Problem with non circular objects

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nzfinescale
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Problem with non circular objects

Postby nzfinescale » Tue Jan 17, 2017 9:43 am

Thanks to Mark my emerald prints now look pretty good.

BUT on to the next problem, which is that objects that should be circular are not. When the wheels below are printed they are visually oval. When the castings are machined that will be a real problem. On a diameter of 13.8mm the wheels are 0.4mm under in the Y direction. That may not sound much but it is very obvious visually.

Capture.JPG


So:
If I print a 10mm cube it is pretty good. About 2.5% under in X and Y. I corrected for this using scale for X & Y in Contour. Z seems about right. This problem seems to be restricted to round objects, so I assume is not machine set up.
I'm printing using the recommended settings for Emerald at 25XY, 25Z. Usually I reduce exposure a bit as it gives sharper detail IMHO, but I thought maybe the print was too soft and stretching. A similar thing happens with Proto on other wheel models - so it is not just an Emerald problem.
I deliberately printed using this orientation so the print was well braced by the detail in Y. I added good supports - even though it should print without them.

With all of this still 0.4mm oval.

In contrast, if I print with my lower exposure, no scaling, orientation of parts rotated 90 degrees in X, no supports (ie what should be the worst case), I get exactly the same result - 0.4mm oval.

I can print these flat. That's a pain though as a) supports are needed that are not nice and b) I can print far fewer at a time. I figure that plenty of users print rings, that I assume need to be reasonably round, so this should be fixable.

Thoughts?
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mongerdesigns
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Re: Problem with non circular objects

Postby mongerdesigns » Tue Jan 17, 2017 3:05 pm

So what measurements are you getting in the x,y and z?
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nzfinescale
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Re: Problem with non circular objects - RESOLVED

Postby nzfinescale » Fri Jan 20, 2017 5:05 am

I've fixed this with a bit of thought, careful measurement, and dawning understanding of how Contour works.

My build area was calibrated by measuring the projected grid, and corrected using the calibration controls. All good, but this is not something that is easy to measure accurately, which is what I needed to be able to do. It's good to within 2-3%, but that's not enough for me.

So having printed my (out of round) model with examples orientated in both X and Y, I found the following:

The critical dimension is 13.8mm. What I had was:

X =13.7
Y =13.4
Z =14.

So on the setup screen I entered 13.8 for the 'original scale' for X, Y and Z, and for the 'actual scale' I entered the values above.

On reprinting, this gave me a perfectly round wheel.

Previously I had scaled the MODEL in Y to try fix the issue. This did not work, although I'm not sure I understand why not.

Thanks To Mark K and Emil for posts that prodded my brain along.

Lawrence

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