Z Axis Drop

[Schwierking]

I'm beginning to have a repetitive problem where my z axis will drop more than it should during a plunge. Initially it would only happen when V-Carving text but now it doing it on my roughing cuts and even my 3d Finish. Drops range from .05 to .15 so far. I've cleaned, lubed and exercised the axis and cant find anything that it is binding up on. I'm wondering if anyone else is having this issue. The only thing I can think to do now is replace the axis assembly.

Thank you

Joe

[Schwierking]

As you can see, this is getting very time consuming and expensive.

[rungemach]

Hello Joe,

It looks like you have already tried to check out some of the "usual suspects".

You can get a z drop by inadvertently hitting the upper z limit when the router retracts. Judging from the pictures it seems that is probably not the case. You can check that by running the tool path in air with no workpiece and see if it gets close to the high limit. That type of problem should be repeatable, and is easier to find.

The intermittent "takes off and plunges" problem seems to happen to a good number of folks, and I have not seen a definitive answer. Intermittent problems are very hard to track down.

The problem can be in the controller, or in everything downstream of the controller (wiring to the motor, axis sticking, etc.)

On the controller side, you may want to check and see if it is getting warm. If this is happening after it has been running for a while, and not when cold, you may have a heat related issue with the controller. The controller does not have any forced air cooling, and blowing a fan across it may help.

On the "everything downstream" side, check your wiring to the motor to be sure it does not look overheated or kinked. You have already checked the axis for binding, etc. Do you have any extra weight on the z axis that would make it harder to retract?

If the z is powering down into the work, and you bits are not slipping down in the collets, and you are not hitting the up limit of the axis, I would start to suspect the controler.

Hope this helps
Bob

[Schwierking]

Bob,

Thank you for the reply. I just tested everything out and Ive found a new symptom. As the z axis was moving up, I heard it thump similar to when it has reached the top. It wasn't at the top however, so I think it may be binding some where. Not sure how to go forward with this though. There is no added weight to the z axis so could it be a backlash screw going bad?

V/R

Joe

[Rando]

Or, it could be that your plunge speeds are too fast for it to lift the router, and it's losing steps more because of too much acceleration. Also, a too-fast rapids
speed. And yes, a tube or a wire getting caught, or too short for the full range of motion, can cause such things.

What are the plunge-rates you set for the tools in your design software (VCarve, etc....)?

If you are using the control panel software, there's a setting in the super-secret settings window (Ctrl-G, 787 is the password) for the amount of
acceleration. Try reducing that somewhat, say 10%, and see if that helps. Also, IIRC, that's also where you set the default G00 rapids speed.

Hope that helps,

Regards,

Thom

[sk8nmike]

Things to check for Z axis problems..

1. The router mount, the HDPE mount will let the router slip down. either replace it with an aluminum mount or place a set screw in it, be careful to not over tighten the screw and bind up the router.

2. Bindings in cables as others have pointed out. Also check for obstructions (wood chips and such) on the lead screw and rough stops on the bearing guides.

3. Electrical bonding. Is your router grounded to the Shark and the control panel? And if you are using a vacuum system make sure it is grounded back to the system too, the static charge build up by the air flow can get high enough to kill the controller when it discharges. A copper wire run through the vacuum tubing back to the vacuum ground should take care of this..