JGRO Step gainning?

[bearwen]

Hello All,
Well I have a question I am running a unmodified JGRO with 260 oz motors powered with 30 volts and a 1/2-10 acme screw and I am cutting at 50in min but when I try to do a portrait that is carved .03 deep the machine seems to gain steps on the long X axis. The way it runs is the project is 5" on the X and 6" on the Y so the machine moves across the X and then steps or .01 on the Y and then runs down the X again it does this for the whole Y axis length of 6" and when I run at 50"in min or more the carving tracks off and gains steps on the X so when the piece is done it returns to Zero and the X is .25-.5 inches in the positive I have slowed it down to 20" or so and it seems to be ok its not perfect but its within .01 so close enough for this kind of work any ideas how to fix this at high speeds as 50" min is ok but still takes more time than I want.

Bearwen

[pminmo]

What kind of stepper driver are you using?

[bearwen]

Phil,
I am using your 3977 and the axis in question is running full step but it did the same thing in 1/2 step. I dont beleive it is electronic based I feel that perhaps there are mechanical problems as it doesnt seem to do it at slower speeds or at least not as bad and when I cut complex parts ie the left side plate for the Z axis carriage of the Joe 2006 it comes back to zero and it is so close that I almost cant measure it were talking 2thousands. It seems to only do it when I run a protrait and the machine just runs X 5 in @55" min and then steps over on the Y by .01 and reverses direction on the X all at the same time at break neck speeds ( I think it maybe a velocity issue but it is not loosing or gainning due to velocity in both directions of the X only in one direction?) thanks for chimming in so quick.

[pminmo]

The thing that I find a little confusing is "gaining steps". Could you have some mechanical slip in the coupling from the motor to the screw? Higher speeds, and sharp acceleration changes would put more stress on the mechanical linkage. With some slipage at sharp acceleration chages might be gaining mechanically, rather than electrically.