I've been using a rotary tool with cutting bits of various shapes to hog out the chambers of mouthpiece blanks. Then I follow up with riffler files. The trouble is that that the cutting bits can only reach the chamber from the window, occluding my view of the cutting process.
 

 I'd like to cut from the bore side, so my thought is to use an extension mandrel to extend the cutting bit's reach from the bore (I just purchased the mandrel so I haven't tried this yet). I'm thinking about mounting the rotary tool handle to the bench facing upward, lower the mouthpiece over the extended cutting bit and move the mouthpiece around to achieve the cut and shaping. Then I could see straight down into the piece from the front as I ream out the bore. 
 

 My goal is to find an easier way to create large chamber pieces which is difficult to do when the chamber is larger than the bore. It seems that vintage large chamber mouthpieces were cast in two halves that were then joined together. Buescher blanks have an obvious seam where the two halves come together.
 

 Any suggestions on how to ream out and shape large chambers? Thanks in advance.
 

You may want to get some telescoping bore gauges to help judge your work progress.

I use a flex shaft with a hand piece small enough to fit inside the bore diameter.  I got mine from MicroMark.  But they did not have it listed anymore a few years ago.  

Long stem burrs are an option.  I have one but rarely use it.  

I like holding the mouthpiece against a table or in my hand while hogging it out from both ends.  It gives me some "feel" of progress while working on it.  Vibra-feedback.   I never tried chucking a flex shaft in a vice.  

> On Jan 11, 2017, at 3:42 PM, jorns4ever@... [MouthpieceWork] <MouthpieceWork@yahoogroups.com> wrote:
> 
> I've been using a rotary tool with cutting bits of various shapes to hog out the chambers of mouthpiece blanks. Then I follow up with riffler files. The trouble is that that the cutting bits can only reach the chamber from the window, occluding my view of the cutting process.
> 
> 
> 
> I'd like to cut from the bore side, so my thought is to use an extension mandrel to extend the cutting bit's reach from the bore (I just purchased the mandrel so I haven't tried this yet). I'm thinking about mounting the rotary tool handle to the bench facing upward, lower the mouthpiece over the extended cutting bit and move the mouthpiece around to achieve the cut and shaping. Then I could see straight down into the piece from the front as I ream out the bore. 
> 
> 
> 
> My goal is to find an easier way to create large chamber pieces which is difficult to do when the chamber is larger than the bore. It seems that vintage large chamber mouthpieces were cast in two halves that were then joined together. Buescher blanks have an obvious seam where the two halves come together.
> 
> 
> 
> Any suggestions on how to ream out and shape large chambers? Thanks in advance.
> 
> 
> 
>