Re: [APML] Vacuum Pump

[Aplanatic@aol.com]

I've made a prototype 4X5 vacuum film back that uses lung power to make the vacuum.  Briefly, the film back consists of a machined 3/16" thick aluminum plate with 0.054" diameter holes, spaced 0.5" on center.  The back of the plate has a manifold cover and an 1/8" diameter hose connector.  A vacuum hose runs to a leak-tight "JB-welded" one pound coffee can.  One port on the can goes to the vacuum back and the other port goes through a valve.  The valve is connected to a hose and then to the human powered pumping port (mouth).

The can acts as a vacuum reservoir, of course.  I pull a partial vacuum on the system by sucking air out of the can and then I close the valve.  If the film back is smooth and finely finished, air leaks into the system so slowly that the vacuum will last many hours.  

I plan on using this simple method for a custom 16" Newtonian hyperbolic astrograph with a 4" image circle.

Dave Rowe

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