Posted by John Swensen on June 23, 2000 at 13:00:09:
In Reply to: Re: Re: Questions posted by Bob Sanders on June 23, 2000 at 10:28:36:
The easiest place to get the O-ring material is from an O-ring supply company in an industrial part of town. Often store that sell bearings also stock O-rings. If you buy (or beg) around a 4 inch diameter O-ring with a suitable cross-section, you can slice off an awful lot of bumpers. Another alternative is to buy straight O-ring stock from a machinist-supply company like MSC (www.mscdirect.com). For less than $10 I bought a foot, each, of every size that might, possibly, fit a tuba. There are other materials that you might want to experiment with, including neoprene rubber (maybe a bit bouncier than nitrile) or silicone (either clear or brick red in color). There is also a blue color, but I forget the material. Going to an O-ring or bearing place with a sample of the size you need is probably easiest.
You probably want the standard 90-durometer hardness (shore D scale), although something softer (like 60 or 40) might work better for the return side (engaged when the spatula is not depressed).
If you want to use a more traditional material, you can cut champagne corks slightly bigger than required, then chew on them to compress and lubricate the cork before forcing them into the holes. However, cork seems to compress more quickly than rubbers, and small stop-arms tend to chew up the cork pretty quickly (St. Petersburg stop arms are notorious for this).