Not a fan of LT tanks

The stiff silicone spatula has had no trouble removing anything stuck to the bed…
The bed is a rubber, itself, and the trick is just safely deforming the surface of the tank to cause the rigid resin to break suction.

A polyethylene scraper should work about as well, but if its hardness is higher than the durometer of the tank surface, it can still scratch it.

The reason iphones look good long term is that most things they come in contact with can not scratch the glass because they are not harder than glass.

Now that I have a bit of a better understanding of the SLA process Formlabs and other printer manufacturers use; it sounds like the primary purpose of the PDMS layer is to aid in bonding the raft to the build platform by compressing the two surfaces together to eliminate any gaps.

Whether this is still required for the subsequent model and support layers is unknown to me as I wasn’t part of the design team. Assuming the PDMS is just for raft bonding; the real engineering feat would be to ‘roll up’ so to speak the PDMS after it’s served its purpose for that particular print.

I see MOAI is working on a DFA (whatever that means) desktop SLA prototype with as 300mm x 300mm x 300mm build volume using submersion technology used in commercial and industrial printers. It still needs a wiper. Maybe that’s what the Form3 will be using too.

The delicate nature of the LT tank’s PDMS lining makes LT (Long Term) a bit of a misnomer. Just saying.

The primary purpose of PDMS is to be transparent (optically clear, which roughly means it will not distort the light emitted by the laser) such that the laser can pass through and cure the resin. It’s used instead of other optically clear materials because it’s a silicone and thus have trouble gluing to most materials, this means that when the resin is curing it bonds both to the PDMS and the build platform, but the bond is much stronger on Aluminium than it is on Silicone.

As for the LT tank, I was also very surprised by the relative fragility of the surface (I read it’s not PDMS, but don’t recall ever reading an official answer as to what material or variant they are using).I have cleaned a lot of standard tanks with the supplied wiper just as described in Formlab’s guides without any issues, I found the PDMS to be quite resilient so I was very surprised that it wasn’t made more clear that the LT tank isn’t.

That being said, if your print don’t fail, as @Ike wrote, I find that the LT is indeed “long term” and I have used several liters of Grey Pro and Tough resin and it still prints like day one. However I have also seen the exact same straight lines across the whole surface when cleaning the tank, they are parallel to the wiper path and cover the same area… I would love @Ike to comment on that and whether we can do something about this ?

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Thanks for the explanation.

In any case it seems that these tanks need to be longer lasting, regardless of whether it’s the standard or LT tanks.

I have been re-coating my tanks for the past 18 months or longer. I use Dow Corning Sylgard 184 silicone to re-coat my tanks, and it’s worked great. The biggest problem is keeping the clear acrylic bottom scratch free. The material is soft and very susceptible to scratches or fogging. Just a drop of IPA on it can leave a nasty mark.

But if you take care of it, you can re-coat the tank quite a few times. I have a couple of tanks that have been recoated at least 4 times.

On the other hand, I believe the new LT tanks are using FEP film as the release medium. The film is very resilient when it comes to reactivity to various resins, but it’s also fragile and prone to scratches and gouging. I’ve used the metal spatula on my tanks since day one, and never damaged the PDMS. I have use the spatula on a FEP tank I have and it’s very easy to gouge and scratch. Once it’s gouged, it stays like that, there’s no fixing it.

However, FEP film is not that expensive. I don’t know for sure if that is what the LT tanks uses, and since I don’t have an LT tank to examine, I don’t know if the film can be replaced. But there are options that use FEP film out there, that are designed to replace the film easily.

Perhaps someone that is more familiar with the LT tank, can chime in on the subject.

On a side note, is if the LT tanks surface is as delicate as FEP, then the gentlest way to remove failed prints is to use your hands. You can use your bare fingers, or you can wear nitrile gloves, to do it, but this way you wont risk destroying the film surface.

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However I have also seen the exact same straight lines across the whole surface when cleaning the tank, they are parallel to the wiper path and cover the same area… I would love @Ike to comment on that and whether we can do something about this ?

That might be more of a question for support, but I think it’s something Formlabs is aware of. I’m seeing a straight line in a standard tank with Ceramic resin at the moment, but I think the tank is otherwise fine, and the lines left by the wiper are not as detrimental to the print the same way that clouding from lots of printing is.

If you can’t see corresponding straight line artifacts/defects in your prints that get printed over those lines in your tank window, I wouldn’t worry about them. If you are having defects that line up (pun sort of intended), I’d contact support.

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You can use your bare fingers, or you can wear nitrile gloves, to do it, but this way you wont risk destroying the film surface.

Please use nitrile gloves.
Please don’t use your bare fingers to touch uncured resin, or things that are wet with uncured resin, and if you get uncured resin on your skin from picking debris out of the tank, or spills, or sticky parts being finished, please wash it off as soon as possible with soap and water (not solvent).

I had massive scratching over the whole surface of an LT tank after only a few builds with rigid resin and build quality crashed to failure after failure. The first couple of builds in Rigid on the new LT tank were perfect. Can somebody explain why the scraper has to touch and push down on the tank surface at all as its main purpose is to leave a film of resin for the next build layer. It just needs to float one or two millimetres above the tank surface, close enough to agitate the resin at each pass. Perhaps even a roller would be better than the current arrangement? Am I wrong?

I’ve touched uncured resin with my bare hands since I started printing (2+ years), and I haven’t yet developed any skin problems. I will qualify this by saying that I’ve only used standard resins (grey, white, clear) and ApplyLabWorks standard resins, but there’s nothing in any of those resins to be concerned with from a health standpoint.

And I wash it right off with dishwashing liquid.

I’m glad to hear you’ve got no problems with it! I also have no problems after some time of incidental contact with resin (including before I joined Formlabs) and prompt hand-washing (although I don’t deliberately dunk my fingers in resin). But I’ve also heard of people becoming sensitized to (acrylate) resin, like one can become sensitized to epoxy, after much less exposure.

You might be immune to acrylate resin sensitization (I don’t know if this is possible) and any other effects of exposure, and you’re free to assume your own risks, but the official advice will probably always be to avoid getting it on your skin as much as possible, like the SDSs for our resins indicate.


But I’m suppose to expect a bad tank and replace the tanks if I don’t print for one month DUE TO soo many print fails…

Same problem here.
The LT-tanks are scratching like crazy. Bad quality for a high price - crap!!!
Since we have our printers we monitor a blatant drop in quality and final inspection.
It is a problem of fast growing companies although it should not be the customer who at the end is paying the bill!!!

Peter Figge

We are quite happy with our LT Tanks, we can print liters and liters of Tough resin without problems. The scratching issue didn’t affect print quality in the past - every time there were quality issues it was either sedimentation (for example with flexible resin) or optics issues (hazy window, dust specks on the mirrors).

However, it would indeed be good if FL would consider a redesign of the wiper, so that it doesn’t scratch the LT tanks that much.

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So when you recoat your tanks… are you just pouring a liquid silicone in and allowing it to self level?

There is a tab on the underside of the wiper arm that protrudes down past the main wiper edge. I cut it off when I first noticed it on my first tank. Formlabs claims this is necessary but I see it as a way to prematurely damage the surface of the tank.

This tab has been talked about in the past, and I think I remember that they removed it on the LT tank’s wiper. Now it may only have been on some of the most recent LT tanks… I’d have to check the LTs I have at work for that tab and the version on the tank.

Anyway, that tab (if we’re talking about the same thing) is at the center of the wiper (under the hinge) while the streaking we were talking about in July were along the whole surface of the tank (at least that’s what I was seeing at the time) so I don’t think the two are related… that tab was definitely an issue though.

My kitchen counter is not perfectly level, so when I do my recoat work, I first put a piece of heavy glass down, and use stacked business cards in the corners to level it off.

Then I put my tank on my scale, and pour the mixed silicone while measuring the weight, then I put the tank on the leveled glass. I put another piece of glass (2mm thick and pretty light this time) on top of it, and check for level (It almost always is still perfectly level), then I do another tank, and put it on top of the glass I just covered the first tank with, and so on. Stacking 4 tanks at a time.

For what it worth, the weight of the silicone is not always the same. Some tanks require a few grams more or less than others, so I now have them all marked. I have one that needs 52 grams, while another one is 57 grams, but the average is 55 grams.

do you vacuum degas the silicone? or are you just relying on the bubbles bursting on their own?

and the silicone is not delaminating from the edges when it shrinks?

The bubbles work themselves out within 1/2 hour or so. I only had one instance where the silicone edges delaminated from the tank, and that was most likely due to the tank not being properly cleaned prior to the recoat.

I was having problems with the LT tanks and advised to change the elevation of the print platform as follows:

"on your Form 2, under “Z Fine Tuning.” To bring the build platform down, make sure you hit the minus button, so that the value displayed reads -0.5 mm. Once adjusted, you can try printing as normal. Your Form 2 will remember this setting for subsequent prints. "

It seems to have worked.

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