Table Base Joinery: Friday Update
Last week I talked about the problems I ran into with the base and my plan to overcome. This week I constructed the base, hand fit joinery, and started the final detailed phase of this project.
The Base
A few firsts this week. One, angled mortises. Two, straight mortises on a tapered piece. Three, an inlaid base. Let me explain.
Angled Mortises
The base is a trapezoid, it has angled sides. That angle is 10 degrees, which is funny because it’s really 80 degrees, but we woodworkers work off of 90, so it’s 10 off 90.
I knew I wanted the tenon to go all the way through the top plate for extra strength. That way the pressure pushing down, trying to make the legs slip out from under the table would wedge the tenon in its mortise making the joint extra sturdy.
But that also meant I needed a long tenon so it had to run with the length of the board.
It also meant the angle of the mortise needed to be in line with the angle of the leg. I had never done anything like that before, but I have made through mortise and tenons with a router. I used the same process, but with a lean.
I put a board under one side of my router until it leaned at exactly the right angle. Then I screwed the board on to the base. Now as I plunged down my router bit would cut at a 10 degree angle. All I had to do was slowly and methodically plunge little by little out of the mortise until all four were done.
Straight Mortise on a Tapered Piece
This could have been avoided entirely had I followed the golden rule, think ahead. Last week I mused about my wormy wood and avoided it entirely by cutting tapers on the legs. That decision came back to bite me, not because I shouldn’t have done it, but because my legs were now at an angle and not all exactly the same angle which meant added complexity in tenoning.
I opted to use my miter gauge set to keep the end of the board flush with the sawblade which cut a straight line through the piece. Then removed material until done. The problem was I had to reset for each side and each piece to ensure the angle was consistently straight for the bottom of the mortise, otherwise the leg wouldn’t sit flat on the ground.
A simple mistake, a relatively easy fix, but extra time added I could remove on my next go at it.
Inlaid Base
Here’s the big, rectangular hole in the slab. That hole is a big mortise for a tenon, the table base top.
I haven’t done this nor have I seen it done on YouTube.
Rather than simply plopping the base on the bottom of the table and screwing it in place I went for an elegant approach.
I created a groove all the way around the base top plate. Then I created a channel in the bottom of the slab the same width but slightly longer than the new size of the top plate.
Essentially, I created a mortise and tenon with room for wood movement across the slab. The base is now secured in the slab without fasteners, but I’ll add threaded inserts and bolts because I’m a belt and suspenders kind of guy.
I am worried about racking, longways on the table if someone pushes themselves back using the table for leverage the table could rock, or rack in woodworker terms.
As the table racks the bolts and threaded inserts will loosen and as they loosen it will get worse. But if the base is in a mortise it has extra lateral strength because the walls of the slab mortise are up against the walls of the tenon (aka cheeks) and the shoulders of the tenon are on the face of the slab giving the inserts and bolts extra support to resist the rack.
Those are good enough reasons for me to overkill this table and put in the extra work to make it perfect. It’s one of those details you’ll never see, but a detail that will make this table stand for over 100 years.