Cant get the Z Axis cut depth to match programmed depth with tbd cnc screw drive

Recently purchased a Superdrive Z Axis screw drive from TBD CNC. They gave me a new number for the $102 setting of 49.909. That however is cutting too deep. I tried their tool on their website for adjusting that number based on what was programmed and what the machine actually cut. It seems to be sending us on a wild goose chase. I enter the new number, cut a test its not accurate, enter the new number, recut, etc. etc.

I then started at 50 for the number and doing that incrementally. It seemed to be getting us closer when we entered 51 it was closer. Then entered 52 and it went over. Went incrementally down from there but now its cutting the same depth as 52. At a loss and was wondering if any one has same problem.



You need to try $102=51.500 or 51.554, or 51.555, etc. Remember you have UP TO 3 decimal places the fudge with to get closer to the cutting depth you need.

Also. You need to check how you are setting the Z height. After each test you need to set the Z zero height. If using a probe method check the probe thickness is correct. then set the Z zero height again.

Ok thanks. I was just reusing the z height from the last test which i originally set with a the probe.

Where do you check to see if the probe height is correct? I understand checking the probe with calipers but where do set the probe depth?

Did you run through this?

Thanks so much. Would have been nice had this been included in the purchase. They only show the X and the Y set up.

Martin. Got it to work! Thanks so much. I got it to within 3000 of an inch. Which even for guitar work is pretty damn close. And the pocket i cut could have had some dust or frayed pieces in the bottom that would account for that

Great. I think a lot of stuff is on websites now to save the cost of printing. I’d be really happy to get .003 tolerances. Probably my collet if off more than that.

One issue we’re still having is when you cut all the way through a piece it cuts into the spoil board. ANy thoughts on that?

Can you put a layer of something on the spoil board that won’t matter if you cut into it? I personally don’t cut all the way down, I leave some material to cut off myself with a knife or rout off with a flush trim bit on my router table. Do you think it is backlash in the Z axis? Have you recalculated the $ for the Z?

The only two main reasons for Z to go deeper than wanted is due to:

  • It was told to go there
  • Mechanical issues like loosing steps, lack of rigidity, inproper Z zero or uneven cut surface

If you zero off the top of your material, say its stated to be 1/2" thick and you set carve depth = 1/2"
The actual thickness may vary => may be thinner => 1/2" carve = going too deep.

Uneven cut surface - Surface is uneven in height relative to Z, can cause variations like described above.
Key work - skim cut waste board (or skim cut a 2nd waste board)

If your surface is skim cut yet goes to deep either zero of the surface board and lift Z a known distance up so it clear the material to be carved, and set carve depth = known distance. Z dont need to be recalibrated even for this to work.

But do calibrate your Z as good as you can. Word of caution, backlash.
Whenever you change direction of travel for one axis the first travel will be every so slightly less than nominal due to backlash. So when you fine tune your steps/mm I suggest you jog all the way to one direction, then do a short jog in the opposite direction before doing a measurement jog along the same path.