Rocking Chair: An Online Course #8: Router Circle JIG or Trammel Arm

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Blog entry by HappyHowie posted 03-02-2016 02:29 AM 1478 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 7: Clamping Form for Bending 8 Strips to Make Rockers Part 8 of Rocking Chair: An Online Course series Part 9: Glue Form for Rockers »

In order to make the rockers for this rocking chair I needed to make a pattern. From these patterns I would make a clamping form from plywood. I will cut eight 1/8” thick slats of my cherry hardwood for each rocker and glue them between these clamping forms. I will use gluing cauls on each side of the clamping form. They will be made from 1/8 inch masonite or hardboard. I will cover them with paste wax so glue will not adhere to them. Thus, the inner form will have a radius of 42 inches and the outer form will be made with a 43 1/4 inch radius curve.

To make these patterns I made a trammel arm from 1/2 inch baltic birch scraps. I used screws and glue to fasten the scrap pieces together along with the short circle JIG I had made earlier to mount my Bosch Colt plunge router.

The images below show the setup of my router and its trammel arm. I drilled a 1/8 inch diameter hole through the trammel arm at a distance of 42 inches and 43 1/4 inches from the inside edge of the 1/8 inch straight router bit I was going to use to cut these patterns.

I laid down a full 4 by 8 sheet of plywood on my garage floor. Then I laid down a half sheet of underlayment and on top of it I laid down my masonite board. From this 1/4 inch thick hardboard I would cut my two patterns so I could make the curved clamping forms.

I would have built that form today, but I had a bad night. I was not feeling that well today. Maybe tomorrow, or the next day I will have my chance.

This photo shows that I am ready to cut the first pattern at 43 1/4 inch radius. I have a black screw fastened at that pivot point.

This photo shows the 42 inch radius curved pattern. I moved the screw to that pivot point.

-- --- Happy Howie

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