Milling a hole - and a hole creeps

[bbatarelo]

Hi all,

I apologise if this has been covered elsewhere, but I don't even know if I'm using a proper terminology for the problem.
So here's the thing - I have new Wabeco mill, linear rails/ballscrews, 2kw motor, comes from factory with Nema 43 6 amp steppers, 1:2.5 ratio - German engineering and in house manufactured. I have my electronics package (Centroid Acorn, Gecko 201X drives), machine is precise, backlash is a few microns and everything is looking generally nice.
However, milling a hole makes a hole creep along x - conventional milling to the right, climb milling to the left. It happens only on X axis. Otherwise hole dimensions are good and no matter what I do (speeds/feeds/acceleration).
Everything is chatter free, end mill is new Widia 3 flute, steppers are working fine (no stalls or anything), my milling numbers are very conservative and material is Aluminum. Setup is beefy vice secured to the table at 4 points, nothing is loose.



This creeping is pretty consistent - not something erratic or occasional - as if it were programmed - except that it wasn't. Hole was produced by Centroid conversational and simulation produces a hole, not this skewed thing. Produced G code looks ok.
Other operations I tried were fine - facing, plunging and cutting slot directly with g code, etc. I don't know what else to try.

Many thanks,
Bruno

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[machinehop5]

can you attach the G Code or upload as a Zip file so we can view the program?

[Jim Dawson]

Try generating the same hole in a CAM program and see the result. That almost looks like a math error in the motion control calculations.

[the_gentlegiant]

Is that a once around single pass hole? Also at what pole position are you starting at? N-S-E-W?

[bbatarelo]

Ok, after consulting on several sides and doing some experimenting - it seems that this is a purely mechanical issue. I wouldn't expect Centroid to have these kind of issues with basic conversational features like a hole. Anyway, what I thought were a strong enough steppers proved to be wrong - it's a deceleration issue. In this photo each layer is 0.1mm deep and after about 2mm of depth, my X would slip about 6 millimetres. In the end, cutting down feed rate brought me spot on. Now I'm on the path of getting bigger power supply and stronger steppers.

Thanks all,
Bruno