Losing steps first .010 of movement

Recently finished setting up my 1000mm machine with an X-Controller and ran the calibration test. This revealed that all of my circles were ovals with the min distance from 10-4 and max from 1-7. I verified that the machine is square and the v-wheels and belts are properly tensions as best I can tell.

After verifying that the POTs were in the recommended position from the installation instructions, I took a dial indicator and measured the actual movement of the X-Axis. I started by moving the X-Axis in the X+ direction in .001" increments. I have to move the machine .003 in order for the dial indicator to move the first .001. And it’s not until I’ve moved about .010" that the machine starts moving in .001" increments like it is supposed to. At this point it will be about .004-.005 behind where it is supposed to be and will stay at that offset no matter how far I move in the X+ direction. If I then change direction and move in the X- direction, the same scenario will play out.

This almost sounded like backlash to me which I thought would suggest that the belt was not tight enough. So I tightened it a bit more, moved the machine and the X belt broke. Fortunately there was enough extra belt for me to recover, but now I’m not sure what needs to be changed to get the correct steps.

Maybe too tight belts? I think I have mine set around 3-4 lbs at the center and 1" of lift using a fish scale to measure.

I have two calipers one a mitutoyo dial caliper the other a cheap $15 harbor fright. Both measure a thousandth of an inch. But that is beside the point, there is no way an x-carve is ever going to be that accurate. Not with a belt drive, any time you move a belt driven system in a direction there will be slight stretching in the direction of travel thus a tiny delay in movement. That is why there is no backlash preventing system in place. That probably what your seeing.

Thanks for that information. I’ll check that tomorrow.

There’s a better thread concerning setting the tension (it’s a post by @RobertA_Rieke I think) but I believe the school of thought is like 3-6 lbs.