|Project by DHS||posted 10-19-2012 10:21 PM||5563 views||15 times favorited||6 comments|
My mortise and tenon joints were a little sloppy and I began to think about how to build a tenoning jig that would improve the fit of these joints and speed the process of cutting them as well. Like other tenoning jigs, this one slides along a table saw rip fence and the workpiece to be tenoned is clamped vertically. However, the jig has two parts connected by rails (second photo) so that the jig position can be adjusted laterally. The trick to this jig, however, is the tenon fixed to the lower part and protruding through the opening in the upper part. It is the same width as the mortises I usually cut. (I cut mine with a 1/4-inch end mill.) This tenon (and the fence and kerf spacer just to the right of it) allow you to cut a tenon to fit precisely into a mortise that you’ve previously cut. If the two workpieces to be joined are the same thickness and the front faces are facing the same direction when clamped to the jig, the tenon cheek cuts are determined by the dimensions of the mortise.
Clamp the workpiece to be tenoned to the jig with the front side facing to the left (away from the jig). Adjust the jig so that the jig’s tenon is even with the front face of the workpiece with the morise (third photo, left panel) and lock it in place with the handscrew. Position the table saw fence so that the blade just touches the front face of the workpiece to be tenoned (fourh photo) and lock it in place. Now, slip the workpiece with the mortise over the jig’s tenon, slide the jig back toward you along the fence (so the blade is no longer abutting the workpiece to be tenoned), and then adjust the jig laterally so that the jig’s fence touches the workpiece wih the mortise and lock the jig in position with the hand screw (third photo, center panel). Cut the first tenon cheek. Now, remove the workpiece with the tenon. Flip the kerf spacer (this is the same thickness as your table saw blade) out of the way, and adjust the jig so that the jig’s tenon is flush with the jig’s fence (third photo, right panel). Cut the second cheek.
Now this sounds complicated when explained in detail, but the operation is really pretty simple. You just use the morise you’ve already cut to line up the table saw fence and then use it again to line up the cuts for both tenon cheeks. You can fine-tune the jig by adjusting the thickness of the kerf spacer. Since you use the mortised piece to determine the position of the tenon cheek cuts the jig will always line up the mortise, tenon, and both faces. And, its fast and pretty darn accurate.
I have searched the internet and the woodworking literature for a description of a jig like this, but have not found one with this design. I think it is unlikely that I’m the first to dream up a tenoning jig that works this way, but I’d like to know if any of you have ever seen a tenoning jig with this kind of alignment system.
I posted a new photo of the jig from a different angle in response to comments that my explanation was not entirely clear and that more photos would help. I also experimented some more with the jig and realized my first description of its operation is not quite right. Think of the jig this way – It’s like a box-joint jig on top of a tenoning jig. This means you can use it to cut single, or double, or even triple tenons that match previously cut mortises. To cut multiple tenons (or one tenon for that matter), you cut all the left cheeks first, reset the fence and then cut all the right cheeks. In more detail, line up the left side of the tenoning-jig tenon with the left side of the piece with the mortise (photo three left panel). Then, adjust the fence so that the left side of the piece to be tenoned just touches the right side of the table saw blade and lock the fence in place. Slip the mortised piece over the tenon and adjust the jig to the left (photo three center panel) and cut the first cheek. If you want to cut a double mortise, repeat this procedure with the next mortise. To cut the right sides of the cheeks. adjust the jig so the jig’s right side fence touches its tenon (photo three right panel). Adjust the table saw fence so that the right side of the table saw blade just touches the jig and lock it. Flip the kerf spacer out of the way, insert the mortised workpiece over the tenon, slide the jig’s fence against the piece with the mortise, and lock in place.Cut the right cheek. Repeat with the next mortise if cutting a double tenon. Adjust the fence to clean out the material between the tenons. Cut your shoulders. Done.
-- Dave S., Bellingham, WA