Custom Mouldings for Arched Window Tops
From contributor F:
A lot of windows out there are not of true or consistent radius, especially the vinyl ones. Some molding guys will take a large piece of paper and thumb tack it to the wall so that the paper covers the window. They then take what is known as a rubbing from the window itself.
This is done by pressing the paper tight against the window outline and rubbing a lead pencil back and forth until you get the image of the part of the window that you need on the paper. You can use the rubbing as a template or as a guideline to set up a trammeled router with to cut your molding blank (CNC if you have one).
From contributor B:
We cut either templates or mouldings for other millwork shops on a regular basis - usually an arch, which is a section of a circle and only needs to be defined by a measured radius. An ellipse or part of an ellipse tends to be more suited to a field template. We have seen the same model elliptical window, as produced by a large name manufacturer, was not consistent in shape and size from one window to the next.
For applying a moulding that was to have a consistent reveal, this would have been a very large problem had these openings not been templated and reverse digitized. As the previous post said, what machine will you be cutting the moulding with? Nothing compares to a quality CNC router for producing accurate, repeatable and fast templates and mouldings. If you do not have a CNC machine of your own - simply job it out to a shop that does.
From contributor P:
We usually measure the radius by rise/run (height/width) then add the reveal to find the arc. Then we use a trammel with a router to cut out the blank, then run it through our moulder or shaper. I would suggest using carbide knives though..
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