The most recent episode of “The Woodwright’s Shop” has Roy Underhill and Christopher Schwarz discussing staked furniture. Part of the discussion is how to layout and cut octagonal tapered legs. Just before CW starts the explanation of how to layout an octagon with a compass, Roy pulls out a gauge that he jokingly refers to as a “Octagonizer”. Of course my ears perked up with interest. The gauge seemed to work much like a center marking gauge in that it registered on either side of the stock. The difference being this gauge had two marking pins and established the extents of a regular octagon. Not much more than that was presented in the show and I was left wondering about this gauge. I have several octagonal tapered legs in my future and a gauge such as this could prove handy.
After consulting the Google, I found that this gauge is a common boatbuilding tool referred to as a “spar gauge”. The gauge is used to layout a regular octagon on a spar blank to aid in the rounding process. It is also quite large. Much too large for working on small leg stock for staked furniture. So I did a little more digging.
Turns out the pin arrangement on the gauge is based upon the proportional relationship of the corner of the square that is removed to create the octagon. More in-depth information can be found here. Using the Pythagoras’ theorem, you find that the proportional relationship of the sides and diagonal of this waste corner if, 1 : 1.41 : 1. So with a little math you can make any size gauge you desire.
With this information in hand I sat down at the drafting table and worked out a design for a scaled down gauge for furniture sized legs. This morning I put that design to the test in the shop. I scrounged up a small piece of maple, a couple of finish nails and made myself a octagonizer for laying out octagonal legs for my staked furniture projects.
It’s really simple to use. Place the gauge on the wood and rotate it until the guide pins make contact with opposite sides of the stock face you are marking. Then either press down to create marks or slide the gauge to scribe in the extents of the side of the octagon on that face of the stock. Repeat for the remaining three faces of the stock. Then connect the points on the end of the stock to delineate the octagon. In the photo below I used a compass to layout the octagon and verify the accuracy of my new gauge.
This thing is fast and accurate. You really only need to mark points on one side. Then take a pencil and set your finger gauge to one of the dots and quickly mark all faces of the stock with that setting. If you like to taper your legs before creating the octagon, this gauge will automatically adjust for the taper as you scribe down the stock. How slick is that?
Anyway, of course I made a construction drawing. I included a chart with a few different sizes that will handle varying thicknesses of stock.
I also dipped my toe into the cold, deep, dark video making waters. Depending on feedback and interest I may attempt to put together another video on the making of one of these gauges. Constructive criticism only, please don’t mock my piss-poor video skills. LOL