the cutter gives it negative profile shift, so at the same shaving diameter the cutter's trochoid moves farther from the mating gear than from the work gear, and near end of life the cutter may interfere with the mating gear. If it does, progressively increase the shaving diameter (set a larger cutter outside diameter) to match the negative shift^[1]One source / reference

Profile modification (crowning and profile modification)

Shaving can apply profile modification and lead crowning. These modifications are used to prevent edge contact at the tooth ends, reduce noise, and raise load capacity and life^[1][2][3]
How crowning is applied depends on the method. Conventional shaving rocks the table with the machine's built-in crowning mechanism. For diagonal shaving, table rocking is fine if the sum of the traverse angle and crossed-axes angle is 55° or less; at larger traverse angles it is better to grind a reverse crown (hollow) into the cutter's lead. For plunge cut, grind a reverse crown (hollow) into the cutter's lead^[5][2][1]
The cutter profile is not necessarily a true involute. The cutter profile is often modified and ground to suit the profile or modification wanted on the work (specify "true" or "work-matched profile" when ordering)^[5][1]
The cutter profile and crown can be reground to compensate for heat-treat distortion. Lead change from heat treatment is compensated with the shaving machine settings^[2][3]One source / reference
When shaving internal gears, the crossed-axes geometry requires a slight crown on the cutter teeth to avoid interference with the work teeth. For internal gears with a face width over 3/4", apply crowning by rocking the work head; for 3/4" or less, or where interference limits the traverse and crossed-axes angles, plunge shave with a differential-serration cutter^[5]One source / reference

Serration patterns to reduce profile waviness and variation

Multi-pattern serrations (Mitsubishi Materials): the infeed in the lead direction of the work is made deliberately uneven to suppress vibration during machining, reducing periodic waviness in the profile and profile and lead variation within the same workpiece^[1]One source / reference
Fine-pitch serrations: the serrations are made at a fine pitch, which increases the number of cutting edges acting on the tooth flank and improves flank roughness^[1][7]
Unequal-land serrations (Mitsubishi Materials): the serration lands at the top and bottom of the profile (tip side and root side), where the generating line is short and meshing is unstable, are made narrower to improve cutting action and reduce variation between the upper, middle and lower profile^[1]One source / reference
Asymmetric serrations (Mitsubishi Materials): the high-pressure drive side over-cuts and loses accuracy, so the land width is made different on the drive and coast sides to even out stock removal and reduce left-right profile variation^[1]One source / reference

Cutting conditions and setup

Read the cutter peripheral speed Vc from a chart based on the work's tensile strength (machinability) and module (Mitsubishi Materials Fig. 8, vertical axis 60–120 m/min). Use a lower speed for larger modules and stronger materials^[1]One source / reference
Plunge cut reverses only once, so the peripheral speed can be 20% higher. If the gear ratio between cutter and work gear is large, the work gear's rotational speed becomes excessive, so lower the rotational speed somewhat^[1]One source / reference
National Broach's guideline is about 400 ft/min at the pitch circle (e.g., a 7-inch cutter on a 10-pitch gear with a 3-inch pitch diameter gives about 200 rpm). For gears where surface finish is the priority, such as aircraft and marine gears, reduce the feed^[5]One source / reference
Traverse feed rate: 0.15–0.3 mm per work gear revolution for conventional shaving, about 70% of that for diagonal, and about 50% for underpass^[1]One source / reference
For conventional, diagonal and underpass shaving, infeed is done in steps; set each infeed within 0.02–0.06 mm, taking the shaving stock into account. Plunge cut uses continuous infeed, cutting in about 0.007 mm in the tooth-thickness direction while the serration action advances one pitch^[1]One source / reference
Back movement (plunge cut): to correct elastic deflection of the work gear and arbor, the infeed is backed off so the final pass is made with little elastic deflection. The amount is generally 0–0.05 mm; too little or too much leaves a step in the lead direction, so adjust while checking the tooth flank^[1]One source / reference
Set the cutter rotation direction and the work gear's feed direction so the serration cutting edges act as up-cut. With the same pressing force, the penetration depth is much greater in up-cut, so machinability is better^[1]One source / reference
Design the arbor to hold the work gear near the tooth root close to the cutting point. This prevents chatter from cutting forces and the resulting loss of gear accuracy and cutter life^[1]One source / reference
Arbor accuracy: bore tolerance about H6–H7 relative to the arbor diameter, arbor runout 5 μm or less (Mitsubishi Materials). National Broach also requires the arbor and fixture locating surfaces to be within 0.0002" and spindle center runout within 0.0002"^[1][5]
Hold the work gear on the same locating surface used in the preceding process (hobbing, etc.) and measure from that same surface. The locating surface must be clean, and parallel and square to the bore^[5][3]One source / reference
The type and cleanliness of cutting oil directly affect cutter life and the finish of the shaved flanks. National Broach recommends a sulfurized oil with 3–3.5% sulfur for steel, with a viscosity of about 135 S.S.U. at 100°F, and says oil that is too thin causes chip scratches on the flank. Use a magnetic separator to reduce contamination^[2][6][1]

÷Formulas

Cutter rotational speed

Nc = 1000 × Vc / (π × dc)^[1][5]

Nc: Cutter rotational speed (min⁻¹)
Vc: Cutter peripheral speed (m/min). Obtain it from Mitsubishi Materials Figs. 8 and 9
dc: Cutter tip circle diameter (mm)

Work gear rotational speed

Gear rpm = Cutter rpm × No. of Teeth in Cutter / No. of Teeth in Gear^[5][2]1 source · reference

Gear rpm: Work gear rotational speed
Cutter rpm: Cutter rotational speed
No. of Teeth in Cutter: Number of cutter teeth
No. of Teeth in Gear: Number of teeth of the workpiece gear

Infeed per pass (conventional, diagonal, underpass)

H ≈ ts / 2sin αbn^[1]1 source · reference

H: Infeed per pass (toward the work gear center)
ts: Stock removed per shaving pass (normal span measurement)
αbn: Meshing pressure angle (normal)

Cutter face width for the diagonal method, Eq. (1)

bc ≥ bce + 5, bce = bg · sinθd / sin(θd + ψ)^[1]1 source · reference

bc: Cutter width
bce: Effective face width
bg: Work gear face width
ψ: Crossed-axes angle
θd: Diagonal angle (generally 30°)

Cutter face width for the plunge cut and underpass methods, Eq. (2)

bc ≥ (bg + 3 · tg · tanψ) cosψ + α^[1]1 source · reference

bc: Cutter width
bg: Work gear face width
tg: Transverse base pitch of the work gear
ψ: Crossed-axes angle
α: Decide according to the serration pattern and whether adjacent features are near the work gear (guideline 4–5)

Table feed for conventional shaving

Table Feed (ipm) = 0.010 × Gear Rpm^[2][5]1 source · reference

Table Feed: Table feed (in/min)
0.010: Starting point for feed per work gear revolution (in)
Gear Rpm: Work gear rotational speed

Table feed for diagonal shaving (effective feed 0.040 in/rev)

Rf = Sine Traverse Angle / Tangent Crossed Axes Angle + Cosine Traverse Angle, Table Traverse Rate (ipm) = 0.040 × Gear Rpm / Rf^[2][5]1 source · reference

Rf: Feed factor
Traverse Angle: Diagonal traverse angle
Crossed Axes Angle: Crossed-axes angle
0.040: Starting point for effective feed (the speed at which the crossing point travels over the work and cutter face widths), in/rev
Gear Rpm: Work gear rotational speed

Theoretical maximum traverse angle for diagonal shaving

Tangent Max. Traverse Angle = Cutter Face Width × Sine Crossed Axes Angle / (Gear Face − (Cutter Face × Cosine Crossed Axes Angle))^[2]1 source · reference

Cutter Face Width: Cutter width
Gear Face: Work gear face width
Crossed Axes Angle: Crossed-axes angle

Meshing frequency (for checking vibration)

Meshing frequency (Hz) = number of cutter teeth × cutter rpm ÷ 60^[4]1 source · reference

Number of cutter teeth: Number of teeth on the shaving cutter
Cutter rpm: rpm

Worked Example　Cutter 97 teeth × 165 rpm ÷ 60 s = 266 Hz. Its 3rd harmonic (800 Hz) matched the machine's resonant frequency, and the tooth-space runout varied periodically

⚠Troubleshooting

Open a symptom to see the possible causes and fixes. The causes are not necessarily to be suspected from the top down. They change with the combination of workpiece, machine and tool.

Scratches on the work flank (e.g., diagonal scratches along the machining marks)^[1][6]p.61

Main causes

Degraded or contaminated cutting oil (foreign matter)
Poor roughness on the cutter's involute flanks
Excessive shaving stock
Nicks on the work
Magnetized cutter
Unsuitable cutter design
Foreign matter entering the cutting point (secondary burrs from the preceding process, iron powder on the work, cleaning residue) is pressed onto the cutting edges and welds (adheres) to them
Regrinding has reduced the meshing pressure angle below the threshold value, so cutting ability has dropped

Fixes

Check and replace the cutting oil, and strengthen filtration and purification
Regrind the cutter (watch the spark-out)
Check and revise the pre-shave tooth thickness (set the shaving stock properly)
Handle the work carefully
Demagnetize the cutter
Make sure the burrs from the preceding process are fully removed (in Yamaha Motor's case, remaining burrs of 0.02 mm or less), and remove residue on the work by cleaning
Replace the cutter before the meshing pressure angle falls below the threshold value / redesign the cutter so the meshing pressure angle changes less
Ask the manufacturer to review the design

Poor work flank roughness^[1][2][7]p.61

Main causes

Degraded or unsuitable cutting oil
Excessive shaving stock
Shared cutter (plunge cut, underpass)
Tooth-space runout during cutter grinding
Fillet interference at the cutter tip
Unsuitable cutter design
With conventional and diagonal shaving, the feed marks are constant, so roughness does not change even if the number of finishing passes is increased

Fixes

Check and replace the cutting oil (avoid oil that is too thin)
Check and revise the pre-shave tooth thickness
Make the cutter a dedicated design
Check the cutter's tooth-space runout (regrind it)
Check the correspondence between cutter outside diameter and tooth thickness, and re-select the pre-shave cutting tool
Use fine-pitch serrations / use plunge cut
Ask the manufacturer to review the design

Poor work profile (pressure angle error and waviness from the preceding process remain)^[1][3]p.60

Main causes

Poor pre-shave profile. If the preceding process leaves a large profile feature (pressure angle error, flank waviness), that feature remains after shaving
Fillet interference at the cutter tip
Unsuitable cutter design

Fixes

Make the profile from the preceding process (hob or pinion cutter) consistent. A consistent pre-shave profile gives a stable shaved profile
Check the correspondence between cutter outside diameter and tooth thickness, and re-select the pre-shave cutting tool (high-addendum clearance of 0.15m or more)
Ask the manufacturer to review the design

Unstable profile / profile varies between top, middle and bottom^[1][6]p.54

Main causes

The contact ratio is low (under 2), and the number of contact points alternates between 1 and 2, so the meshing fluctuates
The meshing pressure angle has drifted from the optimum (regrinding reduces the meshing pressure angle)
Meshing is unstable on the tip side and root side, where the generating line is short

Fixes

Design the cutter by choosing the optimum meshing pressure angle with profile simulation or similar
Keep the contact ratio at 2 or more, and set the new-cutter meshing pressure angle allowing for the amount it will change over the cutter's life
Narrow the serration lands at the top and bottom of the profile (unequal-land serrations)
Modify the cutter profile (work-matched profile)

Left-right (drive side and coast side) profile variation^[1]p.65

Main causes

High contact pressure on the drive side causes over-cutting (stock removal imbalance)

Fixes

Change the serration land width between the drive and coast sides (asymmetric serrations)

Work profile variation (differs from work to work and tooth to tooth)^[1][5]p.61

Main causes

Poor pre-shave profile
Poor turning accuracy (work bore diameter, squareness of bore to end face)
Work runout (arbor runout, fit with the work bore)
Dull cutter
Vibration during machining (shaving machine)
Unsuitable cutter design

Fixes

Review the profile from the preceding process
Improve the accuracy of the work bore diameter and the squareness of the bore to the end face
Check the arbor runout (5 μm or less) and the fit with the work bore (about H6–H7)
Regrind the cutter
Check the vibration of the shaving machine
Use multi-pattern serrations to reduce variation within the same workpiece
Ask the manufacturer to review the design

Periodic profile waviness / tooth-space runout varies periodically (e.g., 4 cycles around the circumference)^[1][4]p.60

Main causes

Tooth-space runout during grinding of the shaving cutter flanks (e.g., waviness appears at 75 μm runout but not at 9 μm)
A higher-order component of the meshing frequency matches a resonant frequency of the machine structure, so the center distance between the cutter axis and work axis varies periodically
A missing chunk of serration (as wide as the work face width or more) gives one shock per revolution and promotes resonance

Fixes

Check the cutter's tooth-space runout and regrind it
Set cutter speeds that do not resonate using the machining condition table, and do not use speeds that resonate (in Yamaha Motor's case, 165 rpm was made a non-settable value)
Inspect the serrations for chipping before and after machining, and do not use a cutter with a chip as wide as the work face width or more
Suppress vibration with multi-pattern serrations

Lead error^[1][2]p.52

Main causes

The crossed-axes angle is too large, so the flank contact area is small and guidance is poor
Arbor runout / poor fit with the work bore
Lead change from heat treatment

Fixes

Keep the crossed-axes angle on the small side, within the range suited to the type of work gear
Check the arbor runout and fit
Allow for the post-heat-treatment lead change in the shaving machine settings

Chatter and vibration^[1][4]p.58

Main causes

The arbor holds the gear at a position far from the cutting point
Shaving machine vibration, resonance
Large module and heavy cutting load / few teeth and a short length of mesh

Fixes

Design the arbor to hold the work gear all the way to near the tooth root
Check the shaving machine's vibration and choose a speed that avoids resonance
Make the infeed in the lead direction uneven with multi-pattern serrations

Root-side profile breaks down / cutter tips wear quickly^[1][3]p.55

Main causes

The cutter tip interferes with the root fillet of the pre-shave profile
Regrinding gives the cutter negative profile shift, and at end of life it interferes with the mating gear's meshing range

Fixes

Check the correspondence between cutter outside diameter and tooth thickness
Use a high-addendum (1.35m or more) pre-shave tool with protuberance, and secure a clearance of 0.15m or more
Check with a trochoid diagram, and set the shaving diameter deeper (larger cutter outside diameter) as the cutter is reground

Short cutter life (few sharpenings, work profile breaks down early)^[1][8]p.61

Main causes

Same causes as work profile variation
Unsuitable cutting conditions
Unsuitable cutter design
Serrations are shallow (left-right difference, tip-root difference, variation around the circumference, or shallow overall)
Low cutter hardness
Complex cutter profile
Excessive shaving stock
High workpiece hardness

Fixes

Review the cutting conditions (peripheral speed, feed, infeed)
Review the shaving stock
Check the serration depth
Ask the manufacturer to review the design, material and surface treatment

Chipped cutter^[1][8][5]p.61

Main causes

Burrs from the preceding process (packed into the serration grooves)
Excessive shaving stock
Fillet interference at the cutter tip
Unsuitable cutting conditions
Unsuitable cutter design (insufficient root strength, inappropriate serration pattern)
Interference with the shoulder of a shoulder gear (stepped gear)
A work with different specifications was machined
High work count (wear)
Chipped before use: grinding cracks from tooth sharpening, cracks during heat treatment, damage in transport or handling

Fixes

Remove the end-face burrs completely
Check and revise the pre-shave tooth thickness
Check the correspondence between cutter outside diameter and tooth thickness, and re-select the pre-shave cutting tool
Review the cutting conditions
Give the shoulder outside diameter and clearance when ordering
Lay the cutter flat and keep it away from other objects
Ask the manufacturer to review the design

The profile passed in the trial but fails in the customer's production-side trial / profile error differs greatly on the same trial work^[8]

Main causes

Differences in measuring machines, in the teeth measured, and in profile control points
Differences in trial machines, in trial conditions, and in pre-cutting (preceding process) accuracy
Measurement mistakes on the trial work, lax pass/fail judgment of the trial profile

Fixes

Compare using the same measuring machine, measured teeth and profile control points (TIF diameter, length of mesh, etc.)
Make the trial conditions and preceding-process accuracy the same as in production

Cutter profile differs from the requirement^[8]

Main causes

Measurement mistake on the cutter profile
Mistake in picking or copying the specified profile (previous profile, etc.)
Mistake in the design instruction
Mistake in the order instruction

Fixes

Check the profile specification given when ordering (true / work-matched profile / separate sheet) and the drawing number of the previous profile

↻Regrinding and Tool Life Management

Guidelines for judging tool life: (1) the work gear profile starts to break down; (2) burrs appear around the work gear flanks that catch when you run a finger over them; (3) a humming noise occurs during finishing; (4) instead of long needle-like chips, short chips like file dust come out; (5) tooth thickness does not come out uniform even when finishing by feeding in to a fixed center distance; (6) the cutter profile starts to break down^[1]One source / reference
When regrinding (sharpening), grind the flanks only the minimum amount. With normal wear, one regrind reduces tooth thickness by about 0.005". For badly worn or damaged cutters, grind until the marks are gone^[5]One source / reference
The number of regrinds is set by the pitch and the remaining serration depth. Shallow serrations mean fewer sharpenings. According to National Broach, a cutter can normally be reground until the serration depth reaches 0.006"–0.012"^[5][8]
There are cases of 80,000 pieces finished on one sharpening, and cutters can generally be reground 4–10 times (National Broach)^[3]One source / reference
Regrinding gives the cutter negative profile shift and reduces the meshing pressure angle. Review the shaving diameter and cutting conditions at every setup (set in the machining condition table of the work standard), and treat the point where the meshing pressure angle falls below the threshold value as end of life^[1][6][4]
Large tooth-space runout during flank grinding produces waviness in the work gear profile. Check the tooth-space runout after regrinding^[1]One source / reference
Watch the spark-out when regrinding (poor flank roughness causes flank scratches). Grinding cracks during tooth sharpening and cracks during heat treatment lead to chipping before use^[1][8]
A magnetized cutter causes flank scratches, so demagnetize it^[1]One source / reference
Handling: even a slight impact can chip a tooth. Until it is mounted on the spindle, lay it flat and keep it away from other objects. Clean the spindle and spacers thoroughly before mounting^[5]One source / reference
In one case, the cutter material was changed to reduce wear on the serration cutting edges and improve the roughness of the slots, and tool life per regrind rose about 10 times, from 1,400 to 13,500 pieces (Yamaha Motor; combined with deburring, cutting-oil purification and cleaning improvements)^[6]One source / reference

◎Tool Inspection

Cutter tooth-space runout: tooth-space runout during flank grinding becomes waviness in the work gear profile (in a Mitsubishi Materials example, waviness appears at 75 μm runout but not at 9 μm)^[1]One source / reference
Serration depth: check the left-right difference, tip-root difference, variation around the circumference, and overall depth (shallow serrations reduce the number of sharpenings)^[8]One source / reference
Serration chipping: place an inspection bench and record sheets in the machining area and check before and after machining. Do not use a cutter chipped by as much as the work face width or more in production (Yamaha Motor's example)^[4]One source / reference
Cutter profile: measurement mistakes and mistakes in copying the specified profile cause profile defects, so measure against the specified profile (true / work-matched profile)^[8]One source / reference
Mounting accuracy: the spindle must be within 0.0002" at the outside diameter and 0.0001" (total runout) at the flange. After mounting, measure cutter side runout; it must not exceed 0.0008" for 12" diameter, 0.0006" for 9" and 0.0004" for 7" (National Broach)^[5]One source / reference
Arbor: bore tolerance about H6–H7 relative to the arbor diameter, runout 5 μm or less^[1][5]
Tool accuracy class: a shaving cutter is a hardened, ground-finished high-precision tool, with its main elements made to Class A or AA tolerances (National Broach). In Mitsubishi Materials' order specification, the accuracy is specified by JIS or other^[5][1]One source / reference
Checking on machined work: look at the all-tooth profile data (profile pressure angle error), pitch error and tooth-space runout (measured with over-pins) to confirm there is no periodic variation^[4]One source / reference

☑What to Specify When Ordering

These are the items to give the tool maker when requesting a quotation or manufacture. Most of them are determined from the gear data table (the table on the drawing).

Item	Why it is needed / how to decide
Supplied drawing, part name, part number	Decide which to base the design on: the work drawing, the previous cutter drawing, or the user specification. Also say whether drawing entries are required^[1]
Work material and hardness	Cutter peripheral speed varies with the work's tensile strength (machinability). High work hardness makes the profile break down earlier^[1][8]
Module (or DP), pressure angle (always state it), number of teeth, helix angle (RH/LH)	The cutter's normal module and pressure angle are the same as the work's. The crossed-axes angle and the cutter helix angle are determined from the work's helix angle and hand^[1][5]
Tip diameter, root diameter (root diameter / tooth depth / tool addendum), profile shift coefficient, face width	Used to calculate the shaving diameter (cutter outside diameter), clearance and cutter face width^[1]
Tooth thickness (circular tooth thickness / span measurement ZM / over-pin dimension), both after shaving and after gear cutting	The difference is the shaving stock. Excessive stock causes flank scratches, poor roughness and chipping^[1]
Profile control length (length of mesh / TIF diameter / rotation angle) and mating gear data (number of teeth, outside diameter, center distance)	The shaving diameter must be smaller than the minimum meshing circle diameter with the mating gear (TIF diameter), and the mating gear data is needed to draw the trochoid diagram^[1][5]
Gear shape (open gear / shoulder gear: shoulder outside diameter and clearance)	To choose a crossed-axes angle and method (underpass, etc.) that avoids interference with the shoulder. Interference with the shoulder causes cutter chipping^[1][8]
Lead (crowning amount; helix true / stronger / weaker) and profile (true / user standard / separate sheet / modification drawing)	For plunge cut, crowning is applied with the cutter's lead hollow, so it is needed for the cutter design^[1][5]
Shaving method (conventional / diagonal / underpass / plunge cut)	The serration pattern (normal / differential) and how the cutter face width is determined change with the method^[1][5]
Shaving machine (model name, minimum center distance)	The cutter's nominal size and number of teeth are determined by the specifications of the machine used^[1][5]
Number of cutter teeth (specified, or left to the manufacturer: nominal size 175, 200, 225, 250 or 300 type), cutter width, mounting width, bore diameter and keyway, helix angle, weight reduction (groove type / hole type)	Relates to mounting on the machine and setting the crossed-axes angle. In principle the number of teeth is a prime number^[1]
Cutter material, surface treatment and accuracy	Life and grindability vary with the material and surface treatment (options in Mitsubishi Materials' specification: SKH51, KHV1, KHVX, HSS-2, HSP; untreated, nitriding-oxidizing, STH treatment)^[1]
Shaving stock (span measurement / OBD) and pre-cutting tool (hob / pinion cutter, drawing number, presence of protuberance)	The pre-shave tool's profile determines fillet interference and clearance. Choose from ordered together, specified, or standard (2.35m)^[1][3]
Trial conditions (rotational speed in min⁻¹, feed rate in mm/min, feed length in mm; plunge T1, T2, T3 and BM; diagonal angle)	If the trial conditions differ from production, the profile pass/fail results will disagree^[1][8]
Cutter hollow amount and cutter profile (true / work-matched profile / separate sheet / as drawn)	To build the work's crowning and profile modification into the cutter^[1]
List of gears to share the cutter	Whether one cutter can machine several gears is judged by the difference in number of teeth, in profile shift coefficient, in helix angle and so on (sharing range table and flowchart)^[1]

Printed from Kezuriba (kezuriba.net/en/gears/tools/shaving-cutter/)

+Related Topics

Sharing one cutter among several gears

If gears with the same module and pressure angle but different numbers of teeth are shaved with one cutter, the differences in tooth count and profile shift coefficient change the balance of contact ratio and acting force, and profile errors result. Strictly, whether sharing works can only be decided by trial machining^[1]One source / reference
Guideline for sharing range (groups of work gear tooth counts): m1.25: I 13–22, II 20 or more; m1.5–2: I 13–18, II 17–34, III 25 or more; m2.25–3: I 14–18, II 17–29, III 27 or more; m3.25–5: I 14–17, II 17–26, III 23–40, IV 35 or more; m5.25–8: I 15–17, II 17–25, III 24–37, IV 35 or more^[1]One source / reference
Procedure for checking whether to share: same normal module → same normal pressure angle → same helix hand → helix angle difference within 5 degrees → face width (for diagonal, plunge and underpass, check with the face width equations) → number of teeth (sharing range table) → profile shift coefficient difference 0.2 or less → shaving diameter > fillet generation diameter → shaving diameter < TIF diameter → clearance 0.15 module or more → contact ratio difference within 0.1 → check meshing pressure angle → check the serration action (plunge, underpass). Classify as open gear or shoulder gear^[1]One source / reference
Sharing a plunge-cut or underpass cutter can worsen flank roughness; in that case, make it a dedicated design^[1]One source / reference

Cutter materials and surface treatments (manufacturer examples)

Mitsubishi Materials' HSP shaving cutter: a high-Co cobalt HSS that raises heat resistance and hardness, with V content kept low so the profile is easier to grind, and heat treatment conditions optimized to raise toughness (chipping resistance). The hardened layer is deeper than the wear zone. In a ring gear plunge-cut example, average pieces machined were 9000 versus 3000 for the conventional product (SKH51 + nitriding-oxidizing)^[1]One source / reference
Mitsubishi Materials' high-performance grade KHVX: a melted material with V added along with Co, which refines and evens out the hard VC carbides to raise wear resistance while keeping chipping resistance. On an SCr420 gear (m2.5, plunge cut), average pieces machined per regrind (REG) were 4,032 versus 1,900 for SKH51^[1]One source / reference
Nidec Machine Tool's MACH3: a high-hardness material with more V and Co and carbide grain size refined and dispersed down to 7 μm. It raises chipping resistance while keeping conventional grindability. Super Coat raises surface hardness (little dimensional change, which limits variation in serration groove depth), and combined with fine-pitch serrations one example kept flank roughness after more than 6000 pieces^[7]One source / reference
Nidec Machine Tool's MightyShield ε (formerly MH02 coat): surface hardness 70% higher than Super Coat-treated products, with improved adhesion and throwing power so the film forms evenly even in the serration grooves. Delivered semi-ground, with the coating already removed in the company's tooth-grinding process. On carbon steel (m1.5, 48 teeth), life rose from 1,595 to 5,832 pieces. Some cutter shapes cannot be treated, so consult in advance^[9]One source / reference

Related shaving tools (other products)

Diamond dressing gear: a gear-shaped tool with diamond abrasive electroplated on the flanks, used to form and dress gear honing stones that grind gears. It has the same shape as the gear to be ground. For details, see dressing-gear.json^[1]One source / reference
Burnishing gear: a tool that is rotated while pressed against a heat-treated gear, with pressure angle and helix angle corrected, to remove burrs and nicks. It is normally used as a set of three (different pressure angles, strong helix, weak helix)^[1]One source / reference
Chamfering (fraising) cutter: a gear-shaped tool that presses down the end face of a cut gear along the involute direction to chamfer it in a short time. There is a type that chamfers only one side of the tooth flank and a type that chamfers the end faces of both flanks; chamfer shapes are tapered (different chamfer amounts at tip and root), parallel (same), and parallel with the root chamfered at the same time. It can also chamfer inclined end faces, and above 15° it should be confirmed by calculation. The chamfer amount is adjusted by the phase of the two blades, and with a built-in eccentric pin the phase can be adjusted with a bolt^[1]One source / reference
Master gear: rotated together with the gear being measured, and the gear's accuracy is judged from the meshing condition. It is also used as the gear that detects eccentricity, tooth thickness, nicks and so on in a two-flank-meshing automatic sorting machine. Mitsubishi Materials makes master gears with TiN and violet coating. When ordering, decide the accuracy class, tool material (DC53, SKH51, etc.), nominal size, center distance, crowning and hollow amounts, and whether an inspection certificate is needed^[1]One source / reference
TRG-Tool (Mitsubishi Materials): a threaded CBN electroplated tool for generating gear grinding. It is highly capable of correcting pitch error and suits pre-processing for gear honing (extending honing stone life and dressing cycles). With its worm shape it can do continuous generating grinding, and because the profile is already built in, no on-machine dressing is needed. In an m2.3, 43-tooth example, cumulative pitch error went from 48 μm (JIS grade 8) to 11 μm (JIS grade 4)^[1]One source / reference

⚙Other Gear Cutting Tools

Hob Pinion cutter Skiving cutter Broach Diamond Dressing Gear Chamfering Tools (Fraising Cutters)Gear Cutting Tools and Cutting Conditions: Overview Comparison of Gear Cutting Methods Machining Trouble Encyclopedia

📚Sources

Values without a mark agree in two or more sources from different publishers. Grade and coating names are the makers' product names, and no comparison between makers has been made. "p." is the body page of the Mitsubishi Materials catalog (C004J-H).