Thread: Router circle cutting jig

Sean,

Nice simple solution - well done.

Your jig has ignited an idea of making a circle cutting jig that attaches to a router fence with the rotational pin poking down. Before I reinvent the wheel here has anyone seen something similar to this approach?

Cheers
Bob

Bob, there was a discussion on just this solution (essentially a pin router) many moons ago on another forum. It worked well, however, you need to have at least two anchor points or the bit can grab and move the piece, causing damage where you least want it.

Originally Posted by Groggy

Bob, there was a discussion on just this solution (essentially a pin router) many moons ago on another forum. It worked well, however, you need to have at least two anchor points or the bit can grab and move the piece, causing damage where you least want it.

Thanks groggy, I can't quite see why you need to anchor a circle at anywhere other than the middle, after a. I can see the router possibly pushing the wood up and needing some way of keeping it down so I have added a bush in this diagram.

Originally Posted by BobL

Thanks groggy, I can't quite see why you need to anchor a circle at anywhere other than the middle, after a. I can see the router possibly pushing the wood up and needing some way of keeping it down so I have added a bush in this diagram.

The arm coming out from the fence needs two anchor points, otherwise it can deflect.

cheers.

I understand now, Sorry I should have posted a plan view.

Yep, that'll work!

Originally Posted by Groggy

Yep, that'll work!

Cool, that's now germinated project #635 - now only 144 projects behind.

Originally Posted by BobL

I understand now, Sorry I should have posted a plan view.

BobL - This is a fantastic idea. I love it. I'd be building it right now if I could think of a use for all the circles I'd cut. My router fence has the t-slot that would serve nicely in securing the jig.

The only potential drawback is the capacity. It looks as though you'd be limited to a circle with a radius about equal to the distance your router bit is from the edge of the table. I would think it would get too tippy if you had the center off the edge of the table.

Again, great idea!

Originally Posted by BuffaloJohn

The only potential drawback is the capacity. It looks as though you'd be limited to a circle with a radius about equal to the distance your router bit is from the edge of the table. I would think it would get too tippy if you had the center off the edge of the table.

Again, great idea!

Ah Ha!, The benefits of having a router wing on your Table Saw is you can drop the saw and move the saw/router fence right across the other side of the table. I just measured mine up and reckon I could cut an 800 mm (31.5") Diameter circle. The jig would have to be fairly substantial to do that and need vertical movement support, see plan C.

Well I needed a couple of MDF circles today so I whipped up a prototype jig, sort of as per the plans I showed earlier on this thread. This one can be used to cut circles diameters of up to 580 mm and amazingly it works every bit as well as I thought it would.

Photo 1 shows the whole jig. The pin around which the circle is turned is a 3 x 1/4" bolt with the head cut off.

Photos 2/3 show a close up of the pin and router bit.

It was dead easy to operate. It's pretty firmly attached to the router fence and there was no need to use a bush to hold down the wood. I used push sticks to turn the 90mm diameter circle shown in the photos. I made a 210 mm circle buy turning it just by hand. You just need to be careful when the circle is close to finishing and slow down so you can control the breakthrough point.

This jig seems like it is capable of a number of things
- used as pin guide for the router.
- the hole for the pin locator does not need to penetrate all the way through the material. I want to try making a wood or metal clamp that straddles across the middle of the wood you want to make a circle from and then use a hole in the clamp so the object being cut does not need a central hole at all and the pin itself then pushes the wood down onto the table. The clamp will also give you something to hang onto while turning the circle
- Once you have cut an outer template it can be clamped to the bench around the router bit and you can then easily rout out insets from pieces of wood that fit inside the template and are lightly held down by the jig with or without the pin. I made a template consisting of a 120mm diameter hole in a piece of 12 mm MDF and used it as a template to rout out a 15 mm deep x 60 mm diameter inset into the end of a 70 mm diameter wooden cylinder. Sure you can do this on a lathe but this will work for other shapes as well.

Very nice Bobl !!!!!!!!!!!!!!!!

I like it. I also like you idea about not needing a center hole. I'm brainstorming that concept now.

If I can only think of a use for all these circles I want make...

Bob, good job.

how about doing away with the slot on the jig. As you move closer to the fence the circle would have to be smaller, eventually disappearing under the jig. If you made the pin end of the jig a little pointed it would give you a bit more room to manoeuvre. maybe marking a slightly oversize circle and cutting the waste off on a bandsaw, to save loading up the router.

Did you consider putting the jig and pin under the workpiece and having a slot for the router bit to work in similar to what Sean had. maybe only a short pin and a simple hold down arm with a central pressure point.

Originally Posted by bpj1968

Bob, good job.

how about doing away with the slot on the jig. As you move closer to the fence the circle would have to be smaller, eventually disappearing under the jig.

I agree the pin slot is not needed. To change the circle radius you just move the fence relative to the router bit.

The reason I inserted a slot is because this jig is a prototype and I had no idea what kind of up/down flexing I would get until I actually made it. By building in a slot from the start I could experiment with the degree of vertical play in the system and I could then shorten the pin/fence distance. In the end it is not necessary

Originally Posted by bpj1968

If you made the pin end of the jig a little pointed it would give you a bit more room to manoeuvre.

True, and you see I had this in my original drawing. In my second prototype I plan on attaching the pin to a piece of Al square section tube poking out in front of the jig.

Originally Posted by bpj1968

Did you consider putting the jig and pin under the workpiece and having a slot for the router bit to work in similar to what Sean had. maybe only a short pin and a simple hold down arm with a central pressure point.

Yes I did but by using this approach you lose cutting depth since the router bit has to also poke up through the equivalent depth of the jig. Also this method makes it essential to have a hole in the centre of the circle whereas my prototype two using a "clamp over" piece will not require this.

Cheers

Today during a meeting I came up with a simple jig to cut a circle using a router without the need for a central hole. I decided to mock up a prototype using MDF. Now I have an idea how well it works I will replace the MDF with maybe Aluminium and maybe use a 3/8" threaded rod instead of 1/4"..

It involves the pin holder from the above posts ,and jig as shown in Picture 1. It's just a length of threaded brass rod and 3 bits of MDF held in position using wing nuts

The jig is placed over the piece of wood as shown in Picture 2. As MDF has a problem gripping MDF, I use a couple of bits of sandpaper between them. To locate the router bit a starting hole on the circle is needed in the wood (not shown)

The wood and jig are then located/connected by a simple press fit to the pin holder . See pics 3&4

Then rotate jig around the pin, taking several passes to perform the cut.

Whala - no central hole needed!!!!

The prototype flexes a bit as MDF is not idea for this sort of thing. Using Al should reduce this.