Bad circles

I’ve read previous posts about bad circles, but I still need help. My circles are coming out as noticeable ovals. The tool has gone around many times, so there is no tool deflection.

How do you determine the proper belt tightness?
How tight should the v-rollers be set?

How about a picture so we can see more clearly what is going on?

My stepper motors are now calibrated properly. There was an improvement, but I am still getting holes undersized and out of round.

My 1/4 inch end mill measures .246 that I did not account for, but it would still be undersized.

In the picture I cut a 2" and 3/8" hole. The positions where I measured are consistently off on both holes.

Check to make sure your x rail is squared to your machine. Bring the rail to within a inch or two of the very front and use calipers to make sure both sides of the x rail are the same distance from the Y plates.

Check the tension on your belts. I had mine too tight, about 5 lbs. Went to 3.6 and it made a bid difference.

HOLY COW the x rail is off about .375 inch difference from both plates! How do I align? Any good video links?

I ordered a digital pull scale to test the belt tension.

There’s a few ways to do this. I don’t recall any videos.

I use some spare 20x20 extrusion that are the same lengths, put them between each of the Y plates and the axis with the machine unpowered and slowly pull the axis tight again the extrusion and then turn on and lock the steppers. I do this for every power on.

If you find it out of alignment a lot, hen your belt tensions on each Y might be uneven.

My x slide is the newer wide single piece.

So far I have calibrated my stepper motors and squared my x axis. I am still waiting for my scale so I can test the belt tension.

I am still getting undersized and lumpy circles. Interestingly, whether I make a peg or a hole, they are both undersized. You would think that since they are routing on opposite sides, that one would be undersized and the other would be oversized.

The pegs in the picture are supposed to be. .5 .

Uneven stiffness between X/Y axis so the amount of system deflection vary during the transition from X/Y and Y/X. Provided the actual bit diameter is true and there is no excessive run-out.

May I suggest the following:

Test #1
Do a 1" and 4" circle (path outside) with your current feed rates etc.

Test #2
Do the same 1" and 4" circle (path outside) but after running the carve once, run it again at the same place, with feed rate at 25% of previous speed and in one, full depth, carve.

If your deviation is the same amount between the 1" and 4" your calibration is probably pretty decent, but tool deflection / transitional play is your culprit.
If your deviation is 4x larger for the 4" version vs the 1" version you may need to recalibrate.
(If a 20" jog equal precisely 20" travel then calibration is okay, defect is due to actual tool diameter/runout/tool deflection.

I did the tests. The measurements are off by the same amount no matter what sized hole. The slower pass did not change anything, so deflection is not the issue.

This seems like a hopeful area to address. How do I balance the stiffness?

As best as I can. When I cut the same circle in the opposite corner of the work area, the same discrepancies show up in the same quadrants.

If you grab the router can you lift the acme screw up at all? Also while holding it try twisting left and right. Any movement?

If the deviation is the same regardless wether you go fast (heavy load) or slow (light load) then its not tool deflection that is your main culprit IMO. I would investigate system backlash.

As I dont have an actual Xcarve myself I hope others with good knowledge will chime in :slight_smile:

Have you tested belt tension yet? I hadn’t seen you update on that.

This screams as a belt tension issue to me.

I set the belt tension last night before I cut the 1" and 4" circles. It is now at about 4.5-4.8 on all axis. I still have the problem.

The y belts were uneven by about a pound before the adjustment.

Can my V roller stiffness be and issue on the circle transitions?

I can move them by hand without forcing, but it is snug.

Too loose or too tight is a problem.

You should be able to spin it with 2 fingers but not with 1. I believe that is the general consensus.

Try 3.6 that was my sweet spot.

FINALLY I saw improvement with loosening the v wheels. Rotatable with one finger is too loose, and rotatable with two fingers is just right (although difficult to do on the x carriage). Why is this not recommended in the initial calibration instructions?

My results got rid of the lump at the 2 o’clock position on the bottom circle; although the 12:00 position and the 3:00 are the values that changed. The top circle is the new repeatable cut. Is this the best I can expect for roundness in the end? On smaller circles about .375 it more of an issue than with larger ones.

Did you carefully recalibrate both X/ Y axes again with a good scale after readjusting the wheels?