• Manufactured by Trig Industries
• 888-483-1221; www.jambmaster.com
• Cost: $495

Routing a perfect rough opening for a door sure sounds like a weird concept. But that’s what the Jambmaster allows you to do. This doorsize jig works on any type of door, prehung or slab, in widths from 18 in. to 60 in.

The heart of the system is a pair of lightweight vertical aluminum frames with built-in router-template guides. The aluminum frame is set to the jamb dimensions, placed in the rough opening, and plumbed using a surprisingly accurate built-in bubble vial. Then you use hot-melt glue to attach flat shims along the inside of the rough opening. (I cut a boxful of shims ahead of time from 2x framing lumber.) Using a bushingguided straight bit, you rout the shims down to mirror the plumbed and squared sides of the Jambmaster. The prehung door then can be slid snugly into the shimmed opening; next, the door is nailed through the routed shims and into the framing. You get a perfectly hung door on the first try.

On a recent project, I used the Jambmaster to set five prehung doors in rough openings. I was dealing with new 2×4 construction as well as twisted old-house framing. I was more than pleased with the results. Despite less-than-perfect openings, the new jamb sides on each door were plumb, square to the wall, and straight.

The manufacturer advertises that the process takes seven minutes per door. On my first day with the jig, I averaged a little less than 30 minutes each by the end of my fifth door. I think that’s pretty good for a system that doesn’t care whether openings are old and twisted or new, square, and plumb. The downside: At nearly $500, this tool is expensive. Still, if you do doors for a living, it might be a worthwhile expense.

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