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Old 07-11-2017, 07:55 PM
wharton1 wharton1 is offline
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Default Z-axis losing steps? off?

Hello,

I have an issue that's been annoying me greatly. Up until about a month ago the Stinger II machine in our shop has been working flawlessly. No problems whatsoever. Now every time you program any sort of Z cut, the DoC is off by about .04 for every 1/4" of depth.

Example
a .07 DoC only cuts to .06"
a .25" DoC only cuts to about .21"
a .5" DoC only cuts to about .42"
a 1" DoC only cuts to about .84"

This happens with single toolpaths and multiple toolpaths with different depths in the same file.

So basically if I want something cut .75" down, I have to setup the cut to .91" to ensure it cuts deep enough.

Any direction on where to start to figure out the problem?
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Old 07-11-2017, 08:47 PM
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Gary Campbell Gary Campbell is offline
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The issue is most assuredly an adjustment. Either something is loose, worn or an electronic gremlin changed your resolution setting.

I am assuming you have ballscrew motion on the Z. First I would strip the Z down, removing the motor and ballscrew and ensure that the Z plate motion is free and consistent throughout the complete range.

Do the same for the ballscrew and nut. Inspect and clean the coupler, paying attention to the ballscrew and motor shafts to see if there is any galling where the shaft may have spun.

Clean and lube all parts and reassemble. Once assembled move the ballscrew up and down thru its motion, listening for any anomalies. Move to top (G53 Z0) Set a rule alongside the Z plate. Line up a mark on the Z plate to an inch mark on the rule. Move the Z down 4,5 or 6 inches and see if the distance moves agrees with the position indicator.
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Old 07-11-2017, 09:02 PM
wharton1 wharton1 is offline
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Sounds good. I'll knock that out tomorrow.

The machine does have an electronic gremlin of sorts. If you so much as breath in the direction of the serial cable where it connects to the machine, it sets off the E-stop. I just have to manually push it in and pull it back out and all is GTG. I've checked all connections and everything internally seems tight.
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Old 07-11-2017, 09:33 PM
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Gary Campbell Gary Campbell is offline
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If they get stepped on a bunch the pins get bent. A new one is only 10-15 bucks
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Old 07-17-2017, 03:56 PM
wharton1 wharton1 is offline
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Update

I stripped down all of Z and didn't notice anything out of the ordinary. Some dust caked on the rail guides is about it. Nothing was loose or had any play whatsoever. Everything was wiped down and lubed. Really the only thing that could have been adjusted was the coupler. I could either tighten so that there was more on the motor shaft or more on the ballscrew. Pretty sure either way is fine.

No change in the Z travel issue. Everything is still very reliably off by about .05 per 1/4" of travel. ie. a 1" DoC requires a setting of 1.2".

I ordered a new cable and had to wait the weekend for that to arrive. The new cable fixed the E-stop from tripping when the cable gets bumped. So that's a win. No change with the Z travel.

Is there anything that could go bad electrically in the Z motor that would cause this? When I was putting it all back together I noticed the Green wire on the machine side of the Z motor connector was broken. It can be pushed back into the connector and everything still works fine (minus the Z travel issue). Any movement of that connector while the machine is on causes small sparks. Obviously not a good thing. No clue how long the wire has been broken. Re-pinning is easy enough, just need to get a couple 4 pin connectors.
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Old 07-17-2017, 04:28 PM
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Gary Campbell Gary Campbell is offline
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Turn the power off! If the connection is sparking you can blow the drive.

Unless you have a crimper for Molex Minifit connectors you will be better off to use crimp style butt connectors. Connect it up, ensure no arcing and see if your Z doesn't get a little more accurate
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Old 07-18-2017, 09:15 AM
wharton1 wharton1 is offline
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Repaired the wire. No change....

Could that motor be shot? Is it possible to slave in one of the other motors and see if that fixes it? Or are they different internally?
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Old 07-18-2017, 10:04 AM
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It could be the motor, but is more likely the drive. You will have to go thru the drive/motor swapping routine to determine which is bad. The problem will follow the bad component.
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