Adding the Trammel
Draw a layout line 12″ from the centerline of your bit to establish the pivot point of the trammel.
The trammel is a scrap of 1/2″ material cut 6″ wide and 20″ long; this width fit my router base nicely. If your router has a wider base, change the trammel width to suit it. Set the router near the trammel’s end to mark mounting holes for screws, as well as to establish where to bore a clearance hole for the router bit. Mark the trammel carefully with two layout lines: one identifying the centerpoint of the router bit and a second drawn 12″ back from this line, before making the bit clearance hole and fastening the router to it.
Slide the trammel along the support block until the router bit touches the outer corner of a trivet blank to set the position of the jig.
You’ll need one of your 6″-square trivet blanks to mount the trammel properly on the jig. With the router bit installed, set the trivet blank in the corner formed by the fences and balance the trammel on it and the square support block. Slide the trammel along the support until the inside edge of the bit just kisses the outer corner of the trivet blank.
Use the dowel’s pivot point line to find where you can bore a dowel hole to complete the trammel.
Make sure it lines up evenly over the support before boring a 5/16″ dowel hole through the trammel and support — right into the base. Center this hole on your 12″ layout line drawn previously. Now insert a 2″ length of 5/16″ dowel to engage the trammel’s pivot action. You’re nearly ready to start routing trivets, but first, make up 14 spacer strips from 1/2″ scrap. Mine were 3/4″ x 14″.
