Mid-Cut Error

[peelio]

I'm not sure how to classify this problem. Over the last month my PRS Alpha has started randomly cutting incorrectly mid-cut. For example, I just spent all day engraving a piece of MDF. I broke the entire job into multiple part files to avoid long, single-file cut times. The files are created in Aspire. I got through 9 of the 10 files without incident but on the 10th file it happened. Suddenly the bit is cutting 3 to 4 times deeper than the file says, the y-axis is off by nearly an inch and the x-axis is off by about 1/8". Soon as I noticed the problem I hit the space bar to pause. I restarted to see if the Z-axis reading was off but rather than being off the file continued on working perfectly as if nothing had happened with all axes back to normal. I let the file finish which took about an hour. I am using the latest version of Partworks and the firmware is up to date as well per SB tech support's suggestion. I am running a Windows 7 PC with an I7 3.0 Ghz processor and 8 gb of RAM. Screen saver is off and the monitor doesn't sleep. It is connected to the internet but that has never been a problem in the 4 years I have had this router.

Any thoughts?

Thanks,
John

[bleeth]

Was there any change to your system in the last month (software upgrade?)
What version of SB control are you using?
From your post you are saying that you didn't have to re-zero your bit? Is that correct?

[adrianm]

MDF is very prone to causing static problems so it might be a static spike upsetting things.

When you do the pause and restart with the latest version of the software it resyncs the positions which would explain why it's correct when you restart.

[peelio]

Dave,
Correct, I did not re-zero and things returned to normal. I am running 3.8.12 and firmware 216. It's possible that Windows upgraded something automatically but I haven't made any other changes outside of upgrading to 3.8.12. I shut off the Windows auto upgrade function but it may be too late if that was the culprit.

Adrian,
Interesting about the static. I have been cutting MDF for 4 years and never had an issue like this. My dust collection is grounded. Is there something else I can do to help with the static?

Thanks!

[bleeth]

John:
Since I'm still running an older software (3.6xx) I don't have Adrian's knowledge of 3.8 version but I have seen quite a few posts that went along the lines of "I've never had this problem before and I recently upgraded to 3.8xxx"
Usually a static discharge will throw your position off. If something in 3.8 can actually detect that and reset to correct position, that's pretty interesting. I'd like to know more about that myself. Chasing down a rare static issue can be vexing. I've been after one myself that pops up sometimes on z zeroing once in a while.

[bill_l]

John,

I ran into the same problem some time ago while using an earlier version of 3.8.x. Immediately after the occurrence, I reinstalled 3.6.46 and ran the same toolpath again and it completed without the mid course error. I've been using the same laptop computer that is over 10 years old without any issues since I got my PRS ALPHA in 2007. I assumed that the problem was connected to the age and speed of my old laptop.

Bill

[jerry_stanek]

You may want to try 3.8.14 as some of those problems have been adderssed

[peelio]

I upgraded to .14 but I haven't been able to cut for 2 weeks because dust collector motor died. After chatting with a buddy of mine we floated the theory that the bad motor was kicking back an occasional charge through the ground and causing the problem. I am cutting now and will let you know how it goes.

Thanks

[robertlock]

i am writing after spending weeks trying to figure out my cnc dilemma.
i seem to have tech support baffled , hopefully someone can help.
i will divide the circle into 4 quarters to make it clearer to understand.
it started when cutting a simple circle, it went 2 quarters way around and then mirrored the third quarter then returned the correct direction for the 4th quarter. ending at the end position of the second quarter. the position display showed it was where it should be but it was not.
it cut this way in the ccw dir. but cut fine in the cw dir.
i have used different programs for design and even had tech support send me a file they wrote . same result.
in order to continue my work i redesigned everything to run in cw dir.
today i went to cut holes 20mm dia. positioned equally in x and y, 120 total. i drew a 20mm circle, offset inside the radius and pocketed clean (spiraling out in cw dir) .75 depth cut in two .375 steps
10 lines in x of 12 holes each in y
first x line cut fine, second also, but in the third the holes started to drift in x
each consecutive hole getting further off track......
i have re tightened all pinions squared up all rails cleaned racks replaced high speed hub, removed checked and reinstalled all wago conections, re installed software upgraded to latest version....at wits end and getting busier
have a prs 4x8 w/4g card, have had no problems with sb since 94 when i bought my 1st.....

[peelio]

No idea if I can help but when did you start having these problems? Did the timing relate to any major system changes?

My problems started in late February and seem to align with the SB software upgrade although I have no other evidence to convict. I broke one project down into 10 different part files and cut them successfully over 11 hours on Thursday and Friday last week. I started a file today and mid-cut I got an error reading "Shopbot No Longer Being Recognized". That was a new one for me. No harm was do to the material I was cutting but I still don't know why it happened. I am running the file again as I type to see if it happens again.

[srwtlc]

Robert,

Is this the first time running a file like this one (a lot of circles back to back)? Do you see any signs of this with any of your other files? Looking at the code, how many decimal places are your coordinates carried out to? It sounds like an old, old issue where CG circles would cause loops that could be reversed and loop back on themselves. The fix at that time was to be sure that there was 6 places after the decimal point.

Attach the first file and I'll roll it around a bit.

[peelio]

I connected my old laptop that has version 3.8.8 on it and I have not had a problem since. That allows the current conclusion that there is something wrong with the latest version or that something is wrong with the other PC. I am going to check the USB ports for problems next.