Form 2 dimensional accuracy?

Is there any feedback from form 2 users on print dimensional accuracy?
I see plenty of arty shaped things being made and that’s good, but I’m in the industrial business making parts, so dimensional accuracy is everything to me.
What are users finding when they measure their prints? For example overall dimensions and inside hole diameters.

I would also like to ask a follow up question related to this. The form 2 has a new laser with an smaller spot size (FWHM). It is my understanding that preform ignores features less than 300(?) microns in size for the form 1+. Is this value different for the form 2 due to the improved laser spot size?

I design and build breathing regulators for SCUBA. A lot of the assemblies require fine threads, o ring seals, and small details. A complete assembly might use 30 pieces, being a mix of machined brass, springs, o rings, and 3D printed parts. I’ve been using the Form2 for about 8 weeks and have printed at least 100 parts. I use mainly the black resin, but also the tough resin if I need a part that has to stretch or bend a bit. The dimensional accuracy seems very good. My perception at this point is that it is somewhat better than my Form1+. Also, I have had only one print failure, and that might have been due to user error. I’ll try to check a few parts and will get back to you with more specifics on the accuracy.

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Glad to hear you’ve had so much success with your Form 2 Charles! I’m attaching a white paper here that goes over dimensional accuracy on page 9. This is for the Form 1+…but you can expect similar (if not slightly better) results on the Form 2.

The laser spot size on the Form 2 is 140 microns (0.0055 inches)…and yes, finer details are possible with the newer diodes.

formlabs-intro-sla-whitepaper.pdf (4.7 MB)

Hi Charles,
Much appreciate you taking time to share your experience. Look forward to the measurement results you find.

I bought my Form 2 to do mechanical prototypes with moving parts and high demands on accuracy. Firstly, I have printed almost 1 liter of clear resin with only one failure which was due to too small and few support points. That said, my first prints were slightly larger than expected and did not fit together as designed, with spacing of about 0.2mm between moving parts. I find that just rinsing the parts in IPA after print does not remove all uncured resin from the surface of the printed part and I guess it therefore renders the part features larger than intended. I now clean the parts in IPA using my old Philips Sonicare electric toothbrush and post cure with a 405nm UV LED nail salon lamp. Contrary to the Formlabs guide, I do not let the parts soak in IPA. Whether or not this is good practice I don’t know but the parts seems to fit together much better than without Sonicare treatment. It would be interesting to have someone measuring the parts using professional measuring equipment. Does anyone know of a suitable STL-file for test printing a pattern of holes, rods etc of various sizes which can be measured?

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Attached is a print test I use on the FDM machines we have: printer test.STL (148.6 KB)

Picture of dimensions:

Just to give you an idea of what I design and build,… the first photo is a complete assembly of a SCUBA regulator second stage. Internally there is a brass tube that houses the valve components. This valve needs to be able to take about 170 psi of pressure. I am able to print these valve tubes with my Form 2 and pressurize that assembly to check the function before I go through the trouble of machining brass. As far as dimensional accuracy, The second photo shows a valve tube that I printed. Here is a quick reference of what the dimensions were supposed to be, and what they actually measure. Sorry, I’m a little old school and everything is in inches, not mm.

Should be: ------------------------------------------ ** Printed part:**
.400 ------------------------------------------------------------ .398
.850 ------------------------------------------------------------ .853
.260------------------------------------------------------------ .260
.500------------------------------------------------------------ .495
3.060 (length)---------------------------------------------- 3.060

I do the alcohol soak by the book, and have not changed any of the print parameters from the stock setting. IMHO, this printer rocks.


Hi Charles,
Really appreciate your feed-back on this, this is the sort of information I was looking for. :relaxed:

The accuracy on that part is amazing, thanks for sharing, the black looks great too, SLA definitely has an edge over DLP with surface finish, sure it has some layer lines but I think that is less obtrusive than voxels especially over 70um xy, in my limited experience anyway.

I have used a few other printers over the years, my last one being a DLP printer. The parts were just never very accurate, at least on my machine (which was not one of the cheap ones, made by a well know company that will go unnamed). I also had and used an FDM printer. The BIG problem for me with FDM printing is that the parts do not hold air. Everything leaks in a million places. I used one for years, and had to paint all of my parts with ABS glue to make them almost watertight. (There goes your accuracy!) Even then they would never seal under 170 psi, I could only make parts that had to take very light pressure differentials (maybe 2-3 psi max). The facet lines can be eliminated by saving the STL as a finer mesh, and printing at a higher resolution. Layer lines can be sanded out if necessary. For this part it wasn’t needed at the time.

Something I am starting to notice, accuracy of the part comes down to maybe 3 factors, the initial calibration must be perfect, resin shrinkage must be taken into account, the resin I’m currently using is 0.4% tested, then there is support generation, this is nothing like FDM and from my experience the hardest part to work out. In general it seems you need a lot more support than you would think and also a lot larger, going big certainly holds the part for an accurate print whereas lots of small points tend to create deformed parts, you do have to spend more time on clean up, I use a Dremel, lifesaver for resin prints.

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