Curved sash window project

[Keith Mathewson]

I'm replacing the last window on a rental. It is a bathroom window with a round arch top.IMG_3189.jpg
It is going to be the same size since the framing and siding are in place.

I have wanted to do a curved sash window for sometime and and now have the opportunity to build one. The concern has always been how to best produce the curved muntins. My fallback would be straight ones as are shown in the pic.

I made a simple drawing to see how accurate I could steam bend a member.
IMG_3455.jpgIMG_3456.jpg

The first attempt went better than expected.
IMG_3460.jpgIMG_3458.jpg

The challenge would be how to profile the muntins once bent. The Preston sash shaves I have are close but not quite the same as the sash planes I have. From what I've read online one cannot bend a profiled piece because there isn't any compression on the profiled part and it will split. However the radius is fairly gentle and the next one I bent profiled.
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At present it appears to have worked. I'll find out tomorrow if there was a failure during the drying period.

[Mel Fulks]

I used to make "circle sash" ,as we called them, often. We would bandsaw just a heavy 1/16th ,then use a shaper and plywood template to trim them to uniform width. Use shaper to cut glass rabbet, then cut profile. Used a spring hold down
on the shaper. We usually used Northeastern white pine. If you can get your method to work accurately ,certainly nothing
wrong with it .

[Charles Guest]

Cut the curve out of the solid. These things were rarely bent since you can't count on the amount of spring back. Wasteful, perhaps, but this sash was never "cheap."

[Tom M King]

What muntin profile shave do you need?

[Keith Mathewson]

Mel & Charles,
Machining it is certainly and option and back when I was doing this to earn a living that would have been an attractive option. It wouldn't have been worth my time to make just one however- too much set up time on the machines. Alternatively I could buy one from a company who is setup to do this kind of work. It would be cheaper if I tracked my time but that is one of the benefits of being retired, how long is takes isn't as important as if I enjoy doing it.

Tom,
I suspect I have most if not all of the Preston sash shave profiles available, the frustration is the wood sash planes I currently own do not quite match. Today a bought a few more wood sash planes on Ebay, perhaps one or more will match better.

[Tom M King]

As many as I have, I still end up having to get custom router bits made sometimes.

[Rob Luter]

Are you planning on locating the muntins between the glass typical of the vinyl window you are removing, or will your new window feature true divided lights?

I use these guys for one off shaped grids: https://cgpglass.com/decralite-sdl/

[Keith Mathewson]

Rob,
This will be a true divided light window. I’ve successfully bent two molded pieces. The spring back has not been an issue given how short the required pieces are. The amount of spring back in the four pieces bent is very consistent. If I had a greater number to make I feel a undersized form could be determined to account for it. However three more and I will have what is needed for the window

[Rob Luter]

Rob,
This will be a true divided light window. I’ve successfully bent two molded pieces. The spring back has not been an issue given how short the required pieces are. The amount of spring back in the four pieces bent is very consistent. If I had a greater number to make I feel a undersized form could be determined to account for it. However three more and I will have what is needed for the window

Looks like a fun project. Will it be single glazed or use lights that are dual glazed insulated? You should have quite a dramatic visual when complete.

[Jim Matthews]

This is a job for scratch stock (custom profile).

http://brfinewoodworking.com/making-a-scratch-stock/