[zirogravity]

Hello Everyone,

I made the most disastrous purchase of my life from a CNC company back in September 2012 on a used CNC machine. The company owner made an incomplete delivery (a part missing critical for safe operation) on a machine and promised a 1 year warranty and support. Needless to say I have been left hanging since and all attempts to get my remaining part have been exhausted. I am resolving to small claims court in hopes of some kind of recovery. I am scambling to get this machine up and running and trying to make the best of what I have in hand to get my business going so your help and empathy would be highly appreciated

A customer of mine and I recently spooled up the machine and practiced on some foam using a guitar model the customers developed. One night it worked fine and the next night we came back and noticed a kind jitter/jerking motion in the Z axis/direction when the spindle/head moving mostly in the up direction and rather smooth in the down direction. When we tried to cut another foam guitar it did OK for sometime then suddenly it ripped right into the part. I am almost certain there is something mechanically wrong with the Z motion. I rather sure it is some kind of integration error resulting from the z axis mechanical system. We are using Mach3/PC controller. As a sanity check we set a xyz zero and then moved the head around/up/down manually (Mach3 keyboard commands). When we commanded it back to zero it came back to the correct xy but wrong z (lower than it should have been thus slicing through our parts during run). We were trying to rule out that we did not make some coding error in the CAM so this gave us some confidence.

Any help on where to start would be highly appreciated. From what I can tell the Z axis uses a (formed) ballscrew on linear rails, DC brushed motor, a gear box, and a coupler.

Thank you,

Wess

[Camfather]

What make and model cnc machine is this?

[zirogravity]

It is a (used) custom machine made by company link. It is a 3 axis machine, brushed dc motors, linear rails, and ball screw using Mach3 PC controller with a 5 x 4 x 3 (ft) work volume/area. Primarily used for foam and composite materials (Ren Shape etc..)

[Camfather]

I am not familiar with mach 3 but it is supposed to be one of the best PC based software's out there, assuming your version is current and up to date, I would rule that out as a problem.

That being said, If I was you, or rather if I had this machine in my shop and this problem, the first things I would do would be to check for faulty cabling to the Z axis motor. If that checked out, and assuming the X or Y use the same motor I would swap one of them with Z and repeat the test you have done to see if the problem follows the motor or the axis. It could also be the axis driver device.

The way I interpreted your problem it would appear to me the machine is loosing "steps" If a known good motor fails the same test then maybe a setting in the software is moving the Z motor faster then it can support do to the weight of the Z axis. X and Y might move fine at high speeds but Z could required more torque and might need to be moved slower. Again, I have no idea about this machine, just what I would do if I was in your position. Hope this helps ya. Good luck and let us know what you find out.

[zirogravity]

Thank you Camfather. I will keep those suggestions in mind for my next steps. As of now we tightened down a z coupler which seems to solve "a problem" but not sure if it solves "THE problem.'" We measured the parallel of the linear rails and discovered a run out/washout from top to bottom. It may be a non issue but I am unsure as of now what kind of tolerances should linear rails hold? Also we noticed that the bolt caps in the rails protrude (i.e. not flush) out of the rail faces which may be causing friction against the slider blocks (the ones with zerk fittings for greasing). As of now I have been setting Z speed in the CAM (Visual Mil Pro) package so I will slow it down per your suggestion until we get more comfortable withe the machine capabilities and limits. Thanks again. Those are great inputs you gave.

[DonKes]

Sounds like you are losing steps.

Slow it down a little and esp cut the acceleration.

Don

[ranchak]

I had a similar issue using Mach3. It would reset one of the X or Y coordinates. I chased it for weeks and finally went with a different control system. Are you using the computer that came with the machine? Make sure that your parallel port cable is securely connected at the computer and control box. Also be sure that the parallel cable is a shielded cable and you are not picking up any interference by it touching something else electrical (had that problem also).