Kossel magnetic z-probe mount with zero X-Y offset to avoid effector tilt problems/errors. Tested 100%.

by paul_delta, published

Kossel magnetic z-probe mount with zero X-Y offset to avoid effector tilt problems/errors. Tested 100%. by paul_delta Dec 14, 2015
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After first disappointing experience with inductive z-probe that was originally (FolgerTech Kossel rev.B) mounted with high X-Y offset from the extruder tip, I decided to dismount it and made another E3D mount for additional filament cooler (check my another things).

But recently I decided to give it another try and designed magnetic mount that holds the z-probe (inductive sensor LJ12A3-4) right under the tip, eliminating offset/tilting errors. I must say that now it works like a charm! Using David's online calibrator (user dc42) it took only 10 minutes to level the bed.

You will need six 9-10mm neodymium disk magnets (something like these http://www.homedepot.com/p/MASTER-MAGNETICS-3-8-in-Neodymium-Rare-Earth-Magnet-Discs-12-per-Pack-07090HD/202526371) and epoxy (I used 5-min epoxy) or crazy glue.

Tip: the power of magnets depends how they aligned to each other. Even 0.3 mm misalignment reduces the power significantly. So, the best way to glue them - to glue two magnets to the printed mount first. Then glue one magnet to the bottom of effector using couple of magnets on the top of effector to hold the bottom one in place (pay attention to magnet poles to make sure they will stick). Then stick the fourth magnet to the glued magnet on the mount, add a drop of glue on the top and put everything in place to cure (see picture). Add some magnets to the top of effector to increase the force and let it cure. Use piece of waxed or parchment paper between magnets to guarantee that they will not glue to each other.

Don't forget to adjust your z-probe height in firmware.

  1. Set Z max height for X0 Y0 Z0 using paper test. Save to Eeprom.
  2. Home the printer using G28.
  3. Attach the probe and carefully move it down using manual control in Repetier Host or Pronterface until it triggers.
  4. Read your Z value - this is your probe height. Save it to Eeprom (in Repetier it's Z-probe height field in Eeprom configuration window).

To organize the probe, when not in use - there is a screw-less mount that clicks right to the 2020 extrusion. The clips are very tight, it should be like this. Just push them hard and they will lock the hook securely.

PS: to use inductive probe with glass bed - just print this adapter http://www.thingiverse.com/thing:1195525.

How it works: https://www.youtube.com/watch?v=83hY3M8QLtg

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Did anyone have issues with the high z offset with this probe?
Im on marlin rc5 and g30 works fine, but g29 moves to the first point and continues to crash in to the bed no matter what offset I set.
Any ideas?

The z-probe height is measured from the bottom of the sensor to the bottom of the extruder?

  1. Set the Z max height for X0 Y0 Z0 using paper test. Save to Eeprom.
  2. Home printer.
  3. Attach the probe and carefully move it down using manual control in Repetier Host or Pronterface until it triggers.
  4. Read your Z value - this is your probe height.

What sensor did you use?

Feb 15, 2016 - Modified Feb 16, 2016
paul_delta - in reply to fabrizziosoares

LJ12A3-4, M12 body thread.

Feb 2, 2016 - Modified Feb 2, 2016

Hey paul!

Tried it out (no images yet - will come) and gotta say: Muuuuch better than before.

Deviation between manual paper method and z probe before using this: +/- 0.20 mm-ish
(probe x offset ~ 25 mm, y offset ~ 15 mm, z offset ~ 1 mm)
After switching to this design: +/- 0.05 mm
(probe x offset 1.5 mm, y offset 1 mm, z offset 115 mm)

The magnets hold the mount securely in place and yes, two magnets are enough. I do prefer the two magnet solution over three magnets, as the mounting area on the effector is very slim.

Fyi: I plan to remix this design to adapt it to mechanical endstop switch. Cause I really like it! :D

Thank you, Paul! :)

Feb 2, 2016 - Modified Feb 2, 2016
paul_delta - in reply to docpayce

Thanks for feedback. Probably mechanical endstop adapter will need 3rd magnet, to have 3-point mount. Such kind of endstop need some push power to trigger and 2 magnet mount may "play".

I tested itwith two magnets (http://www.thingiverse.com/thing:1336745) and it works like a charm. The push force for the endstop is rather low. It was comparable to the spring loaded version of this z-probe.

Kossel magnetic endstop z-probe (zero x/y & low z offset)

Paul, just fyi (I forgot): The clamps to hold the holder in place are tolerated a little bit to harsh. The inner distance is just 20.08 mm but the holder is 20.58 mm tall. Doesnt fit, I had to reprint them. :) BR!

Feb 9, 2016 - Modified Feb 9, 2016
paul_delta - in reply to docpayce

I printed them both with PETG and PLA. PETG is very flexible and it's even too easy to put them in. PLA is harder and clips need more force to apply. First you have to hook one side, then push another side. If it's too hard :) - just scale them before printing in X/Y direction.

Hey Paul I also got this printer for Christmas and have been having alot of trouble with getting the bed level even without the auto level turned on part of the bed is to low part is to high. I also have a problem with the extruder tilting enough at the edge of the x axis causing the sensor to be lower than extruder tip and hit the bed and my prints.

This is well-known problem when diagonal rods are not equal. I made my rods using jig but there is still very small tilt across Y axis. This is the main reason why I decided to get rid of offset probe and such kind of errors. Having zero offset probe now it's much easier to calibrate bed, even with small effector tilt.