View Full Version : What's Causing Inaccurate Circle Diameter?

10-09-2010, 11:44 PM
I am using Rhino4 to create drawing, Cut2D to create gcode, and Mach3 to cut the pattern. It is consistently coming up short - for instance a circle which is supposed to be 11 5/16 ends up 10 7/8. I do not know where to look to find why this is happening. I calibrated the X and Y axes and 6 inches and both measured 6.01 inches. Where to look?

10-10-2010, 04:43 PM
are you using the right diameter cutter in your cam program or the correct offset if hand coding??

10-13-2010, 12:12 AM
I am using a .25 endmill and that's what the cutter diagram is.

10-13-2010, 07:43 AM

6.010 is a long way off in your axes set up, you need to have it at 6.000 if your test block is 6.000, to start with, Backlash has to be at 0.00 as well, if you want to cut accurate circles,You may have something not set right in Mach as well

10-13-2010, 05:25 PM
I used the calibration program to compare the X and y axes. I don't have a test block so I made two cuts in a piece of wood and measured them with a dial caliper - mach3 three compares the two and makes an adjustment internally. I ran that process until both X and Y were the same length. I made a circle in Cut2d and cut it using the contour setting. I used a 1/4 " flat end mill and set it to cut the outside of the circle. I don't know if I am supposed to use am offset in this case and I am new to this and don't how to allow for that.......

10-13-2010, 10:12 PM

You used motor axis tuning,You need to do it like the video to get it more accurate. using a 6" gauge Block a 12" is even better, & you want to use a .0001 indicator to get each axes set at 0.000, the longer the travel for your setting/testing, the more accurate it will be

Once you have set it, then you can start cutting

- Improved Mach 3 Axis Calibration (http://www.youtube.com/watch?v=XkO5tc-jSxw)

Save your program as text, in MSword, & you can post it here, we can see if the program is correct as well