stepper motor grind and position loss at random

[Brett1970]

ARGH! my shopbot has been one headache after another since i bought it new about 3 years ago. It's a PRS standard, 48X96 pc style control box, running a 2.2 HP spindle and i have a vacuum hold down system. When running a cutfile, at random, and it seems it's every other sheet i run, it will be cutting fine, then i hear a grinding noise, machine stops for 1 - 3 seconds, then it continues. The software doesn't know it stopped, so it continues on, with the X Y off, and ruins my sheet.

The other odd thing is i get a message yesterday that says somthing like "the shopbot toolbar has changed, would you like to use the new one?" (no clue) and i did get a comm lost message once too.

This thing ran pretty good till recently, and i have made no changes of any kind. It used to do the above mentioned problem about once every 40 or 50 sheets, i've ruined 3 out of 6 sheets in 2 days.

I cleaned the rails, no signs of wear. I pulled the stepper motors and see no issues with the pinions. i unplugged all my stepper wires to the control box and pushed the gantry against the stops to make sure the gantry was square. I am at a total loss. i am running close to 80 % on the speed test.

i don't remember, but should the stepper pinions turn hard? seems like my gantry wasn't that hard to push in the beginning (with the steppers unplugged and the machine off of course) I know how to set gear lash, and not just mash it till it stops and tighten it down.

Also, my stops have never worked correctly. my machine could be out cutting at X48 Y17 area, somewhere in the middle of the table and i would get the "stop hit" message and it would quit.

I am at a total loss here, i had a saturday deadline i can no longer make, and i've wasted 100.00 worth of material. I've cut this material with the same bit, same speed, etc with little issue. PC is not on the internet at all. Any ideas?

[Brady Watson]

Make sure that both the machine and dust collection system are properly grounded. Run a copper wire off of the chassis of the machine over to electrical ground. Take a bare copper wire (16-20ga is fine) and fish it through the dust hose and put the end to the same ground. Then poke the other end out and connect to the gator clip on the dust foot itself.

High voltage static WILL cause false triggers of your 5 or 24v proxy switches. Ground the machine & you should be good to go.

For your Z axis, it sounds like you may either be losing steps by going too fast on the Z (pull the speed down to 1 IPS on the Z) or your motor driver is 'tired'. If running Gecko brand drivers, ShopBot should be able to hook you up with the correct replacement.

Yes - the motors will resist turning due to the internal 3.6:1 gearbox & magnetic flux from the motor itself.

-B

[Brett1970]

i had a grounding issue very early on, due to a ground loop. I'm sure i'm grounded correctly, i did everything shopbot told me to do for that step. I'm not losing Z, this is happening in either the X or y move, while making a cut. I am thinking it's happening on the X move.

[Gary Campbell]

David...
Do not asume anything. It could be as simple as a broken connection or corroded wire. Do not take anything for granted. To solve the problem check everything.

Brady has listed the steps above. Follow them. In some cases, the SB grounding instructions did not solve the problem. Look here for more info: http://shopbotwiki.com/index.php?title=Grounding_your_ShopBot

Stopping during a move is alsmost a sure sign of static discharge (ESD) Make sure that the dust hose does not contact the Zzero plate or the YZ car when the machine moves

[Brett1970]

well, i definately don't have it grounded like the guide. I have the machine grounded at a leg, a ground to the control box, a ground the base of the dust collector, and my dust collection hose has a wire looped in the plastic itself, with an aligator clip to the dust collection skirt. I used to have a bare stranded wire that ran inside the dust collection hose, but i cut a ton of birch ply, and the cut produces lots of stringy debris, and it would plug the dust collector 1/2 way through each sheet.

I am curious about following up on this shopbot toolbar message, i've never seen it before, nor do i know what it means.

[Gary Campbell]

David...
That message usually means that a change was made that affected the toolbar menu system. This could be as simple as a change or addition to the custom# files, or it could mean a forced shutdown resulted in a registry error.

When SB3 starts it reads those custom files and if there is a change from what is written in the registry, the message displays. If you made a change, then accepting is OK, if not, then it may mean there were some write errors.

[Brett1970]

well, sounds like an uninstall/reinstall is in order. I wish i would write down two things.. i always forget these. command to disable stops, and where to change the value to flip my Y axis!

[jerry_stanek]

I was getting the hit stop on my PRS standard and found it was the ground from the limit switches at the control box I moved the ground to a different terminal and haven't had a stop in over a year.

[Brady Watson]

...and my dust collection hose has a wire looped in the plastic itself...

This is not adequate. The wire is there more for structural support to keep the hose shape than it is for grounding. A bare copper wire THROUGH the hose properly terminated at both ends is a guaranteed way to eliminate static from the DC system. I know it sounds weird, but it works.

As Gary says, don't assume anything if you truly want to solve the problem.

-B

[bleeth]

I can't prove it works but I have never had a ground wire in my DC Hose. I do have it isolated from the rest of the bot by using plywood blocking to secure it to the z in such a way that it stands off from the gantry. Haven't had any problems since I did this.

[Gary Campbell]

Dave...
You have an open air (non AC) shop in South FL. The high humidity there doesnt allow static to generate, other than a few days a year when the humidity is less than 40%.

When my shop was in the Keys, I didnt even know what a grounded DC system was. If you remember all of my DC pipes were PVC. I have Installed all metal ducting here in the land of dry air.

[Brett1970]

well, after updating all the software, and regrounding my machine using the grounding guide, i am back up and running trouble free! thanks guys!!

[jimboy]

David the only good problem is the solved one. And a bunch of heads are always better than one.
Jim