VAT, PDMS and other annoyances

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BobSavage
B9 Maker
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VAT, PDMS and other annoyances

Post#1 » Sat Sep 08, 2018 11:37 am

I've got to admit, the VAT design on the B9 is a significant annoyance that has had me put my B9 up for sale a couple times and if it weren't for the horrid resale value of these, it would have been gone.

Now that that's off my chest, I'm really trying to learn how to use this thing now, but the VAT is again getting in my way.

When I bought the unit a couple years ago I bought 3 VATs. One of them had distortion in the "glass" right off the bat and not knowing any better, I didn't get it replaced. It's been a while now so I forget what happened, but I think the glass separated from the VAT so I threw it away before resin had a chance to escape and mess anything up.

The second VAT, the PDMS in the overflow area immediately lifted up, allowing resin to get underneath. Again, newbie, I just cut it back so most of the lifted section was gone and proceeded to use it. I've learned that once resin gets under the PDMS it works its way onto the glass area. Cured resin under the PDMS on the glass... into the trash.

My third VAT, which I've replaced the PDMS on (I'm a PDMS newbie since I hardly used this machine the first 2 years), I had the same problem as the second one, except the PDMS lifted after I replaced the PDMS, not from the factory. So, resin on the glass but not cured... well, this plastic is soft so in cleaning the inside, I've got some very fine scratches so I used some plastics cleaner/buffing compound for fine scratches, etc. There are still fine scratches.

Thanks if you've read my ranting this far.

So two questions, the first of which is there any third party VAT that's better than the plastic one? I'm thinking something with real glass and perhaps even aluminum? These plastic VATs just seem far too fragile, particularly for something that costs $60+ a pop.

Second question is, how much (if any) fine scratches can be tolerated and still get good prints?

Thanks in advance.

Bob

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Robert Howle
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Posts: 6548

Re: VAT, PDMS and other annoyances

Post#2 » Sun Sep 09, 2018 3:34 am

First, what resin are u using for printing. U should only use soap and water for initial cleaning and only ISO alcohol and micro fiber cloth for final cleaning of the vat widow.

I have had some vats for over three yrs with no scratches. PDMS has to be level and fully cured. It takes 48 hrs if curing at room temp. I did oven or heat curing to speed up the process.

Have u printed the supplied test print to make sure your machine is properly calibrated.

Robert Howle
Dance like nobody's watching!

BobSavage
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Posts: 20

Re: VAT, PDMS and other annoyances

Post#3 » Sun Sep 09, 2018 1:41 pm

Hi Robert,

I was using emerald over the last couple years, though I didn't do a lot of printing. I'm not looking to become proficient printing, using black resin, for the purposes of learning mold making and wax injection.

I did thoroughly clean the VATs I recoated with soap and water which I why I don't understand the PDMS lifting. Considering this happened on one straight from B9 I'm wondering if it has something to do with the vats themselves? I just don't know what it could be other than the surface isn't totally clean, though I did think about doing a light sand on the overflow area to possibly help give the PDMS something to grab onto. I didn't do anything to speed up the curing, just let it sit a few days and it was definitely cured.

So I'm guessing with these fine "scratches," my last remaining VAT is no longer usable?

As far as calibration, the machine is calibrated and focused as closely as is possible and seems to make decent prints when something doesn't go sideways like the PDMS lifting or poor support structures (my inexperience). Interestingly, I had a real rough time getting the tolerances right when I recalibrated the machine for the black. Not being able to get within the specified tolerances, I went back and measured the emerald calibration print from the factory and it wasn't within tolerance either (my final black was far closer than the original emerald print from the factory), which does raise another question.

Are people really getting their machines calibrated within the published specs (+ or - .03mm) on all elements of the test print?


Do you know of any good third party vats? Did B9 move away from the aluminum with glass due to reliability or was it cost? I could probably draw up a VAT in Rhino and have some billet machined locally but perhaps there's just something I'm missing in the process of cleaning or, maybe these very fine lines (they may be from using paper towels) won't affect print quality?

As always, appreciate your help, Robert.
Last edited by BobSavage on Sun Sep 09, 2018 6:14 pm, edited 1 time in total.

BobSavage
B9 Maker
B9 Maker
Posts: 20

Re: VAT, PDMS and other annoyances

Post#4 » Sun Sep 09, 2018 1:49 pm

Sorry... a couple more questions. Do you use the Dynamic VAT Positioning option? Also, do you turn off the grid during printing? I have to re-look, but am pretty sure Dynamic is off by default and grid is on by default?

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Robert Howle
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Re: VAT, PDMS and other annoyances

Post#5 » Mon Sep 10, 2018 12:30 am

Do not use dynamic vat positioning.

If your PDMS is lifting then I would like to see a screen capture of your layout with supports on a typical model u are trying to print.

There should be no vertical force on the PDMS as the vat sliding motion and subsequent layer release should make that a mute point.

I have never had a PDMS release from a vat surface. No sanding or any alteration of the vat surface should be needed.

The only thing that I can see causing the issue might be moisture or some other mitigating material when u make the pour. When u get complete cure are u seeing any bubbles in the PDMS? What are u doing to insure that the PDMS is level in the vat?

Robert
Dance like nobody's watching!

BobSavage
B9 Maker
B9 Maker
Posts: 20

Re: VAT, PDMS and other annoyances

Post#6 » Mon Sep 10, 2018 7:28 am

Robert Howle wrote:Do not use dynamic vat positioning.

If your PDMS is lifting then I would like to see a screen capture of your layout with supports on a typical model u are trying to print.

There should be no vertical force on the PDMS as the vat sliding motion and subsequent layer release should make that a mute point.

I have never had a PDMS release from a vat surface. No sanding or any alteration of the vat surface should be needed.

The only thing that I can see causing the issue might be moisture or some other mitigating material when u make the pour. When u get complete cure are u seeing any bubbles in the PDMS? What are u doing to insure that the PDMS is level in the vat?

Robert


The PDMS doesn’t lift on the print side, it has lifted every time on the overflow reservoir side. So it’s the side where the PDMS is thin from flowing over the dam. The thin layer lifts up and can/does grab and ruin the print as the vat is going back and forth.

Lifting on the left side of the vat is why I was able to trim it back and then continue using the vat. The problem with that is once it has lifted even if trimmed back, the resin has worked its way under and onto the window.

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Robert Howle
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Re: VAT, PDMS and other annoyances

Post#7 » Mon Sep 10, 2018 2:38 pm

How much material are u mixing and pouring? Sounds like not bonding to surface.

Robert Howle
Dance like nobody's watching!

BobSavage
B9 Maker
B9 Maker
Posts: 20

Re: VAT, PDMS and other annoyances

Post#8 » Mon Sep 10, 2018 9:40 pm

Robert Howle wrote:How much material are u mixing and pouring? Sounds like not bonding to surface.

Robert Howle


I think it was like 66ml total (I followed the video instructions from his site) and agreed, it does seem like it didn't bond with the surface, which I would expect if it wasn't clean but I did clean it thoroughly.

It seemed like there was actually too much PDMS on the overflow side so maybe I should use a little less so there's not such a large area of thin PDMS on the overflow side.

Alright... I guess I have two choices. Buy new VATs and figure out how to clean the VATs well enough for the PDMS to stay down or use Castaldo VLT for molds and just have Shapeways grow the models for me.

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Robert Howle
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Re: VAT, PDMS and other annoyances

Post#9 » Tue Sep 11, 2018 2:43 am

I would mix 60ml and try that. On my vats the PDMS only goes about 1/2 inch to 3/4 past the overflow point.

Robert Howle
Dance like nobody's watching!

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