My First Scarf Joint - how long a board do I need?

I learned a few things making my first scarf joint, I hope what I learned helps you.

I started by using the above diagram as my guide. I can do this I thought. Just decide which method I want, measure, cut and glue (very precisely) and I'm done. Except, as I started to measure and make some calculations, I discovered there were questions the diagram did not answer. After building a few CBGs, I do know how long a board I need  if i'm not using a scarf joint. But the diagrams above did not answer some basic questions - is the board necessarily longer (or shorter?) and by how much? And would Type 1 be longer or shorter than Type 2? Does the headstock have to be longer for Type 2? and if not, again, what measurements do I use? Should I leave it to trial and error? No, wood is a precious thing to waste. So I got me a pen and a paper (and I made up my own little sign... sorry, I couldn't resist) and did some math. 

The answer is - the board is the same length for all three, no scarf joint,Type 1 or Type 2.

First, make your calculations as if you were building without a scarf joint to determine the board length (this takes into account your box size, the length of your headstock, etc.). Then, use the following steps to help you measure and cut so the headstock will be exactly as long as what you want, for either Type 1 or Type 2.

Let's say we want the headstock to be 130 mm (about 5 inches). The following templates represent a 3/4 inch thick neck, about 20 mm. 

Type 1 - Measure as shown from the tip of the board. Draw the 15 degree angle as shown, Cut and position the headstock as shown. This will give you the 5 in. / 130 mm you want for the head stock. The fingerboard in this method will cover the glue joint.

Notice the joint is visible on the upper surface of the neck - may want to use this type if you are going to add a fingerboard to cover the glue joint. 

Type 2 is a little different but just as simple. Measure as before from the tip of the board but on the opposite surface. Draw the 15 degree angle as shown. Cut and position the headstock as shown. This will give you a 5 in. / 130 mm head stock.

The upper surface shows no glue joint, so visually it's clean. If the glue joint on the headstock offends you, you can glue a veneer over it. 

For my first test, I actually cut up some rigid styrofoam insulation to confirm these measurements. The results don't look very pretty so I made the above templates to more clearly demonstrate what to do. Hope this helps!

Also, here's a diagram of my scarf joint jig. It is a rectangular box, made of poplar scraps, bolted (but easily removable) to the mitre guide of the table saw. My sincere thanks to the person who posted the photo of this guide in Google images, I was not able to relocate the original photo to thank the author for providing such a simple solution. The bonus of this jig is I can use the saw's mitre gauge to measure any angle I wish to cut.

Comments and feedback welcome!

And here's a photo of the glue up of my first scarf joint

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Comment by Paul Craig on November 4, 2015 at 7:35pm

Also though that type 1 would be stronger since the fretboard is glued over the seam and to both pieces.

Comment by Paul Craig on November 4, 2015 at 7:32pm

Seems that each 1/4" of thickness would need 1" of length.

I'm thinking that the overall length of the headstock for type 1 and type 2 will be the same. Type 2 only looks longer.

I chose type 1 for the overall looks. Didn't want a seam across the headstock.

Comment by Eric Davis on November 4, 2015 at 9:27am

Thanks for your reply, Joe.  Scarf joints are something I want to try in the future, but I'm not quite there at this point.

Comment by Joe Caruso on November 4, 2015 at 9:03am

Paul, thanks for posting this and sharing this rather straight forward method as well. It does work for 3/4" thick boards. My issue was I had some cherry necks milled from a slab and they were a bit over - which meant I had to find another way. (Coincidentally, the cost of the cherry necks, after paying for the wood and having it milled, was about the same for buying oak boards at Loews or Home Depot.) The first diagram also freaked me out for making a Type 2 scarf - what if I didn't want a headstock that long - how do I measure? Which led me to this blog post. Thanks again for your comments.

New thought - there is probably a mathematical factor to modify the 3 inches if the board is greater than 3/4" thick. Think I'll investigate. 

Comment by Paul Craig on November 4, 2015 at 4:24am

When I was making mine, I looked all over the net and the general response was: A - decide the length of your headstock and measure from the desired end, B - add a 1/4" for the nut and draw a line across the board width, C - draw another line 3 inches from the first line, and D - draw a diagonal line from the first line to the second line and cut. This was done on a 3/4" thick board.

This formula worked great and after checking with a framing square with degree marks, it came out to be 15 degrees.

Comment by Joe Caruso on November 2, 2015 at 6:53pm

Eric, the mitre guide reads 75 degrees. But since the board would be clamped on the left side of the box, the effect would be a 15 degree cut. I think I'll replace the photo with one showing the board clamped to the side. Stay tuned. Dan, Primitive Acoustics, glad it helps. 

Comment by Primitive Acoustics on November 2, 2015 at 5:50pm
Thanks for this! I have a love/hate relationship with scarf joints! Love the way they look, hate how much work they are to get perfect.
Comment by Dan Sleep on November 2, 2015 at 12:42pm

Very helpful, thanks!

Comment by Eric Davis on November 2, 2015 at 9:50am

At what angle is the miter guide set on your saw?

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