Need Help Please!!!

[jeff1966]

I have a cnc router and after cutting a square you can measure it and it will be square. Now when I cut a circle it will be right on say the x axis and about 1/8" short on the y axis. I have 2 routers a 4' x 8' and 24" x 39" and both of them are doing the same thing. The 4' x 8' has rack and pinion on the long axis and the other router has ball screws on all 3 axis. I am using Mach 2 software. Can anyone help me with this???????????

[edo]

I don't have a lot of experience with this, but it sounds to me like you're missing steps on the Y movement. You may be cutting too fast. Try slowing the feedrate down and see what you get. On my JGRO I noticed that I get a lot smoother cut on circles by slowing my feedrate from 25 to 15.

If your squares are square, your software is setup correctly and sending the right amount of data to your motors. How big is the circle that you're getting the 1/8" difference on? What G code command are you using?

[jeff1966]

I am using G02 and the radius is 6.5. I did try slowing the feed down from 15 to 7.5 and it didn't help any. I am cutting .500 polyethylene with a .1875 straight end mill.

[ger21]

Backlash maybe? Can you post the g-code?

[edo]

Are you cutting the full .5" depth in one pass? It may be too much for the motor to push through - again, lost steps.

[CNCRim]

I don't have much experience with router, but I have feeling that you have your vector is wrong, it cut an egg shape instead a circle. It work with square, but not arc I think it is program issue. Post part of your program we might see some.