Ebonite is hard rubber. More specifically, it is hard rubber at normal temperatures. It actually has a melting point and, in fact, ebonite can be melted completely down and remolded. We aren't interested in that, but what if we could heat it to its "yield temperature" (the temperature at which it can be flexed) and enlarge the shank opening? That's what I did.
First, I needed something that would have the approximate conical shape as the cork on a saxophone neck (in this case, a tenor). Then, I needed a way to heat the inside and the outside of the shank to above 160F (about 70C). That's about the temperature that ebonite begins to yield but isn't going to actually melt (hopefully). I came up with an inexpensive conical shape that could also be used to transfer heat inside the shank.
It's a common aluminum "ring mandrel," although this one is technically a ring measuring device. An actual ring mandrel is made of steel and allows the ring to be worked or enlarged by using the mandrel as an anvil. Aluminum is too soft for that and is generally only used for measuring. This one has markings on it that show ring sizes (which differ by country) and a reading in millimeters circumference. You can measure the neck cork on your saxophone, or use some charts to get a general idea of what is an appropriate tenor shank opening or, simply open the mouthpiece a little at a time to get the proper size. The picture above shows a vintage tenor mouthpiece on the mandrel at about 52.75 mm circumference. That is a diameter of 16.8 mm. Tight for a tenor.
There are two nice things about using an aluminum mandrel. First, it is can be easily cut. It will be too long to fit into a tenor mouthpiece shank. You will need to shorten it the appropriate amount for using it on mouthpieces. Second, aluminum quickly transfers heat into the shank. Here, I am using a hot air gun, on the lower setting, to slowly heat up the mandrel. It will be impossible to not also heat up the shank on the outside, but that's okay as it needs to be heated as well. I tried to not heat the mouthpiece table and not even get close to the lay.
After a few minutes of heating, I notice the familiar sulfur smell like you get when you rub a cloth hard on ebonite (also caused by heating the surface of the ebonite). I wore a glove on one hand so that I could gently force the shank further on the mandrel when I got the shank hot. I was doing all of this by myself, so I didn't use my infrared thermometer to actually read the shank temperature. I would guess it was probably 160 to 180F. Once it was hot, I needed to get on with my project and so I didn't take a temperature reading.
I gripped the barrel of the mouthpiece with the gloved hand and gently pushed it down on the mandrel, opening the shank by one millimeter in circumference (which increases the diameter by almost .32 mm). Because the mandrel has grooves on it for the numbers, it isn't completely round. I had to quickly remove the mandrel, rotate 90 degrees, and reinsert. I did this several times as the ebonite was cooling, and then left it on the mandrel while it cooled down completely.
I then checked to make sure that I had not effected the table. I was concerned that by expanding the shank I might also enlarge the area under the table and raise it so that the table was no longer flat. I lightly pulled the table across 1500 grit sandpaper laying on a piece of glass. The scuff markings showed that I hadn't effected the table. Even had I affected the table, it wouldn't make too much difference if one were intending to put a new facing on the piece. Getting the table flat would be part of that project.
You may find that when you are done, and the mouthpiece now fits your tenor, that it will not tune properly. It could be that the vintage mouthpiece was manufactured specifically for a horn that had a smaller neck opening. It was "tuned" to that particular horn. Or, it could be that the mouthpiece was a poor design in both shank and chamber. It simply was and is a dud. Or, finally, it could be that the mouthpiece appears to be a tenor piece, but is really a C Mel mouthpiece (as was likely the case with one of the mouthpieces that I was using).
I suspected that one of the mouthpieces I experimented on was a C-Mel. That's not really a problem. First, C Mel pieces aren't in demand and make good material to experiment on. Second, ebonite has another interesting characteristic. If heated back up, it will relax back into its prior shape. It is possible to reheat, and as it cools, put the mandrel back in only to the 53mm mark and let the shank shrink back down. No harm done.
Here is a picture of the shank opening at just under 54 mm circumference. That gives a diameter of 17.15. Much closer to a "standard" tenor shank. Unfortunately, there appears to be no such thing as a "standard" tenor shank opening. Here are some general measurements from a site that has complied them over the years. One of the mouthpieces altered in this blog was a Rene Dumont, which was a trade name used by a U.S. wholesaler to give this piece a French sounding name.
The same process can be used on an alto mouthpiece. You simply need to cut a little less off of the aluminum mandrel. Since these aluminum mandrels are available for less than $10 on the internet, it's not a big investment to have one mandrel for alto and another for tenor. Here is the alternative $2,000 machinist's version for alto. That complex machinery looks like more fun, but it costs way more and takes longer. And the article says that getting the bore perfectly round is difficult. Not so with my quick-and-dirty method.
I haven't tried this yet with other plastic materials, like ABS or PMMA mouthpieces. Actually, I haven't found any of those that have bores that are too small. I do have a cheap Chinese ABS tenor piece that seems to be larger than normal. Maybe I'll try to use heat and my mandrel to shrink it. Most likely, I will ruin it. Just be aware that I do that sometimes.
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