I’ve seen several questions on scarf joints recently. Since a quick search didn’t reveal a recent tutorial, thought I’d contribute.
Disclaimer: I’m not a woodworking or scarf joint expert, guru or genius. Just building instruments in my garage, like many of you. I also know that there is more than one way to skin a cat, so this isn’t presented as the ultimate solution. There are other ways to do this, but I’ve found a method that works for me and am sharing. We’ll be using power tools, so safety first!
This method uses a table saw and scarf joint jig. No room here to describe the jig, but there are plenty of plans on the internet. Here’s a good one:
A quick note on table saws. If you don’t have one, get one. I know, they’re messy and take up room, but it’s also the single most valuable tool in my shop. I bought mine on Craigslist for $75 and, while I’d love to upgrade, it’s built cabinets, flooring, speakers, cajons and many stringed instruments.
What angle do you cut your scarf joint? I’ve seen this question many times and there’s really no right or wrong answer. The general consensus seems to be that anything from 10-15 degrees works great. I chose 11 degrees for several reasons: research, works well with my zero frets and I like the look. Just pick an angle, it will be fine.
You’ll want a sharp, high tooth-count blade. I’m using a 60-tooth and that seems to work well. Also make sure your blade is dead square to the table. If it’s not, you’ll get a slightly tilted joint (not impossible to fix, but why make it hard?) And cut your stock to a workable length since it’s difficult to accurately scarf an 8-foot stick.
Clamp your stock squarely and securely to the jig and make a deliberate cut - not too fast, not too slow. Let the blade do the work. Tip: when the blade makes it cleanly through the stock, stop the saw and wait for it to spin down, then slide it back. Sometimes, when I pull the stock back through the running saw, it messes with the square of the cut and/or adds lots of saw marks.
Now, you have a neck and a headstock. Since 1x2 lumber is ¾” thick, you’ll need to resaw the headstock so your tuners will fit properly. I cut mine to ⅝” since that works great with the Gitty economy tuners. Also, most commercial headstocks are similar in thickness, so check your tuners and cut accordingly. With the fence set and the scarf toward the blade, run it through your saw - and be sure to use a push stick! Sharp spinny things are dangerous!
With your freshly cut neck and headstock, it’s time for some glue. What kind of glue? Any good woodworking glue is fine. Titebond, Elmers, whatever. Gorilla Glue and PL Premium will work too. Just follow the directions. If using woodworking glue, spread a decent coat evenly across the joint. You don’t want gobs on there, but a little extra won’t hurt anything. Squeezeout is your friend. It tells you there’s plenty of glue in the joint.
I use 3 “A” clamps on my scarf joints and that works for me, but whatever clamps you have should be fine. Be aware that clamping pressure will make the joint slide some. One simple solution is to sprinkle a little table salt on the glue (just a pinch). It will create some friction for clamping and dissolve in the glue. Or, you can just manhandle it into submission, which is what I do most of the time. Wipe your excess glue with a damp rag and place the joint on a hard flat surface to cure. Check back in about 10 minutes to make sure things haven’t shifted. If they have, you still have time to square them back up before the glue sets. With woodworking glue, give it at least 2 hours before you remove the clamps. Longer is better. Overnight is best.
When your scarf joint is set, it’s time for some sanding. If you got it perfect, you’ll have a flat, level neck, ready for a fretboard. Mine are never perfect. In fact, I deliberately set the joint just a tiny bit proud of the neck so I can sand the whole thing flat. To do that, I clamp an old belt sander belt to to top of my (flat) table saw and work it till I’m happy. You can check your progress with a metal ruler, looking for gaps and oversanded spots. Sand till flat and you’re ready to go.
You’ve probably noticed that I do my scarf joints in the “over” position rather than the “under” variant. All of my instruments have a fretboard which covers the joint and provides an extra layer of stability for the scarf joint. Everything here works for “under” too.
One final tip: inevitably, I end up with small gaps - either in the joint, around the joint or along the fretboard. This is usually due to minor chipping, etc. Fixing this is pretty easy. Once you’ve identified a place you’d like to repair, clamp the neck for aggressive sanding. Run a bead of superglue in the gaps, let it sit for a few seconds and then wipe the excess off with a rag. Grab a medium grit sanding block and sand the area till you see it disappear. The pressure of sanding will push the sawdust into the gaps, mixing with the superglue and creating an almost invisible repair! Larger gaps may take a couple of passes, but when the superglue is fully cured, the color will match since you’ve filled it with actual joint material. This is a great fix.
I hope this tutorial helps those of you with scarf joint questions. If I missed something, or you’ve got a better idea, please post below. Now, get scarfing!