Half and quarter round window trim

[denver]

I have an opportunity to make some curved outside window trim for some windows with half and quarter round tops. One difficulty is that it's 180 miles away. My brother lives near there, so I asked him to make some careful measurements. There are three half round tops and five quarter round. Here are the measurements I got back (horiz x vert):

Half round: 55 7/8 x 27 3/4, 60 5/8 x 30, 72 1/2 x 36 1/8

Quarter round: two @ 47 7/8 x 47, 40 x 39, 39 7/8 x 37, 40 1/8 x 39

It seems odd to me that H & V radius measurements are so different. The half rounds are closer than the quarter rounds, but none of them match very closely.

Assuming the measurements are correct, what's the best way to deal with this? Can I assume that these are actually round, just less than 90 or 180 degrees? In which case,should I use the long radius dimension? It will be ok if the pieces are a bit long - they can always be trimmed. I just want to avoid major gaps between the trim and the window. I can make trial parts from plywood or something, but I want to get this done with a minimum of fuss.

Thanks,

Denver

[Gary Campbell]

Denver..
It is not surprising to me the differences that you are seeing in those measurements. In trying to do a good job I have gone to the site with trammels, dividers, etc to get accurate measurements, with mixed results.
Here are some things that I have found:
1) The windows are usually not a true radius (usually truncated in 1 direction)
2) In many cases there are extra layers that makes the vertical different from the horizontal.
3) Sometimes the true arc center is not within the confines of the arc window
4) Window Mfgr supplied trims, due to mfg and/or humidity variations are usually off by 2-3" from end to end on a 36" radius 1/2 arc when the center top is held in place.
Suggestions:
1) Take multiple radius measurements and try to find the center point. It is important to get a consistant number for cutting.
2) If you cannot get the same length in at least 3 points, get close and go with the larger radius.
3) Unless the trim is extra thick or wide it will easily be able to follow the curvature of the window if your radius is within an inch.
4) Make sure you make the moldings 3-4" longer on each end to allow for scribing.
Gary

[seana]

Denver,
Have you contacted the window manufacture or looked on there website to see if they have the dxf's of there windows.
Some of the larger manufactures do for architects and builders.

Maybe you will get lucky.

Sean

[fleinbach]

Denver,

I have needed to make trims for curved surfaces and founfd the best way was to cover the opening with a piece of Tyvek and just trace it. Then I drew a grid pattern so I could transter the shape to the Shopbot. It worked perfectly for me.

[btk]

Denver,

Circle Top Windows often have a small straight segment on the bottom. For the Circle tops, I take the width and divide x 2 and get the radius and then add on the small stub legs on the bottom .

This is generally because the center point of the window is more the center point of the round glass and the bottom mullion is below this.

See attached picture... Red Line shows the base of the circle top.

Brian
4960

[denver]

Thanks everyone. Great ideas. I knew I was asking in the right place.

Gary (or anyone), do you make the extra 3" - 4" straight, or continue the curve? I would guess straight, but I've been wrong before.

The trim will be 5 3/4" wide for the half round windows and 4 1/2" wide for the quarter round windows. I'm not sure what kind of wood we'll use, possibly cedar. In any case, these will have to be made in multiple parts, so maybe the measurements aren't quite as critical as I first thought.

This will actually be the first "real" project for me. And I haven't had much time so far to spend on the 'bot. I'm glad it's a fairly simple project, but it's still just a little scary.

Thanks again for all the suggestions.

Denver

[wberminio]

When I went to ShopBot training,Chris,I,believe, had taken a photo of a corbel he needed to duplicate.
He then transfered the photo to a drawing file using
the dimensions from the original.From this he was able to replicate the corbel.This might work.

[garyb]

The only measurement you need be concerned with is the width the rest is all standard radius computation as BTK gave you above.
Don't forget to add to the width if reveals are needed and your extended legs need to be straight.
I would make the owner/builder spec the species of wood or you might end up doing them twice...

[btk]

Denver,

One more thing, if these are for exterior and are being painted, then you might want to look into getting a sheet of AZEK or another Cellular PVC and then just cut out of sheet in a single piece. I think the added expense of the sheet vs. wood will pay off because of no joining required.

The Azek could also be left without paint of just going for the white color.


Brian

[delicacarving]

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