Circle cutting jig for trim router
Posted: Sat Feb 03, 2018 3:37 pm
So I got a bit of time to build a circle cutting jig for my Bosch Colt trim router. The next operation to do on my guitar build is the rosette and soundhole and to be honest, it kind of makes me nervous. Every time I touch a router to wood it makes some kind of unexpected groove or chipout where I don't want it. It also absolutely screams while messing up my stuff. I just hate routers! So I want to try to make the circle cutting easier. I also am cheap and enjoy messing around building jigs ect. So I bought a cheap plastic cutting board (3/8" thick) and a bunch of parts from Home Depot. I got a few 1/4" carriage bolts, some acorn nuts, wingnuts and regular nuts. From work I got a scrap piece of 1/4" aluminum bent into 90 degrees which I cut up into L-brackets. I started by drawing out a template to see if I could fit all the parts together. Then I routed a 3/4" slot halfway into the bottom of the cutting board, followed by a 1/4" slot all the way through for the small carriage bolt to go through. I cut out the shape of the jig on my bandsaw and smoothed the cuts with my block plane (actually cuts wonderfully!) I then tapped a 1/4-20 hole into the rear bracket, and epoxied a short piece of drill rod into the front bracket. I used thread-lock to keep the threaded parts together that I didn't want moving. After putting everything together I was pretty happy, but the minimum cut diameter was about 4", which is about the largest soundhole size from what I gather. So after some going back and forth, I notched out the base of my router, so that the diameter gets down to around 3 1/2". I considered whether this might compromise the router, but after doing it, it seems like there is still plenty of meat there. Anyway, let me know what you think. You could build it just as easy from plywood, but I figured the cutting board would slide easier. Plexiglass would be best, but I couldn't get any thick stuff for less than a fortune. I haven't actually used it yet either... It remains to be seen if this works, but it seems pretty tight.