circles off center

We are trying to cut circles of various sizes...usually 24 - 48" using a bearing mounted in the center of the wood as home. So we home on the center of the bearing and tell the machine to go from there to the edge and cut the circle (bear with me as I'm not the one who is running the machine. I'm just trying to help find an answer). The circles come out perfectly round but offset about 1/2" off center. We are making the circles in Heek's CAD and dropping them into Linux CNC. We cannot solve this mystery. We are noobs and any help would be great.

David

If the diameters are correct, you have your step scale correct, so that's good. I'm presuming you have your machine coordinates established and have touched-off where you intend too.

If you are getting exactly the same distance displacement, I'd suggest looking at the tool definition being used in your CAM program. Is there any offset built into the tool? What is the diameter of the tool? Is your CAM zeroing to the vertical centerline of the tool or to its edge? I'm not sure what program you're using (and I'm not very experienced myself), but I have played with Fusion 360, and it will cut a circular dimension in three completely different ways. It will profile around the outside of a diameter, cutting to final dimension toward the inside of its path; it will pocket a circle, finishing the dimension to the outside of its path; and, it can trace a circle, straddling the dimension line and cutting away whatever material is obliterated by that diameter of cutter -- leaving a circle smaller than the tool path by the cutter width (minus 2r removing equal material across the diameter)

To really figure it out, you may need to crawl through the g-code and see what is happening in the few steps before the program starts to Z down to start your cut. Presuming you are instructing the CAM setup correctly, the tool should move to a starting position one tool-radius farther out than your target dimension, if you're doing a profiling-style operation. Look for a G0 X[Circle Diameter + Tool Radius] or an equivalent G0 Ynnn instruction right before the tool plunges into the cut with Z down. Is that starting where you intend?