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bach 117 backbore



 
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lipshurt
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PostPosted: Tue May 22, 2018 1:01 pm    Post subject: bach 117 backbore Reply with quote

quick question
I recently worked on two bach 117 backbores and both of them seemed to have material removed from about the last inch of the backbore. As if someone removed material with a boring tool on a lathe set at a taper. The taper was straight, and an obvious different angle than the middle area of backbore.

Is that correct for a 117 backbore? is the 117 something like a standard backbore with material removed after the fact, and then maybe the resulting shape copied onto a backbore reamer? i dont have any other 117 here to compare to, but i have seen 117's before and never really noticed it.

I am thinking they were modified. There were silver plated inside.

Any thoughts?
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TKSop
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PostPosted: Tue May 22, 2018 1:12 pm    Post subject: Reply with quote

Does anyone still have the scans from the old kanstul backbore comparator, somewhere?
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Tpt_Guy
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PostPosted: Tue May 22, 2018 1:19 pm    Post subject: Reply with quote

It's possible they are modified.

I have a 117 I sometimes use on C and it looks almost like a GR #3 looking in from the shank end. (Not saying they are the same, just appearances based on light reflection and apparent volume.)

There are some who will say a Bach 117 is just a 24 reamer pushed in further. I mentioned it to Matt Frost and this was his response:

"The Bach 24 backbores (and other 24 designated backbores) that I have measured have had different shapes than the Bach 117 shape. Also different than the Kanstul 117. The 117's I have are 'straight' tapers. And the 24's have more initial taper, then a flatter section then another steep taper."

This seems to debunk the "117 reamer = 24 reamer."

But out of curiosity, what cups were they attached to? It's possible they were created by pushing a 117 reamer into an already existing backbore of a different shape. That may account for it.
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Irving
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PostPosted: Tue May 22, 2018 3:38 pm    Post subject: Reply with quote

I have seen a Bachreamer for a 24/117 back bore. It had a line where you would stop at if you wanted a 24 BB, and another line farther down for a 117 BB as described by tpt guy. Obviously, these reamers were operated manually, so who knows how much attention was payed when the workers were there reaming....which is why you will find discrepancies in the back bores with the same numbers.
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Tpt_Guy
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PostPosted: Tue May 22, 2018 3:47 pm    Post subject: Reply with quote

Irving wrote:
I have seen a Bachreamer for a 24/117 back bore. It had a line where you would stop at if you wanted a 24 BB, and another line farther down for a 117 BB as described by tpt guy.


Interesting. How would one account for the straight taper of the 117 vs the multi-taper of the 24? Simply pushing it in further wouldn't change the shape.

I have a 117 and two 24s. Looking at them both, they are not similar.
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TKSop
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PostPosted: Tue May 22, 2018 3:58 pm    Post subject: Reply with quote

Tpt_Guy wrote:
Irving wrote:
I have seen a Bachreamer for a 24/117 back bore. It had a line where you would stop at if you wanted a 24 BB, and another line farther down for a 117 BB as described by tpt guy.


Interesting. How would one account for the straight taper of the 117 vs the multi-taper of the 24? Simply pushing it in further wouldn't change the shape.

I have a 117 and two 24s. Looking at them both, they are not similar.


Purely theorising...
Perhaps something along the lines of your previous posts last paragraph - if they were initially drilled to a different taper and then the 24/117 (assuming it's the same for argument sake) were drilled in after, then the different depths might determine how much of the preliminary shape were removed? (Ie: partially or totally).

Can't necessarily see why you would, but I suppose it's possible?
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Ed Kennedy
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PostPosted: Tue May 22, 2018 4:16 pm    Post subject: Reply with quote

link

Make impressions of the backbores and check them out. BTW the description of the #24 backbore sounds like the Schilke Schmidt backbore.
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Tpt_Guy
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PostPosted: Tue May 22, 2018 4:19 pm    Post subject: Reply with quote

TKSop wrote:


Purely theorising...
Perhaps something along the lines of your previous posts last paragraph - if they were initially drilled to a different taper and then the 24/117 (assuming it's the same for argument sake) were drilled in after, then the different depths might determine how much of the preliminary shape were removed? (Ie: partially or totally).

Can't necessarily see why you would, but I suppose it's possible?


Definitely a possibility. One of my 24s was cut from a 5A, which is stock shape for that cup so it should be original and not a re-cut. My other one is on an early 70s 1-1/2C underpart. It has very deep stamping matching the font on the rest of the mpc, and the interior of the backbore is silver plated so I would think it's the original as well.

But modifying existing backbores doesn't really explain why all 117s as measured by Frost would have different tapers than all 24s he measured if it's supposed to be the same reamer. All of them being aftermarket mods is not likely.

Confusion abounds!
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Irving
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PostPosted: Wed May 23, 2018 6:54 am    Post subject: Reply with quote

I only stated that I saw the reamer at Giardinelli's back in the day.

If two backbores start out with different shapes, why would you assume that after modifying them, that the result would be the same? Yes, you are introducing the same reamer, but you are assuming that the reamer will obliterate the characteristics of the backbone by installing a new one. Not necessarily true. Also, judging a backbone visually is not very scientific, so no valid information can be obtained by doing that.

Another thing. Pushing that reamer farther in can drastically change the shape of the resultant backbores. Just because the reamer is the same doesn't mean that the 117 and the 24 backbores are similar. The original backbores is at it's narrowest volume where the reamer is entering on the 117 backbores. .One thing that can probably agreed upon is that the 117 is bigger that a 24, since more metal is taken out of it by the reamer.

FWIW, I can see a ledge on my 7E117, where they stopped the reamer. Usually, there is no ledge on a Bach mouthpiece, but this was bought new, so, who knows what the story is there. The mouthpiece plays great, so I never modified the throat or backbore. The rim was horrible though, and my teacher modified it by hand. It's a really good mouthpiece regardless.

Btw tpt guy, the Bach 5A is supposed to come with a 24 bb stock! Maybe yours did, maybe it didn't. Also, you would need to know who made the reamer. Already, Bachs are not consistent so by adding all of the possible variables one can come up with various conclusions. Moral of all this: play what works, whatever stamp might be on your mouthpiece.
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Tpt_Guy
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PostPosted: Wed May 23, 2018 8:44 am    Post subject: Reply with quote

Irving wrote:
I only stated that I saw the reamer at Giardinelli's back in the day.

I do apologize if I came asross as trying to impugn your post. That was not my intention at all.

If two backbores start out with different shapes, why would you assume that after modifying them, that the result would be the same? Yes, you are introducing the same reamer, but you are assuming that the reamer will obliterate the characteristics of the backbone by installing a new one. Not necessarily true. Also, judging a backbone visually is not very scientific, so no valid information can be obtained by doing that.

I never made any assumption. I know well that reaming a something like a 7 into a 10 will remove metal in some places and leave it in others. Mark Curry also commented on this in another thread where he stated that a 24 is actually narrower in some parts than a 10, so opening a 10 to a 24 would result in a hybrid shape. My buddy has a 1-1/2C that he had opened to a 24 backbore. The last quarter inch, or so, of the backbore is still silvered where the 24 reamer is narrower and didn't remove anything.

I may do what Ed mentioned and make castings to compare, just for fun. And the backbore in my M2* does look an aweful lot like a 24.


Another thing. Pushing that reamer farther in can drastically change the shape of the resultant backbores. Just because the reamer is the same doesn't mean that the 117 and the 24 backbores are similar. The original backbores is at it's narrowest volume where the reamer is entering on the 117 backbores. .One thing that can probably agreed upon is that the 117 is bigger that a 24, since more metal is taken out of it by the reamer.

I am still left with a confusion and that is that, from a machining standpoint, it doesn't seem possible, based on the descriptions and measurements, that they could be from the same reamer. If a multi-tapered reamer were justpushed in further, that same multi-tapered shape would simply be seen further up the backbore. It wouldn't change it to a straight taper, especially considering the difference in depth would be measured in thousanths of an inch or millimeters.

FWIW, I can see a ledge on my 7E117, where they stopped the reamer. Usually, there is no ledge on a Bach mouthpiece, but this was bought new, so, who knows what the story is there. The mouthpiece plays great, so I never modified the throat or backbore. The rim was horrible though, and my teacher modified it by hand. It's a really good mouthpiece regardless.

Btw tpt guy, the Bach 5A is supposed to come with a 24 bb stock! Maybe yours did, maybe it didn't. Also, you would need to know who made the reamer. Already, Bachs are not consistent so by adding all of the possible variables one can come up with various conclusions. Moral of all this: play what works, whatever stamp might be on your mouthpiece.

I bought the backbore from Matt Frost, who cut it off a stock Bach 5A. If it isn't a 24, it's Selmer's mistake because it isn't modified except to open the throat to match my Curry top, and it does look and play like my other 24. Mistakes aren't unheard of. I recently got a 2C that was factory cut with a 25 throat and 24 backbore. Someone screwed the pooch because it's clearly visible that the reamer did not go in straight and gouged off center leaving large tooling marks (not to mention, the shank had an incorrect taper). I ended up not keeping it.

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lipshurt
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PostPosted: Wed May 23, 2018 9:22 am    Post subject: Reply with quote

if someone can see a ledge where they "stopped the reamer" that iswhat these two BBs looked like to me. Excepts it looked like the last inch or so was cut at a teper by a single boring bar lathe tool. I was wondering if that is either how a 117 is made, or imaybe that is how the 117 was originally made, and then then resultant shape was copied onto a reamer/mandrel. the latter could easily be the case.
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Irving
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PostPosted: Wed May 23, 2018 2:08 pm    Post subject: Reply with quote

You said: I am still left with a confusion and that is that, from a machining standpoint, it doesn't seem possible, based on the descriptions and measurements, that they could be from the same reamer. If a multi-tapered reamer were justpushed in further, that same multi-tapered shape would simply be seen further up the backbore. It wouldn't change it to a straight taper, especially considering the difference in depth would be measured in thousanths of an inch or millimeters.


Actually, you forget that the backbore that is already in the mouthpiece is tapered, so you are pushing the reamer into a tapered backbore, which will change the proportions of the entire backbore. If the backbore weren't tapered, in other words cylindrical, then as you said, the same shape would be seen further up the backbore.
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lipshurt
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PostPosted: Wed May 23, 2018 3:20 pm    Post subject: Reply with quote

Edited on May 23 cuz one big word was missing.....

if they were made by the same reamer you would NOT be able to see any diference by looking into big end. It would look exactly the same, same shape, same reflections, same light lines etc. The only thing different would be one wojd be about 5 thousandths bigger. If you can see a line where the taper changes on a 117 backbore, it means its not the same reamer as a 24.
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Last edited by lipshurt on Wed May 23, 2018 4:47 pm; edited 1 time in total
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TKSop
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PostPosted: Wed May 23, 2018 3:35 pm    Post subject: Reply with quote

Could Bach's updates over time be crossing wires here?

I mean - could backbores of a certain period have been cut one way and others another leading to differences in shape?

If Matt Frost is saying the Bach's with 117's he's seen are different from the the ones made by Kanstul (which would've been copied from a Bach - but what Bach? A modified one or one from a different era? Maybe?).
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Tpt_Guy
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PostPosted: Wed May 23, 2018 4:50 pm    Post subject: Reply with quote

TKSop wrote:
Could Bach's updates over time be crossing wires here?

I mean - could backbores of a certain period have been cut one way and others another leading to differences in shape?

If Matt Frost is saying the Bach's with 117's he's seen are different from the the ones made by Kanstul (which would've been copied from a Bach - but what Bach? A modified one or one from a different era? Maybe?).


Ya, that may explain it.

http://storkcustom.com/the-backbore-myth/

Here, Stork mentions that Bach backbores did change over time. Matt Frost's MTV backbore is a copy of an outstanding Mt. Vernon 1C backbore, which should make it a #10. I have two of them, and it sure ain't like any modern 10 I've ever played. (I might add that it works ridiculously well, at least for me, on B-cup mpcs.)

So, that definitely could be a possibility.

Quote:
Actually, you forget that the backbore that is already in the mouthpiece is tapered, so you are pushing the reamer into a tapered backbore, which will change the proportions of the entire backbore. If the backbore weren't tapered, in other words cylindrical, then as you said, the same shape would be seen further up the backbore.


This assumes I'm talking about modifying an existing backbore, which I am not. I'm just talking about using the reamer as a first cut to make either a 24 or a 117

In the case of Giardinelli modifying existing mouthpieces, yes, you will get hybrid shapes. Same as what I mentioned about my buddy having his 1-1/2C opened to a 24.

But a mouthpiece such as a 5A that is made with a 24 to start, I doubt will have such an issue, so just pushing a 24 reamer in further to make a 5A/117 will result in the 24 shape further up the backbore.

I do have a question: when did you see the reamer? The timeline could explain any discrepancy.
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TKSop
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PostPosted: Wed May 23, 2018 4:52 pm    Post subject: Reply with quote

Tpt_Guy wrote:
TKSop wrote:
Could Bach's updates over time be crossing wires here?

I mean - could backbores of a certain period have been cut one way and others another leading to differences in shape?

If Matt Frost is saying the Bach's with 117's he's seen are different from the the ones made by Kanstul (which would've been copied from a Bach - but what Bach? A modified one or one from a different era? Maybe?).


Ya, that may explain it.

http://storkcustom.com/the-backbore-myth/

Here, Stork mentions that Bach backbores did change over time. Matt Frost's MTV backbore is a copy of an outstanding Mt. Vernon 1C backbore, which should make it a #10. I have two of them, and it sure ain't like any modern 10 I've ever played. (I might add that it works ridiculously well, at least for me, on B-cup mpcs.)

So, that definitely could be a possibility.


Wonder if that's a similar #10 to the one that Jim New copied from Arturo's 3c - supposed to be quite different to the modern #10, perhaps that's just how they were for a time.
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Miketpt
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PostPosted: Wed May 23, 2018 6:15 pm    Post subject: Reply with quote

A couple years ago had Jeff Parke check out a few new vintage Bach 7EW cornet pieces to hopefully thread a 117 backbore for a Yamaha 11A5 top. Most had much larger throats than #27 since whoever put in the backbore at the factory went too far.



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bop bop
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PostPosted: Fri Jul 27, 2018 7:24 pm    Post subject: Reply with quote

TKSop wrote:
Does anyone still have the scans from the old kanstul backbore comparator, somewhere?

I don't know about the old comparator (new to this), but I noticed the directories at Kanstul are accessible and contain images not listed in the comparator (both backbores and cups):
http://kanstul.com/MPcompare/BB_images/
http://kanstul.com/MPcompare/MPC_images/
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