Milling Radius Window Heads

I recently worked on a custom home that required radius window trim. It’s always a challenging and interesting task to create this special kind of finish carpentry trim, so I thought I’d write a bit about it.

There are a few ways to go about making radius window head pieces. The approach you use depends on the brand and model of window you are casing. In this example, we are working with ‘Eagle Brand’ windows which are manufactured with the jam piece in place. In other words, to trim out the window, all we had to install were the sill, apron, casing legs, and head piece.

In some cases, you can template the radius portion of the window and have the millwork supplier fabricate them for you. This is a pretty expensive option, and for this particular project, supplier wanted $250.00 dollars a piece. We had eleven windows in this house, and we were able to make the head pieces in approximately 2.5 working days. This amounted to substantial savings we were able to pass on to the client.

Here is how we made these particular window head pieces.

First, we laid out the location where the head piece and casing leg needed to intersect.  We then added the reveal we wanted, between the end of the head piece and the outer edge of the casing leg. On these windows, we had 3.5″ wide legs, plus a 1/4″ reveal between leg and window jam, which you can see marked out at 3.75″ (I snapped the photo before adding the 1″ reveal between head and outer edge of leg).

We did the same on the opposite side of the window, then carried this line through to represent the bottom of the stock piece we intended to cutting our radius head piece out of.

In this instance, we were working with a set of windows which we would eventually install a mullion between (a mullion is a piece of wood which caps the divide between two windows in close proximity).

Having made a mark where the head and mullion join, we then measured up and made a mark representing the top of the head piece – in this case 5.5″ up from the previous mark.

The measurement between the marks, representing the top of our head piece and the line we carried through from outside to outside of casing legs, told us how wide the stock needed to be. In this case, we cut our final head piece out of 13.75″ stock.

We then ripped a piece of 1/4″ AC plywood to 13.75″ – the same width of stock we used to mill the final radius piece. A 1/4″ piece of plywood got temporarily nailed in position over the top of the window. The window shape got cut out with a router, carrying the radius lines through to connect the two windows. After we had the inside radius established, we simply used a measuring tape and pencil to create our outside radius, 5.5″ from the inside curve.

After we had the template cut, we used it to mark the head piece on our 5/4 stock.

Since the radius on these windows was not very pronounced, we were able to use a circular saw to rough-cut the head stock to within 1/4″ of the line in our template.

Cut to within 1/4″ of template mark.

Here is a piece roughed out.

And a few more roughed out.

Next, with a few spring clamps, we positioned the template onto the rough-cut 5/4 stock and flipped it over so the template was on the bottom. We wanted the template on the bottom because we were using a 1/2″ flush-cut router bit to cut the stock to its final shape, and the router bit has a bearing on the bottom which rides against the template.

With the template on the bottom, we cut one side with the router, then transferred the spring clamps to the other side to finish the piece.

1/2 flush cut router bit with bottom bearing.

After all of the pieces were flush-cut to the templates, it was just a matter of easing the edges and installing them.

With this method we are able to manufacture just about any type of flat stock radius moldings we come across, right on site, and with amazingly accurate results.

My next post will be about installing 1×6 tongue-and-groove material on the ceilings of an octagonal room. We have a very slick method to do this.

Stay tuned!

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