I have a vacuum port that is 8.75" in diameter, it was attached to a block of aluminum. I am machining a piece of stainless steel to make a blank for it since it is a non-standard size. What are my options on gaskets? Where would I find a mechanical drawing that would be similar, so I could draw this up? I don't want to get too low of vacuum, maybe 10^-5 Torr or thereabouts so I don't have to do a really high temp bake out.
At $10^-5$ torr the vacuum is HV, not UHV. If there is a knife edge on the flange you could use copper gaskets, which are also required for high temperature bake-outs.
Else if one surface is flat you can use vacuum o-rings, like viton, with some light vacuum grease to seal the imperfections. Usually one surface will be flat, the other has a groove for the o-ring.
Read the technical description from any of the vacuum system suppliers in order to get correct specifications for your machining for a given type of seal.
Also note that it may be more effective to by a new port that meets your requirements, but it is always fun to make stuff.
You can also use indium or gold wire.
"Oxygen-free copper is widely used. It is easily machined and has good corrosion resistance. It is unsuitable for bakeable vacuum envelopes due to its tendency to oxidize and create scales."