Volume calculations different between versions of PreForm?

General Discussion
1

Stupid question but I am pricing out a job that I calculate out the volume of material and come up with my cost per part in pewter. I had put in all my math into excell and find that the calcuations are now different. Same part in Open FL calculates to .07ml and newest Preform shows .10.

This might not sound too bad but can be horribly costly when purchasing the pewter for the various runs, usually hundreds of parts so it can be off by hundreds.

Is there a reason the volumes are so different?
Anyone have a simple size of the resin ie how many CM³ per liter? and I can adjust from there.

2

Quick update a 1x1x1 cm cube shows 1 ml in new PreForm and 1.02ml in OpenFL

Which is correct?

1 Like
3

I posted almost the same issue as I price mine pieces like you do. I was told I was wrong. Go figure.

4

It’s strange, wonder if their density settings vary between resins and exposures?

I guess I’ll use the numbers out of FormZ to play it safe.

5

I am getting around 850ml printed on each cartridge, PreForm values. Which means that there is around 15% loss on cleaning parts and/or evaporation, which I consider to be a lot of waste!
Either PreForm is miscalculating the volume values or I am not seeing the whole picture here!

CPinto

6

Density shouldn’t have anything to do with these calculations. You are talking about volume, not weight.

So 1 cm³ = 1 ml. There are no fractions or anything, this is the metric system after all, you can’t fudge basic math.

Assuming we’re talking about a 1 cm SOLID cube, the only possible explanation is that OpenFL tries to account for some type of resin loss, or that for some reason, it enlarges the model ever so slightly.

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7

This is just a shot in the dark…maybe they were able to calculate how much resin sticks to the part when it is complete. I know its a long shot but I could be wrong.

Chris

8

It is definitely a math error, probably a decimal that isn’t displayed ie software shows .00 and might be .0000 that we don’t see.

Putting my values into Formz seems to be much more accurate.

9

Because the Form2 uses G-code to drive the laser and G-code centres the line the laser uses, it is to be expected that the dimensions of a printed cube will be oversizes in the x and y directions by the width of the laser spot. Allowances certainly have to be made for this when designing close fits.

10

I believe preform accounts for this and other discrepancies when writing the gcode.

11

I just imported a 1 cm cube into Preform and my old version of Preform (ver.2.10.2) shows 1.02ml as well. So maybe on the old version of preform, they took something into account that is no longer being done, or more likely, it’s till being accounted for, but for the sake of simplicity, the numbers shown are rounded off.

Maybe FormLabs should step in and tell us why the 0.02ml is/was there in the first place.

FWIW, that 0.02ml on a 1cm cube, ends up as 16.06 ml on a 10cm cube according to Preform, which means it’s amplified 800 times.

12

I think it guestimates based on the slicing and laser width etc, just not a precise calculation unlike reading it from a cad program that can calculate based off of the entire surface. That’s my theory and I’m sticking to it.

13

I think you got it. I think the software takes in consideration the thickness of the laser spot and accounts for it in its calculations.

So in the later versions of preform, in order to produce a more dimensionally accurate print, it reduces the X & Y dimensions by the thickness of the laser spot so the resulting print is exactly the dimensions it should be.

Just for testing purposes I modeled a cube that was 9…925 x 9.925 x 10mm (I assumed 150 micron laser spot), and imported it into preform, and sure enough, it shows as 1.00ml. When enlarged 10 times, there is still a small error, but it’s only 0.88ml, not 16ml. That’s probably because the laser spot is slightly larger than 150 microns.