[TheGreenMachine]

I don't usually cut any arcs that matter much but on these particular parts I need nice clean arcs. One of the arcs that I'm cutting looks particularly bad, I really doubt its chatter because the line/marks are perfectly vertical, I don't hear any screeching, the lines/marks are identical from part to part, and I did this same cut on a smaller mill before without any issues. At first I thought it was a backlash since I have .0040 - .0055 compensated on the x and y axes. But upon further reading and thought I'm not sure this is the case, their is no mark at the quadrant/3 o'clock position and their are marks throughout the arc. The worst of the marks is about .050 after the 3 o'clock position, could that be attributed to backlash?

From my reading the possibilities could include servo loop gain, axis balance, and the resolvers. Does anyone have any suggestions? How do I check if they are bad or calibrate them? And also how do I check the gibbs and straps?

I should also mention that this is a VMC40 with a 88HS.

[fizzissist]

To minimize backlash or gib issues, try moving the work to the end of the table where things are less worn.

To minimize chatter, just in case that's it, try using a much smaller dia cutter, designed for the material and cutting conditions you're using...or change your cutting conditions appropriately.

[TheGreenMachine]

To minimize backlash or gib issues, try moving the work to the end of the table where things are less worn.

To minimize chatter, just in case that's it, try using a much smaller dia cutter, designed for the material and cutting conditions you're using...or change your cutting conditions appropriately.

Thanks, I'm using the whole table and can't move the work and I know its not chatter so changing end mills or work holding won't help.

[holbieone]

it could be backlash and/or lag in your axis motor drives

try a smaller tool and slow down the cutter at the arcs

you also can try cutting the arc point to point

[fizzissist]

Thanks, I'm using the whole table and can't move the work and I know its not chatter so changing end mills or work holding won't help.

If it's not chatter then it's not a backlash problem. Excessive backlash is what allows chatter.

Without seeing the code, we're safe in assuming that you have a continuous arc and not a series of G1 moves that simulate an arc?
Are the lines perfectly vertical and uniform?
You're not re-cutting chips?

...and I know this is stretching it, but are you getting good lube to the table? Stick-slip can give you strange patterns when the lube system fails in a way type machine.

Btw, I found that often sticking a G8 in the first line of the feed move was helping give smoother cuts.

[juniormachinist]

we are having the same problem with out fadal 4020 straight cuts on the x or y axis are good but when we do arcs they look stepped even though the code is point to point It looks as though the x and y aren't in sync is there any way to check the synchronization

[carbidecraters]

.004.005 is too much backlash. You need to get your ballscrews rebuilt at a minimum and new linear rails and trucks at a maximum. The Fadal resolver also may be at fault to which there is a updated resolver available however with that kind of backlash your going to get rough arcs no matter what. IIRC the minimum movement of a fadal is .00005.