Re: Ripples in surface finish
Originally Posted by
G59
Personally I don't know what causes it, but I've seen this ripple effect on servo driven mills.
And I have got the same results on a Bridgeport when hand cranking the Y axis while side cutting with an end mill. Combination of side loading of the end mill, flex/chatter, each individual blade as it cuts, and some run-out or imbalance in your spindle. That is normal.
I don't think it is related to your steppers, or micro-stepping. The steppers are set at 2400 steps per revolution, and are directly coupled to a lead screw with 0.1" pitch. That means the pulsing of your steppers would be leaving an imperfection in your finish every 0.100"/2400 = 0.000045" (0.045 tenths of a thousandth). That would not be visible without a microscope.
If that regular repeating pattern were due to runout, the spacing of the lines would be 0.0076" apart. Spacing= FR/RPM. In the absence of any frame of reference for your picture, I am sure that what you are showing is probably more like 0.050" spacing. So probably not runout.
Originally Posted by
cobrakai
Funny you mention that cause I work with steppers in my career quite often. I use microstepping drives with a resolution of 51,200 steps per revolution. Tuned properly, I can eliminate any perception of steps entirely. They are as smooth as servos and a lot cheaper. I wonder why Tormach didn't do that.
Tormach does. But they are limited on control frequency because of using the parallel port as the pulse generator, so have conservatively chosen a micro stepping rate that makes the maximum pulse rate 16kHz at 110 ipm. The Lead shine drivers they use allow micro stepping to 25600 steps per revolution, but Tormach settles for 2400. That means each mi
Mach 3 documentation says don't try to get faster than 35 kHz, so there is a little room for modification before you hit that limit. Increasing micro step rate isn't going to give you a better finish, and I doubt it will give you better precision in moving the axis, since the error induced by micro stepping is already on the order of backlash and slop in the assemblies.
Originally Posted by
TurboStep
mmm...Interference patterns due to two rotational frequencies.... nice, I forgot that thread.
OP, take a pair of calipers, a magnifying glass, and tell us what the spacing of your marks are.
Tim
Tormach 1100-3, Grizzly G0709 lathe, Clausing 8520 mill, SolidWorks, HSMWorks.