Magnetic print sheet fixation

Hi folks,
I’ve seen many reports on displaced print sheets and had it now myself twice: Something in the print sticks out more than it should (by warping or overextrusion), the nozzle catches it and displaces the magnetic print sheet. Result: Layer shift, print fail. I used paper clips to avoid this, but it seems they are not strong enough, and they get in the way of the print if it’s large. Has anyone already designed something to keep the bed in place, e.g. some lip around the corners of the bed or something? Was searching around a bit, but could find nothing… Any pointers welcome!
Thanks
Hauke

Look for clips/brackets designed to secure glass beds in place, maybe? That seems to me like the same class of problem.

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Hi @ Hauke,

You are certainly looking for something like this:

Link: https://www.amazon.de/D-RECT-Foldback-Klammern-Vielzweckklammern-Briefpapier-Bürobedarf/dp/B085V5VSHC/ref=sr_1_6?__mk_de_DE=ÅMÅŽÕÑ&crid=3MQPJUOVHLOJN&keywords=D.RECT%2BFoldback-Klammern&qid=1649352310&sprefix=d.rect%2Bfoldback-klammern%2Caps%2C79&sr=8-6&th=1

But please put something between the clamps of rubber or stick a strip of insulating tape on the clamps, otherwise you can hit the circuit boards of the heating bed at the bottom and cause a short circuit !!!

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Hi Blauskink,
Thanks for the link - but actually that’s what I currently use, but they are obviously not tight enough. The board moved by half a centimeter, enough to spoil the result completely.
I guess I’ll create something myself, should not be too complicated.

If you are having issues with the print head coming into contact with the print, you need to turn on Z Hop. Filaments like PLA don’t expand or string that much, so you usually don’t need it PLA, but things like PLA+, PETG, ABS, ABS, and many others, may require you to do so. Half the nozzle width is usually enough, but you might need to go up to the full nozzle width, if the problem is more severe.

Also, make sure that there isn’t any wobble in your platform. If pressing slightly on either side causes the platform to wobble/move, then you need to contact support, as you have an issue with your Linear Modules.

Best of luck!

The described problem has only happened to me twice:

  • One ‘tall’ print cracked and warped up so much it caught the head, and as it still had a lot of surface area on the plate, it bumped it. But I would’ve had to kill the job anyway as it was a total fail already
  • One time I regret to say I put the plate on a little offset after removing a prior print, not paying attention, and it caught itself on one of the vertical Z linear units as it tried to trundle the table back between them. Again, I’d have had to stop anyway.

I don’t use Z hop normally but aside from those two instances, this has never been a problem.

Hi @CNC-Maker ,
thanks for the ideas, but I’m afraid my problems would not have been solved by Z Hop. On my first failure, one corner of the print hat warped and lifted off the bed by ~1 mm, and at some point, when the head tried to lay down the next layer there, the friction was too big and dragged the print along. The second fail was due to overextrusion: I used retraction extra prime amount, and was a bit too generous, which led to bumps building up whenever the extrusion resumed after a travel. These bumps I tried to “manage” by once in a while cutting away excess material, but during the night I assume the head, again while laying down another layer, dragged the print along on such a bump.
I had similar problems (warping) with my second 3D printer, which, being Core XY, has a fixed bed, which was not budging. There, the hot nozzle always managed to “dig” through excess material, and although it made somewhat grinding noises, the prints always survived. I have the slight hope that if the print sheet cannot give way, the same will happen on the Snapmaker should I happen to have the same problem again.

If the print warps, it’s a failed print and there is nothing that you can do. The print head hitting the print at that point is just a consequence. You’ll need to address the warping to fix your issue, which almost always means controlling the environment. If you are trying to use something like ABS, or any other material with a high shrinkage rate, an enclosure is pretty much required (even a tent works) and you’ll want to keep the ambient temperature above 40°C, and not too high above 60°C.

If the ambient temperature is to high, and you’ll burn out the Linear Modules, unless you employ some sort of liquid cooling system. For ABS, I keep the ambient temp around 44°C, either turn the part cooling completely off or up to 30% after layer 4, and I usually don’t have any trouble with warping or layer separation at all. Uneven cooling is what causes warping and layer separation. BTW, you never said anything about what material you are using, or your settings.

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Regarding warp equals failed print: I beg to disagree. If a bit of deformation is functionally or aestetically acceptable, I keep warped prints instead of wasting more plastic. A slightly bent corner on a box that houses a sensor in my basement is totally acceptable for me.
I fully agree however that of course you always should look for the root cause of the failure in order to avoid it next time.
In both mentioned cases I used PLA (one at 215°C nozzle, one at 205°C - established by using these brands since a while and generally having good results), print bed at 60°C and all in the “official” enclosure. Ambient temp’s I have not measured, but they certainly will not have exceeded 35°C, and started at ~20°C when everything was still cool. Which for PLA is totally fine. Sliced with Prusa Slicer, max. print speed 60 mm/s.
The warping for me is the result of my awful print bed. I’m a Kickstarter backer, and my print platform is very uneven. So calibration it is always a pain (I use 11x11 calibration, which is usually good enough). In the warped case I suppose that bed adhesion in that corner was inferior, and thus the print was able to lift off. Since the print used the full 350 mm of the build plate, I had no space left for a brim, which I usually do to reduce risk of warping.
In the case of overextrusion I was playing around with retraction settings. I am trying to get the extrusion consistency better (My E-Steps are calibrated): After long travels I suffered from underextrusion through oozing (I see this often in pictures that people show), so retraction/extra prime amount is the answer. In this specific case I had increased extra prime amount as I was still not totally happy with my previous settings, but I overdid it. So at the start of the extrusion after a longer travel, too much material was extruded, leading to said blobs.

Long story short: I guess I can well explain what went wrong, I know what to change, but I’d be happy if the printer would be more forgiving if such things happen, and I hope I can achieve this by fixing the magnetic build plate more rigidly.

Hi @ElloryJaye,
thanks for pointing me at brackets for glass beds - this indeed was a good starting point. In the meantime I designed brackets that hold the magnetic print sheet tight in place, without extending higher than the print sheet, so no nozzle collision danger. The bracket files can be found on Thingiverse. Here are a few images:

The print ssheet fits snugly at 60°C bed temperature, at room temperature it has a little room to wiggle. I have the old platform, so the files are for that. I have two print sheets, both fit/are identical in size - I hope the tolerances for new print sheets are not too large and it will fit for all…
I considered to make the brackets less solid, with holes where no material needs to be, but in the end I thought that they might help keep the corners of the bed warm when left bulky.
The brackets are quite fresh yet, no long term experiences yet, but I assume my concerns are addressed, case closed :slight_smile:

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