How to make a circle cutting jig fully adjustable quick and simple - Woo...

How to make a circle cutting jig fully adjustable quick and
simple

Today I’m making this circle cutting jig, because I need to
cut a really big circle for this table.

It has incremental swing arm, a non-destructive way to
attach it to your material, and is fully adjustable to dial in the exact radius
you want. 

So to get started I ripped a strip off some scrap plywood to
act as the swing arm.  You can make this
strip as long as you want to make as big of a circle you.  For this jig, I am about 2 feet long.

I do have a sketch on my website if you want all the
measurements.

I marked down the center and laid out 1” increments. 

I head to the drill press to drill ¼” holes down the length.

Then I used some ¼” plywood and cut a perfect square and
marked the center.

I used a forester bit to counter sink for a T nut and
switched out the drill bit to drill the through hole.

I positioned the T nut over a dog hole and drove it
home. 

I’m sure I could get a shorter T nut that wouldn’t stick
through, but this is what I had on hand and I didn’t want to drive across town
for a 50cent piece, so I just filled the points flush.

To make room for the shaft of the T nut, I just ran a dado
down the center of the swing arm.

I should mention that your pivot point plywood should be
about the same thickness as your base plate. It will make assembly a little
easier

I ripped of a piece of scrap plywood to start making a
bracket to attach the jig to the router.

I measured the distance between the holes on my router.

Drilled some through holes

Did a test fit and marked the length so I wouldn’t have a
bunch of extra material sticking out, and cut it off at the chop saw.

Then I counter sunk for the heads of the bolts, this would
have been easier before I drilled the through holes, but I’m just making it up
as I go.

I got another scrap of plywood and marked the width I by
holding it up to what I had already made. 
I did this without the base plate attached

Then I marked the length and cut it off at the chop saw.

I pre drilled some screw holes to attach it to the swing
arm, and flipped it over to pre drill some holes to attach it to the mounting
block I had made earlier.

I then glued and screwed it to the swing arm.

I then glued and screwed it to the mounting block in the
router. 

The bolts stick out about a 1 ½” so you can a little over an
inch of adjustability between the pivot points drilled in the swing arm. 

To locate the jig on your work piece, I line the points up with
my layout lines, mark the perimeter so I know where to put the double stick
tape, and stick her down.

I pick a pivot hole close the size I want, and while I am there,
I marked out the radius in inches along the swing arm. 

Then using the bolts, I fine-tuned the radius to my layout
line, and cut the circle.

Stay tuned, my next video will be of the round table
build. 

If you want to see what I have coming for future video, give
me a follow on Instagram, and of course. 
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https://www.briansbenham.com/how-to-make-a-circle-cutting-jig-fully-adjustable-quick-and-simple-woodworking-diy/