Laser offset settings?

I noticed that in most cases the parts came out too big. usually it is around 0,1mm - 0,2mm. I know that we have a setting for x and y in the printer menu, but this just stretches the whole part. If I print a straight tube e.g with inner diameter 10mm and outer diameter 14mm (=2mm wall thickness), the print comes out outside diameter 14,1mm, inside diameter 9,9mm ( = wall thickness 2,2mm) . It becomes a big issue if parts should fit together (male and female part or screws e.g.) and this can´t be compensated by simply change the scaling of the part, but it would be an easy thing if there would be a setting to slightly change the laser offset.

Are there any plans to add this in a future update. Or is there a workaround for my issue? Compensating in the CAD-file is not a acceptable workaround as we are talking of constructions already done by customer in 50% of the cases.

What do you mean by “offset”? There is no numerical value that can be added to or subtracted from the laser position to fix your example. You either add 0.1 or subtract 0.1 and either way you still end up with a part that’s not quite right. To fix your example, the printer would need to add 0.1 when doing the inside of the tube and subtract 0.1 when doing the outside of the tube. Except the printer has no idea about the shape it’s printing, it simply steers the laser where the slicer has told it the laser needs to be steered.

FDM printers are notorious for reducing the diameter of inside holes/pockets. It happens because of the way the plastic is extruded, it inherently oozes in the open direction, which is towards the center of the hole. FDM inner holes always come out smaller. But SLA doesn’t have that problem. If it’s too large on the outside it should be too large by the same proportion on the inside.

Have you actually measured a print like the tube example, or only the outside dimensions of a print? I print through holes in my models all the time and haven’t see this happen. I’m thinking that the inside-of-the-tube problem you outline isn’t actually happening and that if you print this tube and measure a outside diameter at 14.1 the inside diameter will be 10.1 not 9.9.

And that being the case, the scaling feature in the printer’s fine tuning panel will fix the problem.

As we are talking about laser - SLA, the inner and outer lines are drawn vector based (don’t know how to better explain). As the the laser spot has a fix diameter the software has to consider a negative offset of at least half the diameter of the laser spot. I had a closer look into Open FL and found two parameters in the material - ini files. One is called “InnerBoundaryOffset” and the other is “OuterBoundaryOffset”. But for the Form2 there is no chance to edit these two parameters. But it would help a lot in my case to achieve a much higher accuracy of the prints as ( material dependent) my parts came out slightly thicker as they should be. If I use x/y fine tune in the printer with e.g. factor 0,99 a 10mm diameter will correct at the outside, the hole inside will then be even smaller. And if the part is 100,0mm it will be 99,0mm afterwards and 100,1 mm without x/y compensation.

I’m not sure how accurate you can expect a print to be. Better than 0.1mm is asking a lot. It’s never going to be line-to-line accurate. For mechanically accurate parts, I’ve always printed, measured, and tweaked to get a final print that met my requirements. In extreme cases, I print a feature oversized and then machine it on my CNC (I used to do this a lot with FDM prints). Mostly, though, I design in some additional tolerance for the printer and stuff fits together fine.

I expect cured resin has a fairly high CTE. I wonder if you took your tube example and cooled it off a bit it would shrink to the dimensions you wanted.

If the feature support is in OpenFL, odds are it can be made accessible via the printer’s front panel or PreForm. You’ll probably need to drum up some support from other forum members to get the idea anywhere near the “goal line”. But FL has implemented features that were originally proposed here so they do listen.

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