One of the last things to for this jig was to manufacture the sliding mechanism for adjusting the radius of circles I'll be able to cut. I cut a small block out of MDF which fits in the large slot and lays flush on the bottom of the jig. I had to do a bit of sanding to get it to fit in there properly - I didn't want it to be too loose in there - a snug fit works best. As you can see from these two pictures, the block slides up and down the channel on the bottom of the jig.
With the block in place, I drew some lines on it through the smaller 1/4" opening from the top of the jig so I would know where to place the screw I will use for locking the block in place. It's not exactly centered but it doesn't have to be (although you should aim for that if you decide to build one of these yourself).
The next step was to drill a hole in the area I just laid out. This will be for the locking mechanism which is just a screw on the top and a tee nut on the bottom.
Next, I flipped the block over and used a foerstner bit to countersink the tee-nut so it is flush with the bottom (or even a little recessed). I had to tap it in pretty hard with the hammer.
As you can now see, the screw goes in the tee nut through the top of the jig and locks the sliding block into place. So when I'm using this thing all I have to do is measure the distance from whatever router bit I'm using to the center of the pin and that will be the radius of the circle. Easy!
This shot from my last post shows the (almost) completed jig. I cut out a handle of sorts to help me slide the block up and down the jig as well as enable me to lock it into place.
Here is a random shot of some of the supplies I used in case anyone is interested:
I'm almost done. The final step is just to drill a hole in the block for a #10 nail which will act as the pivot pin. Unfortunately, I don't have a drill press and it is imperative that this hole be exactly perpendicular. Any deviation will throw off the radius of any circles I try to cut! I think I figured out how to drill the hole but that will have to wait until tonight and then I can test it out!