Hi, I have a desktop CNC, not big league stuff, but after watching your videos on this, which are great by the way, I've attempted to calibrate mine as I have been unable to cut to spec. I've only had the system and ever done this for the past 2 months so I'm green.

I don't have a digital guage like you have in the video, but I have a 6" digital calipers. So I rigged up with my portable vise and hooked it to the gantry and using the calibration wizard I made multiple runs until I consistenly got 5.000 +-.001 At this point I would expect the system to be calibrated and work like a swiss watch, instead I've got the Taiwanese version. I have a new router, new bits and no runout. Also, I'm cutting .025 cast acrylic.

A simple test of pocketing a 1" circle with a inner .175" circle comes out with 1.025 on the outer and .150 on the inner circle. I have done this numerous times with the same results.

The system consists of:
24"x12"x 3" cutting area
- 282 oz/in steppers on all axis direct driving the lead screw
- 12 Precision linear ball bearings (4 per axis)
- Hardened shafts
- Anti-backlash wear compensating lead nuts
- 3 axis chopper microstepping controller

10 threads per inch, 1/2 step mode, 200 steps per rev
4000 steps per inch should give me .00025 per step

The odd part is it is always coming out .020-.025 off. If the linear runs on X and Y are giving me +-.001, how do I end up with this difference? I have a thread going on the Mach 3 board about this, but was hoping you might know what I should look for. The gcode was generated by the admin over there which rules out any errors from mine. I took a newer faster pc with a fresh install of Mach 3 and recalibrated, same results. I've basically eliminated everything but the controller and motors. If I manually enter the correction values based on the circle dimensions, then the linear runs of X and Y are out. There's no backlash as it's the same 1.025 all the way around. It would also be nice if the builder would return my emails, anyway, just curious if you might know what could be causing this or what to look for.

Thanks!
Mark

I checked the bit almost right away. Being new to this, someone experienced may have caught it right away, but that and my eyes aren't quite what they used to be. I had checked runout by manually turning the bit and looking for variance and didn't see any. But my son said he thinks he sees a slight blur when at speed. So I replaced the collet and nut and apparently that was the problem besides not being calibrated correctly until I watched your video. I still don't trust the calibration as I had it correct last night and tonight it was off by .017 so I had to do it again, but it's cutting a .5" hole .5".

I guess I just got smarter about this stuff. Lesson learned.

Thanks! and again your videos are great!