I’m working on a mahogany repro/homage of a Danish modern mirror. See design photo on paper. I planned to use a router
On a long arm the way you’d cut out a round table, but it turns out that the arc radius is huge, way more than 10’. Any suggestions on how to cut the arc of these rails and stiles? The mirror frame is 30”x50”. The arcs are not the same and they tighten a great deal at the mitres.

Any suggestions welcome.

Thanks.

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Find someone with a cnc and go over with a sheet or scrap of baltic birch. Have them cut curve templates. Think about how you want to use the template. If you will be using a handheld router then make sure the width of the template is such that you have a stable surface for the router.

Bandsaw the curve. Edge sander or spoke shave to clean up. That would take about 15-20 minutes to do.

A couple of things I have done, is to bend a thin batten between to nails while pushing the middle to the right curve. Keep in mind that bending solid wood, about 8 times the thickness will be straight on the ends.

For much larger or longer arcs, I have found that my steel 100' rule is easy to attach to the edge guide on the router. Then out on my parking lot where there is lots of open space, I can clamp the 30' ~ 50' or whatever chosen radius is to a porch post. The steel tape doesn't stretch to swinging clockwise, the cutter will pull tight. Oh, to prevent the tape from snagging on the asphalt, I lay clean strips of hardwood across under the tape to hold it slightly above. And its easy to drive a 16d nail through the material and waste board underneath into the asphalt. For concrete you might need tapcon screws.

Take your frame to a CNC shop and have them cut it. I've made up to 12' trammels. 1/4" plywood with 1x3 cleats on the sides. Alternate the joints in the parts. Hot glue the pivot block on the floor.

Jonathan:

It sounds like you are making one frame and not multiples, so "jigging up" seems like a waste of time. If your frame is not glued together, take the parts to a bandsaw and cut the curves, then sand to the line. If the frame is already glued together, I would consider cutting through the opposite miters to leave two "L" pieces, bandsaw the curves, reglue the miters and sand to the line.

Sandpaper wrapped around a flat wood scraper as the "sanding block" will smooth out the larger curves without dips, and sandpaper around an appropriately sized piece of PVC pipe will smooth the corners.

Mirrors like this were done many years before CNC equipment. After all, we are talking about being able to cut to a line, which is a fundamental woodworking skill.

It will take less time than you have spent on the Woodweb chasing this down.

Hope this helps.
TonyF

10' stick with a pencil sticking through for the line and then handsaw or jigsaw the cut and sand.

LeoG:

The project frame looks like it has a layout line on it already, or I would have offered up the "three nails, two sticks" layout method for a large curve.

I must say that I am disappointed in the number of CNC suggestions for what is really a simple frame with a little bit of hand work.

TonyF

I would have traced the opening on a pc of cardboard and then freehanded half a curve, cut it out and trace it, flip it over to do the other side of the curve. Cut it with a jigsaw and then smooth it off with a spindle sander and then a random orbit til it felt smooth with no bumps in the curve.

Tony - I offered the cnc suggestion not because I have lost all of my hand skills or desire to use them but because I can program and run that frame in 15 minutes with the control and accuracy that minimizes errors, sanding and risk to fingers.
There should not be a conflict between fine furniture making skills and cnc.
I don't mean this post to be mean spirited but to support the benefits of a new machine in the field.

Tom Gardiner:

It is not mean spirited at all. If I had a CNC, and were versed in its use, I would use it all the time, much like my shaper and table saw. I might even become dependent upon it. The machinery and methods that I use reflect the way I was trained, and have worked well for a long time.

Still, I would question the total time outlay for the CNC, from start to finish, for one mirror frame such as the one in question, versus someone skilled in producing it via other methods.

And having to be dependent upon outsourcing for CNC usage on one frame would just not sit well with me. If I were making 100 frames, I might consider it, given the expediency of the CNC, but then someone with a CNC would have already underbid me, and I wouldn't have that project to begin with. But for one frame, it would be a slap in the face towards my own professionalism, part of which is derived from being able to solve problems as they arise and utilize the tools I have available. I would not outsource a task unless it was absolutely necessary, or there was a huge financial or time advantage in doing so.

Perhaps I am just too old and set in my ways, as I have always used these methods to produce work. I just thought I would suggest what I did, figuring that he already had these tools available. To me, using a CNC for that one frame would be like driving two blocks to the post office, instead of walking. To each his own.

TonyF

Long router tramels are awkward but possible. I used this last week to cut a 235” radius on some 68mm thick door frame parts. CNC router would have been easier but don’t have one.
I used the 2 point fixed triangle to lay out the curve but have never come up with a good way to use a router with that.
See the Instagram link for the whole process.

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https://www.instagram.com/p/CAcv9C_D86W/?igshid=17kesuw54804x