An Easy Technique for Pre-assembling Casing
(Photos by Kirk Grodske)
I don’t do a lot of trim work. But when I do, it’s often stain-grade or pre-painted, and the miters have to be perfect! I mostly hang doors, so I rarely have a full-size work table set up—usually, I just have a door bench. Most of the casing I work with is small. At first, I thought it was too small to survive a Clam Clamp, but I’ve learned better (more on that later!). So I came up with a method for pre-assembling casing that will guarantee tight miters and won’t require a large table. For this method, you won’t need to use staples, or biscuits—just glue. But the pre-assembled frames will be so strong that you can carry them in one hand.
I first made several sets of pre-assembly jigs, all of which are perfectly square and have a thin strip bordering two edges. I start by clamping the legs to two of the jigs with A-clamps. A single sawhorse is all I need for this technique.
|The back of each jig is covered with a non-slip material so the jigs won’t slide off my saw horse (I use Solid Grip Liner, Contact brand.).|
|Next, I glue up the miters with Titebond.|
|On wood moldings, I nail the corners with a brad, but on MDF moldings, I let the glue do all the work–MDF casing splits unless you nail it with a 23ga pin.|
|The assembly jigs do all the work. They keep the pieces square, and the A-Clamps help hold the casing flat, so the miters come out perfectly. I made several sets of these assembly tables.|
With multiple assembly jigs, I can leave a frame to dry while assembling another one. As soon as I finish a frame, I pick it up off the sawhorse, carrying it by the assembly jigs. It only takes a few clamps to stay busy.
One word of warning: If you’re like me, and you use these pre-assembly jigs frequently, you’ll want to wax them or coat them with some type of release agent so the casing doesn’t end up glued to the jigs.
The glue sets in about ten minutes.
|By that time, you can carry the frame in one hand and even shake it—the miters won’t open!|
The Clam Clamp Method
Since I first took the pictures you saw above, I was able to figure out an even better way to pre-assemble casing, especially small casing. Now I use a Clam Clamp!
To use Clam Clamps (see Gary’s tool review) on thin casing, I rabbet the assembly tables.
|This technique works much better with Clam Clamps, but the process is the same: Always clamp the casing to the assembly tables first. I position the casing so that it hangs over the rabbet just a bit.|
Once the Clam Clamps are on, the assembly tables make it much easier to move the frame. You can’t get this kind of clamping pressure from spring clamps, and when you use Clam Clamps, the joints are so durable, firing a brad nail through the miter becomes a waste of effort.
(This article originally appeared on GaryMKatz.com.)