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Roller trouble -- learning from my mistakes

I was having some print failures and having difficulty diagnosing the cause.

When cleaning the rollers (LPU cover) I noticed some of the rollers were binding.

In hind-sight, what I think happened is I must have got some resin on the bottom of a print tray, and future prints distributed the resin to the rollers, causing eventual binding.

So I took the rollers off, disassembled them and cleaned them with IPA + PECPADs. It looks like there was a very thin film of grey resin on the rollers, causing the binding.

It looks like the printer is printing successfully again.

I noticed that none of the rollers were actually rolling. I just could not get them to roll with a fair amount of force.
This is a printer with only a few print hours. There are also these pressure marks on both the top cover “nibs” and the separating sheet of plastic on the bottom.

Could it be that the rollers are squeezed too tight between the cover and the plastic sheet?

Your roller holder looks different than mine. They must have changed the design recently.

On the original roller holders, I found the middle two rollers rolled quite easily, but the ones on the ends tended to bind. Formlabs told me that was normal. Seems a little odd for an object designed to roll, that it would normally bind. I suppose it puts a little more wear on the print trays.

I’ll maybe order a new roller holder to see what the new design is like.

What aspect is different? I don’t know if the change
is an improvement, since all of my rollers are binding…

I also see this tape on the aluminum part of the LPU where the screws go, but only on one side.

Maybe it functions as a spacer? But if so, is it enough? And why only on one side?

I take that comment back. Your photo was from an unfamiliar angle and it appeared different to me. But I think we have the same roller holders.

Your second photo of the LPU looks a little different. My LPU has more symmetric black taping.

I asked Formlabs support about the rollers that didn’t seem to be rolling and got an answer I did not expect!

Everything is fine here! I would like to assure you that the rollers are not supposed to roll. The black “tape” is a shim applied to the X-stage to level the roller holder correctly. The shims are applied differently from printer to printer and are not meant to be symmetrical.
First they used to roll, but then we discovered, that they leave a black mark on the bottom of the tank, which caused print failures, and that’s why we blocked the roller holders.

They told me something similar to that. But my middle two rollers roll. The outer two do not.

Maybe the binding comes from the more recent models of the roller holder.