[twstudio]

Hi,
I recently got a used Bear cnc router with a Bladerunner control box and Mach 3 software. I am new to both the machine and the software, and am having some accuracy issues:

When cutting a simple circle toolpath to test the system, I am getting a flat spot on either side of the cut at the outsides of the Y travel, and then a kink in the cut where the machine appears to try to correct itself. The distance across the Y axis where the flat spots are is undersized by about .050 or more on a 6" diameter, and then across the kinks after the flat spots is slightly oversized. By the time the cut reaches either end of the X axis, all is well, then as it continues cutting toward the Y axis the dimension gets progressively smaller until its smallest point where it cuts the flats.

I have checked all belts, pulleys, and pinion gears to be sure they are not slipping; checked all motor tuning and other settings in Mach 3; and re-calibrated the steps per unit multiple times for both the X and Y axes. The previous owners of the machine came out to help with troubleshooting and were as baffled as I am. Recalibrating the steps per unit helped some, but did not solve the problem, and I still have squashed circles. I am generating the toolpath with Vectric Cut 2D, and these test parts were drawn in Vectic Cut 2D.

What am I missing? Any feedback would be greatly appreciated.

Thanks.

[neilw20]

You have backlash.
Setup up a dial indicator and test backlash, then fix the mechanical problem(s).
Mach3 is almost bullet proof. You have a hardware problem.
Don't try to fix the backlash with compensation unless you must make this compromise. You will get rid of the flats, but then the cutter will leave rub marks as axis reversals mean the will be pauses in the motion.

[twstudio]

Thanks for the reply. I will check today with an indicator.

-Tim

[twstudio]

So, I found some backlash and corrected it. This greatly improved my results, but did not completely eliminate the problem. The flat spots are pretty much gone, but the circle is still a little squashed. Do I attribute this to a very small amount of backlash that I could not get rid of, or look for something else?

Thanks for any replies.
Tim

[neilw20]

Now you need to check the scaling for each axis.

[twstudio]

Do you mean setting the steps per unit? If so, I have already done that. If not, please elaborate.

Thanks very much for your responses.

Tim

[neilw20]

Read the Mach3 manual how to calculate the steps per unit.
If circles are out of round..
1. You have backlash on one or more axis.
2. The scaling is still not exactly correct. You might need a fractional value.
3. You are not measuring the circle accurately.
4. A flat on one side can occur when you hit softlimits.
5. The stepper driver is not providing equal steps, or the steps are too coarse.

[twstudio]

Thanks Niel. I have things working pretty well now. It's not perfect yet... I think I still have a small amount of backlash due to some worn pinion gears. Hoping that replacing them will get me the rest of the way there.

Thanks for the help, I appreciate it.

Tim

[neilw20]

If something runs through gears, you will only get rid of the backlash with spring loaded opposing gears, or use timing belt drive.
It is almost impossible, for the average person, with the gear they have to have gears with no backlash.
https://www.google.com.au/search?q=a...ient=firefox-a

[twstudio]

Thanks for the link. I'll see if I can find what I need in anti-backlash.

Tim