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Scarf joint with a tenoning jig.

Posted: Sat Feb 16, 2019 5:20 pm
by Steve Sawyer
Because they're cheap (a decent one can be had for about $50) many woodworkers pick up a table-saw tenoning jig at some point. These are bulky and take up a lot of space, and spend most of their time collecting dust. The bad news (and what keeps this in the tool stable for many of us) is that if you want to do something on the END of a piece of stock these make the operation easy-peasy and SAFE!

Anyway, when I needed to cut a scarf joint, this was what I used. I've done this twice now, once with a "test" neck (since I hadn't made a scarf-jointed neck before) and again just a couple of days ago with the neck that's going on the current build. The one downside is that unlike some methods that make a single cut, followed by a flip-and-glue which can be done from a single piece of stock, this wastes some stock because you can't use the tenoning jig to cut a scarf in the middle of a board, only the end. Thus if working with a single piece of stock, you have to cut them apart leaving enough extra length to account for the scarf. The good news is that it leaves you with a couple of wedges perfect to use as cauls when clamping the glue-up.

1) The first pic shows the initial setup. I needed a 14* angle, so I used my Wixey inclinometer to set the angle on the tenoning jig. By the way, I use this thingumbob all the time for setting angles all over the shop. I've even stuck double-sided tape to it to stick to a piece of stock, and have stuck those little metal plates that they make to stick on phones to make aluminum and plastic items "sticky" so I can stick this on. Anyway, I zero-out the gauge on the top of the table saw, then read out the angle on the upright on the jig - note the 76* indicated (90-14).

2) I make sure that the reference face of the stock is going to intersect with the table precisely at the blade. This is not critical, but it ensures that my blade at max height will be tall enough to cut entirely through the stock, so I want the bottom of the stock to be resting firmly on the table top. I also want a knife-edge from the table saw to minimize planing/sanding of the joint after assembly. I am just using a 6" steel scale held to the jig with a couple of rare-earth magnets.

3) I double-check to make sure I'm going to get completely through the stock. Again, not super-critical, as if you exceed the capacity of the saw, it's easy to finish up the cut with a ryoba saw and a little planing, but it's nice to know beforehand what will happen when I start cutting.

4) Checking that I can get completely across the saw blade without hitting my overarm blade guard. I love the over-arm guard but it gets in the way for some operations, like my crosscut sled. Gonna come up with something improved someday when I haven't anything else to do.

5) The finished joint. Note the burning on the cut. This pic is actually from the test neck I made, and taught me to NOT use a fine-tooth cutoff blade and to NOT make the cut in one pass. The blade is buried too deep, and I'm sure too much swarf builds up creating a LOT of heat. A combo blade works much better, and I made multiple passes, cranking up the blade by one revolution on each pass.

6 & 7) For the sake of completeness, the glue-up and finished joint (in the next post due to pic count limits)
Tenon Scarf 1.JPG
Tenon Scarf 2.JPG
Tenon Scarf 3.JPG
Tenon Scarf 4.JPG
Tenon Scarf 6.JPG

Re: Scarf joint with a tenoning jig.

Posted: Sat Feb 16, 2019 5:21 pm
by Steve Sawyer
Tenon Scarf 7.JPG
Tenon Scarf 8.JPG

Re: Scarf joint with a tenoning jig.

Posted: Sun Feb 17, 2019 1:58 pm
by Freeman Keller
Pretty cool gizmo, Steve. I came up with something far simpler. First, I have a really crappy little portable table saw that I almost never use for guitar building. I also have a really crappy band saw that I do. I settled on 16 degrees for my scarf joint and made a little jig out of MDF that rides against the fence of the band saw. I clamp the neck stock to that, buzz the end off (calculating the length to the short point) and, bob's your uncle.

Re: Scarf joint with a tenoning jig.

Posted: Mon Feb 18, 2019 6:03 pm
by Steve Sawyer
Freeman - A jig like yours is what I'd be using if I didn't have this tenoning jig laying around. A purpose-built jig has some advantages. I just like when I find an opportunity to say "that's why I hang onto all this stuff!" :lol: