Tuesday, February 5, 2008

Jointing for Seats

In an earlier post, I describe the technique that I use for aligning the grain when jointing for a seat blank. Of course, it's nice to avoid having to use anything but a single plank, but in this day of increasing scarcity, making invisible, solid joints is a good skill to have. Here is the way that I orient the grain so that the grain looks fluid on the carved surface.

Most of the difficulty in getting a perfect joint is going to be eliminated at the sharpening station (you're not suprised, are you?!). After much trial and error, I learned that the key to easy and true jointing is a dead flat plane iron. I carefully flatten my stones, which is the key to getting a flat edge, on drywall sanding screen and plate glass. Then I grind the edge carefully until I can hold a flat tool against it and see no light pass through, as show below (there is a window directly behind the blade).

Then I carefully hone the edge. As you can see below, the mirror finish should give an undistorted reflection right up to the edge. We haven't gone anywhere near the wood, and already the important part is over!

I've made a video of the technique that I use. The problem with most jointing, like honing, is the tendency to create a convex shape. With a plane iron, we use a hollow grind to give stability and to fight this natural tendency. I use the same principle for jointing the edge of a board. By creating a very slight hollow in the middle of the board, the plane will ride on the high spots and only cut on either end. When the plane takes a full length shaving of even thickness, I know to stop, and the board is truly flat.

It is of course vital that the pressure on the plane is always over the board. If you put pressure on the part that overhangs in the beginning or end of the stroke, you can round the edge.
If the process doesn't work the first time, simply take a couple of shavings from the middle of the board and try again. Honestly, without a properly flattened plane iron, I cannot do this, so if you have trouble, look to the blade. Below is the unclamped joint. It should sit snugly with nothing but gravity. Good luck!


tko said...

seeing your miiror finish on the plane iron put me in mind to ask... canyou creat a video of your drilling set-up for seats?

rocking R rustics said...

I just bought a set of router bits for making raised pannels, and it came with a bit for making a glue joint. Do you have an oppinion of them over the jointed joint?

Peter Galbert said...

I think that Jean Francois might have a posting on his blog about the mirror set up. I will make a video soon.


I am not sure about the bit you have, but I do know that the more glue surface that a joint has, the stronger it is. However, if the boards aren't dead flat to begin with, the router bit won't correct the poor joint. I find that a dead flat glue joint is always stronger than the wood.

Anonymous said...

Sunweave chairs is also like this product. It is easy to assemble.