Time to talk tenons.
I’ve made tenons using 3 different methods, a router with a straight bit, a stacked dado on the table saw, and a tenoning jig.
I discarded the tenoning jig some time back because it was a pain to set up and keep things square. I never could get the miter bar tight but not too tight and keep things running parallel to the blade which made for tenons that were tight on one end and loose on the other. Long tenons were also a problem since the saw blade will only come up about 2-1/2”. Anything longer needed a different approach. It also had limited capacity to handle wide stock.
My biggest reason for not using it is safety. Trying to hold a 3-4’ board vertical and push it through the table saw with the blade sticking up 2” or more was a recipe for disaster.
I usually use a 3/4” or 1” diameter fluted straight bit when cutting tenons on the router table. The wood is removed in ¼” lifts so the bit doesn’t get bogged down and burn. Set the fence so the distance from the fence to the outside edge of the router bit is the length of the tenon and run a test piece through to make sure the tenon length is correct.
Start at the end and work in toward the shoulder to ensure there is open space between the bit and the fence to prevent the bit from binding.
Using the router table also allows me to use the miter bar to keep the board square to the bit as it is pushed through. Index the next cut slightly less than the diameter of the bit so there is a slight overlap. That keeps ridges to a minimum.
Keeping longer boards square and flat as they are pushed across the bit is a challenge. An alternative is to set up a stop on either side of the bit to match the tenon length and slide the board in towards the fence. This allows more of the board to be supported by the table. The key is to keep the piece squared up to the stop as it is fed through the bit.
Alternatively, lay the board on the bench, clamp it down and clamp a guide on the board, then use a hand router.
I generally use a stacked dado set on my table saw to cut tenons. For short tenons, the dado set can be configured in 1/32” increments up to 29/32”. For longer tenons I set up a ¾” stack.
Set the fence distance using the Wixley fence readout. Don’t forget to subtract the width of the dado stack from the desired tenon length when setting the fence.
Using a digital height gauge set the blade height. The way to determine the height is to measure the actual board thickness, subtract the tenon thickness and divide by 2.
For a 1” board with a ½ tenon: 1” – ½” = ½” divided by 2 = ¼”.
Since I cut the mortises first, I use the calipers to verify the dimensions of the mortise and use them to figure out how to set the dado cut height. I also take 1/32” off so the initial tenon is fat and fine tune the height so the tenons are tight in the mortises.
Test pieces are essential. Here is an example of why. Initially, the piece was going to be 1-1/2” thick but was changed to 1-1/4. The dado was set up for 3/8” (6/4” – ¾” = ¾” div by 2 = 3/8”). For a 5/4 board, 5/4 – 2(3/8) = ½”.
To keep from accidentally cutting to much off a side, lay out the cuts on the boards. I also make all of the top/bottom cuts first, then adjust the height for the left and right sides.
If there are slight ledges on the tenon shoulder, a sharp chisel can clean the difference off easily.
Here is the bottom apron. The open space on the top and bottom are allowances for the tenon to spread when the wedge is driven into the end.
Dry fit everything to make sure all of the pieces will fit properly.
-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"