Stuck at the DIY Test

#1

Me and my fellow students have been given a group project that involves the Moai SLA printer. Since it’s new in our lab the first thing we did was to follow the calibration guide but we already get stuck at the DIY test. The First time we tried it the results were ok but the size was wrong. So we turned the nuts under the vat holder as instructed. After that every time we tried the DIY again the cylinders looked misshapen or just got stuck at the bottom of the vat. Turning the nuts back didn’t help either.
While cleaning the vat we were trying to remove the resin that got stuck but in the process scratched up the bottom of the vat and we can’t get the inlay back in without air being included underneath.
Needless to say, the results didn’t improve. Does anyone know what we could try? We even changed the resin that we use and tried to print without the inlay once but it didn’t seem to help.

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#2

You’ve obviously already learned that you have to be very careful when removing resin from the PDMS layer in the vat. It’s very easy to tear it. If it does tear, then it’s done. You have to replace it. Otherwise, you risk resin curing on the acrylic underneath, and fixing that is much more difficult.

When resin does adhere to the vat or you scratch the bottom, the only way to restore the vat is to sand it down and polish it to a clear finish. There are tutorials on this forum that will teach you how to do that. I’ve had success polishing acrylic vats using wet-dry sand paper and Novus products. https://www.amazon.com/Novus-7100-Plastic-Polish-Kit/dp/B002UCYRZU/ref=asc_df_B002UCYRZU/?tag=hyprod-20&linkCode=df0&hvadid=312201735010&hvpos=1o1&hvnetw=g&hvrand=10567024320167675533&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033301&hvtargid=pla-375316222542&psc=1

To gently clean the PDMS layer in a vat, I recommend using a squeegee with a soft tip that won’t grab the bed. Only pull with the squeegee, never push. Here’s the squeegee that I use:

The PDMS layer can be replaced using most solar cell encapsulant products. The one most people recommend, and the one I’ve had success with, is QSIL 216. You can search this forum to find tutorials on how to replace your PDMS vats. https://www.amazon.com/gp/product/B00E29HOMC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Eventually you might want to ween yourself off of PDMS entirely, and move to the FEP vat. The FEP vats are much less prone to damage, they last longer under the intensity of the laser, and they’re easier to replace. You do have to use the FEP vat in combination with the self-leveling build plate. The only downside is that it’s not a very cheap upgrade.

Addressing your printing problem:
There are many reasons why a print might not stick to the build plate.

First, you need to make sure that the build plate is reasonably level with the PDMS layer of the vat. You need to do this in a vat with no resin in it. Start testing by setting the Z Reset Position (in advanced options) to the default value of 1877 (this is for the PDMS vat using the standard build plate). Then run a program (any program) and see if there’s visible deformation on the PDMS layer. If you can’t see a deformation, then increase the Z Reset Position by 1, and run the program again. If you see too much deformation, then decrease the Z Reset Position by 1. Do this until you can see a barely visible deformation in the PDMS layer around the perimeter of the build plate. It can help to see deformation if you film it with a phone camera and use strong edge lighting. This is the only way that I’ve found to be 100% sure that the build plate is pressing firmly, and evenly, on the PDMS layer.

Another thing that can cause resin to fail to adhere to the build plate is oil or debris on the build plate. I always clean the build plate with isopropyl alcohol after each use, and I allow it to dry fully before using it again.

You should also frequently “rake” the vat with your squeegee to check if there are any debris in the center of the vat. And use a gloved finger to gently rub the vat to check for damage in the PDMS or FEP layer before each print.

Another trick that I’ve used to help adhesion is to dab my finger in the vat of resin (while wearing a glove), and then rub that resin into the build plate, creating a thin layer of uncured resin on the plate. This virtually guarantees that the first layer will be successful, which seems to increase the chances that the entire print will succeed.


I hope these tips and tricks help you guys. Good luck!

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#3

thanks @BrianStone for a very detail reply, to sum up:

  1. be very careful when removing the resins stuck in the vat
    2.there are a few things that could results in fail on the DIY test: z reset position, temperature, laser power and debris in the vat.
    if the problem persist, i would like you to post the picture of the problem and the settings
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