Isla’s Bed – Tenons and End Panels

With the mortises complete, it is time to start on the tenons. Now is the time that careful stock prep and thickness planing will start to pay off.

The cross rails for the head and foot boards require tenons to fit into the legs. When making tenons on long pieces such as these, my favorite method is to use the radial arm saw (RAS) with a dado blade set mounted in it. As with many tenoning operations, having stock with consistent thickness is paramount. Any variation in thickness shows up as a doubling of that error in the tenon. So this is the reason that all of the stock of each thickness that will get tenons be planed at the same time with the cutterhead securely locked. If you are fighting planer snipe then make your rough cut stock long enough to be able to remove the snipe section when cutting to length.

Prior to cutting the tenons, the stock is cut to finished length with an allowance for the tenons. I set the work stop to meet the end of the pieces. The stop needs to be thick enough that it will also work when making the cuts on the rotated stock for the rails. I generally use scrap wood for the stops when cutting tenons. Once the tenon length of cut is set, use 2 clamps to secure it to the RAS fence. With just one clamp, it is easy to slightly push the stop with each piece and end up with inaccurate cuts. Having 2 clamps makes for a steady and rigid stop

Cutting the tenons on the vertical slats

When setting the depth of cut to adjust the thickness of the tenons, the backlash (a.k.a. slop) of the elevating mechanism shows. This is a problem whether using the RAS or a table saw. However on the RAS there is a relatively easy fix. That is to add a digital gauge (basically a digital caliper without jaws) to the column to track the height. The brackets are ordinary aluminum extrusions you can get at the hardware or big box store. I added this a number of years ago, so the exact model is no longer available, but there are suitable replacements listed in the Parts section. In addition to this you will need a digital caliper to measure the mortise width and tenon thickness. Basically you subtract the tenon width form the mortise width and then divide by 2. This is how much you need to raise or lower the saw. Just add or subtract the amount from what is shown on the display when you made the cut and move the head until you hit that number. No need to zero the caliper (and mine won’t 0 any more anyways). If you need to lower the saw (tenon is too thick) you must account for the backlash in the mechanism. Easy – Lower the saw until you hit the number you want, crank one more turn down and then come back up. Now the backlash is taken up. If you dont do this the saw will “walk ” down taking up the lash with each cut and result in too thin tenons.

Digital height gauge on the Radial Arm Saw
Top mounting bracket for the digital height gauge

The rail tenons must be rounded to match the mortises. I use a Japanese style pull saw for the saw cuts and chisel to knock off the corners.

Rounding off the tenon corners

Now that the rails have tenons that fit the legs, measure the exact distance between the top and bottom rails. Add 1″ to this and you have the length to cut the dividers. To fit the rails

The next step is to make the dadoes in both the rails and the dividers which will hold the panels. I use a “wobbler” dado head in the table saw for this. The reason being I can leave the stack dado set on the RAS while I make these cuts as the divider tenons will come next. Wobbler dados have fallen out of fashion and can be had cheaply on ebay or craigslist. Mine is an 8″ 2 blade Excalibur that was originally ~$180 that I picked up like new for $35. The shortcoming of these blades is the dado bottom is not flat except at one particular setting (often near 3/4″). However, for these cuts the dados are all hidden and it does not matter. Set the dado blade somewhat smaller than the thickness of the panels (mine were 0.48″). Given that all of the dadoes are centered as I mentioned earlier, you can make every dado in 2 passes, flipping the stock end for end between passes for a perfectly centered dado. Now, it is a matter of finely adjusting the saw fence to get the width right for a smooth sliding fit on the panels.

Test cuts being made to set the tenon width. This is a scrap of the cross rail stock.

This is a perfect use for your cut off scraps from cutting the rails and dividers to length. It does take a few tries (I average 5-6 ) to get right. Be sure to use a feather board to both hold the board tight against the fence and protect your fingers. Better yet use a “hold down” board clamped to the fence as well as it is easy for the piece to lift as the dado is cut causing trouble during assembly.

Cutting the dadoes. Note feather board and vertical stop block being used.

Test pieces accumulating

The process is repeated for the dividers. Dadoes are cut on both sides and the tenons are cut to length and width to just fit in the rails as they are mounted in the legs.

The panels are cut to fit the openings with 1/8″ clearance in each direction. Now it is time to dry assemble the head and footboard and adjust the tenons as necessary for a good fit.

Foot board dry assembly

Head board dry assembly

The side rails need mortises cut to allow the bolts to be inserted and tightened that connect the side rails to the legs. For the beds I had built in the past, I have used a template and plunge router. However, it is much easier to do on the CNC router.

Side rail tenon to fit the leg and mortise for the bed bolt that secures the side rail to the leg

To see the video of the CNC router cutting the mortise above, see:


6″ digital readout with remote display :

6″ vertical digital readout: