Parts are the wrong size

We’ve got a few form 2 printers using clear resin, and have recently noticed that some parts are 1-2mm too big. I know doesn’t sound a lot, but it is when you are working to 0.5mm tolerance

Can washing in IPA or curing under UV swell the objects?

It isn’t printer specific.

They aren’t warped, just too big.

If this is a systemic error you could try to use the XY correction tool accessible through the printer’s touchscreen.

1-2mm indeed is quite a lot even at the maximum print size.

1-2mm is huge, and definitely not expected.
I’ve recently printed a retention piece to hold a PCB, dimensioned to a tenth of a millimeter, and it fit perfectly.

IPA does swell prints, if you keep them in there for a long time (say, an hour or more).
Curing can only warp them (if thin).

I’d suggest printing some calibration pieces in various orientation and measuring them to figure out which axis is off. If it’s both, the same amount, something is likely off somewhere else in the process.

Which resin were you using?


just using the standard clear resin.

Strange because over the past year we have been fine, and now things are too big

Someone reported Clear getting overcured with latest firmware, i believe, but getting an overcure of 1mm would be crazy. And obliterate all detail on the object. Besides the dimensions being off, did you notice any other artifacts?

If you still have it, try printing an older .form file that you know had good dimensions.

If it prints fine, then you know the printer isn’t the issue, and it’s either PreForm, or something in your CAD / pre-processing chain. If it doesn’t print fine, then you know the opposite is true. Either way, at least one variable eliminated.

since the firmware change over christmas, I have noticed the quality of parts aren’t as good as they used to be, but that is in my opinion

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Which firmware are you on?

I’d like to learn more about this as well. All of a sudden (over the last several weeks) our printed orthodontic models have been printing a little smaller than they should be. Any appliances we make on the digital model does not fit correctly in the patients mouth. I’ve only had the printer since November 2017. All of our initial tests at the beginning produced great results and a couple of months in things were fine, then all of a sudden we were getting requests to redo our appliances. We’ve had two firmware updates that I’m now wondering if might be the cause. I have a support ticket in to Formlabs to see if they can help me. I know nothing about calibration so I"m hoping they can walk me through it.
I’m currently not in our lab but I’ll re-post my current Firmware version later on this evening if that’ll help.
Oh, I’m using v3 Grey Resin.


Orientation of the part can cause dimensional inaccuracy. If you import, say, a cube, in PreForm and rotate 20 degrees X and Y and then 45 degrees Z, and then generate default supports, you may see a slight variation in size toward the corner facing up and away from the build plate.

I think this is due to lack of supports on that far corner. Supports are only added in PreForm to ensure the part will peel correctly and is connected to the build plate, but they also have a side effect of holding things in place.

If you are building with supports and your part has areas that are unsupported but still safe to print (e.g., because the area is within tolerances for maximum overhang angle), it might be worth trying a print with supports added manually (I think what this is doing is helping to keep the layer in place during the peel).

Well, 1 of the printers is on rc-1.16.7-12, and the others are on 1.16.8-19.
Both versions are printing too big. 7-12 is printing 0.5% too big and 8-19 is 1% too big

Finally got somewhere.
On 1 machine we downgraded the firmware to 1.15.4, went back to an older Preform as well, and it is the correct size.
On the other 2 printers, the 2 latest firmware versions, and printing the wrong size.

There seems to be plenty of people out there having problems with the latest firmware versions, not just size issues, but also quality

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Print speedups in recent PreForm versions did seem to be causing issues for some users. Can you try the latest PreForm version (2.15.0) and the latest firmware version to see if that corrects this? Both are available on the release notes page.

at the moment we simply do not have the time to ‘test’ something out which may or may not work.
I also get the feeling that formlabs don’t really want to help with this issue, or are not taking it seriously. It is clearly a firmware, software thing, and I have opened a support ticket, but have now been passed onto resellers…
It has cost us so much money and time, and may also cost us customers, yet customer services at formlabs don’t want to know.
In the past, customer service has been great, but now…

Dimensional accuracy is a top priority for us, and I’ve forwarded many of the threads reporting inaccuracy to our engineering teams so that we can look into it. PreForm 2.15.0 reverses the speedups seen in version 2.14.0 and does seem to correct the dimensional inaccuracy that some users were seeing.

I have noticed that when I import my project into preform since the firmware update the size is always way off. I Regret updating to the new firmware. How do I get it rolled back

Any way to keep the old settings? Everything was working great for me; I use the default support settings, etc., and never had a problem. And I liked having my prints run 25% faster. Am I now the one who has to refuse to upgrade?

(Just provide an option behind a dozen “Are you sure? Use at your own risk!” dialog boxes. The speed improvements are simply too great to give up.)

You’ll need to go back to an older vsersion of preform

and after, use a usb to downgrade the firmware

I don’t mean those old settings. I mean the settings from 2.14.1, the fast version, that some people were having trouble with. Worked great for me, and was fast.

Which PreForm and Firmware versions are you on? I’d recommend updating to the newest versions as those address some of the dimensional inaccuracies users were seeing.