Evan, my vacuum pump works fine, but I have a piece of 'microbore' that I want to use as a cylinder for my next model. I need to discover a way to run the piston up and down about 16 inches or so in this 3 inch i.d. tubing. I have thought about a 'con rod' of sorts with an enlongated hole in it, with teeth machined around the inner surface of it. The hole would be about 18 in long. A pinion on a motor shaft would engage the teeth, and the rod would be guided as it is alternately pulled, then pushed, by the pinion, giving a large stroke without interfering with the walls of the cylinder. Never tried this idea, though it seems to me that the vacuum attainable would be higher with the larger stroke to bore ratio. Just thought I'd throw this idea at you, or anyone interested, to maybe get some feedback.
I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-