Sometimes you need to trace the pattern of an irregular surface. Nothing comes in more handy for this than a contour gauge. Here I'll show you how to make a large contour gauge, but the principle can be applied to a smaller one.

Step 1: Tools and Materials

Tools

Saw
Drill and bits
Ruler

Materials

¾" x 2" hardwood cut to a length you choose (I'm using 23" long maple)
½" x ½" hardwood
⅛" x 12" dowel (you can make your own with this dowel making jig, but I want to enter this in the Handtools Only contest so we'll assume that we're buying the dowels)
Felt
Glue
2 ea. carriage bolts (I'm using ¼-20 x 2½")
2 ea. washer
2 ea. wingnut

Step 2: Cut Your Dowels

This contour gauge is going to be 20" wide with a resolution of ⅛". The smaller the dowel, the higher the resolution. You could even use welding rod if you want the resolution even finer, or larger dowels if you don't need that much resolution.

⅛" dowels means that there will be 8 dowels per inch for a total of 160 to span the entire width. I found some 48" dowels and bought 40 of them. Align the ends and bundle them together with masking tape for even cuts. My saw blade takes out 1/16" per cut, so I cut them to 11 15/16" long.

Step 3: Install Felt

Cut pieces of felt to an appropriate size and glue it on to one side of the two ¾" x 2" hardwood boards. Leave an inch or two bare at each end. These will make the frame of the contour gauge.

I applied the glue to the felt and it used a whole lot of glue. Upon reflection, applying the glue to the wood and setting it down onto the felt would have used less glue and probably done a better job.

Step 4: Make and Install Strongbacks and Fulcrums

Since we're spanning such a distance, it's a good idea to install strongbacks. These are just reinforcements to keep the frame from flexing. It doesn't take much. Simply glue a ½" x ½" strip of hardwood onto the back of each frame half. Set something heavy on it and let the glue dry.

Next, sandwich a couple dowels in between the felt and measure the gap at the end. Cut a small piece of wood to that thickness and glue it onto one end of each frame half. This will become a fulcrum when we install the bolts. The idea is that when we tighten the wingnuts, the clamping force against the dowels will be applied evenly across the middle of the frame.

Step 5: Drill for the Carriage Bolts

Align the two frame halves with the felt facing inward and drill a hole at each end. Do not drill through the fulcrum. The bolts should be closer to the middle to be able to apply clamping force. Install the bolts, washers and wingnuts.

Step 6: Install the Dowels

With the wingnuts loosely on the carriage bolts, install the dowels. Getting them all lined up can be a bit of a pain, but once they fall into place, tighten the wingnuts.

The idea is that you loosen the wingnuts to allow the dowels to slide. Press the dowels against the surface of which you want to copy the contour. Tighten the wingnuts to lock the dowels into place. Then you can transfer the contour of the irregular surface onto some other material. Handy for duplicating, making saddle mounts for odd shapes, or just having fun!