Router Circle Jig
Winter, 2017
While working on the valve table I decided I needed to route out some nice accurate circles in the top and bottom. I didn't have a good way to do that so I made a jig for the router to help me out. It is made out of some convenient aluminum scrap I had on hand and is really crude but hopefully it will get the job done and be useful in the future.
So the basic concept is a screw on base that will replace the standard router base plate. The base will have a series of holes in it that can fit over a nail and constrain the router. So I figured out where things would be and measured out a series of holes. as well as an arc so the router could swing on the plate around one of the securement screws.
![](images/Marking.jpg)
The incremental holes are for major adjustment (IE, a 5" circle vs a 8" circle) while the arcs that allow the router to pivot around one securment screw will allow a fine adjustment on the order of 1/2". Between the two adjustments I should be able to generate any size circle between about 3in dia and 2ft.
I drilled at each increment (shown) as well as drilled a chain of holes on the arc (not shown).
![](images/RadiusHoles.jpg)
I then used a coping saw to turn the hole arcs into curved slots. If I had my mill and rotary table set up right now I would have just milled arcs but chain drilling and cutting out the waste isn't that painful to do.
![](images/Saw.jpg)
When the sawing was finished I used the router to help make a tools for itself (I always find that kind of funny to self assemble). A nice thing about aluminum is that as long as you are careful with what you are doing carbide tipped woodworking tools often do a decent job on aluminum. In this case some simple routing to make a depression to recess the heads of the mount screws.
![](images/Routing.jpg)
I didn't have a bit for the router that was small enough to reach into the chain drilled slots though and they were still a little rough after the coping saw so I cleaned them up some with a small bur in the dremel.
![](images/Dremel.jpg)
The dremel is faster than using little files but still can't do as nice of a job getting everything smooth and straight so eventually I moved on to finishing the arcs up with a file.
![](images/File.jpg)
So after I prettied up those slots the jig was done. It simply screws onto the bottom of the router instead of (or below) the normal base plate.
![](images/Finished.jpg)
The pivot point is just a plain 'ole brad nail with a head a little smaller than the pivot holes.
![](images/Pin.jpg)
Then set it by measuring from the outside (or inside as appropriate) of the router bit to the middle of the pivot pin hole you want to use.
![](images/RouterSet.jpg)
The diameter adjustment isn't super accurate on the first shot (probably within about a 1/16th) but it does make a pretty nice circle. Unfortunately the built in depth adjustment and stop on my router doesn't work that well so I ended up making this groove on the valve table base deeper than I really intended it to be.
![](images/Result.jpg)
There are other better circle routing attachment styles but this one was quick to make with the material I had on hand at the moment and does what I have needed it for so far so I consider it done and usable enough considering how often I need it.