Designing for a photon

[Iain]

So, with the Photons, what do we get in terms of minimal wall thickness, or what is the smallest rivet that it will do?  How about dimples as starting points for drilling for grab irons?

[Chris333]

Really what I do is print the model and then look to see what needs fixed. Rivets that are on the side might come out better then the same sized rivet on the top. I find things like board gaps need to be exaggerated to be seen because resin fills in tiny areas. I can do something like a boxcar with vertical or horizontal siding, but something like a flatcar deck siding will come out flat with no gaps. Sometimes I print 4-5 times before I'm happy with it.

[Chris333]

Plus there are other things. Like say you have a flat side wall on a hood, but you have some sort of internal support. There might end up being a big ripple in the side of the hood right at the same height or slice layer. When it got to that there was more surface stuck to the FEP when it lifted off and that is where the ripples come from. Sometimes I will taper unseen parts so there is no huge change in the layer surface.

This is all with me printing flat. If you angle your prints that might help, but give you step lines.

[Iain]

@Chris333  How thick do you do your hood walls?  What's a good size for a rivet that can be seen but isn't huge?

[kornellred]

I recently bought an Alco C415 model kit from Briggs Models. The body shell components are resin printed on a DLP machine, but I do not know if Mr. Briggs owns a Photon.  Be that as it may, the hood walls are 0.55mm thick (or approximately .020 inches).  For N Scale models, that is really testing the limits.  The C415 shell is brittle, but can withstand reasonably careful handling.  Detail is amazing (as an aside).

An LCD pixel is very close to .0019 inches on a side (square), or 50 microns in metric terms.  (Look at your computer screen - pixels are really tiny)
If you wanted to depict a 3/4" rivet in N Scale, it would take 2 rows of 2 pixels, just like the period in this sentence.  You would, of course, need to augment the rivet in the Z axis (duh).

The Photon (and all other similar DLP resin printers) can do some pretty impressive stuff.  Proper CAD design is a separate challenge, as is selecting an appropriate resin for a job and experimenting with the various printing parameters.