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One of the classic tests that distinguish a skilled carpenter from a wannabe is the ability to hang a door the old-fashioned way: assemble a jamb set, fit the door blank, mortise the hinges, and put all the pieces together.

Hanging a door from scratch is way more time-consuming than installing a prehung, but it's an extremely flexible process. If I need to hang a door in a hurry and can't wait for the lumberyard to order a particular prehung, it's a safe bet that the jamb material and door blank I need are in stock.

More often, if I'm remodeling an older home and need to fit a door to a nonstandard rough opening — or if I want to recycle a salvaged door panel — the solution is to build a custom-sized jamb set and trim the door to fit.

Assembling a Jamb Set

Years ago, before prehung doors became as popular as they are now, you could buy ready-to-assemble jamb packages for popular door sizes that simply needed to be nailed together. These days, the suppliers in my area keep only 7-foot lengths in stock, so even a standard door frame has to be cut to size.

If I'm fitting the jamb to an existing door blank, I measure the door and add 3/16 inch to the width and about 1/2 inch to the height. These measurements represent the inside dimensions of the jamb.

For strength — as well as appearance — I rabbet the tops of the side jambs to receive the head jamb. It's possible to use a trim saw and a chisel to plow out the rabbets, but a router does the job faster and better.

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A square-cut scrap of jamb stock acts as a straightedge.

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Routing a 1/4-inch-deep rabbet into the top end of each side jamb.

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Carpenter's glue.

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2-inch screws ensure that the jambs stick together for the long haul. To prevent splitting the narrow jamb material, all of the screws are countersunk.

Before cutting the head to length, remember to add 1/2 inch to account for the 1/4-inch depth of each rabbet.

Routing the rabbet. After scribing the thickness of the head jamb on the end of each side jamb, I make another pencil mark that represents the width of the router's base plate (measured from the inside edge of the bit) and clamp a straightedge at that point.

I make a test cut on a piece of scrap to verify that my measurements are accurate and that the router's depth setting is spot-on, then I rabbet all of the side jambs one after another.

I fasten the parts together with carpenter's glue and 2-inch drywall screws.

If the door stops are on the job at this time, I'll tack them in place using a method shown on the last page of this story.

Setting the Jambs

A solid-core door panel can weigh 100 pounds or more. To support this much weight, the jambs have to be securely fastened — but they must also rest solidly on the floor. Otherwise, over time, gravity and centrifugal force will take their toll.

I always check the floor with a level to determine whether one side of the rough opening is higher than the other. If the jambs will rest directly on a subfloor, I simply place a shim underneath the low side. If the jambs are set directly on top of a finished floor, as they were on the job shown in the photos, I scribe the high-side jamb and cut it to fit.

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Before putting in the door jamb, the author checks the floor with a level to determine whether one side is higher than the other.

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Since this jamb is resting on top of finished flooring, the high side must be scribed and trimmed, or the head jamb won't sit level.

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A fine-toothed Japanese pull saw is more accurate than a power saw and cuts almost as quickly.

I roughly center the jamb in the opening, using a homemade spreader to keep the width at the bottom the same as at the top. I then slip a pair of shims behind the bottom hinge and pin the jamb by driving a pair of 2 1/2-inch nails underneath them.

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After the jamb is placed inside the rough opening, a spreader keeps the bottom square with the top, while a straightedge ensures that the assembly stays in plane with the wall.

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With the jamb centered in the rough opening, the bottom hinge is shimmed and tacked, with nails driven beneath the shims to permit adjustment.

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Then the top hinge gets the same treatment. Note that although the author is using a prehung door jamb in this photo sequence, installation of a site-assembled jamb set is exactly the same.

I plumb the face of the jamb with a 6-foot level, then shim and pin the top hinge following the same procedure. I don't secure the latch-side jamb until after the door is completely hung.