Making a GTT TFT Display Desktop Case

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Aniso
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Making a GTT TFT Display Desktop Case

Post by Aniso » Fri Feb 24, 2017 2:35 pm

I was finishing a desktop case for a GTT module and wanted to demonstrate the process.

First I start with a 3D print of our case design. This first photo is after initial application of some Bondo. The specific Bondo product is "Glazing and Spot Putty" which is a one part paste full of VOCs and cancer which requires adequate ventilation. It sticks to the PLA of the print very well, but I do sand it to roughen it up first (and remove high spots).
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After application of Bondo, it is sanded on a flat surface. It is important to build up the Bondo against a flat reference. You can not "free sand" until the very final steps. After each sanding, the object is painted with sanding primer. I do this to provide a layer of color for sanding the next coat - when I see the primer exposed, I know that I need to stop sanding. This shows the painted piece.
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Next more Bondo is applied.
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This is then carefully sanded bit by bit until as much Bondo is removed as possible without sanding beyond the previous layer.
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This process is repeated until all the low spots have been filled.
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And this is the piece just before the final (or second final) application of sanding primer.
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After this, the piece is sanded one last time with very fine (800) sandpaper and painted with color. I should continue this thread and fill in details. Any interest?

Aniso
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Posts: 283
Joined: Tue Aug 14, 2001 6:00 pm
Location: ...I could tell you my velocity...

Re: Making a GTT Desktop Case

Post by Aniso » Wed Jan 17, 2018 4:13 pm

I imagine that there could be a thousand questions about this depending on the skill-set and experience of the question asker, so I want to try to address a few that I can think of in the form of a FAQ.

Q: Material issues?
A: These have all been printed in PLA - nice non greasy PLA from filaments.ca
It is difficult to over-emphasize how sensitive the finished product is to even moderate heat. Tests in a temperature controlled oven show that it is not safe beyond 50 degrees C. Technically speaking, PLA is not supposed to be a problem at that temperature, but it will deform slightly in very ugly ways. To mitigate the problem, it has been proposed to use a carbon filled PLA product which is supposed to have superior temperature stability, but I have not tried it. Let me know if you do!

Q: Is the painted finish like a car?
A: No, not from what I see. The paint I have used is called "Perfect Match" by Dupli-Color and the clearcoat from the same company. It goes on real nice and I could not be happier with the quality and consistency, but even with several coats of clear on it, it is still much more sensitive than a baked car finish. That said, it is beautiful.
One surprising issue that no-one expected was that if the radius of a corner is too tight, the paint on the corner will eventually crack and pop off leaving the corner looking like it was hit and chipped. The secret is too soften all the edges and corners sufficiently to prevent it. I eventually got consistent good results with a radius slightly larger than 1mm.

Q: Can I just sand down the PLA to get a smooth surface and then paint that?
A: No. I want to believe that it is possible as well, but the pattern of the 3D print will always come through. It is amazing. One would think that a couple coats of sanding primer would work well, but my experience has been that if there is not at least a skif of Bondo under it, you will see the print lines.

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