Theory: bed magnets bias inductive probes
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I've been having a heck of a time getting consistent readings out of my Pinda2 probe (at least that's what it was advertised as). When I do a bed profile mesh, it's always failing and always in the same places. I rotated the steel sheet to see if the problem followed, and it does not. This is on a spring steel sheet sitting on a 8mm aluminum tooling plate with magnets sunk into it.
I placed a machinist's straightedge on it and it's dead flat as expected, and then started wondering something...
"What if" some magnetic flux is getting through the steel sheet. If the inductive probe happens to probe right over a magnet, I wonder of that flux would bias the trigger height. Has anyone else seen or heard of this as a factor? I may try an experiment where I do multiple trigger height tests approaching a magnet and see what happens.
I've been battling this probe's varying readings long enough that I ordered a BLTouch, just to see if I can get some consistency. I'd like to stick with a no contact inductive sensor but am not sure I can trust what I've got.
Scratch-built 350mmx350mm coreXY, linear rails, ballscrews, 3 Z axis, Duet3 6HC, v3.3, Tool Board v1.1, BondTech LGX + Mosquito hot end
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@kb58
I'm not sure if magnetism plays a role here, but the 'permeability?' of the magnet material is different for aluminum tooling plate, so you will get different readings. Same applies to (countersunk) screwheads. Even when they are flush to the bed surface, they 'pop out' in the heightmap.
Only way out is to use IR probe or BLTouch or not probing around the objects -
@kb58 thats why the MK3 only probing where non magnets are
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Just to add a conclusion. Swapped in a BLTouch, and all bed related issues vanished. It was indeed the bed magnets messing with the inductive sensor. FWIW, I have a spring steel sheet on top of the build bed, and thought it would shield the bed sensor for any variations in the perceived surface, but guess not!
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@kb58 said in Theory: bed magnets bias inductive probes:
Just to add a conclusion. Swapped in a BLTouch, and all bed related issues vanished. It was indeed the bed magnets messing with the inductive sensor. FWIW, I have a spring steel sheet on top of the build bed, and thought it would shield the bed sensor for any variations in the perceived surface, but guess not!
There are magnetic systems that use a flexible magnetic material which does not seem to interfere with inductive sensors but the ones I have seen have a temp limit.
Frederick
