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Banjo Build

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S. Heslop:
So a while back I had the silly idea of trying to build banjos to sell. And for a good while I was building stupid tools to do jobs the hard way.

Before I built that drum sander I decided to just start actually building a banjo to see how it goes. Then I got distracted again by a friend asking me for help in building skateboards and built that drum sander. I finished the sander but the skateboard thing fell through so I'm getting back to continuing that banjo.

That's my life story out the way. So I started by making some wooden hexagons. The main wood i'm using is meranti, a sort of cheap knock-off mahogany.


Despite being careful, I didn't get the angles right. I really have no idea how people manage to do those fancy segmented turnings. I guess they must cut the last segment to fit.

They were glued in two halves and then the joining faces were sanded flat.


Anyways after being left in the house for two months the meranti hexagons held up fine, but the top one made from goncalo alves shrunk enough to make a huge gap, the individual segments also twisted a huge amount. It's not a very stable wood, evidently.

The idea is that fancy banjos use a metal tone ring that sits between the skin head and the pot, and that gives it a brighter tone. So instead of that I'm going to use a hard wood as the top layer in the pot. That said, i'm not a big believer in tone. I guess there are differences, but which one is better is highly subjective. But it's still something I wanted to try.


The meranti hexagons didn't warp at all, but weren't perfectly flat to begin with. So I sanded them true on the drum sander.


These were then glued into a stack, on a board of plywood. It was awkward with the thing sliding about on the glue. If or when I do this next, i'll probably drive some pins into the wood to prevent that. A layer of paper should hopefully make it possible to separate the pot from the plywood once it's round.


There was still that top layer to sort though. The goncalo alves was too warped to try forcing flat, so I went through my basket of hardwood to try find something else. I first tried using a piece of chechen, and after cutting it up I realised I didn't have enough wood. I'd checked to see how stable chechen was online before cutting it up, and it seemed to rate fairly well. But I was fed up at this point and decided to just cut some apple wood and see how that goes.


That was then glued up.


Tomorrow I'm planning to build a rubbish wood lathe to turn the inside of the banjo. The outside will probably be sanded on the spindle sander. I'd actually built that sander with the intention of using it to sand banjo pots round internally, but i've since deiced that it wasn't the best of ideas. I guess i've warmed up to the idea of awkward dangerous looking wood lathes after building the drum sander.



I measured up some various scraps in the garage and here's what i'm going with so far. I'll probably add a bit more bracing to the headstock side of things, but there's no point in drawing that up I suppose.

vtsteam:
Simon, have you considered splining those end grain joints? Make a jig for your tablesaw and run the pieces through, then rip up some spline stock and glue it in. You can do that to individual pieces before assembling, or do it at the joints to the ring you.ve already made. It will be easier and much better than doweling for this kind of joint -- gluing surface area where it should be, and grain running across the joint. And you don't need to buy (or make) dowels. If you really want to lock it, spline, and then dowel from the face through the spline, ie wooden fasteners.

S. Heslop:

--- Quote from: vtsteam on March 21, 2015, 09:42:34 PM ---Simon, have you considered splining those end grain joints? Make a jig for your tablesaw and run the pieces through, then rip up some spline stock and glue it in. You can do that to individual pieces before assembling, or do it at the joints to the ring you.ve already made. It will be easier and much better than doweling for this kind of joint -- gluing surface area where it should be, and grain running across the joint. And you don't need to buy (or make) dowels. If you really want to lock it, spline, and then dowel from the face through the spline, ie wooden fasteners.

--- End quote ---

Oh by pin I meant like veneer pins, tiny nails. Just tapping them in a bit and cutting most of the rest off, so that it doesn't want to slide as much when clamping up each layer. I'm a little worried that I might not have gotten each layer lined up properly and won't be able to turn it 11 inches. But if that happens I guess i'll just turn one of the layers a bit narrower than the top, and try pretend it's something decorative.

I'm not expecting the end grain joints to hold that strongly, most of the strength will come from the edge grain joints with each layer.

vtsteam:
I see. I thought it was just a single thickness, and you were making several at a time.

Woud it be possible to do a single thickness with a splined joint (or a couple splines per joint)?

Apple is a beautiful wood.

Lew_Merrick_PE:
Simon,

I have been making 5-string banjos for 51 years now.  One of the things that makes the job a lot easier is to cut your "shell wood" into thin (call it 2-2.5 mm thick) strips and laminate them inside of a (hollow) circular jig.  Here in the U.S. nearly all banjo heads are 11 inches in diameter -- making 10.950/10.900 inches the correct OD for the shell.  The circular clamping jig I use has the OD set to 15 inches -- which means that I can use it in my table saw to "trim off" the (inevitable) "mismatch" at the top and bottom edges.  I "wax" the ID of the jig to keep glue from sticking to it.

My "ID Clamp" is an inner tube from a hand truck (5 inch hub, as I recall) that fits on an inner (about 7.5 inches OD) piece with an extension that allows me to inflate it to clamp each "layer" as I laminate the shell.  I find that (about) 30 psi works really well.

I normally make my shells 3.5 inches tall, so I start off with a piece of wood that is 3.75 inches wide and 34.75 inches long.  I "dress" the face of the stock on my joiner and slice off a piece on my bandsaw, take it back to the joiner, and repeat until I have all my strips.  I then use my thickness sander to finish each "layer" to thickness (.090 inches for my approach).  I cut them to length, steam them, and insert them into my jig and force them to round using the "ID Clamp."  The "outer joint" of the shell gets located under the heel of the neck, so the slight "mismatch" is (virtually) never seen.

I make my frailing banjos with a (roughly) 10 mm thick shell.  Bluegrass banjos get a (roughly) 20 mm thick shell.  After the slightly over-tall shell is complete, I return it to the "circular jig" and use that to trim it to length.  I then glue "strips" to the bottom of the shell and trim them flush using a trim-router.  I can then, if so desired, route a "perfling rabit" for final clean-up trim.

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