How to deal with cutter compensation...

[jeffreymcgrew]

Hey, got a question. Let's say I've got a 1/2" bit two-flute straight bit, in a router, in a PRT w/a 4G upgrade. I cut something soft with a stepdown of 1/2" and at 4 ips, and I get very little cutter flexing going on. Nice clean cuts, and very close to perfect. Now, same cut, but in a much denser multiply maple. I get a lot more bit flex, enough to make the part almost 1/64" off. This is cutting with two passes, one climb, and then one conventional.

OK, so, I totally understand that bit flex is something that you simply can't get 100% away from. But I've got three questions:

1. Would taking shallower passes lessen the flex?
2. Would a spindle and/or vacum hold-down give better results? There is a little vibration when cutting.
3. Should we just add a little offset to the toolpaths when cutting denser materials to compensate for the flex? Is this what y'all do?

90% our cuts are more than accurante for what we're doing. It's just that I'd like to get into those fancy stepped miter joints and such, and that much flex is going to be a problem...

Thanks!

[ccw]

Jeffrey,
Yes Yes and Yes
chip load,Feed and speed are always a factor with getting good cut quality. IE deflection
in the cut is an indicator that to much of a load on the bit.
the other thing I would look at would be to check my pinion gears make sure the are tight I have had that problem before.
Mark

[beacon14]

You can also do a roughing pass/finish pass where you rough out .02" oversize or so, the final pass should have less deflection as it takes less of a load.

[elcruisr]

Also consider tool sharpness. If your tool isn't razor sharp then when you're cutting harder materials you're just introducing more flex because it's "pushing" harder to make the cut.

[jeffreymcgrew]

This is all great. I'll run some more tests.

Totally understand that it's all about the chipload with cut quality. Didn't know it also mattered so much with bit deflection.

As for tolerances and tightness I just went over everything prior to doing the tests and fixed any problems that cropped up from the last few months of production running.

The bit I ran the tests with is new and sharp.

[andre]

Jeffery
I discovered all of the above. Instead of trying to nail down the perfect feed rate and rpms, I simply picked the toolpath I wanted to use and adjusted the size of the dado to get the right fit. In my case I believe I use an inside to out tool path climb cut and add .015 to the dado and I get the right fit. I stopped trying to figure it out and just accepted it. You will want to double check all your motors and roller wheels to make sure you are not getting any play any where. Also I am using a router not a spindle so I dont have the control on rpms like a spindle does.