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Topics - NiOBoBeO

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Hey everyone. I posted about this a few weeks ago, but the thread died and can't be accessed any more- so here it is again.

I have a 'JoesCNC Hybrid' that I have been trying to debug and I cannot get backlash comp to work properly. I suppose that's a bad way to describe it- from what I can tell, the software is taking up the correct amount of backlash, but the movement that follows is poor. This is an issue as the end mill really starts to warm up when the move is slow and rough.

I have read / watched Hoss' information on backlash compensation and the odd results, and as result, I had started out with my backlash comp velocity set to 100% and the shuttle accel to 0.005s. Obviously, this did not resolve the issue. I have played with several different combinations of shuttle accel and % velocity, here is I brief log:

1. Followed the advice of several threads by changing shuttle accel from 0.005 to 0.05, and then to 0.5. Each change made the affected movement more and more rough, 0.5 being the worst.

2. Given trend, placed shuttle accel at 0.0005s. The movement is still messed up (see videos), but this is the smoothest setting.

3. Any change to % velocity for backlash comp does exactly that, but after the backlash is taken up, it begins to move rough once more.

Here are links to videos that show the issue (CAM set to 80 ipm, but slows down to 20 ipm on negatives):


Given the number of different shuttle accel / % velocity combinations I have tried, I am really hoping there is some other setting that is causing the issue. I have attached my current .XML file for reference, but feel free to ask about anything.


General Mach Discussion / New Machine Configuration & Backlash Comp Issues
« on: February 22, 2012, 08:49:05 PM »
Before I start, I would like to say that I have spent the last week or so reading forum after forum about the various woes associated with backlash compensation. It was only about halfway through my search that I realized the odd relationship between mach 3 builds and the G540 controller... I guess its been cleared up since 09'-10'??

For the last couple of weeks I have been struggling to put the finishing touches on my 'JoesCNC Hybrid" rack and pinion CNC router. The main issue is that when enabled, the backlash compensation causes very rough movement when the compensation is actually utilized. Here is a short video where the machine moves around a 10" x 10" square, ending with a diagonal move to the center:


Thus far, I have tried the following:
1.Tore down and rebuilt each of the mechanical components twice in an effort to remove as much mechanical backlash as possible. In general, I am very pleased with the results: backlash of 0.0043" in the y-axis and 0.0070" in the x-axis (zero-backlash nut in the z-axis does a great job).
2. Re-read the mach 3 manual and performed a careful step-by-step re-installation of the software.
3. Verified BIOS settings for the parallel port.
4. Sent my controller back to Gecko to have them take a look at it. They couldn't find anything specifically wrong with the drivers, but they replaced the motherboard as a precaution.
5. Tuned the g540 trim.
6. Changed shuttle accel setting. I read several accounts of people changing this value from 0.005 (my current setting) to 0.05, and 0.5; the vibration that you hear in the video gets worse and worse as I go toward 0.5 setting.

Naturally, I can turn off backlash compensation and everything sounds / moves fine. I wanted to see if anyone else has run into this combination of symptoms before I request phone support, but if it gets to that point, I will post the results. My XML file is attached.


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