Perfect Miter Joints Every Time
The trick is to assemble door and window trim with biscuits first, then nail it in place.
Synopsis: An experienced builder shares his time-tested process for installing miter joints — a process which saves time, requires less skill, and yields better results. In the authors case, it also put an end to his habit of falling off of mud-buckets used as improvised step ladders. This article highlights a logical and methodical approach for cutting miter joints and casing.
Ten years ago, my approach to installing casing was fairly traditional: Measure, cut, test the fit, walk back to the saw, trim the cut. Then one day, I climbed onto a joint-compound bucket to test the top piece of trim on a doorway a few feet upstream of a short flight of stairs. Microseconds later, I felt my feet describing an arc about my head and proceeded down the stairs like an otter wearing tennis shoes. It’s amazing how such a short trip can get so rocky, so quickly; it made me realize my methods (and stepladder) needed an upgrade.
A few months later, I happened to work with James Chambers, a talented trim and cabinet builder from Old Saybrook, Conn. He cut, biscuited, and clamped his casings together on the floor, then installed them as a complete unit. His miter joints were perfect, and the installation nearly flawless. By the next job, I had abandoned the mud-bucket shuffle and converted to the preassembly method of casing, which has improved work quality, reduced both the level of skill and hours required for the job, and extended the useful lifetime of my lower back. Here’s some of what I’ve learned over the years, wrestling with and pinning miles of casing.
Get set up, then cut the miters
When the material arrives, my crew and I orient it in the cutting room so that a 16-footer does not have to be spun end for end in a 14-ft.-wide room. I like to cut the miters before cutting the stock to exact length and prefer to have the outside edge of the casing against the fence when cutting them; this placement eliminates any tearout on the inside edge of the miters.
I always cut two sample 45° miters after setting up the saw station to ensure that the result is square and that all the details line up. After the necessary adjustments, someone starts cutting the miters, either lefts or rights for the trim on the sides of the doors, or door legs as we call them. This way, I don’t have to change the saw angle repeatedly. By placing a strip of blue painter’s tape on the miter saw’s extension wings as a reference, I can cut the door miters quickly an inch or so long and cut the square ends later. Once a bunch have been cut, they can be slotted for biscuits at any time. In addition, if the cutoff from one door leg is not long enough for another leg, it may be long enough for a top (or head), which can be cut after the legs are finished.
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