How to cut sorbothane?

See if you can access a lab supply catalog. There is a device used to cut holes in rubber stoppers used to connect various pieces of glass ware. I don't know max diameter available. The device is basically T shaped - the horizontal being a handle (like a wine bottle opener). The vertical being a cylindrical cutting tool (circumference of bottom edge sharpened)...the diameter determining the size of the hole you create in the rubber stopper. Haven't worked in a lab in some years...might be old tech now replaced by something more convenient. Typically, these came as a "nested set" of multiple sized tools...smaller diameter inside larger inside large etc etc. The rubber we cut was very hard (and thick, 1" or so). Seems like it should work on sorbothane - I just don't know what diameter you are looking for.

http://www.allpaxcorp.com/cgi-bin/a/products/punch.html?id=exRaobFb

Check out the link above...you want a hollow puch gasket cutting tool (I think). Don't know costs or if you can just buy one size.

Tvad - Hey - sorry, I missed that you'd already purchased a punch! ("nevermind")

As I understand it, different durometers of Sorbothane absorb different frequencies. Anyone ever stack different durometers on each other to create a more universal frequency absorbing pad?

I see a lot of misinformation here, some of it corrected. Sorbothane is designed to be compressed to a precise weight loading, which is directly correlated to its effectiveness (absorption coefficent); you have to use the Sorbothane calculator to determine the correct size for the weight you have. I doubt the Herbie Discs have any where near the same capability, but I have a few sets and still find them useful for many situations.  Sorbothane occasionally has a negative synergy on sound, whereas Herbie's Discs almost never do.

Use durometer 40, unless supporting something very light. Heavy duty sheers is probably the best tool. Cut squares, as you will not be able to cut accurate circles or use a punch (unless you can apply at least a few hundred pounds of pressure).

I experimented extensively with Sorbothane when I was starting out, using it under my components and even under my speakers (some products on eBay or Amazon, with names like SorboGel are not actual Sorbothane and are a waste of time). Sorbothane is the most economical absorber/isolator on a tight budget. As I got into higher end systems I moved to Townshend Pods and the adjustable Gyrotension Vega, which are much more expensive, but also deliver much more effective isolation.