Gourd Banjo

Skewering the Gourd


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Break is over, and there is some afternoon left, so I decided to go ahead and skewer the gourd. This is another big step that is not reversible should I do it wrong. I basically have to make two holes in opposite sides of the gourd that the neck tailpiece will pass through. There are a lot of constraints on those two holes, for example:

I have to keep all of that in mind while I cut these holes.

First, to get the elevation of the front hole correct, I measured the distance between the top of the fingerboad and the bottom of the neck. That distance is where the bottom of the front hole must be to make the neck level with the head.

Elevation

I used my ruler to draw a line straight across the top of the gourd from front to back. I chose the front of the gourd to be a fairly flat place in order to make the mating of the neck heel to the gourd somewhat easier. Then, I drew a line down from the center of where the neck will go and measured down from the top to the distance I measured on the neck and drew a line.

Since that point is where the bottom of the hole must be, I measure up from that mark 3/8 of an inch and marked the center of the hole at that point. Since I made the neck blank out of dimensioned lumber, the tailpiece is 3/4 inch thick, so half way up is 3/8 inch. Here is what I got.

First mark

You can see where I erased the first mark, which is where the bottom of the hole will be and marked the center of the hole up 3/8 inch. You can also see where I wrote "heel" next to it so that I won't get the confused about the front and back of the gourd. Hey, things have not been going all that well today!

The position of the hole at the tail end is a bit more tricky. I want to put it up just a bit higher than the one at the heel of the neck so that the neck will be tilted down. Having a little angle on the neck will make the action lower over the neck when the strings are on it. The question is, how much higher should I make the hole?

I did some quick calculations to see how much of an angle would result in a particular elevation of the hole. I measured the diameter of the gourd, and it is just about 11 inches across where the tailpiece will pierce it. I want to point the tailpiece (and therefore the neck) down by 2 to 3 degrees. So I need to calculate how much to lift up the rear hole in order to put an angle of 2 to 3 degrees on an 11 inch stick.

Here is a drawing of the tailpiece deflection as it goes through the gourd;

Neck Angle
n = length of the tailpiece section = 11"
a = angle of the neck
d = deflection upward of the rear hole

tan(a) = d / n = d / 11

I want to figure out what d is to provide a neck angle of 2 - 3 degrees. We can go ahead and solve the equation to get.

tan(2.5) = d / 11

so

d = tan(2.5) * 11 = 0.480"

That is just under a half inch. Or we can try out some numbers for the position of the rear hole and get the following angles.

a = arctan(d / n)

For 1/4" a = 1.30
For 3/8" a = 1.95
For 1/2" a = 2.60

Since a folk banjo like this will be played with a rather high action anyway, and since there will be no way to adjust this angle once it has been set, I decided to be conservative on the angle and set it to about 2. I went with the middle number, 3/8". None of this is very precise anyway because the gourd is not exactly 11 inches across where the tailpiece goes through it and I cannot measure that precisely on the gourd, etc. etc.

I marked off the same location on the rear of the gourd as I did on the front of the gourd, and then I moved it up 3/8 of an inch and called it done.

First mark

You can see the marks on the gourd. I also wrote "tail" in large letters so that I would not screw up this hole either. You just can't be too careful.

The tailpiece is 3/4 inch thick, so to start the holes in the gourd, I will drill a 3/4 inch hole using a brace and bit.

Brace

I picked up the brace, used, for a couple of dollars years ago at a rummage sale. I bought the bit new, also many years ago. Using a bit like that is a joy, and it cut a two perfect holes through the gourd in a matter of seconds. The point of the bit is a little screw that screws into the wood and pulls the bit through it. I just held the gourd between my legs and turned the bit and the hole made itself.

Holes

You are looking at the front hole in the photo. Now I have to make the holes larger and rectangular. I measured the width of the tailpiece in the approximate locations where it will go through the gourd and marked a rectangle for each of that size, centered on the hole. I made these deliberately small so that I can cut the holes to fit the stick later. They must be snug against the tailpiece to keep it steady.

Front

Front

Rear

Rear

I threaded my coping saw through each hole and used it to cut the holes square.

Square

Then it got tedious. I put the tailpiece through the front hole and slowly enlarged it to make the stick go further into the hole each time. I simply took off a bit more of the gourd and tried again. Over and over again.

Part way

Part way in.

Rear

Barely into the rear hole.

Almost there

Almost there.

I used my chisel to do the fine paring of the sides of the hole to make the neck go all the way through.

Chisel

I went back and forth between the front and the rear hole. When one got loose, I would cut on the other one to allow the neck to advance a bit. Here it is almost done.

Done

Here is a closeup of the neck to gourd joint.

Joint

I need to carve the heel of the neck to make it fit the curve of the gourd. I went through my scrap box and found a length of electrical wire for that.

Wire

That is just an old piece of houshold A/C wire from a previous project. I will bend it into the shape of the surface of the gourd.

Shape

Then I put the wire next to the banjo neck and transfer the curve to the heel of the neck.

Transfer

This is going to be a complex 3-D shape to carve since the gourd curves in both directins at once. To get a start on it, I will make a straight cut with a saw that will take out a bunch of the wood. I drew a straight line close to the curved one with my ruler.

Straight

I cut that wedge out using my panel saw.

Wedge

Here it is with the wedge cut out. I cut those two cheeks off after I took the photo.

Cut

Well, here it is. For what it is worth, I now have an approximation of a fit of the neck heel to the gourd.

Fit

You can see in this closeup, though, that it really is a rough approximation.

Closeup

I want it to fit better than that, so I will have to carve it into a bowl shape somehow. But the day is over, so I will have to carve the neck heel some other time.

I spent about three hours on this part. Three hours to cut two holes in the gourd and slice one piece off of the neck heel. Woot! But they are really really important holes.


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Last updated December 2, 2007