The Holtzapffel Project #7: Constructing the base: lots of big mortises and tenons

With the top in good shape, I went back to constructing the base. I previously milled and glued up the thick (3.5” x 5”) legs. Milling and gluing up the stretchers was more of the same, so I didn’t get any pictures of that process. I made the long stretchers by gluing up two boards, one of which was 3” longer on each end to make a ready-made tenon. For the end stretchers I decided not to use the ready-made technique since I wanted to try out a new Freud dado stack for the tenons.

The next step was mortising the legs. I laid out the mortises for the long stretchers by laying the ready-made tenons on the legs. I decided to add edge cheeks and shoulders to hide the mortise a bit, so I inset the layout lines for the mortise a half inch in on the top and bottom.

I used a router and a 1/2” up-cut spiral bit to hog out the mortises. I used an edge guide and some clamps as stops. This setup worked ok, but the way my edge guide worked I had to reset my stop clamps when I moved the edge guide in and out. This was a major pain. It also would have been nice to have some way to fine adjust the edge guide. I probably won’t be making 1.25” wide mortises (requiring 3 passes) again any time soon, so I’m not in the market for a new edge guide yet, but I’m sorely tempted.

On the other hand, the shop vac did an incredible job sucking up the waste. The slight loss of visibility was well worth using the shop vac and dust collection attachment. Here’s a picture that I took right after finishing a mortise. No dust! I hadn’t realized that this attachment came with my router until now. What a fantastic attachment.

After routing all the mortises, I squared them up with chisels. Here’s one of the mortises for an end stretcher.

With the mortises made, I made the tenons for the end stretchers and reshaped the tenons for the long stretchers using the dado stack on the table saw. While I was able to make very fine adjustments and creep up on the right depth of cut to fit the mortises, I hated having sawdust thrown back in my face. I quickly learned to put a respirator on when doing this. I don’t know if this will be my preferred way of making tenons. The amount of sawdust created was probably a function of the XXL size of these tenons, so maybe it won’t be as bad on normal sized tenons.

Here’s a picture of the end assemblies and long stretchers. I used the drawboring technique to pin the tenons. I did some practice joints with some store bought dowels and found out that they were oblong and left nasty gaps in the finished joint. I decided to spring for the Lie-Nielsen dowel plate that I saw Mike use in his construction.

Basically you just pound a piece of wood through the hole to make the dowel. Here’s a case where I ended up with a bad dowel. Two faces on the square peg are not being cut by the dowel plate, so it didn’t create a nice round dowel. You really want the wood to ‘bloom’ all around the hole in the dowel plate as you pound the peg through.

Here’s a picture of the biggest mistake I’ve made so far in putting together this bench.

I had to shim the tenon on the bottom there, because as I was fitting the tenon I removed material from the wrong cheek. The really bad thing was that as I was doing this, I kept checking it by reinserting the tenon in the mortise and the faces of the leg and stretcher weren’t flushing up. So I kept removing material from that same cheek! ARGH! I didn’t realize my mistake until I had already removed a little more than a 1/32nd of an inch.

So, with the base together, it was time to attach it to the top. After maneuvering the base to get the front face flush with the edge of the top, I traced out the tenons on the top.

I laid out the mortises on the back side a little oversized to handle wood movement of the top.

Here’s my last mortise. I was glad to be done with routing and chiseling these bad boys.

The moment of truth! Is it going to fit?

Yes! It fits!

Okay, it didn’t really go in all the way the first time. I had to wrestle the base out of the mortises and do some tenon trimming a couple of times before it went in smoothly. But it sure was a good feeling when it all came together!

This was quite an exercise in making mortise and tenon joints. I learned a lot from my mistakes and I’m sure making mortise and tenons for normal sized furniture will be cake compared to this.

-- Kevin