Calibration with a steel plate and a magnetic sheet  

RE: Calibration with a steel plate and a magnetic sheet

The Magnetic Sheet WILL disturb the XYZ calibration process!

The Pinda is looking for tiny copper pads in the surface of the heatbed, the magnets will mask the effect of the copper pads. 

regards Joan

RE: Calibration with a steel plate and a magnetic sheet

The Magnetic Sheet WILL disturb the XYZ calibration process!

The Pinda is looking for tiny copper pads in the surface of the heatbed, the magnets will mask the effect of the copper pads. 

regards Joan

RE: Calibration with a steel plate and a magnetic sheet

Hello Joan,

Thank you for your answer. I have moved on since. Indeed the magnetic sheet disturbed the induction probe. I removed it and the calibration was done correctly. However, we had to find another solution to hold my flexible steel plate. So I put neodymium magnets under my heatbed and away from the copper pads on the surface of the heatbed. It works. However I wanted to know how I should go about calibrating my Prusa MK2s printer with a steel sheet that is 0.7 mm thick. I have to calibrate without the sheet is added in Z the thickness of the sheet? I admit to being a bit lost. Do you have a solution.

Thank you in advance. Sincerely, JLuc

RE: Calibration with a steel plate and a magnetic sheet

Hi Jluc, 
there are two separate calibrations. 
XYZ calibration is done with the plain Heatbed and relies on the copper pads, 
Live Z Calibration is done with the build plate installed above the heatbed. and should not need offsets. 
regards Joan

RE: Calibration with a steel plate and a magnetic sheet

I sometimes use a ferrotype plate instead of the Prusa sheet and it calibrates just fine. 

RE: Calibration with a steel plate and a magnetic sheet

Where did you get the plate??

RE: Calibration with a steel plate and a magnetic sheet

Posted by: @jella_joe

Where did you get the plate??

It's a photographer's ferrotype plate for doing wet darkroom prints. I  got it from a guy in our photo club who doesn't do wet printing anymore. 

Fits right on the magnetic Prusa bed. Gives a real good shiny surface to the prints. Now you gotta be sure to recalibrate to use it and hairspray to be sure it sticks. 

RE: Calibration with a steel plate and a magnetic sheet

Salutations,

   I recently ran across a tech that describes one individual's journey upgrading his MK2S (MK42?) non-magnetic heat bed and placing neodymium magnets underneath his heat bed and holding them in place with little mounting braces/cups that anchor to the posts which secure the heat bed to the Y-axis carriage. The individual used 6 of these magnets (with a 12kg pull-rating) to hold his removable steel sheet, which he purchased on Amazon, (along with the magnets and was nice enough to post direct links to the products used) experiencing great success and providing pictures in his post.

Here is a link to what I am referencing: https://3dprintnation.com/diyprintbed/ ; and from what I've read, a number of individuals have had success with this modification. As an individual who can follow instructions well, I find myself confused to have only run into calibration and probe issues since my installation of these magnets upon the underside of the heat bed.

   I personally find myself "at wit's-end," as it were, with this seemingly simple little upgrade for my MK2S. Most likely due to my ignorance about the PINDA sensor and its fine tuning. I also cannot deduce or discover where these "little copper sensors" are on "the surface of my heatbed" either; unless the copper sensors are located above the mounting screws. Therefore, I am unable to discern where/how to orient them in order to allow the PINDA to read the copper sensors.

   I can remove the magnets, install the heat bed and print perfectly, without error and without re-calibration even. Once I install the magnets under the bed again, the PINDA moves from failing during the initial 9-point check at points 9(first point nearest home), 8, or 3(the 3rd to last point at the distal end of bed) to failing after finding all initial calibration points, but reading them as "too far away" and not completing the second round of the 9 point detection. It has afforded me a small number of other errors, all after I had tweaked one thing or another, all pertaining to Mesh bed leveling/XYZ calibration. Remove the magnets and the printer sings to me again. I feel I've definitely "sprouted a few more silvers" over the matter. I've replaced the bed thermistor when it failed, I've taken the machine apart for cleaning and put it back together with much success, re-routed wires for the cool little chain-link-housing I printed for it, I upgraded the nozzle to a hardened steel .4 and had minimal issue during any of these operations, I will note also (I guess to proclaim any competency).

Would anyone (@joantabb you've been slaying it with the assistance, I see) please be able to advise on either(or all):

The location of these copper sensors on the MK2S heat bed?

A link to the specifics about the PINDAs placement, elevation, heating "protocol and contraindications?" I know the sensor requires heating, but I don't understand when or what is too hot (or even the implications of a "PINDA too hot"), desired temperature or how (besides editing gcode to report PINDA temp before print start) to even know what temp it is. What height the PINDA should be placed at, etc.

I'm running the 3.2.3 firmware on the printer and 2.5 with the slicer, both Prusa.

A friend of mine didn't have a safe place to house his MK2S anymore and I offered to take care of it, which means I also get to learn it meow and print whatever I desire. I have pieced my understanding together from an array of sources including and primarily the Prusa resource base, but most material readily available pertains to the upgrades. Any assistance would be welcome. Thank you.

RE:

the nine pads are only used for XYZ Calibration. 
Live Z on a Mk2, normally looks for the heating tracks. 

when you put a metal sheet over the bed, the pinda looks for the metal core of the sheet for Live Z. 
Unfortunately Magnets tend to disrupt the Pinda sensor, so if you can note where the Pinda tries to sense the bed, and put the magnets somewhere other than under these positions, you should be golden. 

the reason I seem to comment so much, is that I am a Moderator, and try to help as much as I received help when I began printing about seven years ago. Sort of Paying forward, the help I got in the past... 

you would be surprised at the number of issues that were discussed seven years ago, that still come up today.  

with the Mk2 Pinda, I find it best to always start a print with the extruder about 60mm high, and near the centre of the bed. the Mk2 printer Pinda (usually the Pinda1 version, is not thermally compensated so if you start close to the bed, the pinda heats up  more than if you start a long way from the bed, a warm pinda has a different sensitivity to a cool pinda, so you can have difficulties with Live Z if you start a print heating at different heights. 

good luck, regards Joan