Rifling on Conn 3?

[paysonmcc]

I was going through some mouthpieces for students to use and found a Conn 3 in the pile. I checked to see if it was clean enough to play and found something really cool in the throat of the mouthpiece: rifling! Has anyone seen this on any other mouthpieces?

[ghmerrill]

Brand Turbobore: https://www.mundstuecke.ch/en/

[Olofson]

Glenn Zottola mouthpieces hade riffled backbore. Some of us tried them in the 60s.
Yes that´s right JohnL, not riffled. stepped.

[harrisonreed]

Best Brass also has mouthpieces like this.

[JohnL]

That's a really tight twist.

Best Brass also has mouthpieces like this.

Are those cut in a spiral? It looks more like they're simple circumferential grooves.

Glenn Zottola mouthpieces hade riffled backbore. Some of us tried them in the 60s.

I thought Zottola used a stepped backbore. That's certainly what the patent says.
https://patents.google.com/patent/US2798402A

[Crazy4Tbone86]

At one time, I had a lot of the Elkhart Conn mouthpieces. I don’t remember “rifling” marks like that in any of those. Perhaps someone made some aftermarket modifications with a reamer or a drill bit?

[BGuttman]

I'm certain it was aftermarket. My Conn 3 has no rifling in the aperture (or anywhere else on the piece).

[tbonesullivan]

That really looks like a failed attempt at reaming out the throat. Maybe they used a cylindrical file?

[JohnL]

At one time, I had a lot of the Elkhart Conn mouthpieces. I don’t remember “rifling” marks like that in any of those. Perhaps someone made some aftermarket modifications with a reamer or a drill bit?

I'm thinking maybe a tap?

[timothy42b]

Off topic a bit, but a tap and die set can be useful.

I just helped assemble a handicapped ramp for a neighbor who'd had surgery. It's an assortment of pieces to be used temporarily so gets moved fairly often. The crew ran a tap down every threaded hole and a die across every threaded piece before assembling. That avoided a lot of frustration over munged up or just dirty threads.

[paysonmcc]

I was able to take a look at the throat in a little better light. The sliver plating is only missing in the throat, so it is definitely modified. To me it looks like the throat was first drilled out and then "tapped".

One thing that is hard to see from the picture is that the total length of these marks are about 0.5 inches long, and are very uniform. It really looks like an attempt to try a new modification, and not a slipped bit.

I'll plug it in my Bach 36 later and see how playable it is.

[CharlieB]

Not threads.
Definitely rifling.
Done with a broach.
One out of hundreds of experimental trombone mouthpiece designs.
Curious to learn how it plays.

[JohnL]

Not threads.
Definitely rifling.
Done with a broach.

Honestly, I don't think it was a thread tap or a rifling broach (at least not anything standard).

Consider:
If it's a thread, it's a very coarse pitch (I count five threads per 1/2").

If it's rifling, that's a lot of grooves (I count at least eight and we can't see them all) and a fast twist (the grooved section is about 1/2" long and the grooves go more than a quarter of the way around - that's a twist rate of 1 turn in less than 2").

Do the grooves extend all the way through the throat (i.e., can you see them at the very bottom of the cup)?

[harrisonreed]

It's not rifling. Those grooves are too deep (for that bore size) and the twist rate is too fast.

It's like cannon sized grooves on a .22 bore.

Also you can see the job wasn't done right near the backbore / throat mating point. The grooves skip, almost like they tried coming in from the other end.