1.5mm Base not from PreForm prints paperthin

Hey Fellow Form Users!

I am printing rings and creating the supports in Matrix/Rhino rather than in preform. The base I created was 1.5mm. Whenever I create a base and supports in Rhino and put it flat on the print table (ignoring the prompt that says some objects have no supports) the base prints paper thin. The rest of the object comes out fine! But the base is barely there to scrape off the build plate.

I don’t have this problem when I set the base thickness on preform to 1.5mm. I get a nice solid raft that comes off easy.

What’s am I doing wrong here?

Thanks!

From what I know, the printer over cures the first 2 millimeters or so for strength. This results in a loss of height. I’m guessing that your 1.5mm base is being over cured and coming out much thinner because of this process. You probably want to make your base 2.5-3mm in Matrix/Rhino.

Preform probably does the math ahead of time so if you want a base of 1.5mm it might actually create it 2-3 mm accounting for the over curing (if that makes sense).

This is just an educated guess tho as I am still somewhat new to the printer and I am not a 3D designer.

Kevin’s right that the printer “over compresses” some or all of the layers in the base (meaning the effective distance moved in Z during the printing of the base is less than the layer height of the print). The base thickness you get is not the base thickness you set.

The way I think it works can be seen if you watch the printer carefully when it starts a print. The resin tank is on a spring loaded base, and the PDMS has some compressibility too. You can see the resin tank move downward as the build plate bottoms out at the start of the first layer, and this repeats for some number of additional layers, but it isn’t happening any more when the actual model is printing. The first few layers of the base are intentionally printed at a “below zero” Z coordinate. Those layers are less thick than the layer height of the print. Once the layer number is high enough the build plate no longer bottoms out on the resin tank, all the remaining layers print at the layer height of the print.

PreForm outputs 20 layers for the base at 0.1mm. Should be 2mm, right? I just measured the thickness of a base from a print I did yesterday. It’s 1.39mm thick. So there is roughly a 30% loss in thickness due to the compression on my machine.

I’m willing to bet that the amount of compression varies. The machine’s Z axis zero reference is not going to be the same from printer to printer due to manufacturing tolerances both in the machine structure and individual resin tanks. But the way the printing process is designed, within some tolerance range doesn’t matter to the outcome. Which is why the printer can be “fine tuned” for the Z reference, to adjust for when the tolerance range becomes too large.

The compression is, as I understand it, a key component of getting the base to adhere to the build plate, So I would increase the thickness of the base in Matrix/Rhino rather that mess with the printer’s Z axis…

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Great. Thank you guys so much. I haven’t had a chance to create something with a Matrix/Rhino base since I got this info but I will add a few millimeters thickness to any base that i build “manually” in the future.

MUCH APPRECIATED :slight_smile:

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