Inconsistent Backbore Centering on Bachs

[jadickson]

Just an observation and a hypothesis about Bach mouthpieces.

When you look at the backbore opening of Bach mouthpieces, you will never find two that look exactly the same. The walls vary in thickness, the "teeth marks" (whatever they are) vary, and some are more centered than others. This is even true today, when they are made using CNC technology.

For example, here are two Bach 3Cs that are relatively new:



The one on the right, which is more centered, plays much better than the one on the left, and much better than other 3Cs I have that are also not as centered.

So maybe this is part of "finding a good one". The good news is that you can go to a music store and look at the backbore opening of every 3C they have without opening the plastic packaging before you decide which one to buy.

I think it was user Lipshurt who made a comment in another thread that it takes twice as long to truly center a mouthpiece on a CNC machine than it does to cut the mouthpiece. I guess that's probably why Bach does not do it consistently.

Just wanted to throw this out there. Happy weekend.
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Justin Dickson
Middle school band director. Still learning.
www.BandmateTuner.com

[HERMOKIWI]

You're basing your analysis of the degree of "centering" of the backbore on what you observe in terms of wall thickness at the open end of the shank. "Centering" involves analyzing how the backbore aligns with the cup and drill hole. The backbore could be well centered in the mouthpiece overall even if there was a significant difference in wall thickness at the open end of the shank.
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HERMOKIWI

[TKSop]

I bought a mouthpiece that wasn't quite centered recently - emailed the manufacturer to ask if it was likely to cause any issues, they said they doubted it but very kindly offered to replace it anyway.
Top quality service and I'll be using them again (but I'm not going to name them).



If we were speculating... I'd wonder whether it could have some strange effect on the gap - I mean, I recall the GR gap formula relies on the wall thickness at the end of the shank as one of the factors determining gap?
So would the thickness not being constant all the way around have a weird effect there somehow?

[B. Scriver]

GR took a few moments out of today's schedule to type this up:

"The walls vary in thickness, the "teeth marks" (whatever they are) vary, and some are more centered than others."

We don't know for sure but those little teeth marks are probably something they do in process for an operation. Maybe when they clamp it with the robotic gripper to use automated buffing. It is possible the pressure and fixture on the gripper it too high and this is why they wobble in the receiver. The from of the shank has been deformed from the clamping. There was a discussion on "wobbling in the receiver" from in another thread so we watched the video and it took about 10 seconds to see an issue with their process. We don't know if the teeth marks are related but it makes sense.

"This is even true today, when they are made using CNC technology."

CNC machine technology only means you can make more bad/scrap parts faster. The key is an updated process and very in-depth knowledge of many areas. Not just knowing how to run a CNC, knowledge of GDT, SPC, Machine controller set up, inspection, tooling, speeds/feeds, and more.

"I think it was user Lipshurt who made a comment in another thread that it takes twice as long to truly center a mouthpiece on a CNC machine than it does to cut the mouthpiece. I guess that's probably why Bach does not do it consistently."

It does take a very long time to center a mouthpiece in a chuck. Even when doing that you have to make sure it had no run-out on the rim side or the shank side (parallel), so I think boring soft jaws for each rim would need to be done unless you have an ATI or adjustable Chuck to get it dead on with a .00005" indicator. Or bore a bronze collet for that exact rim you are going to be clamping on. Oh, you still have not put the backbore in. You need to have a way to center the tool. If not it will follow the path of the through drill and not be centered at the cup/throat side. This would drive the cost of the mpc up about $100 each. Key to solving this is process.

""Centering" involves analyzing how the backbore aligns with the cup and drill hole. The backbore could be well centered in the mouthpiece overall even if there was a significant difference in wall thickness at the open end of the shank."

This is a big issue and here is how you can check that. Often if they don't align you can't tell. Get a gauge pin .144" to .1500", keep getting bigger and bigger until they don't go. Put the last one that fit in and look at it with a bright light coming from the backbore. The throat hole will be oblong. (Not on a GR) In our thinking this is why players clock or index a mouthpiece. If all align and that means the receiver to leadpipe too.

No clocking or indexing should be needed. If clocking helps, either the throat to cup, backbore to receiver, or receiver to leadpipe have an alignment issue.

"If we were speculating... I'd wonder whether it could have some strange effect on the gap - I mean, I recall the GR gap formula relies on the wall thickness at the end of the shank as one of the factors determining gap?
So would the thickness not being constant all the way around have a weird effect there somehow?"

It would have an effect. If the backbore was off and receiver was off to the leadpipe, with measuring we could tell you where to clock a non-GR mpc in a specific horn. The formula will still get you in the ballpark. Issues will come up. To have all 3 areas align costs a lot of money in tooling, making fixtures and extra steps to get it right. Is it because they don't know how to make this happen, can't afford to do the extra work, or just don't care? The only way you will ever see a GR mpc with a issue with the shank walls is if somebody puts a reamer down it after market. The will not happen with our process.

Gary Radtke
www.grmouthpieces.com

[Norman]

Wow, what an insight, thank you! As time goes by, more and more people will understand that a 50$ mouthpiece might indeed be more expensive than a 150 or 200$ one...
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[jadickson]

Thanks for the great post, Brian and Gary. Extremely informative.

[dstdenis]

Wow, great thread. Thanks all!
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