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Does anyone here have the measurement between the 2 legs on a Bach 50 main tuning slide? I'm looking at one that's 4 9/16 " and I want to make sure that's normal. Thanks.

To be more precise, I get 4.535 with calipers

I have a 1995 50B. It measures 4.525

Thank you.

I have gotten several different readings on 50 TSs before. Mostly in the 4.535 range. Also, they usually arent parallel

octavposaune wrote: ↑Sun Jul 11, 2021 5:29 pm I have gotten several different readings on 50 TSs before. Mostly in the 4.535 range. Also, they usually arent parallel

Presently, I’m away on vacation for a few days. So I am not able to measure the Bach 50s that I would have access to.

I think Ben’s last sentence is the most important. The Bach 50 tuning slide legs are rarely parallel. I don’t think I have ever seen one (factory built) that was close. The last 50 that I rebuilt arrived with the legs narrowing by over .040 inch……and those tuning slide legs are not very long!

Sometimes the legs almost need to be slightly misaligned or in some way imperfect. I've got a horn where the tuning slide slips closed under the weight of the counterweight. You can only put so much thick vaseline on it, so there has to be a dent, a bend, an out-of-round, or a misalignment to offer enough friction to keep the tuning slide where you want it.

hyperbolica wrote: ↑Mon Jul 12, 2021 10:19 am Sometimes the legs almost need to be slightly misaligned or in some way imperfect. I've got a horn where the tuning slide slips closed under the weight of the counterweight. You can only put so much thick vaseline on it, so there has to be a dent, a bend, an out-of-round, or a misalignment to offer enough friction to keep the tuning slide where you want it.

That's... not how it works. The tubes just need to be sized correctly.

"That's... not how it works. The tubes just need to be sized correctly"

It is common for manufacturers to make their tuning slide tubes loose. This has the benefit of making tolerances larger for production. There can be a much wider range of "acceptable variability" with wider tolerance. That can also allow for "interchangeability" to be achieved over a large production run.

However, this does mean that situations such as tuning slides moving too easily can arise, and, the need to correct the issue for the player.

The problem with tuning slides being out of parrallel is the induced tension that comes when the tuning slide is moved. There may be "some" tension when the slide is closed, but as soon as the slide is pulled out, the tension increases significantly, and can greatly affect the performance of the horn, in a negative way (most of the time)

Of course loose slide tubes can leak, too.

Ideally the tuning slide is parrallel, with well fit tubes that provide a good seal. That way there is no induced tension, and an even responding horn, regardless of tuning slide position, results.

Okay, getting off my high horse...

hornbuilder wrote: ↑Mon Jul 12, 2021 12:11 pm "That's... not how it works. The tubes just need to be sized correctly"

It is common for manufacturers to make their tuning slide tubes loose. This has the benefit of making tolerances larger for production. There can be a much wider range of "acceptable variability" with wider tolerance. That can also allow for "interchangeability" to be achieved over a large production run.

However, this does mean that situations such as tuning slides moving too easily can arise, and, the need to correct the issue for the player.

The problem with tuning slides being out of parrallel is the induced tension that comes when the tuning slide is moved. There may be "some" tension when the slide is closed, but as soon as the slide is pulled out, the tension increases significantly, and can greatly affect the performance of the horn, in a negative way (most of the time)

Of course loose slide tubes can leak, too.

Ideally the tuning slide is parrallel, with well fit tubes that provide a good seal. That way there is no induced tension, and an even responding horn, regardless of tuning slide position, results.

Okay, getting off my high horse...

I've got a '59 48h that my tech induced a small amount of bulge into the tuning slide legs to keep them put. They might have been polished a little too much or they might have been this way for a while, don't know how they got that way. Either way, it's one of the nicest playing horns I've ever owned. The "fix" didn't change the response of the horn perceptibly.

I have always thought that having both legs of a tuning slide the same exact length was a HORRIBLE DESIGN. If you have a player who puts the tuning slide in slightly askew and keeps forcing it, the tuning slide legs will instantly go out-of-parallel. However if the legs are different lengths, the player can put one leg in first and the other one should go in with no effort if the instrument is assembled correctly.

I am well-aware that having the legs two different lengths is not possible for many tuning slides. There is just not enough tubing to work with on many instrument designs.

Concerning the loose tuning slides......I DO NOT recommend making the legs out-of-parallel or creating a "bubble" in one location of the tuning slide in order to eliminate looseness. A good technician should be able to fix that properly by adjusting the entire length of tubing. I had a relatively new trumpet in my shop today with a loose main tuning slide. I expanded the entire length of the inner tube 1 or 2 thousandths of an inch and the tuning slide worked exactly the way it is supposed to........it pulled slowly and evenly when tuning slide grease was applied. It was also air tight.

The owner was concerned that I might have made the bore size larger than the original specifications (.459 inch). We checked it after I expanded the tube and it measured at .458 inch. In other words, the original tube might have been well under it's advertised spec.

Back to the original question....

Now that I am back from vacation, I am able to measure the Bach 50 tuning slides that are here. One is perfectly parallel at 4.534 inches. The other Bach 50 is not parallel.....it is 4.539 at the ferrules and angles inward to 4.530 at the ends of the legs.

The horn with the parallel legs plays much better, but I cannot claim that the more-precise tuning slide construction is the reason. The other horn has an assortment of damage and stress issues.