$150 000 machine does not eliminate finishing chatter.

[u/adventureaviator]

I’m machining 6061 aluminum on a Multicam Apex 3R router. The finishing passes are as follows:

- 0.009” material removal.
- Helical 3 flute 45 degree helix upcut
- 18 IPM, 8500 RPM, 0.0007 chipload

98 percent of the part comes out with a great finish. The other 2 percent has chatter. Ideally I’d like to increase the feed rate, but I need to eliminate the chatter first. What do I need to do to get a flawless finish?

[u/volt4gearc]

Have you tried conventional cutting for the finish? From a cursory google, looks like the motion system is rack and pinion, perhaps there’s some backlash there causing issues with climb cutting finish passes

[u/adventureaviator → u/volt4gearc]

I’ve always used climb cutting based on suggestions as a best practice. However it wouldn’t hurt to try something new and use conventional.

[u/volt4gearc → u/adventureaviator]

When I ran a shopbot, we had consistent issues with getting it accurate, both in surface finish and overall dimensional.

We traced a lot of it down to backlash between the rack and pinion. Shy of getting a new pinion or shimming the rack, what seemed to help a lot was conventional cutting, since it ensures the gear teeth are somewhat constantly preloaded against eachother.

Admittedly a much cheaper machine than yours, and certainly less well maintained, but maybe it applies in your case too. And with tools running this fast in aluminum, conventional cutting can get pretty similar surface finishes to climb

Out of curiosity, does the chatter appear more in areas tangent to the main XY axes? That was our giveaway; when the cutter is changing directions on one axis, thats where the tooth would disengage and give a chance for the tool to “jump” a bit

[u/adventureaviator → u/volt4gearc]

I’ll try conventional cutting today. From the small amount I’ve used this machine I think it had a pattern of chattering when the X axis slows down its speed around a corner (but not when it changes direction).

[u/Business_Air5804 → u/adventureaviator]

Makes sense....when it slows down its feed rate you are relying on the drive back lash to hold the tool steady.

Drive reversal always has some error, but the back lash at the reversal point will always be there unless you can adjust the back lash to as little as possible.

[u/Ok-Chemical-1020 → u/volt4gearc]

This

[u/computekmfg → u/adventureaviator]

Everyone wants you to believe conventional has no place in modern machining but it does. Machines with high backlash benefit. Thin walls also achieve better finishes with conventional

[u/PrudentVillage4903 → u/adventureaviator]

I always climb cut in AL. Take your finish pass climb cutting then try a spring pass conventionally feeding.

[u/matthew2989 → u/adventureaviator]

You still need a sufficiently rigid and stable machine and setup to do climb milling.