Skewed cutting on a new 48" Buddy

[mccoyspace]

I've been really unsuccessful at getting my new Buddy to run part files consistently. This began with my first file, the shopbot-supplied file to drill mounting holes for the sacrificial board to be bolted to the holes in the aluminum table. In the two-pass process, slightly larger 'counter-sink' style holes are cut, then the tool comes back and does smaller plunge holes through the material. In my case, half of the plunge holes were nowhere near the countersink holes at all, just cut kind of randomly into the material.

Now I'm trying to do actual work (well, test work) and there still are a lot of inconsistencies. I'm cutting models of human figures into 2" thick foam, using PartWorks 3D to make the cut files. Things look fine in the software preview. When the machine is cutting it will suddenly skew way out of alignment and start cutting several inches over from where it should be. Run the same file again, and it cuts properly. Here you see two different runs of the same cut file. There were no physical problems of the material moving or constraints on the motor movements.


3946

A similar thing is happening between roughing and finishing passes. The finishing pass will suddenly veer off course and hack into a section of the material an inch or so away from where it should. You'll see that in the lower part of the picture, the finish pass was working, then in the upper part it crashes.


3947

I'll add that I've tried two different computers setups to control the shopbot (but neither of them exactly match the suggested specs...).These two pictures come from the two different machine configurations. In terms of communicating with the machine and other basic operations, everything seems OK. Just suddenly, without warning, the bit is driving off somewhere it isn't supposed to.

Any suggestions?

[erik_f]

I have never had this problem, but I have seen that grounding issues suggested many times for this type of problem.

[beacon14]

Indeed, proper grounding is the first step to try to eliminate these types of problems. Do a search on this forum for "grounding".

[kivimagi]

Are you losing steps.. That is a big issue with the buddy system if the pinion has too much tension against the rack.

It usually happens on the traditional "X" axis, i.e. the motor under the table.

If you are only off in one direction, and not in both, I would check that.

[dana_swift]

From your cuts it appears the X and Y axes are moving with the same command.. that has the odor of a bad controller board. It would be worthwhile to check your USB communications reliability also.

My suggestion is to call tech support. The photos are showing a consistent malfunction of some kind, my bet is your controller board is where the trouble is.

D

[dubliner]

Loosen the v rollers on the Y carriage, then re-tighten firmly but where the car will glide left & right with no binding, also look at X movement as Ryan suggests. I had the exact same problem. In fact to see if you have it, loosen the Y motor bolts and slide the car back & forth by hand, I bet you have binding. I have the exact same results in my trash pile.

[mccoyspace]

An update.
As suggested, I adjusted the X and Y v-rollers. I also dropped the speed slightly (based on results of the speed test). It seems to have helped. Things were looking good last night.
Thanks!

[harryball]

I'm glad it looks like you've solved the problem. From first hand experience, if your V rollers are too tight and the table does not slide easily it can cause binding and step loss. So making this adjustment sounds like a reasonable fix. If it crops up again let us know, we'll keep throwing ideas at you and/or call shopbot support direct.

/RB

[dubliner]

Bring your speed back up, you'll be fine :-)