Where to measure bore size? Conn 18H Director

[tedthetrumpet]

I'm trying to measure the bore size of a Conn 18 Director from 1992.

Where do you measure bore sizes? I'm assuming it is an interior diameter? Inside the bottom of the down side of the slide, at the stocking end, I'm getting .485 on my micrometer. On the up slide, however, I'm getting .498. That would seem to make it dual bore: which seems unlikely?

Or am I doing something wrong?

Thanks!

[Posaunus]

You're pretty close. Conn listed the bore size (both slides) as 0.484". Apparently, though, your upper slide is (nominal) 0.500". If this is true, someone has modified your slide and installed parts from a 0.500" bore trombone. Sort of bass-ackward - dual-bore slides have the smaller bore on top, the larger on the bottom.

Is this a Coprion (copper) bell?

Apparently (per Derksen), "MacMillan-Conn moved production of student model instruments to Japan in 1971."
So yours was probably made in Asia. The slide must have been replaced later.

I had one for a while. Not a great instrument. I gave it to a student. How does yours play?

[brassmedic]

Turn the outer slide upside down and see if it fits. If it doesn't go on, then someone must have put .500 bore tubes on the top side as mentioned.

[Doug Elliott]

I think there may be misinterpretation of the description:

"Inside the bottom of the down side of the slide, at the stocking end, I'm getting .485 on my micrometer. On the up slide, however, I'm getting .498. "

The "down side" is the upper tube and the "up slide" is the lower tube, if you interpret "down" and "up" as air flow direction.

And the business about whether you can turn the outer slide upside down doesn't work on King 2B tubes - it's dual bore but you CAN turn the slide over. The inner slide tubes are different inside but the same stocking OD.

[BGuttman]

This is an 18H (Conn) which should be 0,485" on both tubes. If the slide was modified to have one 0.485" tube and one 0.500" tube (with a larger outer tube to match) you should not be able to reverse the slide.

Note that if the stockings are expanded, the inner diameter of the tube will be too large. You should be measuring away from the stockings.

[greenbean]

Measuring at the end of the stocking is tricky because the very bottom edge of the tube might be oh-so-slightly curved inward. I would take several measurements, rotating the tube, to get a "consensus."

Of course, it is only a Director. You could play it if you have to, regardless of bore.

[tedthetrumpet]

Thanks for all replies!

Yes, my description of 'down' and 'up' was to do with the direction of air flow. So, if my measurements are correct, then the dual-bore thing would be the right way around.

Not Coprion, no.

Turning the slide around is possible, so the stockings are the same size, even if the bore isn't.

I'm going to go back and try to measure again more carefully. I did have it in to a repairer recently becuase it seemed to me one of the slides was loose in the receiver. When it came back, the guy in the shop mentioned something about it 'turning out to be a big job'. I'm wondering if by any chance they replaced one of the slides without telling me!?

Also, yes, it's only a Director, so, whatever. The only reason I got into this is that I'm about to put it up online for sale, and someone is bound to ask me what the bore size is.

It plays fine for me, but I'm only a trumpet player dabbling in trombone. I'm getting rid of it for three reasons. The main one is that despite the repair the slide is still annoyingly sticky and I don't enjoy practicing on it. Second reason is that I've gone back to my other Director, a 1969 16H, which I prefer. Third reason is that I'm looking at picking up a Yamaha 354, and owning three trombones would be one too many!

[brassmedic]

Thanks for all replies!

Yes, my description of 'down' and 'up' was to do with the direction of air flow. So, if my measurements are correct, then the dual-bore thing would be the right way around.

Not Coprion, no.

Turning the slide around is possible, so the stockings are the same size, even if the bore isn't.

I'm going to go back and try to measure again more carefully. I did have it in to a repairer recently becuase it seemed to me one of the slides was loose in the receiver. When it came back, the guy in the shop mentioned something about it 'turning out to be a big job'. I'm wondering if by any chance they replaced one of the slides without telling me!?

Also, yes, it's only a Director, so, whatever. The only reason I got into this is that I'm about to put it up online for sale, and someone is bound to ask me what the bore size is.

It plays fine for me, but I'm only a trumpet player dabbling in trombone. I'm getting rid of it for three reasons. The main one is that despite the repair the slide is still annoyingly sticky and I don't enjoy practicing on it. Second reason is that I've gone back to my other Director, a 1969 16H, which I prefer. Third reason is that I'm looking at picking up a Yamaha 354, and owning three trombones would be one too many!

Looking at your first post again, I now notice you said 1992, and I'm pretty sure that would have been .500 bore. The .485 14H was made earlier. As mentioned, inner slide tubes are often curved in at the end. I'm guessing that either you aren't getting your calipers past the constricted part, or the tech did replace the inner tube, but with an older .485 tube. In that case it would still go on if you turned the outer slide upside down, but that smaller inner tube would be a loose fit in a .500 outer and probably leak.

[baileyman]

Isn't the bore i.d. revealed nicely at the tenon?

[Crazy4Tbone86]

Isn't the bore i.d. revealed nicely at the tenon?

Not necessarily. Many trombones have a short section where the inner slide does not extend all the way up to the end of the tenon.

[tedthetrumpet]

Just to close this off: I did the measurements more carefully, it's actually .500 on both legs.