Jigsaw circle cutter


Anyone make a circle-cutter jig that attaches to a jigsaw? I have a Bosch jigsaw and I need to cut several large arcs, radii ranging from 35 to 55". The stock is just too large to handle for my bandsaw. I'm cutting 1.5" MDF to construct wood-bending forms. I wonder if the router would handle this job (maybe more accurate 90-degree cuts?) TIA
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Phisherman wrote:

Could you just take some masonite or 1/4" ply or something and maybe make one out of that? The leading edge of the blade would have to be colinear with the different holes for different radii in order to get accurate measurements, I would imagine.
The only other issue in my mind is attaching the jig to the shoe of your jigsaw. Are there predrilled, pretapped holes for that sort of thing? I'm pretty sure my POS Skil doesn't have them, but then again, it's a POS. Another option would be 2-sided tape, perhaps.
Hope it helps, -Phil Crow
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"Phisherman" wrote in message

The router, with the addition of a trammel base, may be the perfect tool/jig for this task.
An adjustable trammel base for your router can be made in a few minutes from 1/4" mdf/plywood.
Here is a picture of a smaller one I use frequently ... making/dimensioning one for your task should be intuitive.
http://www.e-woodshop.net/images/Trambase.JPG
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Phisherman wrote:

Unless it's a honkin' big router I'd make multiple passes in stock that thick. Circle guides that size for routers are easier to find than for jigsaws--shouldn't be hard to make one up though.
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--John
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I would use the router. Smooth cut that would require little if any sanding. I assume that you are laminating two pieces of 3/5 to get to thickness. If so, the easiest way would probably be to not laminate them then cut all the way through. That is quite thick. While it would work in multiple passes, you would have trouble keeping the kerf clear of dust, Cut one piece of MDF to shape, laminate another to it, rough that one close to the first with a jigsaw then trim it flush with a flush trim bit in the router. This should go rather quickly as you can glue and brad the laminations together and cut immediately as long as you keep the brads out of the cut line.

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Should be 3/4.

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'Phis' . . .
Don't 'kill' the router, or yourself. Let your jigsaw do the 'grunt' work, and use the router for the 'finesse'.
MAKE the adjustable trammel for the router . . . don't necessarily need a real big one. {Use the heft to hold it in place, rather then you pushing it down}.
Lay out your circle and use the jigsaw . . . freehand, with a course blade to make the cutting easier . . . as close to the OUTSIDE of the line as YOUR skills / nerves permit.
NOW take the trammel mounted router {use a bit with an ANGLED cutter for a smoother shearing cut} and get a fine, to the line, finish.
ANOTHER option . . . if you are going to make A LOT of these. . . is to make 1/4in Hardboard templates {I do this with certain boat parts - for accuracy & repeatability}. The stuff is easy to work with - you can hand-sand right to the line. I paint the entire sheet with WHITE water-based primer - a nice semi-matt surface that takes pencil marks easily - before lay-out & cutting. Afterward, I 'treat' the cut edges with epoxy for abrasion resistance.
Regards & Good Luck, Ron Magen Backyard Boatshop
"Phisherman" <noon

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It would be easy enough to just make one by attaching a piece of masonite or something similar to the base of your saw, extended to one side or the other, with a pivot hole or holes. Same principle as a router circle cutting jig. No doubt the router would cut a truer 90d edge, but for bending forms, (or most anything else for that matter) the Bosch should be adequate.
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Larry Wasserman Baltimore, Maryland
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Do you need permanent forms? We make a lot of bending forms for window jams and I used to make a permanent jig for different sizes. Now I use brackets to make the forms. You can cut L shaped brackets out of a good quality plywood and screw them to a wood floor or a piece of scrap plywood. Just lay out your radius on the floor (or plywood) and screw the brackets on your line using as many as you like. Once you've made your 55" bends take them off and set-up for another size.
Mike O.
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The router would be your friend for this.
Make the circle cutter out of 1/4" birch plywood.
Phisherman wrote:

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