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If you want to automatically calibrate & level your printer, you need some way for it to probe its own print surface. Sometimes this is done with force-sensitive resistors (FSRs), and sometimes it's done with a Z-probe. For my auto-calibration firmware, I use this Z-probe:
The probe can be put together with about $15-20 of hardware, and three printed parts. Not too bad! Measured repeatability has been under 20 microns (1/5 of a layer height at 0.1mm), sometimes lower, even zero. For a good calibration that will tolerate 0.1mm-tall layers, I recommend a probe with repeatability under 30 microns, so this is fine.

The idea behind automatic calibration and bed leveling is fairly simple. The controller uses the Z-probe to tap the print surface in a grid. The depths at each point are then fed into a couple of algorithms that know how to turn a depth-map into a useful calibration.

I'm choosing today to post this thread because I think the probe is really "done" now. It's been around since 2013, gone through a few design revs, etc., but I think this is the last upgrade that will be needed. I added two mounters, one for on top of the effector and the other for below it, that constrain the probe and stiffen it significantly, so that the probe's wiring can't bend the probe as it moves around. Additionally, the bottom mounter has extended "feet" that project just a little bit past the end of the probe. If a loose wire or a firmware crash prevents your controller from reacting to a probe hit, and tries to drive the probe into the print surface, the "feet" will transfer the load to the effector, so you don't snap the delicate mount on the probe itself.

I think I will work on FSR-based probing after this.

Have you seen how the Pup printer does its probing? It actually uses a tilting hot-end that's got 1 screw resting on a snap switch to do the job.

That design is interesting, but I'd still have to run wires upstairs. I want to get away from that. It is good to use the probe tip, though. Offset probes are TERRIBLE for calibrating a delta. You never get anywhere near the same quality of calibration that you do when the probe is dead center on the effector. It just introduces too much error.

I like this. Do you have any video of the calibration in progress that you can post?

Hypothetical question here. Could you safely remove the nozzle and probe through the heatbreak of a E3D V6?

This would speed up the process of calibrating by not having to remove the hotend for the most part.


[img]http://wiki.e3d-online.com/images/3/39/ ... -BREAK.png[/img]

That is a pretty good idea.

Or if you find a very small drilbit to fit inside the nozzle that is attached to a switch on the other side.

Actually half of this procedure is calibration and the other half can be considered automated teaching.

What i saw in a project some time ago was they would machine very pointy end effectors for the industrial robots, and then they would use those to teach it the various points it had to visit.

mvansomeren wrote:I like this. Do you have any video of the calibration in progress that you can post?

Nope, sorry.

KAS wrote:Hypothetical question here. Could you safely remove the nozzle and probe through the heatbreak of a E3D V6?

The E3D has to be heated to 280 to remove the nozzle. You'd have to remove it and clean out any excess filament, because if you don't, it will bind with the probe shaft and cause a crash. After the probing, you'd have to heat it up again and reinstall the nozzle. I think it would be faster and easier to just remove the hot end. Even with all the space alien stuff on my effector, I can still swap it in five minutes. The calibration data is saved to the SD card, so you don't have to run it again unless the printer is moved or seriously bumped into.

Can you post the parts you used to build your probe please? for instance the magnet and rod length you used?

ClosetNerd wrote:Can you post the parts you used to build your probe please? for instance the magnet and rod length you used?

I built one of 626Pilots Hall probes using the instructions on the thingiverse page. Has all the information you need.

http://www.thingiverse.com/thing:161753