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Bottom printing
There is another expensive kick starter SLA printer has appeared, the Titan1. This is very similar to the Form1, but larger. These are both bottom printers and a lot of the expense is tied up with special non-stick layers, to allow the print to peel off the bottom of the tank.
If the galvos could work printing upwards, Peachy could achieve bottom printing without this expense. First a thin layer of saline in the bottom of the tank, then a layer of resin (which floats on the saline). You drip in ordinary water, which floats on the resin. This would have a float which floats on the normal tap water as it drips in and raises the print from the resin layer. In this way, no peeling is required as the saline maintains a separation between the tank bottom and the resin.
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The purpose of these other SLA printers printing from the bottom up is to have a dimensionally consistant, solid, flat surface to print from. If you float a layer of liquid under that to stop adhesion, you lose that. In theory, you could drip in a very thin layer of saline into the Form1 or the Titan and turn off the mechanical peeling mechanism for each to get the same kind of look you get from the Peachy.
Thing is, not a lot of the expense of the Form1 and Titan1 is in the peeling system, it's in the control boards and galvos and servo and screw drive. The peel system for the Form1 is a $5 solenoind and a hinged plate. The biggest innovation of the Peachy isn't printing from the top to avoid adhesion problems, the very first 3D printer in history was a top-projection SLA with a kind of a drip-system, after all. The innovation was replacing about $900 worth of controller board and overengineered industrial galvos with a simple analog AM processing board and a set of bare-bones galvonometers that MacGuyver would be proud of.
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mmmmm not quite sure I understand that. I read somewhere (wish I could remember where) that the special tank with the non-stick coating was rather pricey !!!! Perhaps I was just having a senior moment. I was never in any illusion that the control system was cheap.
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There is also the way that I have suggested. For this method you would start with a layer of saline and a layer of pure water each at least as thick as the z dimension of the finished print. The resin would be sandwiched in the middle. Then the saline would be slowly lowered. I think the downside to this approach versus your idea is that the container will need to be over twice as tall as the print. With your approach of the print floating the height of the container would only need to be a little more than the part printed. However it has the downside of the added complexity and problems dealing with the print actually floating.
I think that it might be possible to find some coating to spray on the bottom so that the peeling method can be used, but I am not sure how advantageous using the peeling method will be in the first place.
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Rylan did a few experiments over in this thread about curing the resin through a layer of water. It had unexpected and rather undesirable consequences...
Basically, the surface tension between two liquids is much higher than between a liquid and air. meaning that in between each layer, you have to wait much longer for the resin to creep across the surface of the print before you can get your next layer evenly cured. Another advantage that the bottom-up SLA printers have is that there is only vaccuum between the print and the plate when the print peels off, and the resin for the next layer rushes almost instantly (technically at the speed of sound). With the Peachy (and other top-down SLA), surface tension and flow actually have to be accounted for and can slow the process down a bit. Increasing that surface tension would necessitate lots of time between layers, or a significant 'dipping' system almost like the peeling systems of the bottom-up printers.
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