Several months ago an old friend of mine stumbled upon the idea that he would like an Alphorn so he asked me if I would be interested in making one for him.  Liking a good comical challenge, I did a little research and found that they are traditionally made from whole spruce trees growing out of the side of a mountain where over time, the trunk of the tree grows into a J shape.  After felling the tree, they debark it, split it in half for hollowing and then join the halves back together. 

Having no spruce trees available, much less mountain sides for them to grow out of (I live in a town aptly named Plano), I looked for more modern approaches.   Most seem to laminate pieces of wood and then manually  shape the halves and join them together.   Many of them are segmented which makes them easier to store and transport.   I found one website where he cut long tapered staves and then rounded and shaped the inside and outside before joining the halves together.  The bell was glued up from blocks like a segmented bowl and then shaped by hand using an angle grinder.   I decided not to go the staves or hand shaping route but instead decided to see if  I can use my CNC machine.   So the next step was to make a design that I can use on my machine. 

The design process was probably the simplest part.  The website that used the staves had some measured hand drawings so I used those dimension and went to OnShape CAD to create a design.  I won't bore you with the details but after a couple of hours of work, I had this design drawn up based upon those measurements. 

To provide a sense of scale, the long blue pipe is about 120" long.  The interior dimension is just under 1" at the small end and 3.385" where it meets the bell.  The interior bell opening is 7.44".  To make this manageable on my 24x24" CNC bed and to make it easy to store and transport, I broke the long pipe into 4 segments.  The large end segment is about 28" long and the other 3 are about 32" long.   The thickness is about 3/8" throughout.   The goal is the join the segments and the bell with 5" sleeves.  I have not decided whether to make them on the CNC or perhaps on my lathe but each sleeve will be glued to one segment and slide into the next. 

To make this machinable on the CNC, each segment is sliced in half so that I can hollow the inside and round the outside with the halves then glued together.  The bell segment required slicing it into either 4 or 6 pieces for machining.  I started with 4 but later decided that it would be better to slice into 6.   I really only had to do 3 slices as the others are mirror images which I can handle in the CAM software (Vcarve).  I initially tried to slice the bell in Vcarve but managing 3 double sided slices in a single job proved to be too complex to manage so I went back to Onshape to create the slices.  That way each 3D slice is managed as a separate job.   Switching to 6 slices also made it so that I could use 2-by stock for each layer of the bell and requires no laminations to get the dimensions needed.

 
You will notice that lower of the 3 slices actually turns out be 2 separate pieces from opposite sides of the bell.  These proved to be the most difficult to setup and machine on the CNC.   They are nearly vertical but not quite so and I still had to machine them from both sides to get the inside and outside curved surfaces of the bell where the bell also makes its curve.  So after creating the design and breaking down into manageable sized parts, each one was exported as an STL file for Vcarve.  

I really wanted to make this from spruce but spruce sized large enough for this are hard to find this far south.  I initially tried some SPF from Lowes (which turned out to be fir)  but it turned out to be too brittle and tear out on some of the more delicate areas was pretty bad.  I switched to Southern Yellow Pine from Lowes and it machines much better.  Lowes carries some really high quality SYP.  You have to dig through the stacks but I usually manage to find some straight, fine grained stock with no pith running through them.  

Since the bell was going to be the most challenging, the next installment will be about setting up and machining the bell parts.