The Double Axis CNC Razing Machine: How It Cuts Gear Teeth

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  What the two axes actually control on a double axis CNC razing machine
• 2
  Stock allowance, cutter speed, and the limits of the method
• 3
  Tooth forms a double axis CNC razing machine handles well
• 4
  Inspection and what the finish actually buys you
• 5
  Setup, tooling, and the errors that cost the most
• 6
  How we set up a double axis CNC razing machine job
• 7
  Shaving, grinding, and honing: which finishing step fits

On a single-axis gear shaving head, the cutter sits at a fixed crossed-axis angle and the table feeds the workpiece past it. Correction of tooth form comes from cutter profile and from how the part is presented. A double axis CNC razing machine adds a second servo-driven motion, usually the radial or the tangential slide, so the cutter position changes while the cut is running. The two motions are interpolated by the CNC, not set by hand.

The practical result is that flank shape is no longer fully baked into the cutter. The control can tilt the cutting contact along the tooth width, which lets one cutter cover crowned teeth, tapered teeth, and slightly different helix corrections in the same setup. That is the whole point of the second axis. It buys form flexibility, not raw speed.

Both axes ride on preloaded ball screws and high-precision bearings. Any backlash shows up directly as tooth lead error, so the mechanical build matters more here than on a simple plunge shaver. When we quote gear work, the machine condition and the axis calibration records carry as much weight as the nominal specification.

One boundary to fix early: a double axis CNC razing machine is a finishing process. It removes a thin layer from a pre-cut gear. It does not cut a gear from a solid blank, and it will not rescue a blank whose tooth thickness is already out of range.

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  Axis 1Carries the cutter head at the crossed-axis angle.
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  Axis 2Adds a second interpolation, typically radial or tangential.
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  CNC linkCoordinates both motions for one generated flank path.
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  DriveServomotors on ball screws, preloaded to remove backlash.

Shaving works on a narrow allowance band. Leave too little and the cutter rubs instead of cutting; leave too much and the cutter loads up, the tooth form drifts, and cutter life drops fast. For a typical module 1–4 steel gear, the allowance that behaves well is small: a few hundredths of a millimeter per flank, split across the rough hobbing pass and the shaving pass.

Cutter speed and feed are set from the material. Soft steels such as 1018 or 1045 shave cleanly at moderate surface speed. Case-hardened blanks must be shaved before heat treatment, because the process needs a tooth flank soft enough for the cutter to shear. If you harden first, shaving is off the table and you move to grinding or honing.

The double axis gives control over crowning and taper that a fixed head cannot match. Crowning is the slight barrel shape across the tooth width that keeps contact away from the tooth ends under load. Taper is the deliberate thickness change from one end of the tooth to the other. Both are set in the control, and both can be adjusted per part without a new cutter.

What the process does not fix: index error from a bad blank, a wrong helix angle, or a tooth thickness outside the allowance window. Those are upstream problems. Shaving follows the blank it is given, so a sloppy hobbing operation shows through the finish.

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  Best casePre-cut gear with uniform allowance and stable blank.
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  Poor caseHardened flanks or inconsistent tooth thickness.
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  CrowningSet in the control, no cutter change needed.

Cylindrical spur and helical gears are the bread and butter. Straight and helical flanks with a consistent module and pressure angle shave predictably, and the double axis lets the operator dial in lead correction across the face width. For a gear that has to run quietly, this is where the process earns its place.

Crowned teeth and small conical teeth are the cases that justify the second axis most clearly. A drum-shaped tooth contact pattern spreads load and reduces edge stress, which matters on shafts that see bending. With a fixed head you would need a specially dressed cutter; with the interpolated axis you program the crown.

Internal gears are a different story. The cutter has to reach inside the ring, and the geometry limits how much correction the second axis can apply. Shaving internal teeth is possible on some machines but the process window is tighter and the tooling is more specialized.

Very large gears fall outside the class of machine this page covers. If the part is beyond the work envelope, the honest answer is that shaving is not the process for it. Send the drawing and we will say so rather than quote a job that will not hold form.

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  Strong fitSpur and helical gears, crowned flanks, taper teeth.
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  Tighter fitInternal gears and small conical tooth forms.
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  Outside scopeBlanks larger than the machine envelope.

Shaving improves surface finish and tooth form together, and the two are measured differently. Finish is read as Ra; form is read as lead and profile deviation, usually on a gear measuring center. A double axis CNC razing machine can bring a flank into the Ra 0.8–1.6 μm band on clean steel, with tighter finishes possible when the cutter is fresh and the allowance is right.

The gain that matters on the shop floor is noise and contact pattern. A shaved gear runs quieter and its contact patch sits where the design intended. That is why the process shows up on automotive transmission parts and on drive gears for industrial machinery, where a whine in the assembly is a warranty problem.

Inspection has to cover more than the finish number. Tooth thickness, runout, lead, and profile all move together, and a part that passes Ra can still fail on lead. At GreatLight we hold ±0.005 mm on machined features and inspect 100% before shipment, with raw material checks and in-process monitoring upstream of final inspection.

Reports are available on request. If your drawing calls out a gear measurement chart, say so at the quote stage so the inspection plan is built around it rather than bolted on at the end.

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  FinishRa 0.8–1.6 μm typical on steel flanks.
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  FormLead and profile checked on a gear measuring center.
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  Tolerance±0.005 mm on machined features.

Setup starts with the cutter. Crossed-axis angle, center distance, and the depth position all have to be set from the drawing, and a small error in center distance shows up as a tooth thickness error. The second axis does not forgive a bad center distance; it just moves the error around.

The most expensive mistake is running the wrong allowance. Operators who leave a heavy shaving stock to save a hobbing pass will burn cutter life and lose lead control in the same shift. The second most expensive is a dull cutter. A worn shaver stops cutting and starts rubbing, and the flank gets burnished rather than finished.

Crowning is where the double axis pays for itself. Once the crown parameter is dialed in, the same cutter runs on parts with different crown requirements. On a fixed-head machine every crown change is a tooling event. That difference is the reason the second axis exists, and it is worth understanding before you specify the process.

Keep the calibration records. Axis calibration, ball screw condition, and cutter wear logs are what let us hold lead on a repeat order. If a gear program runs for a year, those records are the reason part 5,000 matches part 1.

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  Set firstCrossed-axis angle and center distance.
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  WatchAllowance width and cutter wear.
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  KeepAxis calibration and cutter wear logs.