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  #1  
Old Mon 22 October 2018, 17:58
Diplocaulus
Just call me: Gary
 
Kearney
United States of America
Quick Question, if I am replacing a faulty stepper...

Do I just rewire and bolt on the new one and move on, or is there another step regarding software I need to consider? I am new to my job, and have picked up a lot fast, but I think before I got here the z axis was sent into the spoilboard a few times, so when I zero the z axis, it all appears alright but when I tell it "goto zero" it sends the bit into the material. Long story short I think it's skipping gears, and think I should replace the z axis stepper. Will the new motor (same make and model as previous) need any sort of registration to the mach3 software, or will it just run?
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  #2  
Old Tue 23 October 2018, 08:39
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
It should just run.

What motor is it? You may also have an issue with your lift cylinder. The piston arm that supports the weight. Where is this MechMate working in an company environment?
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  #3  
Old Tue 23 October 2018, 12:38
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
As Mike said, stepper failure is really, really rare.

In theory, the lift cylinder balances your Z-axis, so that if the motor is completely removed the Z axis still stays in the same position. If the lift cylinder is too powerful, the axis goes up, if not powerful enough, it goes down.

In practice, the lift cylinder is often off by a pound or two, but the motor can overcome it. While I'm at it, the lift cylinder should be installed "upside down", so that the lubrication inside the cylinder runs down to the piston seal at the bottom, and not vice-versa.

You appear to describe a symptom where the axis holds steady until you attempt to move it, and then bit moves downward. I can think of a number of ways this can happen:

- The Z axis is set up backwards.
- The Zero point of the axis in the software is actually below the spoilboard
- The pinion gear is loose
- The wiring to the motor has a break
- The driver for the motor has gone bad
- The control signals for the driver are bad.

Questions:
If you pull the motor out of the rack does the gantry go up or down? With a lot of force or a little?
If you jog the axis upwards after you zero it, does it move? Upwards? Does jogging the other way go in the other direction?

Everything you've described sounds more like a software issue, because the axis does not move until you tell it to. If it's actually disconnected due to a bad motor or wire, I would expect the imbalance to send the axis all the way up or all the way down whenever the power is off. The fact that the spoilboard has been hit a few times tends to confirm that the software setup isn't quite right - something about the zero-ing procedure isn't well understood.
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  #4  
Old Wed 24 October 2018, 09:08
Diplocaulus
Just call me: Gary
 
Kearney
United States of America
We've only had the machine a couple months, in a moderate use industrial environment.
We cut eps foam and PU foam, so there isn't a ton of resistance from the material. We can run PU foam too fast but can run EPS as fast as the machine will go, most of the time. I can zero the motor using a tool setter, at which point it lowers slowly, makes the touch, then retracts slightly. If I hit goto zero, the motor then retracts slightly more and drops to the z zero. Most of the time it will make a "chonk" sound in the moment it changes direction from up to down in the "goto" function, then plunges the bit into the material. It is eps foam in this case so no worries, but from that point on the zero is miscalculated and will no refer to the job zero in relation to the machine zero, so it will make it's final pass (fairly consistently) about 1/4" into the spoilboard. Before I worked here the bit had been driven into the table a few times, during setup or bad files, etc. I was thinking the z stepper had maybe been damaged during this time. When I watch the "auto tool zero" and "goto zero" functions very closely at the pinion, the motor seems to be acting up, but it could be a loose gear. I will check that.
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  #5  
Old Wed 24 October 2018, 09:21
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Okay, you've clearly got a handle on the software side, so I will flip to:

- Pinion gear grub screws on rack
- Pinon and rack not meshing cleanly - the Chonk
- - wear on the rack or pinion.
- - spring not strong enough to hold pinion engaged, especially when:
- - Speed of movement to zero is faster than all other moves, and outruns the system.
- Motor not powerful enough / axis unbalanced
- Motor dead

Fingers crossed it's your pinion gear grub screws.
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  #6  
Old Wed 24 October 2018, 09:52
Diplocaulus
Just call me: Gary
 
Kearney
United States of America
I did find the gear was loose, it didn't appear to be moving independent of the shaft but after marking it have seen otherwise. Thanks, I'll see if tightening it fixes the problem.
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  #7  
Old Wed 24 October 2018, 17:40
Diplocaulus
Just call me: Gary
 
Kearney
United States of America
So, the gear was loose but I have have tightened it and have still gotten the z to dive into the material by hitting "goto zero." The z is highlighted red on mach3, which I haven't figured out yet. We have some limit switches but I am not sure if they work yet, I am wondering if setting soft limits would help the z axis issues.
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  #8  
Old Thu 25 October 2018, 21:21
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Man, I liked it better when we had a single symptom and naive writers <grin>

I'm not a mach3 guy, so maybe someone else can help with that. That red seems likely to indicate we don't have the zero we expect. From what I see of internet searches, it means that the Z axis is not homed. Do you actually have limit switches for the Z? That seems weird. Is there a Z touch-off plate that isn't in use? That would be consistent with diving as low as you can, trying to find the touch-off.

I think you need to figure out what the correct Z zeroing procedure is for this machine.

And I suspect all the crashes are what loosened the grub screws.
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  #9  
Old Mon 29 October 2018, 08:14
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
What I noticed is that you've written about a "machine zero" and a "job zero". To me, that means that the "machine zero" is found by using a touch plate laid on the spoil board and the "job zero" is found by placing the touch plate on top of the material that you are cutting.

For finding the "machine zero, the procedure to use is to put the z-zero metal plate on spoil board, and then use the Mach3/4 canned cycle to set the real zero (zero = sensed contact point - thickness of contact plate). Doing that will accurately set the zero point to be the surface of your spoil board. If your CAM software program uses the spoil board as "zero", then you are ready to run.

If "job zero" is referenced to the top of the material, then your "job zero" is off by the thickness of the material if you use the "machine zero" procedure. So, if "job zero" is referenced to the top of the material that you are cutting, then place the z-zero metal plate on the top of the material (instead of on top of the spoil board) when you zero the z-axis. By doing that, the top of the material becomes the z-zero "zero" point and all z-axis cuts would require a negative distance in the g-code file.
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  #10  
Old Tue 30 October 2018, 14:05
Diplocaulus
Just call me: Gary
 
Kearney
United States of America
Thanks guys, it's not solved yet but we are replacing the spindle so I can't play with it at the moment. I have a feeling the gas spring may have been the culprit, it was mounted correctly and is still lifting but seems really jerky after I have gotten it out of the machine. We will take a closer look at the software when we install the new spindle and I'm sure something will stick out. I'll keep you updated.
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  #11  
Old Tue 13 November 2018, 09:43
Diplocaulus
Just call me: Gary
 
Kearney
United States of America
Hello, I'm back to ruin some days. Thanks again for all the replies, I'm trying to isolate the problem. We replaced the spindle with the water cooled Huangyang setup, and while we are having a couple issues there, unfortunately the z axis issue is back. Lemme tell you what I know/don't know.

1. The gas spring was misaligned slightly to the z axis movement. It was pushing against it's part of the gantry and making the "chonk." I saw this while the spider was off the machine and fixed it. It no longer makes the "chonk" but still dove into the material yesterday.

2. I ran the canned tool zero function to the top of the material and didn't move any axes before hitting "goto zero." The z axis lifted slightly and then dropped the tool into the material about an inch, and reads 0.000 on the DRO with the bit an inch in the material. There is no longer a chonk but a sort of mechanical bump at the top point of the lift, I haven't been able to identify it yet. This is still a couple inches from the top of the maximum extension of the gas spring, so it's not skipping a gear from hitting the hard stop.

3. I replaced the gas spring just for fun. No change.
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