Quick VAT rehab

I have found my calling as a VAT killer. FEP can't take more than one or two attempts before I get it to fail, so I print bareback.

Consequently, I destroy a lot of PDMS layers, and usually in such a way that I have an acrylic on acrylic mess after the damaged pdms is removed. If you get away without having cured resin stuck to the bottom acrylic, the PDMS layer can be rehabbed in as little as 4 hours, start to finish.

I tried QSIL at room temperature first, but the edges never cured, even after 5 days. Being impatient, I turned to the following process.

You need 

QSIL 216 (around $35 on amazon - the 1pt kit will rehab 5 to 6 vats, or in my case the same vat 5 to 6 times)
A sharp knife
An accurate gram scale.
Mixing cups and stirrers.
Convenient tools to remove the existing silicone.
Your kitchen oven.

Use the knife to slit the silicone along the edge of the vat. Once you get one edge free, you can usually pull the whole layer out in one piece.
Use your fingers to get anything still on the bottom off.
You will probably need a tool to get the stuff around the edges and corners - I use a flat head screw driver.
Wash the VAT in soapy warm water. Dry completely, and inspect for remaining silicone and/or surface scratches (if you have scratched, no worries, it's just going to take a bit longer)
If the vat is clean and dry, you are good to go.


get out your QSIL, mixing cups, and tongue depressor stick stirrer. Measure out 6 grams of part B and 60 grams of part A. Mix for about 3 minutes, making sure to scrape the sides and bottom of the cup.

You are going to make lots and lots of bubbles. Don't fret.
Once mixed, use a "high pour" to drizzle the silicone into one corner of the VAT, allowing it to flow into the rest of the surface.
Once you have poured it all, you can assist the coverage by a few tilts, making sure the mixture has reached all edges and corners.
Then place the vat on a level surface and let it sit for an hour or two. Most of the bubbles will have disappeared.

Use compressed air, to gently disperse any bubbles that remain, or to drive them to the edges or corners where they won't matter.

Turn your oven on to it's lowest WARM setting. You are shooting for roughly 100 degrees F, give or take. My oven dial has the word WARM on it, I set the pointer to the R in WARM, with is well below it's first listed temperature of 200 degrees.

pop your VAT in to bake. Check it in a half hour. If the oven is too hot, the walls will be bendable - turn down the heat a notch. If all looks good, let it cook for another hour and a half, then check again.

It's done when a puff of compressed air no longer will move the surface in the corners and edges (don't test the middle! it cures first, and you don't want do disturb the nice smooth surface).

If the corners and edges are set, you can remove the vat and use it right away.


If you were unfortunate enough to have cured resin stuck to the bottom of the vat, under the PDMS - there's a lot of pia work to do.

1st, you have to shave / scrape the cooked resin off while drying not to scratch the surrounding clear acrylic too badly.

When you get down to the last bits, sand the remaining off using automotive wet/dry sand papers. I usually redo the whole bottom of the VAT just for good measure. If the scratches are very shallow you can try starting with a 400 grit paper. I botch things up much worse, so I start with a 180 or 220 grit, then follow with 320, 400, 600, 1000, and 1500 (I told you this was going to be a bit more work).

If you happen to have 3M polishing papers, you can use them too - 4000/6000/8000 grits/mesh.

Finally, apply some metal polish (brasso) and buff it off.
wash and dry 

Now you're ready to mix, pour, and cook as above.

Comments

  • robjos1robjos1 Member, Backers
    Thanks for the fantastic write up, which resin are you using generally?
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Nice job @Gary.

    If there is any PDMS left on the edges, it will inhibit the cure of the the newly poured PDMS. I've been successfully removing all of the PDMS cleanly when I refreshed two of my vats, so I do the room temperature cure for 48 hours and it comes out looking great. I put a cover over the vat that stands off the vat slightly to allow the silicone to off-gas but try to keep the dust out of it.

    Ron
  • GaryGary Member, Backers
    I forgot to mention to cover the VAT while curing -- good catch Ron. I just lay a heavy paper or cardboard on top to keep junk from falling in. @robjos1 - I have a bit to say about resins. But I'm not quite ready yet. I have been successful with MakerJuice Red, and MakerJuice Yellow. I have had horrible results with Maker Juice white and blue and also with Make Solid White.  The resins matter I  have Maker Juice black and  green waiting to be tested. If anyone has experience with them I would love to hear.  For MJ yellow and red I @ 50 micron Z I am using 6 base layers @20,000 ms,and 6500 basic exposure. I would like to cut back the basic exposure a bit. I get the best resolution @6000 ms, but most models I print wont' stick, even if I  increase the base layer exposure. So I'm working with 6 layers @20000 and the remaining at 6500 with MJ yellow or red.


    I will be trying MJ black and MJ green in the near future. Stay tuned :)
    I was unable to get a good print with MJ white or MJ blue or SolidWorks White. I did get good prints with Solidworks castible, but ran out of resin before I nailed down the settings. (my god that shit is expensive!) 
  • chizchiz Member, Backers
    Excellent post, @Gary! I know it's just a matter of time before I refer to this article.

    I think I killed my vat and I'll try to refurb it myself until I get to replace it with the metal vat. When cleaning my stock vat, I noticed some goo-like substance around the edges which I thought is just resin. I continued removing the "goo" until I realized that it might not be the resin but the PDMS! Still I'm not sure as I'm not familiar with the stock vat layers. I know the bottom of the vat has clear acrylic, PDMS and FEP but I'm not sure which. I which Gary's article had pictures but I imagine it would be very tedious to take pics as each step was made.

    Few questions I have:
    1. Can anyone tell me what are the layers in the bottom part of the stock vat? My understanding is:

    (             resin            )
    -------------- FEP -----------
    ------------ PDMS ----------
    ------- clear acrylic -------

    2. I thought FEP is made the topmost layer since FEP is slippery to ensure the printed layer doesn't stick to the bottom of the VAT. How does one know it's time to replace the FEP?

    3. Not sure what the PDMS layer is suppose to do? Is this just used as sealant to avoid the resin from sipping through the sides of the vat? If so, can a regular silicone glue/sealant be used instead?
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    @chiz, the goo is uncured PDMS that apparently cannot cure due to exposure to something in the corners like excess acrylic solvent or something dirty/oily perhaps when it was originally poured.

    Your layer map of the vat is correct.

    The FEP is a thin adhesive film on top of the cured PDMS layer. If you damage the FEP from removing stuck prints or rough maintenance, you can slowly peel it off the PDMS and potentially put another piece on. It is very sticky, very temperamental and you will pull your hair out trying for 'perfection'. Been there, done that. That is why the flexible vat is the way to go in the near future. ;)

    In the traditional system, the PDMS layer is the build surface. In the Draken vat, the PDMS layer is used to cushion the FEP layer. Think of it like the pad under your carpet. If you tried to peel a print from FEP connected to a very firm substrate like the acrylic, it would be very violent because the FEP cannot 'give' or flex when being pulled apart. The PDMS will provide that 'give' and make it a little easier to peel from.

    If you are using a FEP layer on top, you can technically use any clear silicone that allows UV light to pass through it without degradation. I also recommend one with a low durometer shore hardness to provide that 'give' I talked about earlier, but not too soft that the printed object starts to deform the silicone. Sylgard 184, which is the textbook silicone for use in SLA printing, has a durometer of 43A so that would be the reference to follow. I use the Qsil 216 PDMS when I recoat or build new vats. It is cheaper than Sylgard 184 and works just as well as I can tell.

    Hope that helped!
    Ron
  • chizchiz Member, Backers
    edited February 2016
    @Ron

    Thanks again Ron for the usual quick response and I admire that you have the most experience around these forums when it comes to SLA printing. ^:)^ I remember some terms from my Chemistry and Physics classes but don't recall "durometer shore hardness" and all the other stuff you guys talk around the forums. Definitely a learning experience for me. 

    As for my vat... I think it's false alarm but again, I could be wrong. The goo/gum-like substance appear to be uncured resin that was left in my vat. I doubt it's the PDMS because based on my google-ing, the FEP could withstand most chemicals including resins. I inspected my vat and it appears the FEP is still intact. No bubbling, lifting, etc., has occured yet. So I'm thinking the PDMS layer, being underneath the FEP, may still be intact and my vat is still usable.

    I followed Gary's advice on cleaning the vat using dishwashing liquid but it's a PITA trying to remove the uncured resin that's stuck in the walls of the acrylic vat even with a scrubbing pad. Assuming I successfully clean vat, I'm thinking of putting FEP around the edges of the vat to prevent resin splashes to stick to it. 

    I wonder what's the cost differece between PTFE or FEP sheet vs acrylic sheets. Wouldn't PTFE or FEP sheets be a better material for the vat wall so it would be easier to clean/maintain?
  • rkundlarkundla Member, Moderator, Backers, Ultimate Backer
    Thanks @chiz, I like helping here on the forum and hope everyone has as good of an experience with their Draken as I have had with mine!

    Thick fluoropolymer can get expensive and bonding them together more difficult. Imagine trying to get the PDMS layer to cure to the sides of a teflon vat... ;) Probably not gonna work quite right.

    Putting FEP film on the walls would help. My original vat had FEP up the back wall and when my other resins were eating away at the acrylic, the wall with the FEP was still in pretty good shape.

    Now, I made a clear acrylic vat myself from laser cut cast acrylic goods and using the B9 resins I have had no crazing or other disintegration of the acrylic material. I don't remember if I used the new vat with my MakerJuice.

    Hot water and soap, using a paper towel will get uncured resin off undamaged acrylic walls. If they are damaged however, you will never get them clean because the acrylic has bonded with the resin and it is now a strange goopy mixture that you can physically scrape off, but it will reform as soon as new resin touches it. :( You shouldn't see it causing problems with new resin as long as you wipe off as much of it as you can.
    Ron
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