I made 2 test prints, one yesterday and one today
First test print : As good as or better than pretty much anything I’ve printed up to now using sylgard/qsil coated glass for my vat floor. The printout had a flawless surface finish (much better than sylgard or qsil) and extremely sharp features. One thing I did notice was a very slight convex rounding of the center of the finished printout. I believe this was caused by insufficient tension on the FEP film combined with the resin not having enough time to squeeze out to an even thickness between the build plate and the FEP after the vat tilted up and build plate dropped down between exposures (this proved to be the case).
Second test print: I’m just going to come right out and say it, silicone coated glass vat floors don’t hold a candle to tensioned FEP. Flawless surface finish, sharp features and only a slight bowing along the parts long dimension from resin shrinkage. This is what I changed in the second printout: I increased the FEP tension and made sure the 4 tensioning bolts had as even a torque as I could by feel (I think this cleared up the “convex” issue mentioned above). I lowered my exposure by a half second (I’m not exposing the resin through glass and silicone layers so I felt I could lower the exposure). I also adjusted the parts wall thickness to a uniform 1mm (I think I can use even thinner walls with the FEP vat floor)
As far as I can see using FEP under tension for my 3d printers vat floor seems to be better than using sylgard/qsil coated glass by a long shot. Only time will tell but getting such good prints on the first and second tries must mean something.
The part is 112mm Long X 64mm Wide X 11.95mm High
Both prints were made with Fun To Do Industrial Blend resin (I will test Makerjuice resin later this week).
With the exception of the first 2 or three layer exposures (the full face of the build plate in near contact with the FEP plus long base exposures) the peel was only noticeable when large flat areas were being peeled and only barely when peeling those areas.
My vat tilt and build plate raise/lower were much larger than they needed to be for these prints (I was using a much deeper vat before). This allowed the part to lift out of the resin during printing trapping bubbles between the build plate and the FEP during exposures, amazingly, this did not cause any problems at all even in the large flat areas.
The gasket clamping the FEP worked like a charm, no slippage of the FEP at all which is good because for the second test I put the FEP under a decent amount of tension.
I will probably hack together some sort of tension gauge so that I can maintain and monitor the FEP’s tension. A torque wrench or driver would also be helpful if I can find one with low enough settings.
I think I will lengthen the tensioning bolts and add some stiff springs to them so that any stretching of the FEP during printing will get soaked up.
A note to anyone thinking about making a vat like this out of acrylic: use cast acrylic do not use extruded. Extruded acrylic has locked in stresses that will cause you no end to problems. Also, cast acrylic can be cleaned with almost anything, a drop of alcohol on any machined edge of extruded acrylic will make it crack.