Saturday, August 4, 2012

Adjustable Mortise Gauge

With the wooden thumbscrew finished I turned my attention to constructing a much needed adjustable mortise gauge. The style I decided on has two adjustable beams with a nail inset in each end to act as a scratch awl. With this design I can adjust the width of the mortise as needed and I am only limited by the length of the two beams. Another feature I feel is a must when using a thumbscrew is the captive pad, it prevents the thumbscrew from marring the beams.

The wood for the gauge is from a white oak beam I salvaged from a barn that was built in 1867. It has a wonderful caramel color and is quite dense.  I am very happy with this tool.

When tapping threads in a piece of wood the same rules apply as making the screw. Use fine grained wood. Normally I would not use oak, but as mentioned earlier this oak is very dense and hard. I’m guessing it has to do with either the age or it could be that I counted 32 growth rings in the small section that makes the head. This tree had to be well over a hundred years when cut down in 1867.

The hole for the tap has to be straight and smaller than the diameter of the screw. If you buy a threading kit it should tell you what size drill bit to use. I just practice on scrap to make sure it’s the correct diameter and tap that before using it on my project. With this oak I used my post drill to make sure the hole was straight. Post drills are really more for metal, but I don’t have a drill press so I used it. When I made my slitting gauge I used an auger bit and just eyeballed the hole and got it straight. I think that was more luck than skill.

I used linseed oil to lubricate the tap and I ran the tap through it a couple of times. One side note; the linseed oil made the threads swell up and the screw would not fit at first. After an hour the wood soaked up the oil enough that the screw worked with no problem.

Below is a pic of my most useful marking gauges. This is strangely part of my bucket list. I want to construct as much as possible all of the tools of an eighteenth century carpenter and joiner like the Dominy’s. Then I want to build a small cabin using those tools and outfit it with the ironwork and hardware from my forge. Kind of strange I know, but I’ve given up on the idea of getting a job at a living history museum (there hard to find)  so I guess I will make my own.