I have more news. So, I use the same vacuum setup for investing and casting. The other day, I’m casting. My vacuum pump is a heavy duty model that cost me quite a few pennies. It stops pulling a vacuum. I shrug, figure it needs the oil changed (probably clogged with investment particles) and switch over to my backup pump (about 2/3 the strength of the big bubba). I have a lot of commissions to get through, so I put the big pump on the to-do list of future Charlie and carry on.
My next 2 casts are terrible. Really bad - orange peel, porosity, and flashing. Not just the formlabs, but the wax models too. I adjust my burnout schedule to a slower ramp, etc. but it’s even worse. So, I email R&R and get no response. Finally, I download the datasheet for plasticast, and find the answer: The initial degas of the investment has to happen in under 2 minutes. Normally, that’s fine, but with my smaller pump, it’s closer to 3 minutes. Plasticast does not like that. It especially does not like me reducing the amount of time I’m mixing the investment so I can pull a full vacuum on the slurry.
Long story short - the quicker you can get a collapse on your initial degas of your slurry, the better your casts are going to be.
I don’t think this is true of all investment powders - I’ve tried 4 so far with this resin. However, it does appear to be true of the R&R plasticast. The bigger your pump, the smaller your chamber, the better.