Learn how to make a scribing tool.
As a follow-up to my last article, A Better Way to Scribe, this article shows how to make a scribing tool. All that is required to make this scribing tool is a scrap piece of wood, two 1-1/2” long 8-32 machine screws, two washers and two knurled nuts. If you would like the exact dimensions that I used, you can download a dimensioned drawing in PDF format. Alternatively, you can use your own dimensions and shapes to suit your needs when you make a scribing tool.
1. Mill the blank – Start by milling a straight, square blank to create the scribing tool from. I chose maple because it is hard and durable. The accuracy of each preceding step depends on the accuracy of the blank so make sure it’s dead-on straight and square. The blank should measure 1” thick, 9/16” wide and 10” long. It’s a good idea at this point to make a couple of blanks if you have the spare material, that way if you make a mistake along the way you can easily make a new piece.
2. Cut to length – Cut the three sections of the scribing tool to length. The reference leg should measure 4-1/16”, the middle section 2-13/16” and the marker arm 2-3/16”. A cross-cut sled on the table saw works well for this along with some hold-down clamps to keep your fingers far away from the blade.
3. Lay out holes, joints & tapers – Measure and mark all the center points for the holes as well as the defining lines for the half-lap joints. A marking gauge set to ½” works best to mark out the lines for the faces of the half-laps. Also mark the lines for the taper on the reference leg.
4. Drill holes & countersinks – Drill a hole in the end of the marker arm to match the marker of your choice. If you use a short Sharpie, a 3/8” diameter hole works well. The Sharpie has a taper on the body so the further you push it into the hole, the tighter it gets. Drill the screw holes in each section to match the diameter of the hardware you are using. The holes should be just big enough so that the screw passes through but not so tight that it threads into the wood. Also drill a countersink at the bottom of the holes in the reference leg and the marker arm to match the size of the screw head. Using a drill press and brad point bits for all the holes will make them more accurate.
5. Cut tapers – Cut along the two lines drawn earlier for the tapers on the reference leg. The bandsaw works well for this followed by a block plane to smooth the cuts and keep the tapered faces flat.
6. Cut the joints – With the small size of the parts, the safest way to cut the half-lap joints is by hand. Use a fine hand saw to cut along the waste side of each of your layout lines. After you’ve finished cutting each joint, finish up with a chisel taking light paring cuts until you’ve reached your layout lines. Using the chisel to finish up gives you smooth, accurate surfaces for the scribing tool to pivot on.
7. Radius ends – Form the 9/32” radius on the ends that require it. Using a stationary belt or disc sander is a quick and easy way to achieve this.
8. Chamfer corners & form finger indents – Ease all the sharp corners of each piece to make the tool more comfortable to hold. Either a block plane or sand paper work well. Depending on how you intend to hold the scribing tool, you can form finger indents with a drum sander to give your fingers a place to register.
9. Install hardware & assemble – The final step is to install the hardware and assemble the tool. Epoxy the heads of the screws into the countersunk holes to prevent the screws from turning when the nuts are tightened. Once the epoxy has cured, assemble the tool and place a washer and knurled nut onto the end of both screws.