Circle distortion?

After a recent question being answered I reset my center start point more accurately by using a v engraving cutter to get it as close as I could and adjusted my holding jig and cut the circle. For some reason it seems to be flatter on one side the cut and speed are not fast so there shouldn’t be any distortion and the material is quite soft also. The compass in the images is set up on the center point and is correct on the start of the cut but as you can see from the compass position on the other side its out. The lead on the compass is the inside of the cut line where the internal cut should be. Any suggestions as to why this may be happening.

Start with mechanical issues first. After that repeat the circle and if it is consistently not round then a calibration of the stepper motors is in order. However usually it is a mechanical problem like v-wheel adjustment on SO3-4. The newer machines HDM and SO 5 do not have v-wheels so calibration would likely fix it. You have to change the stepper motor steps per MM. The calibration process is here on the forum.

If you have an SO3/4 then check belts, pulley set screws and v-wheels. If an HDM and/or SO5 then lubricate your rails before doing the calibration and changing the steps. If you get inconsistent result then it is likely mechanical. If the circles are ovals in different areas of the spoilboard then it is calibration. Just solve any mechanical issues FIRST.


Are you sure you are on the center point? Seems if you were to move the center point of the compass over half the distance of the cutter, you would have a different result. The circle looks pretty circular in the photos, but your * in the center does it look centered.

Just saying that what you think is center may not be.

Maybe try this with a V bit with a tiny inner circle (1/16”) and the your same outer circle. This would have the CNC mark the center and the mark the circle.

Have you calibrated for belt stretch?

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