More frusteration - sudden leveling issues

I couldnt believe how nice the lines were printing on the print I was doing - it was beautiful, until the print head moved to the back of the plate.

I know, I know, everyone has the problem

But damnit, its like clockwork, as soon as I read someone’s post about a problem I suddenly inherit it

Nozzle so close to the plate in the back that it wont extrude, so far in the front it wont stick, in the middle REALLY nice, nicest ive seen so far! This matterhackers stuff likes to lay down on a low temp.

Trying this heat it up then calibrate method, mr snapmaker can you please allow us to calibrate with the bed heater on :frowning:

Short answer:
No: because the current flowing through the bed when the temp control circuit turns the heater on is enough to trigger the inductive sensor, ruining the calibration.

Longer answer:
Yes, but requires the firmware to be re-written so that immediately before taking each probe the bed heater is shut off, and then turned back on.

I haven’t looked into this in detail, but I’m thinking this is not that hard to do, actually. I could try and work something up in the firmware if you’d be interested in help test it. I’m thinking I can just add like 2 lines to the probe routine to disable/enable the heater at the start/end of each probe, but otherwise leave the bed temp alone.

Hell yeah ill test that out!

Makes a lot of sense

PS im hearing some buzzing again - another module on its way out perhaps? stay tuned!

I am at least excited about getting some glass on this which would help since its so flat and inflexible (i hope).

Mcmaster has adhesive magnetic sheets, although not large enough for the bed size in high temp, but at least for regular temp to give it a whirl to see if i cant get it to detect thru the glass like you did

As frusterating as this machine is I am having way too much fun trying to make it work.

I just turn on the bed and heat it up to 10º above what I’m going to be printing at and then let it get to temp. (If I have time I’ll let it sit for 15-30 minutes) Then when I go to calibrate it turns off and there’s enough carry over that I find it stays close enough to the printing temp.



Yea that seems to be adequate for most peoples purposes. Although it looks quite simple to do, really. Comment out the disable_heaters line, and in each probe just turn off, probe, turn on.

Also I’m not detecting through the glass, just to be clear. The print sheet is on top for that.

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I like it, simple solutions like that make the world go round.

Ohh, you are not printing on the glass directly? fiddlesticks.

I thought maybe the magnetism was allowing it to reach.

Well, that doesnt mean i give up.

The sensor only reaches 2mm, it won’t go through the glass.

However, I am making steps towards a differential IR non contact sensor working that will work with glass. Stay tuned!

That’s why everything was already disassembled on the bench from that other thread :stuck_out_tongue:

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Theres always the fifix too, but yeah surely it cant be too hard to figure out. Even an ultrasonic sensor could do the trick, if the range is appropriate for it.

our prox sensors at work have a 3 mm range, but if you use ferrous metals it increases to about 6, so i guess in my head it was doable.

I haven’t really seen them used for precision distance detection. A 40kHz sensor has a wavelength around 8.5mm, which makes it tough to get below about 0.3mm precision.

There are industrial ultrasonic sensors in the MHz range, but I have a feeling those will cost more than the machine by a long shot.

Yeah perhaps, at least on an affordable scale

I use on at work on a product and am able to fine tune it pretty well to see in a specific window, but yeah mm ranges are a different story.

I guess even if you used the print sheet to calibrate could always remove it and z offset, but im eager to see what you come up with

Question from ignorance.

@brent113, the CNC tool touch sensor you showed us a while back, could that be used to calibrate the print head (and perhaps even the laser)?

Yes. My thoughts exactly - a laser project could be located precisely with that. Would require swapping the toolheads briefly. Maybe that could be solved separately

You could simply connect your machine with luban or octopi over USB and heat the bed with the terminal, now you can do the calibration from the touchscreen with heated bed.

The very first command run after the touchscreen issues G1029 A to start auto calibration is disable_all_heaters(), and then it begins to cool down.

I’m proposing changing that behavior so the bed will remain a constant temperature throughout the entire calibration cycle, which if people are interested in 7x7 or larger grids would be required as the bed would cool off too much from the start to end. And even a 5x5 grid I think would benefit from it.

If you stay connected to the terminal the heat will stay. - try it, it works.

Ok, so that is the other problem - if the heater turns on while it’s performing a probe the EMF generated from the heater coil is enough to false trigger the probe. It needs to be synchronized so that before the probe occurs the heaters are turned off.

That’s why they originally pulled the feature to perform a quick probe check before starting, they were having random failures occur and decided just to pull the feature entirely.

You are maybe correct, but I had nearly the same offset or warpement of the bed, measured with the Probe sensor and a dial indicator.

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Ha, good enough! Glad it worked for you. The probing happens fast, maybe you got lucky?! Or maybe it’s usually fine, and just some people get unlucky?

There is a pretty well understood interaction, in general, between inductive sensors and heated beds, this isn’t the only machine that has that issue.

Fun fact, in addition to the bed current generating a magnetic field, inductive probes are also sensitive to movement in static magnetic fields, such as the ones surrounding the strong magnets under the bed. That can cause early triggering as the probe descends, the movement inducing a current in the sensor windings via Faraday’s Law. Additionally, they are heat sensitive. Prusa added a temperature sensor in the probe to compensate for the probe triggering early due to high temps.

Really, inductive sensors have a lot of problems.

inductive sensors are sensitive to alot of things, which is why i thought we could defeat the short range thru the glass with something highly magnetized

i use their weakness to my advantage at work


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