Problem cutting arcs, backlash?
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.
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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.Originally Posted by fizzissist
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
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.
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
.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.
We have had good luck with our Fadals milling mostly soft steel and aluminum up to 5 axis. We are always looking for spare parts :) If you have a broken down Fadal give a shout.
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