I seem to get a lot of chatter when I'm machining larger rotors. Is there a different tip I can use? Am I doing something wrong?

A lot of people condemn the cutting tip right away when they get chatter (and you DO need good sharp cutting tips), but the culprit is generally the way the rotor or drum is mounted to the brake lathe.

Size really does matter

There are several ways to combat chatter. The first and foremost is to make sure the work piece is mounted to the lathe correctly. We must make sure to use the largest bell clamp or backing plate that will fit inside the hat area of the rotor (the backside of the rotor that slides onto the axle hub). If you're using the bell clamp method be sure to use 2 bell clamps close to the same size (one on the back side and one on the front side) and as large as you can as this will support the rotor equally on both sides. If the rotor is not supported in this manner it will induce chatter. The same goes for the backing plates. Use the largest one that is able to fit.

Tighten everything

The second is to double check that you have everything tight on the lathe; screws that hold the tip onto the holder, (also check for any metal filings or dirt under the tip) the red locking knobs are secure, no more than .001” run out in the arbor.

Use sharp cutting tips and silencer straps

The third is always machine with sharp cutting insets; a dull insert will not cut cleanly and will induce chatter. Also be sure to use silencer straps or clamp on silencers to help absorb any other vibration that may occur.

Perform preventive maintenance

Overall just keep the brake lathe maintained. Check the boots, cutting tips, holders, periodically check run-out in the arbor, and make sure you use the correct mounting cones and bell clamps when mounting the rotor to the lathe. We always are quick to condemn the tips when we come across chatter but 9 out of 10 times you will find that the true culprit is how the rotor is mounted.

Find more technical tips in the Goodtool Technical Library.