Sunday, December 30, 2018

American Trestle Table - Part III: Cutting Half-Laps for Mortises

The last of the cherry laminated beams is now in the clamps. Hopefully today I will get in the shop to clean them up, plane them square and start cutting tenons.
Danger, Will Robinson! More on that later.
Since I cut a total of twelve half-laps for the six mortises, I thought I'd do a little photo essay on how I did it. It is pretty simple, and hopefully once the tenons are cut everything will fit perfectly and look beautiful.
  1. Too bad it rarely works out that way.
  2. I shouldn't have cut twelve half-laps for six mortises.
The key to getting these to line up perfectly is to be accurate with your layout of the joint. I did everything in pairs: two half laps, which I then glued up to make a laminated beam with a mortise, followed by the next.

I marked where the lines should go with dividers in order to eliminate measuring mistakes, used a marking knife to make a line, deepened it with a chisel and notched out a triangle of wood where my crosscut saw could sit to start the cut.

Once the ends of the lap were defined with the saw, I made a few relief cuts to aid in chopping out the waste in the middle.
Two precise cuts, and a few eyeballed relief cuts in the middle.
To rough out the waste, I start by using a chisel and a mallet. I only go half of the depth required at first, to see how the wood is going to behave. The first chopping goes down a ways, but not all the way through. I'll turn the piece over and do the same from the other side to avoid blowing out wood on the other side, which might show on the final piece.
Halfway in and halfway down.
After knocking out chips from the whole width, I go back and move my chisel again to the 1/2 way mark. Since this is half of the half, it is a little lighter of a cut.
Move the chisel back to take about half of what's left.
I keep going back 1/2 of the remaining thickness as long as I dare, then I get really close to the line and make an angled cut to add a bit of a chamfer that will hopefully help avoid blow out later.
Roughing out a bit of a chamfer to help later.
Now, I turn the board over and do it all again.
Second time, same as the first.

Here's what it looks like when I'm ready to move to the next step.
Using a mallet on a chisel to bash out waste like this is efficient for rough waste removal. What I do now is use the chisel with hand pressure only to knock down some of the high spots, which will save time with the router plane. If I'm not using a router, I will do this part very carefully, checking my work often, until I am down to the lines and everything is square.
Chiseling across the grain with hand pressure only to refine things a bit.
Make sure to keep all of your body parts behind the pointy end for safety. For control, you can hold onto the chisel with your off hand to guide the cut.
Guiding the cut with my off hand.
When I'm as close as I dare, I finish off the joint with a router plane. We've saved a lot of time by roughing out the joint to this point with a chisel, and this plane is going to flatten and measure everything to perfectly flat for us.

Take light cuts with this tool, it should be thought of as a fine finishing tool for joints like this.
The end result should look something like this:
Feeling pleased with myself only lasted an hour or two: I exclaimed a profanity while sitting on the couch watching TV with The Frau later that evening. It only then dawned on me that the feet only were to get this kind of joint, the braces at the top were supposed to get a bridle joint.

The bridle joint allows the grain of the leg to appear to go all the way up to the table top, leaving room for your eye to see the mortise for the trestle by itself.

Structurally, the mortise and tenon on the top brace will be fine, but now the mortise and tenon for the trestle will be right next to the now visible joint for the cross brace.

I'm committed now, since I have no more cherry on hand to do the braces over again. We'll see if I get that far before I have to leave again for Spain. But, in the end, it is a small detail that might not look too bad. We'll have to see.

I can always paint it like I originally planned.


  1. Replies
    1. Thanks, Ralph. Indeed it will. Hopefully I won't have to resort to that, but it was the original plan.

  2. Ups!
    Been there.

    Drink some champanhe and you forget it until next year, LOL

    Have an Happy New Year - or at least a good party!

  3. If I understand the issue properly, at least it's at the top and under the tabletop so won't be seen. But you'll know ...

    Happy New Year to you and yours.

    1. Hey Matt, thanks for the comment. You are right. It's a pretty small issue, I think it will look fine when it's done. However, there's nothing that says I can't do it over if I don't like it. :)

      Happy New Year to you, too!

  4. Brian,

    Nice work and a good tick tock of cutting the joint. The forehead meets palm moment is all to familiar.


    1. Haha, thanks Ken. I think I'll give myself a concussion one of these days.