Need to lay out an arch? You’ll need some trammel points and a beam of sufficient length. After a survey of what was available to buy I decided to make my own.
Why three? Most simple arches can be formed with just two. Approximations of ellipses, the so called “bricklayers arch” similarly use two. If you want to draw true ellipses though, you’ll need three. So go ahead and make three and thank me later, haha.
I recently had a chance to read both Hasluck’s “Carpentry & Joinery” and Collings’ “Circular work in Carpentry and Joinery”. They’re both excellent texts and Hasluck’s stuff is in the public domain, so go treat yourself to a bit of free knowledge if you care to understand a bit better what modern carpentry has been reduced to.
The wedge and point sit in a gentle sliding dovetail, which keeps things from popping out of place. Both are contained within the long grain of the vertical clamp side. I used a thread box to cut the threads for the screw and tap the threads. Really, they’re just made out of a little scrap I had lying around. The points are 1/4″ mild steel.
I was asked recently to cut an arch-top molding for the inside of an entryway door. Its no small feat, really the domain of specialized shaping machines in custom mill shops. I’ve seen a tilting router setup that can do some decent profiles in a home shop, but how did the carpenters of old make this stuff before shapers and profiled knives? Radiused hollows and rounds of course. A look at carriage makers planes is very instructive.
The layout for the molding I have to cut wasn’t one listed in the books I have, but follows a standard model that I was able to deduce once back home in my shop. Fun stuff!
As an aside, have you ever noticed how much Mentos “The Fresh Maker” candy look like bi-convex go stones?