Build Your Own SLA/SLS

How are folks ensuring that their projection is square? That is to say that the image isn't skewed in any way. The basic calibration grids don't really capture this or give you a direction in which to correct.

Any tips would be great.

I used a small ruler on the surface of my vat. I projected a calibration grid, then measured the total length of each side of the outlines. I remember having to adjust my mirror slightly until it was square. I didn't want to use the projector keystoning feature, so I moved it all manually

I drew a rectangle the size that I wanted the projection to be (3"x4") on a piece of paper. I placed the paper on the vat floor and adjusted the alignment of the projector and zoom to match the rectangle.

I would measure the diagonals with a caliper, if they are equal the projection is square/rectangular. I've found that using Creation Workshops "show blank" is good for both squaring and sizing (for example, the image width and height for a 1024 X 768 projector is 102.4mm X 76.8mm). I cut a piece of vellum paper and set it on the vat floor to make measurements.

I print a grid on a regular piece of paper with the laser printer. I make the grid the size of my build area which is 6" x 4.5".

Lay it right on top of the PDMS in the vat. Since I use Mach3 for control, I use the Mach3 interface to adjust the focus of the projector (lots of small text helps get a good focus)

Jon