Another day, another challenge

General discussion of topics that don't seem to fit anywhere else.
nalmeida
Posts: 46
Joined: Fri Aug 07, 2015 1:18 pm

Another day, another challenge

Postby nalmeida » Tue Nov 03, 2015 3:21 pm

Machine: LittleRP
Projector: Acer P1280
Resin: Spot-A GP
Slicing: 50 micron

Hi once again guys, got stuck with yet another problem while printing an object. This is the original object:

Image1.jpg


An this is the placement in Creative Workshop (It's slightly angled so that the top is facing the vat):

Image2.jpg


And now the problem, as you guys can see the sides are curved near the top where they meet the face, this happened with this project and others that I oriented this way. I know I could try other orientations but this is the one the gives the best results overall. Any ideas/sugestions on how to avoid this:

Image5.jpg

nalmeida
Posts: 46
Joined: Fri Aug 07, 2015 1:18 pm

Re: Another day, another challenge

Postby nalmeida » Tue Nov 03, 2015 3:22 pm

The other picture, as you can see the sides curve when meeting the face :(

Image6.jpg

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James
Posts: 167
Joined: Mon Dec 02, 2013 1:56 am
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Re: Another day, another challenge

Postby James » Fri Nov 06, 2015 4:26 am

It's the same reason your holes are not coming out, over exposure. Take a look at the roof area. It looks ok, right? Yet, the bottom open area is bent inward and then the end of the car body looks ok again. Why? It's because as you print the resin is accumulating exposure and by the time you get to the end of the print the unpolymerized resin has accumulated enough exposure that is being over exposed. When light polymerizes the resin the resin shrinks a tiny amount, but if you keep applying light it keeps shrinking. This is probably one of the top 3 biggest problems with SLA printing, i.e., shrinkage, even after the print is finished, e.g., when sunlight hits a finished print and causes it to shrink unevenly and warp. Just before it prints the end it is printing a U shaped so the ends curl inward from shrinkage and then when it starts printing the end the whole surface of the end is also shrinking but the structure is keeping it from curling or warping in the X,Y, directions. The shrinkage is not happening fully exactly at the time of layer exposure, it's happening slowly over several layers of exposure thus causing it to have the curved shape that reconnects at the end of the car body in the proper location.

Those globs you see are caused by over exposure as well.
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