Measure the bore of a trombone

[askersbrass]

Hi there, where, on the trombone can I measure the bore? Is a Bach 36 with a trigger always medium/large bore?/Askersbrass

[Burgerbob]

That's a .525 horn, medium bore with small shank mouthpiece receiver

[BGuttman]

You can try to measure at the end of the slide, but:

1. Modern slides have expanded metal stockings so the inner diameter is wrong.
2. Some slides have a barrel shaped stocking so the inner diameter is wrong.
3. Some soldered on stockings make the diameter of the inner at that point wrong.
4. Some slides have the ends of the stocking flared in to make putting on the outer slide easier and thus the measured diameter at the end is wrong.

Best way to measure bore accurately is to use a deep caliper that goes beyond the stocking to the unaltered slide tube. Not always easy.

Most slide tubes use a standard diameter and thus will be one of a set of values (in inches, ±0.005): 0.465 (rare nowadays), 0.485, 0.490, 0.500, 0.508, 0.515 (not common now), 0.522/0.525, 0.547, 0.562, 0.578.

[hyperbolica]

One thing to watch out for. Your measurement, regardless of equipment or experience, is not likely to be exactly the nominal bore size. Especially for inside diameter measurements. There are several factors that affect the measurement: where you measure, the angle you measure, the force you use to measure, manufacturing tolerances that have to hit within a few 0.001" of a nominal value, backlash in your calipers, etc... So if you get a value of 0.550" or 0.545, don't panic or assume there's a catastrophic error with your horn. I'm always suspicious of people who claim to get nominal readings every time. There's probably some fudging or estimating going on somewhere. Best practice for measurements is to take several measurements and get an average. Mfg tolerances are all about statistics, and you're not likely to get the nominal value every time.

[tbonesullivan]

1. Modern slides have expanded metal stockings so the inner diameter is wrong.
2. Some slides have a barrel shaped stocking so the inner diameter is wrong.

Is this true? I thought just the thickness of the outer wall was different. I've never seen any change on the interior diameter near the end where the drawn in stocking is. I always assumed that the tubes were drawn onto the same size mandrel, and they use a smaller diameter die for most of the slide tube, and then stop when they reach the area where they want the stocking to be.

could be wrong though.

[ghmerrill]

Hi there, where, on the trombone can I measure the bore?

Go with the other answers here. You really don't want to try to measure the bore. Even if you invest in the tool to do that, you can easily damage the tube if you don't know what you're doing. If you really need to measure (why?) -- instead of just finding out what the stock bore size is -- take it to a good brass repair tech or a machine shop.

[Doug Elliott]

1. Modern slides have expanded metal stockings so the inner diameter is wrong.
2. Some slides have a barrel shaped stocking so the inner diameter is wrong.

Is this true? I thought just the thickness of the outer wall was different. I've never seen any change on the interior diameter near the end where the drawn in stocking is. I always assumed that the tubes were drawn onto the same size mandrel, and they use a smaller diameter die for most of the slide tube, and then stop when they reach the area where they want the stocking to be.

could be wrong though.

You are correct.

Sometimes the end of the inner tube measures a thousandth or two small because chrome plating tends to be thicker just inside at the end.

[hornbuilder]

You can try to measure at the end of the slide, but:

1. Modern slides have expanded metal stockings so the inner diameter is wrong.
2. Some slides have a barrel shaped stocking so the inner diameter is wrong.
3. Some soldered on stockings make the diameter of the inner at that point wrong.
4. Some slides have the ends of the stocking flared in to make putting on the outer slide easier and thus the measured diameter at the end is wrong.

Point 1. This is false. Tubes are double drawn, so the inner diameter stays the same the whole length of the tube.

Point 2. Also false, see answer to point 1

Point 3. Also false.

Point 4. This is true "in some cases", depending on how the end of the tube is made.

[askersbrass]

That's a .525 horn, medium bore with small shank mouthpiece receiver

Thanks fore fast answer //Askersbrass

[JWHartley]

It is interesting that double drawn tubes is an old technology. I have found some H.N White (King) marketing literature from ~1913 touting their double drawn slide tubes.

When one is measuring something like a slide bore, what accuracy is one expecting?
You could read a scale/rule to maybe 0.01"? (I doubt it even though they are graduated that fine)
Good calipers are claimed to be accurate to 0.001" (Starrett electronic), but that would take careful use. (More likely +/- 0.002")
Micrometers are good to maybe 0.0001"? But at those levels, temperature becomes a factor.
A machinist might want to use gauge pins to measure a small bore like this to get resolutions of 0.001" or less.

-Jess

[Doug Elliott]

All of that depends on the skill and experience of the person doing the measuring.

[askersbrass]

Thanks fore fast answers /Askersbrass

[ghmerrill]

https://www.mscdirect.com/product/details/86425006

[Posaunus]

https://www.mscdirect.com/product/details/86425006

Since every trombonist needs one of these sets, perhaps we could form a TromboneChat Buying Group and get a 10% discount?

[ghmerrill]

I don't have anything quite like that, of course.

But I do have one of these:

https://www.temu.com/6pcs-set-8-150mm-5 ... nymbdk6lln

I can't remember where I got it. Harbor Freight, maybe?

[JohnL]

https://www.mscdirect.com/product/details/86425006

Kinda on the large side; 1.5"-12"

I spent a few years working in a (steel) tube drawing mill and measured a lot of tubes using a telescoping gauge and a micrometer. It takes some practice to get accurate measurements.

What I do now is measure the OD of the stocking using a dial caliper and the wall using a ball anvil micrometer. If the stocking is barrel-shaped, you need to be aware of that and take case take your measurements the same distance from the end of the tube.

If you want to get really precise and accurate measurements (and have money to burn), you can always buy a three-point inside micrometer like this:

54VK61_AS01.jpeg

WORD OF WARNING: always be careful to not use too much force turning the thimble of the micrometer. If you crank down too hard, you can damage the tubing.

[AtomicClock]

Why not just see how much water fits into the lower tube and measure its length?

[ghmerrill]

You mean ... use MATH?

[ghmerrill]

Kinda on the large side; 1.5"-12"

Sorry about that. Also, for the cost of some of the Starrett (or Mitutoyo) stuff, you should probably just buy another trombone.

[OneTon]

Hi there, where, on the trombone can I measure the bore? Is a Bach 36 with a trigger always medium/large bore?/Askersbrass

They’re usually the same size bore unless someone monkeyed with it or it was Joe Alessi who carried it out of the factory. Nominal large bore is usually 0.547 inches and medium is 0.525 inches. Small bore consensus is usually 0.508 or below. Good quality machinist (full round) ball gages and Starrett or Mitutoyo micrometers are not prohibitively expensive. Sometimes a machinist supply has remanufactured micrometers for less. Don’t be cranking down hard on ball gages or damage can occur. Avoid half round gages.

[JohnL]

Also, for the cost of some of the Starrett (or Mitutoyo) stuff, you should probably just buy another trombone.

Then I'd have two trombones that I didn't know the bore of...

[AtomicClock]

Why not just see how much water fits into the lower tube and measure its length?

I just tried it on my 36. 101 grams of water and 29 11/16 inches* yields .515. The nominal .525 would take 105 grams of water, which is well within the errorbars of my apparatus. In fact, I actually poured 105.8 g, but then estimated 5g of it spilled onto the floor.

(*) - mixing measurement systems. Yay!

I'm always suspicious of people who claim to get nominal readings every time.

Whew!

[Burgerbob]

Why not just see how much water fits into the lower tube and measure its length?

I just tried it on my 36. 101 grams of water and 29 11/16 inches* yields .515. The nominal .525 would take 105 grams of water, which is well within the errorbars of my apparatus. In fact, I actually poured 105.8 g, but then estimated 5g of it spilled onto the floor.

(*) - mixing measurement systems. Yay!

I'm always suspicious of people who claim to get nominal readings every time.

Whew!

Won't work on the upper tube since there's a leadpipe taking up some volume.

[Posaunus]

Why not just see how much water fits into the lower tube and measure its length?

I just tried it on my 36. 101 grams of water and 29 11/16 inches* yields .515. The nominal .525 would take 105 grams of water, which is well within the errorbars of my apparatus. In fact, I actually poured 105.8 g, but then estimated 5g of it spilled onto the floor.

Now THAT is a classic indirect measurement system.

Perhaps you used low-density water?

[timothy42b]

Insert a tapered object, maybe a cone. Mark with a felt tip pen, use a pair of calipers to measure the diameter at the mark. Average the two* measurements.

I just tried. Of course the more care you take in putting the cone in exactly square and then getting the calipers exactly perpendicular the better, but still your tubing is probably no longer as round as it was at the factory. I got .544 for a first try on my Bach 42B.

Bonus advice, something I just learned: with an unknown Allen (hex) socket, press your finger hard against the hole, compare the mark to the wrench set. You can grab the right size the first time.

* Humor. A pair of calipers is still just one item.

[JohnL]

Insert a tapered object, maybe a cone.

In the absence of any other suitable object, a mouthpiece shank will often do the job.

[AtomicClock]

Perhaps you used low-density water?

If anything, I lowballed the density. I used the numbers for water at 70F, even though coming from the cold tap, it's surely less.

[ghmerrill]

101 grams of water and 29 11/16 inches* yields .515. ...

I see a mass measurement, a length measurement, and a diameter measurement. But I'm having trouble with a general mass/length/diameter equation that gets you that result. I see diameter and length measurement giving me volume. But don't you really want a volume measurement for the water instead of the mass? Or were you doing the conversion implicitly? Why not use the volume measurement directly -- since, after all, you could as easily have used hydraulic oil, alcohol, or chicken soup? Just curious about the whole grams thing.

[AtomicClock]

I have a pretty accurate and precise scale. I do not have precise volumetric measuring tools. It's a kitchen, not a chemistry lab. Water is close to 1g/ml (1g/cc), but the USGS can get me closer (https://www.usgs.gov/special-topics/wat ... er-density).

[brassmedic]

Insert a tapered object, maybe a cone. Mark with a felt tip pen, use a pair of calipers to measure the diameter at the mark. Average the two* measurements.

I just tried. Of course the more care you take in putting the cone in exactly square and then getting the calipers exactly perpendicular the better, but still your tubing is probably no longer as round as it was at the factory. I got .544 for a first try on my Bach 42B.

Bonus advice, something I just learned: with an unknown Allen (hex) socket, press your finger hard against the hole, compare the mark to the wrench set. You can grab the right size the first time.

* Humor. A pair of calipers is still just one item.

Won't work. The stockings are usually rounded off at the end. I use a ball gauge and then measure the ball gauge with calipers. Insert ball gauge just past the end of the tube; when you pull it out it will flex enough to clear the restriction in the tube and will spring back to the correct position.

[brassmedic]

Ever look at the specs of the slide tubes Allied sells? Very odd:

Conn 6H - .501
King 3B - .509
Conn 78H - .526
Bach 42 - .545
Bach 50 - .560

[Posaunus]

Ever look at the specs of the slide tubes Allied sells? Very odd:

Conn 6H - .501
King 3B - .509
Conn 78H - .526
Bach 42 - .545
Bach 50 - .560

What are the specified tolerances?

[JohnL]

Insert a tapered object, maybe a cone. Mark with a felt tip pen, use a pair of calipers to measure the diameter at the mark. Average the two* measurements.

Won't work. The stockings are usually rounded off at the end.

Yup. The tapered gauge technique isn't really good for giving you a precise, accurate bore measurement - but it's handy for figuring out if you've got a .547" slide or a .562" slide, and it'll also tell you if your King 1480 slide is single bore or dual bore.

[brassmedic]

Ever look at the specs of the slide tubes Allied sells? Very odd:

Conn 6H - .501
King 3B - .509
Conn 78H - .526
Bach 42 - .545
Bach 50 - .560

What are the specified tolerances?

It says +/- .001

It's strange because those are not the bore sizes published by the manufacturers of those instruments.

I'm skeptical that their measurements are as accurate as they claim. I ordered some tuning slide inner tubing for a project. The OD of the tubing wasn't even close to what the catalog says.

[Matt K]

I wonder if they're publishing the measurement at the top of the slide, and may intend on the length being cut by a small amount and it opens up to the published aspects a few mm below the top? That's the only thing remotely sensible that I could see from my armchair quarterback position

[Crazy4Tbone86]

Getting back to the original inquiry.....

The terminology for trombone bore categories has changed in my lifetime. When I was a teenager back in the 1970s, there was a very specific grouping of trombone bore sizes. I am presently looking at a Bach catalog from September of 1997 (still has Models 6, 8 and 12) and the same terminology from the 1970s is used for tenor trombones in that year:

Small bore tenor trombones = .495 and smaller
Medium bore tenor trombones = .500 - .509, (sometimes included .515 on brands like Reynolds)
Medium-large tenor trombones = .525 (.522 on the Conn models)
Large bore tenor trombones = .547

At some point in time between 2000 and the present, the "lingo" in the categories shifted. While it is unclear exactly where the .508 and .509 are categorized, I believe that most people presently think of trombones in these categories:

Small bore tenor trombones = .509 and smaller
Medium bore tenor trombones = .522 - .525
Large bore tenor trombones = .547

However, the market information for some brands has NOT shifted. If you look today for a Bach 36 trombone (.525 bore) with a licensed dealer on the Internet, it will still be advertised as a "medium-large" bore trombone.

As for the measuring of the inside bore of the inner slide, be very careful. It takes an experienced person with the proper tools to get an accurate measurement. I think some of the previous posts present some of the measuring issues accurately. The cone or tapered rod technique will NOT work (as Brassmedic has explained).

[Crazy4Tbone86]

What are the specified tolerances?

It says +/- .001

It's strange because those are not the bore sizes published by the manufacturers of those instruments.

I'm skeptical that their measurements are as accurate as they claim. I ordered some tuning slide inner tubing for a project. The OD of the tubing wasn't even close to what the catalog says.

It is difficult to trust Allied trombone slide parts to match their catalog measurements. While I have used Allied for many years and they have been very good for me, they have occasionally "substituted" parts from other brands because someone there determined the part(s) to be "close enough" to the described part(s). Allied has sent me Getzen .547 inner slides as a substitute for Bach .547 inner slides on at least two occasions. The outer diameter for a Bach 42 inner slide stocking is supposed to be .578 inch. They sent me slides with .580 stockings which was a Getzen part. The unfortunate thing is that one time I had the entire slide assembled before I discovered the issue. As you can probably predict, the action on the slide was never quite correct.