Z height consistently raising up

[Doug Haffner]

I recently moved my shopbot to a new location and once everything was set up, I have tried some test cuts.

The issue is that over a series of cuts, it is losing Z by raising up. Even if it's an air cut, by the time it's completed, it was 1/4" higher than at the beginning.

I thought about electrical interference and tried running a seperate wire direct to Z nowhere near other wires, but it didn't make a difference.

It is an older PRT.

Suggestions?

[gerryv]

I don't think it would make much difference but any chance you reconnected the springs in the wrong place or left something of weight off?

Perhaps more likely, is it possible that something is binding when the Z is descending, thus causing lost steps "going down" and thereby leaving the impression that it is gradually climbing as it moves up and down?

[bleeth]

Doug:

Clean and re-grease the z rack and check the pinion for wear, as well as tightness. Cleaning the rack can be a chore as wood particles tend to turn into hard bits over time and you may need to get in with a brush and acetone to loosen them up and then blow it out with air. Can be messy.

[genek]

Very messy. recommend that you put plastic down. I found that pouring some acetone down next to the gears and moving by hand the easiest way to clear that area... Hard to reach in with tooth brush unless you drill the handle and mount the brush to a long piece of wood.
also get you a large needle and syringe that you would use to inject flavoring into meat with.. Fill with white Lithium grease to grease your gears with... also get a shot tube that will just go on the needle when heated. his gives you a longer reach.. keep two needles one with the tube and one plain... works great on other greasing jobs.

[Doug Haffner]

Thanks!
So far, so good. I cleaned the Z rack and pinion with acetone, then re-coated with white lithium....messy job for sure.
At the moment, it seems to be cutting fine and right on the money.

[bleeth]

That's one of the most ignored bits of tool maintenance there is. I would also suggest switching from white lithium to regular grease. It is heavier and will adhere better and last longer, although you are apt to get some nice stains from leaning over the table!
Doing as much HDU cutting as you do those particles get everywhere!

[gundog]

I use a product called Gear Shield it comes in an aresol can with a tube so it is easy to apply. It seems to be graphite based as it is very black in color and if you get it on your clothes it is there forever. It foames as it is put on and really stays in place well.

Mike

[Doug Haffner]

Well dang.
I thought it was cleared up, but after an hour long carve in some pvc, it was about 1/4" higher at the end and the carve was clearly off. Crud. Is it possible the driver may be going bad?

[genek]

Dough check and see if z moves easy in the off position then with the machine on see if it can be moved. you may have a lose gear.

[bleeth]

Possible but not likely. As Eugene suggests, check that your pinion gear is screwed down tight and also check it for wear. Make sure that there is proper tension on the motor mount so the pinion is engaging the rack properly.

I'm assuming with that kind of difference, there is no issue with your spoilboard not having been shaved since the move. If you haven't, do so. After moving re-leveling the x-rails and then shaving the spoilboard is absolutely required.

BTW: Would you check my last post on CSA and see if you have an idea or two?

[Brady Watson]

Doug,
You could most certainly be 'losing' a driver if it is a 3G or older PRT with on board drivers (non-Gecko). Those drivers 'get tired' even when they are treated properly and run lightly.

If I was tracking down this problem, I would turn off the control box & then un-seat and re-seat each motor wire on BOTH sides of EACH connector from the Z motor back to the control box using a Wago tool (looks like a lower case f) A small regular screwdriver can also be used with care to compress the spring loaded wire retainers if you don't have one. Sometimes a poor connection can make them run with only one coil getting energized, which equates to 1/2 power. Pull apart both connectors; put them back together. Then turn on the box and do some testing.

If the problem persists, you can turn off the control box and unplug the Z motor wire and plug it into the A driver. Run the VI command and swap Z for A and vice versa. Run that and see how it works. Make sure the unit values for the A are the same as the Z (UV command) or it won't go the correct distance. Some of this is redundant, but that's OK.

Let me know how you make out.

-B

[Doug Haffner]

Finally!
Success.
Switching to a different driver solved the issue. I suppose I'm going to have to seriously consider an upgrade from the old board/computer next year.

Thanks so very much to you all for your fast help. It was a good idea to do the cleaning and other things, so all good.

Doug

[Brady Watson]

Glad you got it going again. The 4G upgrade is WELL worth it. It will be like getting a completely new tool when you do it - so no worries.

-B

[hespj]

I forget what the terms are now, but if remember correctly if the resolution multiplier (is it?) has changed it can cause your problem. Or at least it will cause the problem if the tool is jogging more downwards than it is up, or visa versa.

John