Re: parallel bore
Posted by Tom 2 on April 06, 2008 in reply to parallel bore .:
I think they probably vary quite a lot over the years. I used to have two 4B mouthpieces. One was the old style (1960s?) brass silverplated mouthpiece with a much larger diameter than the current ones.I really liked that mouthpiece. The other one was a newer nickel silver one. Many years ago I had an engineer friend of mine cut (bisect?)the nickel one with as fine a saw as possible. What we observed was that there was indeed a short (about 3mm) parallel section leading from the bottom of the cup into the backbore. Also, the flare of the backbore was very slightly parabolic/ barreled rather than V-shaped.
Some years later, by chance, I met the maker of Paxman (and PHC) mouthpieces and I mentioned my findings. He didn't agree, claiming that, as you say, there is no parallel section, and furthermore he disagreed about the parabolic back bore.
I can only imagine that at some time there may have been a transitional 4B during the switch (why?) from brass to nickel silver. The older brass 4B definitely has a parabolic backbore as I have made a mould of it, but I don't want to destroy the mouthpiece so as to find out whether there is a parallel section.
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