Router brushes causing problems?

[matt_raymond60]

I have an older (but not a cable model) 48 by 96 Shopbot that I haven't got to use very much for various reasons. Now I have some work for it and am having problems. It occasionally jerks and loses it place in all three axis's thereby ruining what I am trying to cut. I read several of the posts on here that I thought might help and am fussing with it trying to check all of those items. One thing that I was curious about though is whether or not my router brushes might be causing problems. It is an older router and is in need of replacement. I do have a new router and mounting bracket that I bought off of the forum some time ago but haven't installed yet. Wasn't sure if worn brushes or something might be causing some kind of static that could be affecting the mighty Bot? The last time I used the machine it worked fine.

Thanks for your input!

Matt

[paul_z]

Check the dust collection system grounding. Static can cause exactly what you are experiencing.

Paul Z

[bobmoore]

I think Paul hit it on the head. Run it with the dust collection off on a dry day to test it out.
Bob

[matt_raymond60]

The dust collector was my first thought, haven't used it for the last few tries. It will cut one or two pieces fine then spaz out. If I shut the computers off then back on I can get another one or two out of it before it freaks out again.

[steve_g]

Matt

How hot is your shop? We've had some hot weather in Texas lately... just wondering if your computer is having issues.

SG

[donek]

Is this a PR model? It would be kind of gold colored rails made out of strut.

I've run a machine like that since 1999 and never had a single issue with static. In my experience, there are 4 potential problems. If it's not a PR, then completely ignore what follows.

1. you've got a driver board going bad.
2. you've got a broken wire in one of your cables, making a driver board go bad.
3. the hold down clamps are too tight and causing the system to bind up in one or more locations.
4. the seam in the rack gear is not consistent and the machine is binding and loosing steps when it crosses that seam.

In reality 3 and 4 may be masking 1 and 2 as those problems will overwork the stepper motors and heat up your driver boards.

diagnosis: open the case and feel the heat sink on your driver boards. If it feels hotter at one location, that board is likely going bad. Be sure to double check continuity on every wire running from that driver board before fixing or replacing the driver board.

grab the hold down bearings as the machine travels the entire length of the rail. If you can not stop that bearing from spinning by squeezing it, it is most likely too tight.

does the machine always loose steps at the seem in the rack gear. If so, you could try reducing the tension between the motor and the rack.

The only other possibility I can think of is a motor burning out. It's not impossible, but I've never had it happen.

[matt_raymond60]

I am getting back the Shopbot again finally. Still having the same problems. It has been hot in Dallas but not much worse than last year in the shop. I am thinking about pulling my driver board and sending in to have it checked out. I have one small job that I need to get done on it first. Seems like if I shut the computers off then back on again the first operation will go just fine. If I try to run it again without shutting everything down then somewhere in the next operation it has a hissy fit. Still not using the dust collector just in case but it doesn't seem to have any effect on it.

[matt_raymond60]

Also, there doesn't seem to be any certain area of the table where the problem seems to occur. It does it randomly whenever the mood strikes.

[steve_g]

Matt:
Sean has experience with an older machine like yours... be sure to check all his suggestions! How fast are you cutting? Have you confused inches per second and IPM? Have you tried running from another computer? Have you tried the speed test to eliminate communication issues?

Just guessing...

SG

[donek]

Also, there doesn't seem to be any certain area of the table where the problem seems to occur. It does it randomly whenever the mood strikes.

The working fine on the first and going bad after is a good indication it's heat related. I had a broken wire in one of my cables last summer that caused a driver board failure. It did so 2 or 3 times before I found out it was the wire. If you're not afraid of soldering, the driver boards are quite easy to repair. Post a photo of your machine and the inside of your control box. The easiest way to determine the culprit is to feel the heat sink or put a laser thermometer on it. The excessively hot chips will be the ones to pay most attention to. Check the temp on the motors too. If it's hot, there's something going wrong.

Chris Burns at Shopbot is the expert on the older machines. I recently converted to version 3 prt controller and he diagnosed my problem in less than 20 minutes on the phone. Call him. He'll get you figured out.