Wooden ring fabrication?

[Tom Andersen]

Hi guys,
we have a round window and I plan to fit a wooden ring with thermo glass to its back to add thermal insulation. See attached picture of window. The internal diameter of the ring should be about 33 inches, the outer diameter 37 inches, and the thickness around 1 inch. I do neither have a lathe nor a band saw but various routers, a table saw, planer, jointer, etc.

How do I best make it? Any references to articles?

Thanks in advance
Tom

[Aaron Berk]

Wish I could help, but I'm in a similar plight my self.
I'm planning on gluing up a large solid wood arch, then hooking my router into a giant trammel and routing the crude glued up arch, into a perfect half circle molding.
Could the same thing be done in your case, something like a large circle cutter?

[Gary Herrmann]

Trammel arm. Drill a hole in the center of the wood. Create an arm with a router attached to the end with the center of the bit located at 18.5" (your outside radius) + half the width of your bit. Put a nail the diameter of the hole in the center through the other end of the trammel arm and through the hole in your stock. Repeat this process with the bit located at 16.5" (your inside radius) + half the width of your bit. You can make the trammel arm out of ply, mdf etc. A faster option is to buy one of those circle jigs and use it. Like these: http://www.woodcraft.com/family.aspx?familyid=3582

You'll need a long enough straight cutting or one of those downshear bits and make a series of passes - don't try to do 1" all at once. You could even flip it over to avoid tearout.

Undoubtedly, there are plenty of folks that could explain this better than me...

[Chris Tsutsui]

If you can't get the router jig to work. Use a homemade compass to draw a pencil circle, then a bosch Jig saw followed by sand paper.

Some might frown at me though I had to make a bunch of bass traps and that's the method I used for about sixteen 2-foot diameter rings.

I wish I had a router and a nice jig, but I didn't...

Here's my bass trap padded and fabric wrapped:

http://www.flex-innovations.com/roomtrap4sm.JPG

[Lee Schierer]

I would build up an octagonal frame large on the outside and smaller inside than the finished dimensions. Then mount the octagonal frame to a piece of plywood. You can do this with double sided taped strips. Draw alignment marks on the plywood showing the location and orientation of the piece on the plywood. These marks will let you remove and reorient the piece as needed to work on the front and back with out getting off center. Mount a router to a trammel or circle cutter and route the outside surfaces front and back. You may need to attach a block the same thickness as your frame in the center for the trammel to work. Once the outside surfcaes are done. Route all the inside surfaces, which may destroy your location marks so be sure you think through the logical sequence before you lose the orientation marks.

[Chris Padilla]

I used Sketch-Up to play with some ideas for you.

The angle I chose was 15 degrees as referenced from the circle's center.

To join up the segments to form this polygon, or actually, it is a 24-gon, you would cut 7.5 degree miters in each piece.

As I've drawn it, the segment width is just under 2".

The more segments you have, the smaller in width you can go...the less segments you have, the wider in width you'll need.

I would want to strengthen the miters with biscuits at the minimum but splines, dowels, and dominos all would work fine as well.

Now you can use the methods outlined by others to cut a perfect circle. You may wish to determine if your window is a perfect circle first...cut some cardboard templates first to make sure.

[Aaron Berk]

Wish I could help, but I'm in a similar plight my self.
I'm planning on gluing up a large solid wood arch, then hooking my router into a giant trammel and routing the crude glued up arch, into a perfect half circle molding.
Could the same thing be done in your case, something like a large circle cutter?


Here's an oval version of the jig I'm planning on using, came out of a Woodsmith magazine.

[Ed Kilburn]

I had the same problem when I built my round bar. There was a support post in the center, so I made a trammel from MDF a couple of bearings and a skate wheel. The trammel was adjustable and I used it to cut all of the curved parts for the bar.
I first laid up a polygon, 3 layers thick of 3/4" hard maple, screwed to the 3/4" plywood base from the underside. Then cut the shape with the trammel and router. Sanded it with the Bosch 6" DA and lots of hand sanding. After removing the screws from the under side. The Chicago rail was removed and stored, to be put back on after the plywood base was covered with 3/4" hard maple.
BTW: I tried the 7518 PC router first, it keep overloading. Switched to the Bosch 1619 with the same bit and it ate right through the maple. I now keep the PC on the router lift for light work. The shaper and 5hp overarm router gets the heavy work.

[Aaron Berk]

That's an awesome bar, and an ingenious way of building it.
Looks sweet.

[Joe Scharle]

I have, among others, a Milescraft circle cutter that should do the job for you. It has a sliding arm that makes adjusting very easy.
I would sandwich (carpet tape) 2 pieces of 1/2" MDF, hot glue that to a piece of cheap 1" rigid foam (BORG). Run a spiral bit around the outside and then the inside. Carefully pull the rings loose from the hot glue, then separate from the carpet tape. MDF paints up real well.

[Jim Heffner]

You might want to make a type of trammel arm attached to a jig/sabersaw. Use a center pin as a pivot point and set the radius of the circle and start cutting! Another alternative is to make a circle cutting jig
attached to a tablesaw crosscut sliding jig. George Berry "The Wood Guy"
has a video on his site about that jig...it works if you take your time and watch what you are doing and don't rush the cut!

[Bill Huber]

I don't know how to do it but I have been thing about how I would try.

So if I took a board, in this case around 8", and then just cut an arc from it. Then cut the inside arc. Do this 4 times with a router and then use splines to glue it up.

You would have to use some turners tape to hold the board down but wouldn't this work?

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