Wednesday, March 25, 2009

Irregular Situation III

The next steps in the process of making the irregular sawhorse were the legs. Determining the diamond-shaped profile for a leg which slopes differentially took a fair amount of head-scratching and multiple contacts with Togashi-sensei, as mentioned in the first post in this thread. There were several drawings involved, and they get a bit complex - here's a stripped-down illustration, showing in red the shape of the leg required:

You might notice that the corners of the leg do not meet the diagonal axis line of the piece.

With the shape determined, I set about preparing the rough stock, in some lovely dense Kootenay-region Douglas Fir, and then making a sled to process the leg shapes in the planer. The jig is essentially two pieces of MDF connected with a piano hinge:

The wedges can be seen protruding from one side. These wedges are made as precisely as I could make them. I then made up another MDF jig to fix the blank from which the wedges are cut:

Here I'm running the wedge-maker jig through the table saw:

Once the wedges are made and the sled configured, I do a test run on some scrap stock and check the results carefully, then adjust the jig as necessary. Then I run the legs through the planer, one round for one side, then I run the leg through the planer without the jig to make a pair of parallel faces, then the jig is reset with new wedges, and the complimentary faces are processed:

With a different amount of angle requiring removal from two different faces, and only a slight difference between the angles, it would be easy to get confused, so I mark the end grain of the legs before planing to keep everything in order:

The legs came from reclaimed stock, and I chose to patch one of the more egregious flaws - which happened to be right where a through tenon would emerge. Here is the patch after gluing but before final planing:

Then I lay out and knife the legs for the stretcher (nuki) mortises, along with the bottom cuts and top cuts, and of course the top tenons:

Then I chop out and pare the mortises, cut the feet, and rough cut the tenons. After all that, I then finish plane the legs:

Then I chamfer the arrises:

Here's the beginning of the processing of the tenons on the tops of the legs, the rips of the side tenons done on the table saw with a tenoning jig:

The arrows identify the outside corner of the legs - it's important to take extra steps to avoid confusion - this I have learned by experience.

--> go to post IV

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