Thread: A new mortise gauge

I have made several sets of marking gauges over the years, each set getting a little fancier as my skills & access to equipment improved. A few years ago, I made a mortising gauge based on the Stanley 78/79 principle, where the moving point sits in a dovteailed slide adjusted by a screw. These are considerably easier to set than the more basic model, which has a slide that you adjust with finger pressure. This gauge has served me very well, but I have always nursed this desire to have a go at making a gauge based on the 77, which has an internal slider adjusted by a captured screw. The advantage of this system over the 78/9 style is that the knob stays in position while the slider moves internally - it doesn't screw out past the beam like on the 78 and 79, making itself vulnerable to accidents.

The stumbling block was the cross-shaped slider, and I entertained several ideas on how to make it, each of which semed a bit cumbersome. Then a couple of weeks ago, the solution hit me squarely between the eyes. It was simple & obvious, & I have had all I needed to make it ever since I started slitting bras saw backs a few years ago! With the slitting jig made for the saws, I was able to cut out the shape I needed from a length of 3/8 x3/4" bar easily & accurately (pic 1).
pic1.jpg
Two short lengths were then cut off for the end pieces. Drilling an accurate hole through the remaining 75mm bit took a lot of care & sweat, but I managed to get it close enough. About 15mm is tapped for a 5mm thread, and the remainder bored out to clear the screw. I then threaded a brass rod, and turned the end down in two steps - 4mm to go through the rear end piece, and 3mm, which was threade to take the knob which captures the screw (pic2).
pic2.jpg
The two cheeks of wood for the beam had to be grooved, which I managed accurately enough on an inverted router, then clamped it up with the end-pieces & drilled for the rivets which will hold it alltogether. Before assembly, I drilled holes in the brass for the marking points and silver soldered them in place. I discovered during that step that the metal in drill bits will NOT silver-solder. In the end, I made points from the tang of an old needle file. The tang is soft enough to work with a file in its raw state, & after I had shaped the metal to 1/16" diameter, I hardened it, then ground the points & soldered them in place.

Assembly was pretty straight-forward, but made a bit more difficult because I decided to bed the end pieces in epoxy as an added fastening aid. That was awkward enough, but my first try failed, because I stupidly cut the cheeks to length, and when I tried to pein the rivets (bronze welding rod) I propmtly split the wood. So nothing for it but to start over, this time leaving 20-25mm extra , and trimming after assembly.

The fence of my new gauge is a little wider than on my old gauge, because the one thing I felt could be improved on it was the width of the fence, so it is 66mm wide instead of 50, Doesn't seem like much, but it makes quite a difference in some situations. Here is the finished gauge with the old one (pics 3 & 4).
pic 3.jpg pic4.jpg.
I made the beam 165mm to keep it more compact - can't remember what length it is on a 'real' one, but I recall it as being shorter than the 200mm beam on my old gauge. I have never needed more than half the beam length on the old gauge, so I decided to keep this one shorter....

Cheers,