Help me turn this into a circle

Carefully......

Barry Irby

I would attach it to a piece of plywood and attach a block to the center the same thickness as the ring. Then use a tramel and a router.

The tramel could be as simple as a stick with a hole in one end for a nail and the other end a hole to accept a guide bushing for a the router. You can also attach the tramel to the router. It needs to be wide enough to support the router and not be tippy.

After you cut the inside to a circle you can use a rabbeting bit in the router or you can adjust the tramel and straight bit to do the job.

Re: Help me turn this into a circle

Henry (Raleigh NC)

Two somewhat different ideas. Unsure what tools are at your disposal.

Secure piece to a plywood piece large enough to cover the entire frame.

Find the center and use a large compass - jig saw to carefully cut the circle. Cut sanding block with right curvature to smooth. Router with rabbet bit to cut the lip.

Or - draw and jig saw cut the inner part of a circle out of a template board. Smooth as needed (sanding)

Center the frame onto the board and attach.

Use jig saw to rough cut the inner edge, then Router for smooth edge. Router with rabbet bit to cut the lip.

Just a few ideas

Re: Carefully......

John McGaw

That's how I'd do it although having those screws right next to where the cuts would be made would be a bit worrying.

a different approach

Bill Tindall, E.Tn.

I have never used a router and trammel so I would not make this my first attempt (which, I suppose, is why I never learned to use a trammel).

One of the fringe benefits of learning to use some hand tools is the confidence to saw to a line. If you can do it with a hand saw why not a saber saw? I would find it a trivial task to draw the circle and then saw the inside, just kissing the pencil line. Then rout the notch with a pilot bit.

Disk Sander Fixture

Yonak

I have a jig I attach to my disk sander for sanding to a round shape. It has a few different size platters, for different ranges of circle sizes, attached to an arm that can be set at any distance from the sanding disk. I hold the work down with a center clamp but, since you've already got the center cut out, another style of hold-down would work.

I rough cut the circle on the band saw and spin the edge against the sanding disk. This shapes the outside edge. The inside edge could be shaped in the same fashion on the spindle sander with a similar but different jig.

Oscillating spindle sander

Re: Help me turn this into a circle

Derek Cohen (in Perth, Australia)

Tim, I've not had to do this before, but I have pondered on the concept over the year with the idea that I might build a wooden steering wheel. This is how I would do it ...

1. you need the centre (hub point) of the "wheel". The wheel needs to be secured and turn from or at this point.

Think of how one might turn a circle at a disk sanding jib.

2. The idea is to turn a circle on a router table against a straight bit.

Do the outside first, and then shift the wheel closer in and do the inside.

3. The outside can be shaped with a full length bit, but the inside cannot. The inside needs to be done second as the fixture centering it will prevent the router table turning through it. So do the inside in two segments. Lower the router bit so that it only cuts half way. Then remove the centering fixture, and complete the shaping using a pattern bit.

Regards from Perth

Derek

Re: Help me turn this into a circle

Larry Clinton At Frankfort, (Central) Indiana

Personally, I would make a template from OSB that has the correct inside diameter. I would do this with my router and a trammel.

(If I screw up the osb, it's cheap). Once I was satisfied with the template, I would double back tape it to the frame and use a straight bearing bit in my router and round out the frame ID.

Then it is an easy job to add the relief groove using a router and bearing guide.

Excellent - better than my idea. 

Circle frame finished - here's how I did it 

Tim Greif - West of Chicago

Thanks for all the suggestions. I ended up using a trammel, something I've never used or owned. Fortunately, my local Rockler had one on sale for $29.99 - they call it their circle cutting jig. It's a neat little accessory worth looking at. No affiliation, just happy with its results.

I mounted the frame to a partial sheet of plywood on four pieces of scrap hardboard to hold it off the plywood. That allowed me to trim the frame inside without getting into the plywood. I also mounted a piece of pine and hardboard in the center for the pivot point of the trammel. I mounted the frame with the front side up, which was a mistake, since I had to flip it over to cut the rabbit in the backside, also using the trammel. That meant remounting the frame and re-centering the pivot piece, something I would not have had to do it I just started with the backside up in the first place. I had originally planned to do the rabbit with a normal pilot rabbit bit without the trammel, but the bit that I have cuts a 3/8" rabbit, more than I wanted. And I have no larger pilot bearings to make it take a smaller cut. So I had to use the trammel to get the rabbit I needed.

The Rockler trammel cuts from 10-52 inches diameter. It uses a T-slot fitting on the underside that holds either a pin-point center pilot or a post-type pilot that fits nicely in a 9/64" hole. The T-slot fitting is hollow with internal reverse threads to accept the desired pilot. My only comment is regarding the left hand threads. It's recommended that you cut in a counterclockwise direction to avoid loosening the pilot insert. That's the correct direction if you're trimming the outside of a circle. However, if trimming the inside of a circle like mine, moving counterclockwise results in makeing a climb cut. That's fine as long as you're aware of it and use caution to avoid the router getting away from you. If I were to do this again, I'd just put a little threadlocker on the pilot insert and cut in whatever direction you're comfortable with.

Overall the frame turned out just like I wanted. Sorry this is so long. I just figured someone might benefit from my experience and details about the Rockler jig. Thanks for looking.

Excellent.....

Barry Irby

Glad it worked out for you.

You could have done it with the face down and a 1/4" bit in the router and then changed to a 3/4" bit and cut the groove by resetting the depth. Would not have had to reset the trammel at all. Ain't hind sight wonderful?

I find routers to be very interesting. Sort of the simplest of tools. Just spins a bit. Unlimited possibilities.

Question

Pat Evans

Why was the inner circle necessary? Why not leave that segmented and just cut the rabbit?

Answer

Tim Greif - West of Chicago

The print that will get mounted in the frame is a perfect circle. I suppose a 12 segment regular polygon would be ok, but I just felt it needed to be circular to better match the artwork. Now I just need to find someone to cut a circular piece of glass. My thought was that would be simpler than cutting a 12 sided piece of glass.

Let me re-phrase

Pat Evans

I was trying to suggest that the circular inner opening wasn't necessary. That could be left segmented and just cut a circular rabbit. It is the rabbit that will accept the picture and glass. The frame beneath the picture and glass could be segmented. Doesn't matter since it's already done, but could have been done with one less operation.

Re: Help me turn this into a circle

ebd

Cool. Now I know what a trammel is. Handy little bugger. Anything like it that can cut an oval?

BTW - I like the look of the 12 sided outer edge and the circular inside. Might use that on a bowl someday.

Along those lines - I would have mounted the segmented ring in my extended Cole Jaws, turned the inside to a circle and then turned the recess. When you've got every hammer in the book, every project looks like a nail. LOL

Re: Help me turn this into a circle

Barry Irby

You want to cut an oval? Look up a Trammel of Archimedes. I made one to make an oval coffee table for my DIL. Then she asked for a dining table, also oval, so I expanded it. Mine is crude but functional. Difficult to explain, but fun to use and watch. Check it out on Google and YouTube. Might also put in Making an Oval. Some people call them Smoke Grinders or Do Nothing Machines. By adjusting them they can make long skinny oval or nearly round ones or anything in between. Not sure whether it makes an oval or an ellipse of even what the difference is.

Re: Help me turn this into a circle

AZ in Colorado Springs

If you look at a race track, like Indianapolis, you get the sense that an oval is a rectangle with rounded corners.

An ellipse has no straight sides. If I recall the definition correctly, it all the points equidistant from two points. So, a circle has one center point. An ellipse has two foci.

Take a piece of scrap plywood. Put two nails about 8" apart. Tie a 12 piece of string to both nails. Use the tip of a pencil to push the string out tightly, then trace the shape (you'll have to reposition the pencil when you get out past the nail). You'll be tracing all the points equidistant (the length of the string) from both foci (the two nails). Vary the positions of the nails and the length of the string to change the dimensions.

Of course, this won't work with a router (run a bushing along a piece of string) so you need the jig Barry described.

Re: Help me turn this into a circle

TomD

I would call an oval a circle with inserted straight sides.

And ellipse is a circle that is stretched, so it is 1 on the x axis, and 2 on the y, as an example. The math formulas for area and circumference are the same as the circle, other than to account for the ratio difference, so a 1x2 will be the same as a 1 diameter circle (1.57), x 2 (3.14).