Wednesday, April 7, 2010

Measure Once, Mark Twice

Relative dimensioning is a very important concept. When I make my design, I know that my final product will not have exactly the same dimensions as my design. No one cares if the side stretchers are exactly 18", or if they are 17 61/64" long. The eye will not notice this. The eye will notice gaps however. This is why I measure once, and mark twice. First I measure out the distance between tenon shoulders for the left side stretcher (18"), and then I lay the right stretcher next to it and mark a line next to where I just marked. This way, I have two stretchers with the critical dimensions identical. I do this for most of my components, usually measuring once with dimensions from my plan, and then transferring these marks to other components. When you are doing this you must keep track of your reference faces, and only reference off them. This will ensure consistency. A reference face is a part of a board (ex. the face, the edge, the end) that you know is exactly flat and square to the other reference faces on the board.

Using the techniques explained above, I got a lot done on the table. I started with the legs, sawing them out, and then planing them down to 1 1/2" square. As you can see, I didn't notice a large crack in one until I cut it out, which annoyed me because it's a lot of work to cut them out.
The leg to stretcher joinery is fairly straight forward, it's all mortise and tenon. To make the tenons, I tried out a new method. First mark a heavy line for the shoulder. Then pare away some material to make a vee groove. This makes a very clean shoulder line when you go to make the crosscut shoulder cuts. The line for the shoulder is transferred all around the stretcher (remember to only use the reference faces to reference your square). Then I make the shoulder cuts and chop out the bulk of the waste with a chisel.
After the waste is chiseled out almost to the line, I switch to the router plane and make light passes to reach the line. This is one exception when you can work off a face that isn't a reference face. To cut the back of the tenon (on a non-reference face), you can reference the router plane's sole against the face, because the tenon will be trimmed again later.

This makes a very nice, consistent, and square tenon.The mortises in the legs are drilled out and cleaned up with a chisel.

1 comment:

Gye Greene said...

Niiice router plane! :)