Problem with Z axis

[MagTDK]

I've been testing my CNC Machine I built and have come across a problem.

My Z axis depth cuts are wrong. I'm losing depth to the point were I'm just cutting air. So the more I jog it up and down the further up it goes from it's original home position. I have even droped my movement down to just 10 inches per minute with the same thing happening.

I did notice it sounds a little different when jogging down. I hear something like bumps in a road that are spaced apart. (but motor sounds instead)

I'm using xylotex 269 oz. motors so I would think it could handle the weight. I even took it all apart and reassembled it, but nothing.

Anyone know how I can fix this?

Here is a drawing of what my Z axis looks like:



Note: I have two hex nuts located around the thrust plates on each side (next to lovejoy coupler) that is not shown in the picture above.

[Madclicker]

Sounds like you're losing steps going down....pretty sure of it. Real pics might lets someone guess where the problem might be.

[Oldmanandhistoy]

Strange are your pipes/bars dead parallel? Could be binding if they are closer at the bottom than at the top? Also is the screw parallel with your guides?

John

[MagTDK]

I loosened my guide bars to the point were it was hardly touching, but that didn't fix the problem either.

Another problem I have is that no matter what I seem to do (and this goes with the x and y axis as well) I can't get all my bearing wheels to touch the guide bars. There is always like 1 or 2 wheels not touching. Even after I try to adjust everything. But it doesn't seem to matter much since my x an y scale seems to be right on the money. Its just trying to get my z axis working.

[Oldmanandhistoy]

Even stranger; what is your frame made from? I ask because the bearings not all touching seems like twist is involved?
Just trying to eliminate some possibilities.

Also maybe a daft question but do you have flats on your motor shaft and screw?

John

[project5k]

hmm i can see the twist being a potential for the bearings not touching.. i wonder if maby the 2 issues are in some way related... i would think that you would be more likely to loose steps going up rather than down.. unless the plunge rate is too high.. but reducing the speed would eleminate that issue... maby motor tuning? ramp speed? but then again i would think it to be more likely to loose going up than down... just a couple off the wall ideas to consider... maby the screw or nut has something funny about them so that there is gobs more friction in one direction that the other? i did run into a machine at work that had an antibacklash nut, and in one direction i was smoothe, and in the other direction it would bind.. hmmm sure gets me to head scratching....

[MagTDK]

Also maybe a daft question but do you have flats on your motor shaft and screw?

I have a flat on my motor end but not my screw end. But when I check my couplers set screw it appears to be nice and tight.

i did run into a machine at work that had an antibacklash nut, and in one direction i was smoothe, and in the other direction it would bind.. hmmm sure gets me to head scratching....

I think today I am going to try fliping my antibacklash nut around to see if it reverses the problem (lose steps going up instead).

I will even try running my Z axis disconnected from the machine laying in a horizontal position to see what that does because I have to try something to try and fix this problem.

[ger21]

What software, motor voltage, VREF settings???

[MagTDK]

What software, motor voltage, VREF settings???

The software I'm using is Mach 3. The VREF settings are set to 3.35V. And the motor voltage is set to whatever is coming from the power supply. The power supply I'm using is from the xylotex 4 axis kit.

[Oldmanandhistoy]

Have you tried the nut the other way round (I’m guessing is not the problem)?
Sounds like you have an unusual problem there .

If nothing else this post will get your thread back to the top of the page and may get noticed by some one who might have the answer . Also I am intrigued to know the answer to your problem.

Good luck,

John

[MagTDK]

Well I still have the problem.

Here is what I have done so far to try and fix it.

1) I switched in another motor. Nothing

2) Removed one of the thrust plates incase of mis-alignment with the acme screw. Nothing

3) Laid my Z axis flat as if it were the Y axis. This way I could rule out weight. Same problem.

Next up I think I'll remove everything except the screw and backlash nut and try again. Because other then that, I don't know what else to try.

[Oldmanandhistoy]

Hi,

Try changing the wiring from your Y axis to the Z may be a board problem?

John