Coping crown molding with an electric jigsaw is much easier when you attach a radiused auxiliary base to the jigsaw’s standard flat base. But I was stumped about making this modification until I spotted a golf ball on my shop bench.
As shown in the drawing, I started by cutting the ball into unequal parts. I did the cutting on my bandsaw after driving a couple of 3-in. drywall screws into opposite sides of the ball to act as handles. The screws kept my fingers a safe distance from the blade. Then I made a perpendicular cut in the larger portion. Still at the bandsaw, I cut a slot to accommodate my jigsaw’s blade.
Next, I drilled a couple of 1/8-in. holes in the saw’s base, on opposite sides of the blade, for a pair of screws. I positioned the slotted golf ball as shown in the drawing and affixed it to the base with a couple of small screws.
This jig provides a pivot point right where the blade enters the back side of the molding. As a result, I have the control to make exact relief cuts. I have found that longer blades are useful for cutting big crowns. Different configurations could be obtained by cutting the ball into segments of various sizes.
Jim Delvin, Des Moines, WA