Back when I made this marking gauge, I thought I pretty much had it all figured out with the mistakes I made there (see the bottom of the post). But it turns out that one of them was kind of unresolved; how to get the arm to have no play whatsoever (as it was, the arm would swivel a little horizontally because its hole wasn’t a perfect fit). I’d thought of a bunch of stupid ideas, from making the arm trapezoidal to mounting the tightening screw diagonally, but mostly, I forgot about it because it still “kinda” worked and that’s all I cared about.
Then when I was milling the frame components for the new nightstands v2 project, I needed more than one gauge, so I grabbed one of my old Stanleys and noticed that the arm didn’t budge at all. Neither did my other old Stanley. Both of these were rectangular-like arms tightened with a screw from above, like the one I’d made. What did they do that I didn’t?
I flipped them over and found the answer.
The bottoms of the arms are slightly convex and the hole in the marking gauge stock is slightly concave. The gauge on the right is a Sweetheart-era Stanley and is a really good fit.
Upon realizing this, I immediately knocked the wedge and blade of out the arm of my shopmade gauge, pulled the arm out of the stock, and used my Taiwanese shave to put a slight radius on the bottom of the arm. Then I put a rasp into the stock and made a mating surface, and the result looks like this:
The fit doesn’t look terribly appealing to the eye, but doing just this much instantly solved the problem, and I’m really lovin’ this gauge now. At that point, I figured that I’d better get back to milling rather than try to make this dorky tool look better. That was a couple of days ago. I finally got around the taking the photos today. It took about five times as much time to take the photos and write this post than to actually fix the problem. Peh.
(And maybe someone else out there has already figured this out and posted something that I haven’t read.)
[Edit (17 June 2011): OK, so I finally bought The Anarchist's Tool Chest by Christopher Schwarz, and unsurprisingly, on page 118, he talks about this problem. His solution is to do the wedge-jams-the-arm-into-a-corner thing. That works, but he gives short shrift to thumbscrew-tightened models, which is, of course, an injustice, because they work fine after you do what Stanley (and whoever they stole the idea from) did. Also, he says that the thumbscrew is knurled brass. Well, I couldn't source any brass for mine, and a lot of new ones sure aren't solid brass, if they contain any at all. I think a wooden thumbscrew is best (Stanley used these), but I don't have a tap and threader, so I couldn't do this. Anyways, it's another datapoint.]