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Woody Tubaphone Build Full Write Up

Posted by dpgetman on Sunday, October 4, 2015

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Tools I used:
Drill
Drill press
Dremel with drill press
Miter saw
Table saw
Router

After one failed attempt to make a banjo pot, I have just completed my first successful banjo build.  I am making this post about the build on the hangout because I would likely not have been inspired to attempt the build or had the know how if not for the volumes of information available through the hangout and hangout members.  

I am also posting because the build involved the construction of a wooden tubaphone, which I have never seen before, so I thought a record of it would be helpful to other folks who wanted to try it.  

Below are also many links for the sources I used, parts I bought, and inspiration I took, all from hangout members.  These are the folks I benefited from most (thanks fellas!).  Note, in particular, Bluestem Strings Open Back Design Primer and LeVan Banjos Building a Banjo Series.

Bluestem Strings
http://www.bluestemstrings.com/index.html
www.bluestemstrings.com/pageBanjoDesign.html (Open Back Design Primer)

Ken LeVan
http://www.banjohangout.org/archive/251301 (Building a Banjo Series)

Rickard Banjos
http://rickardbanjos.com/site/

Hickler Banjos
http://www.hicklerbanjo.com/Home.html

Tools I used:
Drill
Drill press
Dremel with drill press
Miter saw
Table saw
Router

The pot I set out to make has a walnut body with a cocobolo rim cap, a tubaphone style tone ring made out of cocobolo, and a silver spun sleeve with a brass tube that sits on top of the tubaphone.  The pot is 5/8” thick, 3” deep from rim cap to the top of the silver spun ring, and 12” in diameter made up of three block-rings, each made out of 8 segment blocks.  

The tubaphone tone ring is 5/8” thick with 1/8” inside, top, and bottom walls, a 1/4” outer wall  and a 1/4” trench with 32 holds drilled around the inside wall.  Here is a pic of the dry assembled rim.

I chose walnut and cocobolo after reviewing Hickler Banjo’s Wood Tonering Test page: http://www.hicklerbanjo.com/Testing.html.  I made the 12” wooden tubaphone because I have always wanted to, but never played, a 12” or a tubaphone banjo, and couldn’t afford to buy one.

I purchased a 1 1/2” x 4” x” 36” piece of walnut and a 1” x 4” x 24” piece of cocobolo from a local hardwood supplier and took full advantage of the “cut offs” bin, which most of these folks have, where you can get good deals on the relatively short pieces of wood you need for this kind of project

The printable chart I used to make the measurements for the segments I found on the Bluestem Strings banjos site here: http://www.bluestemstrings.com/BluestemBanjoRimSegmentGuide.pdf

Cutting the Rim Blocks

After several failed attempts to cut tight 22.5 degree angles on the 8 segments with my miter saw, I came up with a table saw solution that gave me very tight angles:

cut your rectangular blocks slightly over the longer side length in the rim segment guide
line them up as one block, top face to bottom face, and clamp
set the table saw angle to 22.5 degrees (if you are cutting an 8 segment ring)
cut one angle on the clamped block
flip the blocks and set the fence on the table saw to the length specified for the long end of the blocks in the rim guide
cut the opposite angle

Note: keep those little triangles from the edges for each ring, they will come in handy later

Once the walnut and cocobolo blocks were cut, I arranged them on a piece of wax paper on top of a 13” square of 1” thick formica, wrapped them with a nylon tie-down tight, and then clamped each piece to the formica, ensuring that the edges were flush in case the tightening process pushed one edge up over the other, which happened on several, and let dry overnight.

Routing the Rim Blocks
 
To route the rims sections, I used a circle routing jig I bought from Rockler.  Once the octagons were dry, I outlined the rim center and screwed the outer edges of the octagons to pieces of scrap wood.  Then, I used the seam lines of the octagon to find the center. for the jig to anchor in.  I glued four of the triangles I saved from cutting the blocks on the table saw together into a diamond shape that was the same height as the blocks, using the triangles from the block cutting ensures that the hight in the middle is the same as the height on the outer edge.  Then I drilled a hole in the center of the diamond the same diameter as the anchor peg on the jig and lined the bit up about 1/8” from the rim cut I wanted to make, to leave room for sanding down later on the drill press drum sander.  

I set up each rim segment prior to beginning routing because I wanted to use exactly the same measurement on the jig for each to ensure the rim segments were the same, cutting the center for each and then moving to the outside for each.  I cut the center before the outside because I anchored the octagon on the outside, you could do either I suppose.  I cut with a 2” long spiral cut router jig, coming down into the wood about 1/4” at a round to prevent the bit from pushing out.  The spiral cut bit works better than other bits because it cuts all the way up the bit, rather than just at the tip, and produces less tear out.  Even at 1/4” per round, I still found irregularities along the rim and some bit drift, but the extra 1/8” gave me some wiggle room to sand away at the end.  I repeated this process for the outer cut.

A key element of the tubaphone assembly is a deep, but thin shelf or shoulder for the tone ring to sit on so it has the freedom to vibrate.  Before glueing the cocobolo to the walnut, I routed a shoulder into the top of the walnut ring about 3/8” deep, leaving a 1/4” of walnut for it to glue to and 3/8” of gap for it to ring over.  It is important to do this before you glue them together as cutting this shelf would require a specialty bit once they are assembled.

I also took the opportunity of having the router table set up and the segments not yet glued together to cut the rabbet for the purfling at the bottom of the walnut rim segment.

Once the rims and tone ring shelf were cut, I glued them together, even though I planned to cut a 1/4” segment from the cocobolo for the rim cap and a 1/8” segment to expose the center of the tubaphone.  I did this to add stability for cutting the top of the tubaphone and rim cap from the cocobolo section, which were the hairiest part of this process.  To get a tight fit, I made a jig with two 12” rounds of formica for the top and the bottom which I secured with bolts on the inside and clamps on the outside and let dry overnight.

Wooden Tubaphone Tone ring

Once the rim was glued up, I turned to the wooden tubaphone tone ring.  I tried this once before and realized the importance drilling the 32 holes around the inside of the ring before routing the trench.  Routing the trench first leaves very weak walls that will fracture if you try to drill through them.  Drilling the holes first gives you a good chunk of wood to drill into and routing the trench after does not affect the holes in any way.

Already having a Dremel, I splurged on a Dremel drill press, a 1/4” Dremel router bit, and a cutting wheel.  

I made a right angle brace out of two flooring boards to back the rim up against, lined up the cutting wheel just below the 1/4” line from the top of the cocobolo, eased the wood into the cutting wheel about 1/8” deep and then eased the rim around the brace to keep the Dremel from pushing out.  I repeated this process until I got about halfway through the rim, then reversed the process to cut into the rim from the inside using a convex brace that operated in the same way.  Note that I also added a wooden brace for the Dremel press with zip ties.  Even though I took great care to make a straight cut, this still turned out a little uneven, so make sure you leave some room to sand down the unevenness.  

I then repeated this process cutting another 1/4” thick ring, one for the rim cap on the bottom of the rim and one for the top for the tubaphone.

To drill the holes in the tone ring, I used a handheld drill set flat on my bench with a shim on the back, making sure it was pointed level as they are usually at an angle when set flat on a tabletop, and set the tonering on a pair of flooring boards t a shallow angle and clamped to a deck I made for my tabletop drill press so I could adjust the height to meet the bit and slide the rim into the drill bit.  I used a foster bit to avoid tear out.

I cut the trench in the tubaphone with a Dremel router bit using the Dremel drill press with the rim set against the same right angle brace so it could rotate (brace not in pic).  I made sure to leave a thicker wall (about 1/4” thick) on the outside to accommodate the brass rim, which touches down right at 1/4”, without putting pressure on the tubaphone top over a void.  This was a little harrowing, because of the width of the walls, but went smoother than I expected.  The drill press was less stable than I wanted it to be, but I made a brace to keep it level with little trouble.

Once the trench was cut, I glued the top of the tubaphone on straight away because of the fragility of the top (anything can happen in a garage shop and its infinitely easier to cut a glued segment than to glue such a thin piece) using the sandwich jig I used to glue the pot segments earlier on.

Then, I shaved a 1/32” strip off the edge of the tone ring/rim assembly to slide the silver spun sleeve over using a router with the rim backed up against the right angle brace I made.  This process was tedious and required a very thin shave, then a test fit with the sleeve, then a deeper shave, then a test fit, etc.  I was able to get a very tight fit, though.  Go slow.

Purfling

The purfling was not time consuming, but I did not get it exactly right.  The standard length of the purfling available where I am was a bit too short to make the circumference of the pot, so I had to make two joints.  Thought I tried to get them precise, there were gaps at the ends that I filled with wood filler.  

Drilling the shoe bolt holes

I used the notched tension hoop I bought from Bill Rickard to measure the spots for the shoe bolt holes.  NOTE: you cannot flip the tension hoop to measure these as they are not precisely the same on either side, which I learned the hard way.  You must measure with the notches facing upward, just as it will ultimately sit on the pot.

To minimize tear out, I routed a base to rest the rim on in my drill press out of some old butcher block the same diameter as the inside of the pot.  Then I taped the inside of the pot and used the drill press to make the holes.  

Rim Sanding

To sand down the rim to the diameter I needed to match flush with the diameter of the silver spun skirt, I used a right angle brace I made out of old floor boards to hold the rim flush against the drill press sanding drum for the outside and a block I attached on a sliding anchor to the drill press table to brace for the inside of the rim.  I then locked the braces in, sanded a bit until there was no friction, sized up the sleeve, and scooted the brace a bit closer and sanded again until I got the proper diameter for inside and out.

Neck Shaping

I picked up a “shop second” neck from White Mountain Banjos months ago which, considering the craftsmanship Ron Grimsley puts into his work, I considered a real favor (thanks Ron!).  The headstock was too thin for his production quality, so I opted to make a headstock and volute cover out of leftover cocobolo.  

I used a hot pipe method to bend the headstock cover and opted to carve the curve out of the volute, considering the steep curve and the brittleness of cocobolo.

I used the drum sander on my drill press to shape the volute piece.

Then I glued the pieces in place and used a coping saw and Dremel to do the final shaping.

I followed the same procedure to do the heel cap.

Neck Attachment

To attach the neck to the pot, I went with a “Rudy Rod” method.  Special thanks to Rudy at Bluestem for his detailed write ups on this technique.  Be assured, it is as elegant, efficient, and effective as he asserts.  Ken LeVan has done some very interesting things with this approach as well, which he was also kind enough to post.  LeVan and Bluestem have slightly different approaches, I went with a hybrid.

Bluestem Strings http://www.banjohangout.org/archive/270727

LeVan Banjos http://www.banjohangout.org/topic/305112

Using leftover walnut and cocobolo from the rim construction, I made a dowel still with two 1/4”  x 1 1/8” strips of walnut on either side of a 1/4” x 1 1/8”  strip of cocobolo.  I glued these together and then cut the stick in half perpendicular to the cocobolo strip right in the middle.  Then I took each half and routed a half circle trench along the middle so when I glued them together, I had a 1/4” hole running through the middle.  Then I traced the arc of the rim along the edges and sanded them to fit flush with the inside of the rim.  

To measure the height of the neck, which I asked to be precut for a 12” arc, I located the middle of the neck heel between the bottom of the tension ring cut and the heel.  Then I measured the approximate location in relation to the top of where the head would be and drilled a 1/4” hole in either side of the rim.  I then attached the neck to the rim with a nylon tie-down and strung it up.  With the strings on, I could then inch the neck up and down until the strings were the appropriate distance from the fretboard.  When I had it right, I inserted a pencil I filed down to a 1/4 diameter and slid it into the rim hole to mark the neck.

Here are the pictures of the dry assembly.  It sounds wonderful, I will post sound files asap!

 



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