Spar Gauge

Instructions

This is a spar gauge. It is used to help guide the process of turning square tapered parts to round. It is used to mark out the arrises of an octagon on square tapered parts. These marks are used as a guide for making that square tapered part into an octagon. From there it can be more easily shaped into a round tapered part. I like using hand tools to do the shaping like a small drawknife, spokeshaves, curved card scrapers and cloth backed sandpaper. I made mine in a hardwood from a blank that is 5" long by 2" wide and 3/4" thick. Mill this out in the typical fashion. I placed it on my workstation with the long narrow edge facing up. (See photos) You can use just about any cutter size that can cut to a depth of at least 1". Cut the "notched" side first. I cut the outer “arrow” shapes first with auto pass to full depth. Then I cleared out the center notched area next with auto pass to full depth. Since this is an inside cut I use a large offset so that it clears out the very center initially and then the final pass cleans up the rest. To make the pencil holes I helix cut the holes as deep as my cutter will permit. It’s nice to use a 1-1/2” cutter for this. The size of hole is 9/32” which fits a typical hexagon shaped pencil. The “Shaper” logo pencils are a little bigger at ~5/16”(8mm). You can use a negative offset to make the hole larger. Make it a snug fit so creep up on the final size and test. Flip the part, while keeping the same reference edge, to cut the rest of the pencil hole through. I like to make sure my pencils can’t slip out so I make a couple of pilot holes for some common drawer slide hardward/cabinet screws. Use what you have since it doesn’t need to be specific. I have included a cut file for that but honestly its probably easier to just drill it by hand. To use the spar gauge you place the notch over the square part and angle it until the tips of the “arrows” contact the sides of the part. While keeping them in contact with the sides slide it along the taper and let the pencils mark the top surface of the part. Repeat this process on all sides of the part. Use any tool you prefer to remove the corner material between the marks. This will result in making an 8 sided part.