Once you have the dial, the door is built to size so the inside of the frame overlaps the dial by Va". This would be relatively easy if it weren't for the arch (at the top of the door frame) that has to fit around the "moving moon." Since this arched piece presents the biggest problem, I started with it.
The best way to cut the arch is with a router and trammel attachment — because a router produces a true, clean edge that needs very little sanding. (I used a Sears router and multi-purpose router guide No. 9 GT 25179, see Woodsmith No. 21.)
This approach works just fine . . . until the router makes its final pass, and the inside and outside sections of the arch are separated. Trying to control the router and both pieces as they break free is more than I really wanted to handle.
Instead, I used the following procedure to keep everything connected wrhile the routing was done. First. I cut the top rail (C) to final length (allowing for the tenons that will be cut later).
However, the initial width of this rail should be about ¥»" wider than needed, see Fig. 2. This extra width allows you to position the cut for the arch so you don't have to rout all the way to the bottom edge. Then after the arch is cut, the inside waste can be removed by simply trimming off the bottom edge.
routing the arch. The first step in doing all of this is to determine the location of the pivot point for the trammel attachment. First, mark a parallel baseline 37/«"
from the top edge of the door rail (C). (This measurement is the final width of this rail.) Then mark the pivot point at the center of this line, see Fig. 2.
pilot hole. To rout this arch, I wanted to use a Va straight bit, making a series of passes, and lowering the bit about Va" with each pass. But in order to lower the bit, I had to drill a Va" pilot hole. This hole is positioned so its outside edge is exactly on the inside edge of the arch. Since the radius of the arch is 2%", I centered this Va" pilot hole 2%" from the pivot point, see Fig. 2.
To cut the arch, 1 simply inserted the trammel attachment in the pivot hole, lowered the straight bit about Va" into the pilot hole, and locked the trammel arm in place.
Then as the arch is routed, the bit should cut at least as far as the base line, but not all the way to the bottom edge, see Fig. 3.
After the arch is routed to full depth, trim the bottom edge off of the rail so the final width is 3%", see Fig. 4. This trim cut will also remove the waste piece inside the arch.
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