Dimensional inaccuracy

Dimensional inaccuracy

We are currently using this printer to make dental models that we then use to fabricate ortho retainers on.
I have been printing very successfully for the last 2 weeks and not really run into any issues to speak of. However, after doing some checks it seems that the prints we have are slightly bigger at the base than the original plaster cast model we make. Its not huge, probably less than 0.5mm but ideally this should be zero.

What is the process for using the adjustments in the printer menu to change this?


The attached files (f1-calibration.zip.form (311.0 KB)) should help you get setup and printing accurate models pretty easily. All files are zipped into an archive, then renamed to have a .form extension so I could upload them here. Rename stripping the .form extension, then decompress the archive to access the three files in it.

Overview of Form1+ Calibration Steps

* Determine how 'off' the machine is at it's default settings by
  printing the stepped calibration object, and then carefully
  measuring it with a metric digital or dial caliper.

* Enter the precise, actual measurements into the spreadsheet

* Set X & Y scaling in the printer to the values from the calculator
  with the 'Fine Tuning' menu in Preform.

* Scale each model in *all axes* by the amount shown in the calculator.

Detailed Steps

1.) The first thing to do is to reset the fine tuning scaling to factory
defaults for X&Y. This is in the help menu I think. The printer
needs to be plugged into the computer with USB to do this. If you have
changed the z-offset to adjust the way parts stick to the platform, you
can leave that as you have it. We'll fix Z in Preform itself.

2.) Print the stepped calibration object at full scale. You should print
it at the resolution you typically print at. Fully post-cure the
calibration gauge before removing any supports. Three or four hours in
direct sunlight should be good.

3.) Carefully remove just enough supports so your caliper can get
in to measure across the wider steps for X&Y, and down to the ledge
with the caliper's tail for Z. Keeping most of the supports and the base
attached keeps the gauge more rigid and accurate.

4.) As you measure across the steps, enter these actual measurements
into the spreadsheet calculator. When you've entered all of the X, Y,
and Z measurements, the adjustment values will be correct in the lower
part of the calculator.

5.) Adjust X&Y in the 'Fine Tuning' control menu of Preform to the
values calculated. This will be a one-time setting, and will stay this

6.) IMPORTANT: Every object you print from now on MUST be scaled in all
three axes (e.g. the overall scale) to the value from the calculator.
Do this as the first thing you do to the model when you bring in the
stl file. If you add supports first, then scale it, all of your
supports disappear, and must be redone.

7.) To verify the calibration is working correctly, print the 2cm
cube gauge *at the calculated scale* and measure it for accuracy.

Good luck, and let me know how it works out for you.

Is this the same process for the Form 2 as well?

I don’t have a F2, but yes, I believe it is. The fundamentals are the same, and the software is the same. Try it and let everyone know. You can always revert back to default if you don’t like the results. I created these tools because I need high precision in my prototyping. After adjusting this way, the 2cm cube gauge (in archive attached to this post) is within ~20um of dead on. That level of precision is simply unheard of for an SLA printer in this price range. That’s less than 1/1000" off in any direction.

Note the shadow of the dial’s needle here…

If you’re interested, this cube was done in a hybrid resin mix:
50% tough
30% clear
20% Vorex black

Which is a good combo, however I still like 50/50 tough/clear better.

This is great info, thank you for sharing! Have you found the accuracy is still good as you increase part size? I’ve been looking for good information on accuracy before I purchase a form 2, having trouble finding anything definitive.

My parts are not much bigger than the cube gauge, so the accuracy is fine for me, but I would guess that as the part size increases to the full envelope of the machine, the measured inaccuracy would increase, but I suspect that as a percentage of total part size, it would be similar. I have not wanted to waste the resin to know that for a fact though… :wink:

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