Printing unicorns on diffraction grating  

Printing unicorns on diffraction grating

I was inspired by an AdaFruit learning guide on printing on diffraction grating and my wife's love of unicorns to print this:

This is the Flexi-UnicornFlat.stl model from here: http://www.thingiverse.com/thing:2835053

Now, this wasn't my first attempt... I first tried the simple suggestion in the learning guide to just tape the edges of a square of diffraction grating to a print-bed and print on that. I didn't get a picture of the setup, but this is the diffraction grating that I used from Amazon.com:

This was not the way to go. Because the diffraction grating was just anchored at the edges, the natural curling of the PLA filament that I was using (Prusament Galaxy Purple) caused each of the segments to curl up individually, and eventually the nozzle started knocking pieces off. Here is an example of one of the pieces, this is the bottom surface. Nice gentle curve... (Don't know why the forum decided to rotate the image 180°, sorry about that):

But, I knew I was on the right track because the first layer did pick up the pattern from the diffraction grating film:

So, I decided that I needed to apply the grating as a full bed sticker. Lucky for me I happened to have a spare steel sheet from Printed Solid that was still bare metal on one side. So, time to make my own print surface.

After searching for "3M" sheet adhesive, I realized just how many types and formulations there were. Checking the data sheets for the ones that I could find available in pre-cut 10"plus sheets on Amazon.com, I eventually decided on 3M 468MP (this pack comes with six 10"square sheets and an applicator):

Applying the 3M adhesive to the steel sheet, and then because the diffraction grating is only 6" wide I applied two strips to get full print-bed coverage. Then trim the excess film and adhesive all around the steel sheet. I just avoid printing across the seam between the two strips of grating film. It looks really good:

Until you realize that I did a crappy job and got bubbles under the grating film... (grrr)

So, in an attempt to avoid issues with the nozzle dragging across the bubbles, and to lower printing time I printed with 0.3mm layers. Except for in the middle where the curvature of the hinge parts approach horizontal. For that I used the variable layer-heights to bring the layer height down to 0.05mm. This actually leaves in the finish of the sides an interesting racing stripe:

But, the wife loves it so I think I did good.

FWIW, I haven't yet tried to remove the grating film from the spring steel so I don't know if my adhesive choice was a good one or not. I have printed many things on this film (actually many batches of this same unicorn so my wife can use them as gifts this holiday season) and the film seems to be holding up well. I did discover that if the smooth PEI sheet really likes to be cleaned with Dawn and lots of hot water, this print surface needs to be cleaned with Dawn and lots of hot water regularly. The film is PET, so I'm only printing PLA on it.