Recently we were asked to install interior finish trim casing on a house worth of windows 14 in all and a few doors. The house was mostly ready for painting with the exception of the window trim.  Installed it looked like this.  It’s going to look great when it gets painted.Most of them were straight forward rectangles (above), but 3 of them had curves introducing a few challenges.  The trim consisted of regular primed 1×4 sides and bottom.  The head casing was 1×4 with a 7/16″ sash bead on the bottom and a 1/2″ sash bead on the top, all stock moldings.

detail of head casing with mitered return

The beads were both 1 1/8″ wide so they got ripped down.  Next I glued and pinned the sash to the 1×4 and let it dry.  That way I could cut the miter returns with two cuts instead of fitting each individual piece or 6 cuts.   I pinned top and bottom at the same location about a foot apart so that I could avoid the nails when cutting to length.  Even though a carbide blade goes right through a 23 gauge pin, I like sharp blades.  I reinforced all the cut returns with pins and glue and sanded the corners.

Here’s how the curves turned out.  Needs paint.

eyebrow window with casing

oval window with simple casing

picture window with half round trim

As you may be able to tell MDF was key here in cutting curved flat stock.  If this were a stain grade job, I would have used an architectural veneered MDF panel with solid hardwood beads for the curved trim and solid 1×4 hardwood for everything else.

I installed the eyebrow window first.  The extension jamb must have come from the manufacturer and was installed so I just needed to do the casing.  Starting with a 8′ long by about 16″ wide piece of MDF, I screwed it over the top of the window extensions leaving room to get my arm underneath.  I took a sharp pencil and scribed the curve.  I also marked the inside locations of the jamb on the MDF.  I extended the curve line 6″ beyond the inside jamb mark on both sides with a straightedge then slightly curved it by eye.  I jigsawed the bottom curve out then with a belt sander trued it up to the line.  The bottom bead 7/16″ thick was really a bit more than 3/8″ and the reveal of the trim around the window 3/16″.  So I needed to remove an equal 9/16″ from the bottom curve.  My rabbeting bit set (Whiteside) had bearings for a 7/16″ cut and a 1/8″ cut.  So I made a rabbet cut with each bit then flipped the MDF and used a bottom bearing flush bit to finish.  Now I set my scribe to the 1×4″ width and scored a top line, cut it and sanded it true.  Now I took a adjustable square and marked the 9/16″ line on the wall above the window and tacked the piece to the wall.  I scribed and cut the side casing then marked the ends of the curve to length.  With the curve back off the wall and ends cut and sanded it was ready for the beads.  The 7/16″ and 1/2″ thick bead molding had no problem bending to the curve, so I miter returned one end bent it around with some clamps marked it for length then cut and returned the other edge.  Clamps, glue and brads held it in place along the curve.  When I installed it, I screwed the two ends to framing and pushed the middle up to the 3/16″ reveal line because the beads were installed with some tension and were trying to straighten the piece.  I used trim screws to attach most of this piece to the framing and brads to the jamb.  The rest of the casing was straight forward trim cutting the two sides to length then the bottom.

eyebrow window with casing


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