2 days work down the drain!

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ChrisInEstes
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2 days work down the drain!

Post by ChrisInEstes »

2 days work down the tubes! This really screws up my Friday.

Something went wrong somewhere in the system. What (I think) I told the machine to do is not what it did.
The pics below will show my problem. The r in Taylor is shifted over onto the o. Looks like the whole rest of that line of lettering has shifted with the r. The tool path in the VCP preview shows correct, the actual part is wrong.

Any ideas as to what went wrong, where it went wrong, and why it went wrong?

Chris
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Re: 2 days work down the drain!

Post by Paul Z »

Looks like missing steps to me. You might be cutting to deep in one pass or the carriage is binding up somewhere. Steps were missed and from that point onward, all cuts will be offset.

Paul Z

PS Also make sure that your material did not move.

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ChrisInEstes
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Re: 2 days work down the drain!

Post by ChrisInEstes »

Paul Z wrote:Looks like missing steps to me. You might be cutting to deep in one pass or the carriage is binding up somewhere. Steps were missed and from that point onward, all cuts will be offset.

Paul Z

PS Also make sure that your material did not move.
I agree, it looks like it missed a bunch of steps all in one chunk. It's offset ~1.25" @ 1000 steps per inch. Somehow, if it lost steps, it happened in one chunk of ~1250.

Here's what I know so far:
The material didn't move.
It wasn't the cut depth or feed rate... The pass depth was only 0.125" with a 0.125" bit @ 60ipm and 12000K rpm in soft wood.
I don't feel any binding in the gantry.
The system is electrically grounded, & no dust collection happening, so I don't think it was a static discharge, but I wouldn't have a way of testing for that.

I have a call in to my customer. He has a trade show coming up, and if it's tomorrow, I'm not sure how I'll get him a sign for his booth. Yikes! If it's at the end of the month I'll have time to remake it from scratch.

Chris
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Re: 2 days work down the drain!

Post by John Murphy »

I have lost a couple of stepper drivers in the last few years. One started to loose steps, and the other burned. I'd have to side with the lost steps, whether it be an electrical or mechanical issue.

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Re: 2 days work down the drain!

Post by scottp55 »

Chris, Was it repeatable in an air cut? Just curious.
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Re: 2 days work down the drain!

Post by Nthkentman »

Had a similar issue myself a few days back. The axis screw drive was loose on the shaft resulting in misalignment.
Check the fixing of the drive to the ballscrew or shafts
If you can't fix it with a hammer you've got an electrical problem !

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ChrisInEstes
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Re: 2 days work down the drain!

Post by ChrisInEstes »

Further testing:

I ran the same tool path again, and it cut correctly. So, as expected, it wasn't a VCP issue.

All the ~1300 steps came in one chunk. The way the machine is built I don't see how it could be something mechanically loose in the drive train. If it was, it would show some other symptoms. I'll pull the covers and give it a good going over to make sure.

So, it points to a loss of ~1300 steps in one chunk of about 1/3 of a second.

The X-Axis gantry runs on round steel ways with pillow block bearings. There is protection to keep chips out of the bearings, but if a chip made it's way into the bearing maybe it could have acted as a wheel chock jamming it up for a little bit.

If it was the stepper motor itself, what could be the causes of that? Loose wire... maybe starting to fail?

Thanks!
Chris
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Re: 2 days work down the drain!

Post by Leo »

I would bet a STRONG cup of Keurig coffee it was lost steps.

That has happened to me FAR MORE times than I care to count.
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Re: 2 days work down the drain!

Post by Paul Z »

I wonder ... Is it possible that it didn't "miss steps" but instead missed and entire move or jog command??? Is the humidity dropping where you are and the event was really static? If so, time to fix it before the humidity gets even lower.

If you are a power excel user, you can often read the file in excel and look at the x,y moves in an analytical environment.

If you catch the error early enough, you can use wood filler or bondo to "erase" the mistake. If you are comfortable with editing toolpath files, you can recut the mistake parts without recutting the entire file. (Excel can make this editing easier.) Do not try this unless you are very familiar with editing cut files.

Paul Z

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Re: 2 days work down the drain!

Post by ChrisInEstes »

Paul Z wrote:I wonder ... Is it possible that it didn't "miss steps" but instead missed and entire move or jog command??? Is the humidity dropping where you are and the event was really static? If so, time to fix it before the humidity gets even lower.

If you are a power excel user, you can often read the file in excel and look at the x,y moves in an analytical environment.

If you catch the error early enough, you can use wood filler or bondo to "erase" the mistake. If you are comfortable with editing toolpath files, you can recut the mistake parts without recutting the entire file. (Excel can make this editing easier.) Do not try this unless you are very familiar with editing cut files.

Paul Z
It could have missed the entire move command. If I was thinking, I would have checked where the tool ended up after I stopped it and sent it home so I'd know whether or not it went back to the starting X,Y,Z position. At this point, I have no way of telling if the 1300 pulses were sent to the steppers and the stepper couldn't move, or if the control box didn't actually send the pulses. I just know it missed them all in one group.

I took the gantry cover off and checked the drive train for looseness. Everything is tight. I pushed hard on the gantry while it was moving to see if I could get it to miss steps, and it just pushed me out of the way w/o missing a step. All the power/signal wire connections are snugly plugged in.

I used to have static issues a long time ago and with a different controller. It was then that I drilled a hole in the shop floor and drove in a 6 foot copper ground rod, and grounded the router chassis, spindle, and control box. That solved my static problem. I checked all the grounding points and they're all tight. It is generally very dry here, but it's actually been a little more humid than usual. It still could have been a static discharge, though.

I can't patch the flub on this one. It's finished with clear waterborne poly, so there's nothing to cover up a patch. It'll have to be remade from scratch.

Onward!
Chris
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Re: 2 days work down the drain!

Post by dhellew2 »

Even a small power glitch could cause the problem, one small enough that the computer/router/etc. does not go off. I've had this problem before (too many times), now I have UPS's on everything. Dale
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Re: 2 days work down the drain!

Post by ChrisInEstes »

dhellew2 wrote:Even a small power glitch could cause the problem, one small enough that the computer/router/etc. does not go off. I've had this problem before (too many times), now I have UPS's on everything. Dale
Oooo... Good idea! I've had that problem before, too. It's got a UPS on it, but I should test it to see if the batteries are good. I've had 2 other UPSs lately that the batteries died on. They normally beep when a battery goes bad, but maybe I missed it.

EDIT: UPS tested and checked good.

Thanks,
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Re: 2 days work down the drain!

Post by IslaWW »

Chris....
If you have eliminated mechanical, and you have almost eliminated electrical, you will go to what would be my first choice as the cause of the problem, which is static discharge. This time of year, tech support lines at virtually every CNC brand light up with static gremlins. Those in the cold country and at altitude are the first to call, then as winter, and the dry air that comes with it, moves south, so do the calls and emails.

Here is an article that I wrote last year in response to dozens of call like yours. http://www.camheads.org/showthread.php?t=3800

IF you adhere to this... to the letter, including the wire installed inside the hose to the machine, only extreme cases will prove to be problematic. Those are solved by adding a conductive flex hose. ($$$$) But, sometimes necessary in winter, at altitude, when cutting MDF, plastics or HDU and PVC foam sheets. You have the motherload of problem potential, but it can be solved.

Please note where it says grounding, I specifically say to the electrical system ground, which by code has its own ground rod. In many cases installing a driven rod, which is common in extremely large facilities, mostly for lightning protection, will cause more problems than it will fix with CNC machines. In some cases where it does help, there was something else wrong.
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Re: 2 days work down the drain!

Post by ChrisInEstes »

IslaWW wrote:Chris....
If you have eliminated mechanical, and you have almost eliminated electrical, you will go to what would be my first choice as the cause of the problem, which is static discharge. This time of year, tech support lines at virtually every CNC brand light up with static gremlins. Those in the cold country and at altitude are the first to call, then as winter, and the dry air that comes with it, moves south, so do the calls and emails.

Here is an article that I wrote last year in response to dozens of call like yours. http://www.camheads.org/showthread.php?t=3800

IF you adhere to this... to the letter, including the wire installed inside the hose to the machine, only extreme cases will prove to be problematic. Those are solved by adding a conductive flex hose. ($$$$) But, sometimes necessary in winter, at altitude, when cutting MDF, plastics or HDU and PVC foam sheets. You have the motherload of problem potential, but it can be solved.

Please note where it says grounding, I specifically say to the electrical system ground, which by code has its own ground rod. In many cases installing a driven rod, which is common in extremely large facilities, mostly for lightning protection, will cause more problems than it will fix with CNC machines. In some cases where it does help, there was something else wrong.
Thanks Gary, That's a good read. I should have mentioned that I don't run dust evac on the router. Yeah, it makes a mess, but because of the low humidity here, I don't risk it.

The reason it's all grounded through the copper rod is the fact that several times per year lightening strikes the power lines around here, so I don't want to give it a path to my machine.

I do make negatives of each different tap handle shape to act as a holding jig. That get's me square with the drill bit. I just haven't found a way to hold that jig in place for the quantity of handles I now have orders for.

Thanks!
Chris
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Re: 2 days work down the drain!

Post by dhellew2 »

You can run dust evac on the router as long as everything is grounded. Use flex pipe that has wire, cut off a little extra duct and ground the wire on both ends. If your ducts are pvc run a bare copper wire inside the pipe, grounding both ends.

Dust flying in the air is a potential explosive, just like sugar dust, gasoline, and starch dust not to mention bad for your lungs. The spark from a spark plug or motor is enough to ignite the dust.

Our annual humidity average is 8 and I have dust collection hooked to every machine and floor sweeps on the floor. My ducts are all galvanized metal, and all the gates are metal.

There is a lot of good information on the web and in books on how to install safe dust vacuum systems.

dh
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