So here’s a step by step process I used to cut the inner and outer arches. The basic plan is to dry fit the door frame, set up the pivot for the circle jig, cut a groove for the outer arch, move the stiles out of the way while keeping the arch clamped in place, cut a groove for the inner arch, use a jig saw to cut through the grooves, then use a flush trim bit to finish the arch cuts.
Step 1: This time around I learned to cut a board to fit in the middle and mark its location on the stiles. I measured the inner and outer arches and marked them to be the same width as the stiles, 7 1/4”. Note that I used a clamp across the frame to hold the pivot board in place. Will this cause a problem later on? Stay tuned.
I center punched for the pivot pin and set up the fancy circle cutting jig to make the outside cut. Note that the distance for a 30” radius arch is actually 30 1/8” to allow for 1/2 of the 1/4” bit. The outer arch is cut on one side of the bit, the inner arch on the other.
I then move the stiles out of the way while keeping the arch and pivot board clamped to the table. Both curves use the same pivot point but have different radii. The inner curve is 22 3/4” radius curve (to make the width at the top of the arch 7 1/4” to match the width of the stiles). Now I would have pictures of cutting the inner arch but as you guessed it, the pivot board was not secure and the pin popped out of the jig, so the cutter went a little whacky to use a technical term. Thankfully I had marked the position of the pivot board on the stiles so it was quick and easy to re-establish the correct distance. This time, however, I screwed the pivot board down before moving the stiles out of the way and cutting the inner curve.
And here’s a closer shot of the resulting mistake. So how did I fix this? Did I start over? How would you have fixed it? I’ll show my solution in the next blog.
To finish each cut I just cut through each groove with a jigsaw then used a flush trim bit to smooth out the curves, and Viola! You’ve got yourself an arch. Albeit one with a pretty bad gash, still an arch though. Another little thing. I clamped a couple of scraps to each end to prevent tear out. And because of gash caused by the mistake I didn’t flush trim the outer arch at this point. I just trimmed it with the jigsaw.
-- tim hill www.newcalshop.com