Craig, that looks really sweet!
Here is mine. I made a feature where you set the depth of cut using pieces of your actual binding and purfling. I got the idea from someone describing Mike Mahar's purfling scorer to me, which uses a similar idea. Please forgive the rough construction of the machine
The first photo here shows the 2 pieces separated. The lower part rides in the slot in the bigger part. You can see the "donut" part is screwed on and is made from the Lee Valley jig making material. I can never remember the exact letters, uhwm or something like this. When doing an arm bevel you can take it off and use the extra depth to route a larger channel which is very helpful.
Attachment:
jig-from-below.jpg
This next photo shows the 2 pieces attached to each other. There is a threaded knob that locks it in from above. The arm part that rides against the guitar adjusts in and out with the brass screw and can be locked in position with the 2 small allen screws in the upper and lower round guides. It should be set to be perfectly parallel to the router bit and locked in place.
Attachment:
jig-offset-arm.jpg
This is a view from above. You can see the locking threaded knob that holds it all together. Also, you can see that the upper part of the lower section is firmly butted up against the cross piece on the main housing. It should be tight against there when you set your lower dowel (the part that rides against the guitar) parallel to the router bit.
Attachment:
jig-from-above.jpg
Then, you loosen the threaded locking knob and insert a piece of binding between the upper part of the lower arm and the cross piece. and.... whammo your offset is perfectly sized to your piece of binding. You lock the knob back down and go to town. Once that channel is cut you raise the router bit a some and insert your purfling next to your binding and cut the next channel. If you are worried about the glue line swelling things you can insert a piece of friskit material or maybe even some typing paper as some precaution.
Attachment:
jig-from-above-with-binding.jpg
I find this very useful because I usually make my own purfling and this allows me complete flexibility in how thick it can come out. I don't have to worry as much if I am a few thousandths too big or small for my bearing set. Eventually I will remake it a little prettier but for now it works great. I am using 1/4" downcut bits to do the cutting. I got a deal on some long ones, that is why the donut is so large. If I made it again though I would keep the donut that big for the reasons stated above. I had previously made a large version using the same idea that uses a full size router and requires you to move the guitar over the jig. I still use that first and hog out most of the binding ledge with a 1/2 shank router bit. That leaves only a small amount for the lam trimmer to clean up and it never is really working too hard.
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