Conical Gear Treatment Tool: How Bevel Teeth Are Actually Cut

• 1
  What a conical gear treatment tool does to the tooth flank
• 2
  Paired gliders for small and medium modules
• 3
  Paired cutters for larger diameters and higher output
• 4
  Mashing cutting plates for modules under 6 mm
• 5
  Where the tool choice stops being obvious
• 6
  Setting up a conical gear treatment tool
• 7
  Which conical gear treatment tool fits the job

Bevel gears do not have a constant tooth profile along the face width. Both the tooth height and the tooth thickness change from the outer cone to the inner cone. That is why a single form cutter cannot produce the whole flank in one plunge. A conical gear treatment tool works by generating the flank: the cutter and the workpiece roll against each other while the blade sweeps through the tooth space.

The blade geometry follows the gear's cone. The cutting edge sits at the nominal pressure angle of the gear being cut, so the flank that comes off the tool matches the pressure angle the design calls for. Get that angle wrong by a degree and the gear will still turn, but the contact pattern moves toward the toe or the heel and the load lands on a smaller area.

There are two ways to bring the blade into the tooth space. In the paired approach, two cutters are indexed into adjacent tooth spaces and cut both sides of a tooth at the same time. In the alternate approach, a single cutter plate works one flank, then the workpiece indexes and the other flank is cut. Paired cutting halves the number of passes and holds the tooth thickness more consistently.

The tool also sets the root line. The rear corner of the workpiece is formed by how the glider is seated in the spindle seat, so the seat runout becomes part of the tooth geometry. A seat that runs out 0.02 mm will show up as a root line that wanders along the face width.

Paired gliders are the workhorse for conical spur gears in the module 0.3 to 20 mm band. Two gliders sit in adjacent tooth spaces and treat both sides of the gear tooth in one indexing cycle. Because the two blades share the cut, the radial force on the workpiece stays balanced and the fixture does not have to fight a one-sided push.

The blade's tooth angle equals the nominal pressure angle of the cut gear. This is the whole point of the design: the flank is not approximated, it is copied at the correct angle. When the pressure angle of the gear changes, the glider set changes with it. There is no universal glider that covers a range of pressure angles.

The rear corner of the workpiece comes from how the glider is installed on the spindle seat. That seating is a precision fit, not a clamping afterthought. If the seat is worn, the glider tilts slightly and the tooth thickness tapers along the face width. Operators check seat runout before a setup, not after the first scrap part.

Paired gliders suit low to medium volume runs and gears where the tool cost has to stay reasonable. They are slower than cutters, but for a 2 mm module gear with 20 teeth, the cycle time difference rarely justifies the tooling jump.

Paired cutters, often called strawberries on the shop floor, handle conical gears with a larger diameter and more teeth. The cutting plate carries a large diameter and many teeth, and it cuts both flanks of the tooth space at once. Productivity typically runs 2 to 4 times that of paired gliders on comparable work, mostly because the cutter can take a heavier chip load per pass.

The geometry is different from a glider. The teeth of one cutting plate are launched diagonally between the two teeth of the other plate. That staggered entry spreads the cut over more of the plate circumference, so the load per tooth drops and the plate runs cooler.

The cutting edge itself is curved. This is what produces the drum-shaped tooth that meshes well under load. A straight flank would contact the mating gear at the edges first, concentrating stress. The curved flank contacts near the middle and spreads the load as the gear deflects.

Paired cutters make sense when the gear is large, the batch is long, or the cycle time has to come down. They cost more to make and to sharpen, so for a one-off prototype the setup cost may not pay back.

Mashing cutting plates treat conical gears with a module below 6 mm, and the plate diameter usually lands in the 400 to 600 mm range. Each plate carries fan-shaped blocks, and each block holds 4 to 5 knife teeth. The block is the replaceable unit, so a chipped tooth does not scrap the whole plate.

The coarse cutting teeth are arranged with the upper edge gradually rising. The tooth lift is roughly 0.1 mm from one knife to the next. That small step is what divides the chip: each knife takes a thin slice instead of the full depth, which keeps the cutting force low on small, thin-toothed gears.

This design is aimed at small gears with intricate surfaces, where a heavy single cut would deflect the workpiece or tear the flank. The trade-off is tool complexity. More knives mean more edges to keep sharp and more setup points to check.

If the module is above 6 mm, mashing plates are the wrong tool. The chip load per knife gets too high and the rising-edge geometry stops helping.

Module alone does not decide the tool. A 5 mm module gear with a wide face and a long batch may still run better on cutters if the machine can take the load. A 10 mm module gear with a narrow face and a short run may be cheaper on gliders. Read the face width and the batch size together with the module.

Machine travel matters too. Our largest travel is 4,000 × 400 × 150 mm, and the medium platforms cover 750 × 1,150 × 550 mm. A gear blank that fits the work envelope may still not fit the cutter head clearance. Check the swing before assuming the setup is possible.

Heat treatment changes the plan. A gear that is cut, then case hardened, will move. The cutting allowance has to account for distortion, and the flank angle may need correction so the finished tooth lands on the drawing. Cut-and-harden is not the same as cut-to-finish.

Finally, the tool has to match the machine's generating motion. A glider set that was designed for one machine's roll ratio will not produce the right flank on another machine without a setup change. Treat the tool and the machine as one system.