Build Your Own SLA/SLS

There have been trials using a smaller amount of resin floating on water for top down printing. I did some looking around this am and can't seem to find the references. I am considering doing some experimenting with printing top down also and this seemed like an ideal solution to the cost of filling the tank. It wouldn't take much for me to swap things around to try this if I can find enough information on the liquid used to float the resin.

http://www.peachyprinter.com/#!
Laser based, not DLP projector

They are using a saline solution, but I suspect many liquids with a heavier density would work. The real trick is finding a liquid that won't mix with the resin. I'm wondering is mineral oil will work.

One thing that I do not understand very well is how new/fresh resin is added to the top cured surface... Maybe the cured resin is slightly less dense than the fresh one... But in that case, how is the piece retained close to the surface? (And not submerged)... Maybe the water bellow
Anyway, controlling precisely the Z-high with water drops seems tricky...

I'm actually thinking right now about trying to build something similar to the peachyprinter idea, but with a projector and a better measurement for z axis control. My best thought so far is a 0-1psi pressure sensor. Using the same idea of constant water flow to raise the z axis but use pressure to determine depth. Precision could be an issue though, it would need to output to 1/1000 of a volt (4V/psi) to equal .05mm resolution. I don't know if that would end up being any less finicky than the drip system...

asked the makerjuice guys directly. As long as the water is saturated with salt (not saline but has a density greater than the resin , the resin will float and theirs no mixing.

As far as resin over the top, one way is to run a sweeper bar across the surface after each -Z move from a slice. This is a commercial fix that the powder printers also use.

lower platform 1 layer
add resin (very small amount)
sweep flat
expose
repeat

Warmer resin allows for thinner layers it lower viscosity and surface tension.

Our printer, the Noble 3D Printer, (open source) is using top down with resin floating on saltwater, works quite well. it enables us to have what we believe is one the largest build areas, 270mm x 200mm x 400mm and easily expandable. You can find the instructions, (work in progress but 80% completed), on how to build one on our website www.Noble3DPrinters.com/open-source

What happens when the pigment settles to the bottom of the resin layer? does it stay at the boundry between the resin and the saltwater or does it settle to the bottom of the saltwater layer where you can't just stir it back up.

Greetings to all;
An interesting Video Link floating resin; http://education.mrsec.wisc.edu/309.htm

Regards Sid

If anybody else has tried this I'd like to hear your troubles. I did it and it is just medium OK, but I haven't been working with it long.