Inventables Community Forum

Proper calibration of Z Axis. Do this before using (or NOW)

Issues:

  1. The setup instructions only discuss calibrating the Z-axis in the X plane
  2. There is no provision for adjusting the Z-axis in the Y plane
  3. The provided wasteboard is not 100% square to the X and Y machine axes, plus the wasteboard was not entirely parallel to the Z-plane

Consequences (why you should correct this:
1 and 2) No matter how well you calibrate the Z-axis to the X plane, your machine is relying on all the assembly parts to provide a true Y-plane calibration “out of the box”. This will never happen since there are too many variables. (slop in connecting the slide rail to the endplates, manufacturing tolerance issues, etc.). In my case the calibration was off by a significant amount.
=> Your end product simply won’t be accurate to your input file. Fine if you are doing artsy v-carving, but for precise pieces, it’s a non-starter
=> No matter your best feeds and speeds, you will easily break small end mills. The deeper you mill, the more likely this will be to occur.
3) If you are always cutting away from fresh stock in the x and y axes, this isn’t an issue, however, if you want to A) Remill a piece, and you use the printed guides for setup or B) Only mill a side of a piece, your work will be off (ever so slightly

Solution:
Fortunately, the fix is almost trivially simple.
A) Drill and tap 2 holes (TOTAL) directly between the centerline of the holes on the X-Carriage used to mount the Z-axis rail. I used #8, but whatever works for you - whatever tap and machine screws you have around.
B) Assemble everything per the instructions fully, attempting to get the Z-axis as close as you can in the X plane. Tighten everything down
C) Using some scrap MDF or Plywood (~ 12" by 12" to give yourself some working room to calibrate in the next steps, perform a facing operation on the entire workpiece (just be careful of the clamps!!)

  1. Get a precision 1" 1/4" shank. I got a Whiteside 6210 CNC Spoilboard Surfacing Router Bit, 1/4" Shank
  2. I used Fusion 360 with the following settings:
  3. 1000 mm/min feedrate (ALL) except for 200 mm/min plunge feedrate. Works great, no burning. Spindle speed MINIMUM (16k RPM)
  4. Bottom height -0.5mm (this is the amount of material to remove in the facing)
  5. Single pass
  6. Pass direction 0 degrees. Stepover 25mm. This will visually highlight the amount of calibration you’ll need to do.
  7. No lead in or lead out, straight line transition.
  8. Run it. If you Z-axis is calibrated perfectly, the MDF should look like as smooth as a factory surface, in which case, you are lucky and skip to step K below.
    D) If your test run looks like you can put it up on your house for siding (which mine did) It’s time to calibrate. LEAVE it clamped to the spoil board.
    E) If you have them installed, completely remove the dust arm brackets. You don’t want to measure against these at all.
    F) Take this opportunity to tighten the v-wheels on the Z axis. Grind down an old 3mm Allen key so you can get it in the lower bolts
    F) Loosen up the z-axis rail “tight enough” that it stays on, but loose enough you can adjust it.
    G) Using a machinist’s square AND YOUR wonky 12"x12" test piece as the reference plane, first align the Z-axis with the y-plane (going to use the new holes you tapped.) MAKE ALL YOUR CALIBRATIONS against the spindle carriage. If the top of the spindle carriage is leaning toward you (mine was a LOT) insert a machine screw in the LOWER hole you tapped (if the carriage is leaning away, use the top hole, and do everything in reverse). In my case, slightly tighten the top 2 bolts so the carriage doesn’t fall down and turn your machine screw in until the spindle carriage is perfectly perpendicular. GENTLY tighten the mounting screws on either side of your machine screw.
    H) Now slightly loosen to top screws again and align the Z-axis with the X-plane, per the default instructions. Use a rubber mallet to SOFTLY tap the carriage. Tighten all 4 screws and continue to check for perpendicular in both axes as you do so. Once all 4 screws are properly tight, do a final check. Repeat the process until perfectly perpendicular in both directions. DONE.
    I) Reinstall the dust shoe rails, etc.
    J) Re-run your facing operation on your scrap, remembering to take off more material. If your z-axis is calibrated correctly, it will now be flat.

K) Now its time to take your calibrated machine and face the spoil board.
L) Use all the same settings as step C above, EXCEPT:

  1. Sketch/Stock size 750mm (X), 760mm (Y)
  2. Pass Direction 90 degrees
  3. Stepover 22mm
  4. From other side
    M) Your spoil board should have been “factory parallel” enough that 0.5mm faced the entire surface. If not, run again a tad lower. NOTE: If your spoil board still looks like crap, with ridges or “ocean waves” repeat the calibration procedure, but this time, you don’t need your test piece, you can calibrate directly against the spoil board, since it’s been machined.
    N) There should now be a nice ridge on the left and right sides of the board that you can use to align your workpieces to the TRUE machine Y-Axis and setup/clamp down your parts with a machinist’s square against this ridge.

This is my first post, so hopefully, I’ll be able to add pictures as a follow-up.

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Example of pre- and post- calibration:

Here is where you drill and tap (one on top, one on bottom):

This is the machine screw inserted on the bottom, in the calibrated position:

When done, perfectly flat, no gaps, and Parallel to the Z-plane:

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OR…
You simply tram in the machine during assembly (like you’re supposed to do) and then calibrate the 3 axes.
I don’t know how far your machine is off, but mine was fairly close out of the box.
And after tramming it in, the whole machine is within .004" (I was pleasantly surprised)
After calibrating the 3 axes with gage blocks they are within .0015"
Plenty close enough for woodworking.

Jan, what adjustment did you use to tram the machine? It has so few areas to adjust. The only logical thing I did was loosen the 8 bolts connecting the end plates, and maximized that, but that wasn’t close to enough. I have my set screw in over 1mm, which is over 1/2 degree out of plane. I followed the setup step pretty carefully, and there was no mention of this. Perhaps I missed something.

Someone may correct me if I’m wrong, but if I’m not mistaken, Inventables advertises the machine accuracy to be within ~.005". (Which I think is pretty good for a hobby machine)
It sounds like you’re not doing anything wrong,
If it is that bad, you should determine the offending part and contact Inventables.
They will replace it and usually overnight.
If you don’t want to go through that, you can very carefully open the holes up in the end plates and couple of thousanths.

hmmm… I’m really not sure what it could be (an offending part). I was very careful in assemble to make sure everything was measured correctly and square as I was going along, and honestly, everything lined up really well. I may have made an error somewhere, but at any rate, if other experience the same issue, this is a pretty easy solution. I was a bit surprised the first time I faced a workpiece with a large diameter bit and experienced this. All my other wood tools are zeroed in pretty well, and it was my fault I didn’t at least check this before running it. This is my first mill - table saw, miter saw much easier - fewer degrees of freedom :slight_smile: