I have a Form 3 that I’m using to prototype a small snap-together enclosure, about 50 x 25 x 15 mm overall. As you might imagine, the snap fixtures are pretty small, with minuscule overhangs and lever arms. Before we drop oodles of cash on a mold for mass production (ultimately in polycarbonate), I need to validate how the top and bottom half fit together.
I’ve had this Form 3 for a long time–since 2018 or so–and I use it only a little…consistently, but infrequently, as the company I work for only occasionally needs to draft new designs. I’m using a new tank and Black 4.1 resin cartridge, but finding that just about everything I print is slightly too thick.
Examples:
The walls should be exactly 2.0mm thick, but they consistently measure 2.25-2.3mm thick.
A small round button insert should have a 5.85mm diameter but consistently measures 6.05-6.1mm
It’s not an overall scale problem (like the whole thing is sized up by some percentage), but specific features come out thicker than they should. I’ve tried curing vs. not curing, and I’ve tried orienting the part in completely different ways. I can’t seem to make the extra thickness go away.
I’ve tried the same models on a Snapmaker J1 IDEX filament printer, and while the output has the comparatively worse finish quality you expect from a consumer filament printer, the dimensions are actually much closer to the model.
I don’t have a second Form printer to test with easily, and I currently have only one tank and cartridge. Is it possible that it’s something about this resin? Most of my previous tests have been with Tough 2000 because that’s what those designs called for; this is the first time I’ve printed with Black v4.1. All I really need is something dimensionally accurate. I can get another tank and different resin, but I’d like to know why this is happening before I spend $300 on an alternative I might not need in the first place–or that might do the same thing again.
I’ve attached a couple of images showing one sample difference in spec vs end result. And, in case it helps, the STL for the specific part half shown in the photos. Original models in STEP or other formats might also be available if needed for troubleshooting.
From the first image it looks like the dimension you are measuring is also a supported face. The supports in my experience will always lead to dimensional issues. I would try and move the supports away from key dimensions and reduce the overall touchpoint sizes as far as you can
@jrowberg Thank you for bringing this to the forums and I would be glad to offer some suggestions
Reduce the number of supports on that surface. If necessary, reorient the part so that the surface does not need to be supported. Please see our guide on * orientation best practices.
Please check the expiration date on your resin. This is on the sticker on the bottom of the cartridge. It will be in the form of a date.
If after you take these steps, you are still seeing the same dimensional issues, please reach out to our support team here. We will gladly help you troubleshoot this issue 1 on 1 .
Point taken, and I agree that supports can impact dimensions, especially at the level of accuracy I’m hoping to achieve. However, even oriented differently, I didn’t see meaningful improvement. Here’s another image showing another copy of a part printed in the same orientation, but measuring a different feature; I intentionally snapped it in half so I could get a perfectly accurate measurement of the thickness of the middle of that face. It was printed almost upright, e.g. the “slice” or break here is parallel to the build plate, so the thickness involved should have been impacted 95% by the X/Y axes rather than the Z axis or any supports (of which there were none anywhere near this break). This should be exactly 2.0mm, and here it measures 2.26mm.
@jrowberg Can you confirm that the prints are coming off of the printer with this issue or is this after your wash and cure cycle? Please share your post processing workflow, including washing, drying and curing your parts.
@KCasey This is after washing, but not always after curing. I have tried skipping the cure step to see if that makes a difference, but it doesn’t seem to. I wondered whether Black v4.1 is supposed (or expected) to change dimensionally during the recommended cure process, and if there is even the possibility of this–especially if it would shrink rather than expand–I will be sure to perform the cure step every time.
First, some stats about the tank and resin:
The tank and resin were bought and put into service at the same time, at the end of June 2025.
The resin cartridge expiration sticker shows April 2027. The cartridge is just about empty now. It’s been left in the machine since I started using it, since it’s the only kind of resin I need at the moment.
The tank (v2.1) has 44 hours printed, 195 days with resin. The “Tank Lifetime” screen on the printer claims that the v2.1 tank doesn’t have a maximum recommended lifetime with this resin.
A visual inspection of the tank doesn’t reveal any issues I could identify; the bottom looks perfectly clean, and I haven’t encountered any printing problems or artifacts that would suggest debris or small bits of cured resin stuck anywhere (I have run into this a few times in the past, so I know what to look for).
I inspected the optical window just now, and the only thing I saw was a few areas where a faint pattern of dust was visible. I used a non-abrasive cloth to remove this, checked again with a low-angle phone light, and put everything back. I doubt this tiny bit of dust is to blame for the X/Y dimensional increase, but I’ll gladly print another test set to see what happens.
Concerning my workflow:
Print parts (obviously).
With nitrile gloves, remove printed parts from build plate (breaking them off the supports entirely) and pre-wash them in 99% IPA in a small container.
Remove pre-washed parts and put them in a new, small container with fresh 99% IPA, thoroughly wash for 15-20 minutes with gentle manual agitation. (With my low print volume and small part size, this is more efficient than using the whole Form 3 Wash machine.)
Remove fully washed parts and let them air dry (no UV) for 15-20 minutes.
Cure at 60 deg. C for 60 minutes, per Formlabs’ “full cure” spec for Black v4.1 resin. (NOTE: I have skipped this step sometimes for dimensional tests, as noted above.)
Unless you would recommend something else, I’ll try a new test print after the minor optical window cleaning to see what the latest results look like. Before I do, can you confirm that the parts oriented as shown in the screenshot below should NOT have any significant dimensional inaccuracy on the large flat faces–the ones pointing generally left in the first image? You can see in the back view that I intentionally excluded any support points on the back side of the same area, opting instead to let the bottom of the part support that open flat area as the print progresses.
I would recommend always performing the full cure on this material, yes, You will want to make sure that the parts have dried for at least 30 minutes so that the IPA does not absord into the parts causing them to swell. Washing these parts more than 10 minutes in IPA can cause IPA to get into your part and could be part of the reason you are seeing the increased thickness.
I would recommend not leaving these parts in IPA for more than 10 minutes and letting them dry for at least a half hour before curing.
This orientation overall looks. The view in the second photo the one in the back right . that one does appear to have less supports. You may want to manually add a few to make sure this does not fall off supports whilst printing.
A food dehydrator set to a low temp for an hour or so also works very well to pull IPA out of the parts. I am skeptical that the parts are swelling that bad, but may account for a bit of the offset. 15-20mins in the wash station also seems excessive to me, especially if you are using relatively fresh IPA.
I printed the part on our Form 3 with Black V4, washed in IPA for 10 min and cured at 60° for 60 min.
Then measured it, the printed dimension are in brackets and are very close to the model dimension. The wall dimension is very close to the OP’s first image.
Hope this is helpfull.
Also the model does have different wall thickness between the long and short sides? Not 2.0mm?
Thanks, Andrew! That was a far more thorough reply than I anticipated. I really appreciate your effort.
First, you’re correct: two of the walls (in this version anyway) are thicker than the shorter end walls or the main flat wall area. In light of that, your measurements look great.
I did the same thing you did with a test print on my end:
Fresh IPA wash for about 8 minutes total
Air dry for 30 minutes
Cure for 60 minutes @ 60 deg. C. (including the temperature ramp-up that should help dry even further before the UV started)
My results are not better than before. The 2.0mm walls are about 2.25mm on my calipers, and the 2.4mm walls measure about 2.75mm. FWIW, I also measured right after the wash but before the dry/cure process, and the numbers were the same.
One more question for you and @KCasey: I often don’t take the parts off the plate and process them for a while, even multiple days. The print just sits there hanging on the build plate in the machine (at a sane room temperature, no UV) until I get to it. This particular print sat that way for about 36 hours before I cleaned and cured it. Would this delay potentially also cause dimensional issues? I wouldn’t imagine so, since that would affect any very long-running print, but I ask anyway.
Aside from trying a different resin+tank or (if I can somehow get my hands on it) a different machine, one other thing I should do is validate my digital calipers. I have no obvious reason to mistrust them, but at this level of precision, I shouldn’t assume anything anymore.
@jrowberg Leaving your print in the printer for 36 hours should not cause dimensional issues. The resin on the part when in the printer is not curing. So this would not likely be the issue. I would recommend swapping out the tank and if after that does not fix it, reaching out to our customer support team with your .formfile , photos that you sent here and your diagnostic logs. We can then work 1 on 1 with you to get your part dialed in.
I’ve left the prints on the build platform for over 3 days without any issues with dimensional accuracy.
The only time we’ve had accuracy issues with Black V4 resin is with thin (< 1mm wall sections) is some swelling when using the Form Wash Solution and to a lesser extend with IPA if the parts are washed for longer than 10min.
