Replacing a mortise door knob - take a whack at it? Or get help?

July 3, 2021 3:32 PM

I’m trying to replace a mortise doorknob. However the new unit just barely doesn’t fit in the hole where the old antique one was. Should I get this done professionally? Or try and whack at it with a chisel. I’m scared of wrecking the door. Photos and video Linked.
posted by cacofonie to Home & Garden (6 answers total)

You can do this if you are handy. I had a similar situation, and I used a sharp box cutter and sliced away the wood a little bit at time until the new mortise fit in both the cavity, and so the face plate was flush with the side of the door. Take the lock and trace the the size of it, and then work away on it slowly and deliberately and you should be ok.
posted by momochan at 4:18 PM on July 3, 2021 [1 favorite]

You can do this. A wood rasp will help with enlarging the cavity. If that's not easy to find, you could wrap coarse sandpaper around a narrow square-shouldered stick, like a paint-stirrer.
posted by Glomar response at 4:25 PM on July 3, 2021 [2 favorites]

If someone called my old work and wanted it done it would start at 120 bucks.

It's too tall right not too wide? If that's the case use a sharp chisel and shave the top and bottom of the hole until it fits, use a sharp chisel. Make sure the handle will still go through the holes too.

Patience is a virtue.
posted by Max Power at 6:00 PM on July 3, 2021 [5 favorites]

Best answer: Make sure your tools are sharpened before you begin and go slowly. The door does look like it could get broken if you went at it forcefully. You might do better with a wood rasp than a chisel.
posted by Jane the Brown at 7:40 PM on July 3, 2021

Best answer: A 6" nail file (like the laser etched DiamonDeb) or the surprisingly good chromium carbide surfaced file on a larger Swiss Army knife would probably do the trick.
posted by jamjam at 1:36 AM on July 4, 2021

I try to avoid those inexpensive mortise locksets but have been forced to use them in some cases. You might look around and see if there is a salvage place that sells old door hardware nearby. It is generally pretty easy to open those old interior type locksets, decrud them, apply a small amount of oil where needed, and put them back to work.

I don't know where you find a rasp that narrow. The chisels from the big box tend to be sharp when you buy them.
It looks like it is too tall to me, I am predicating the answer on that. Before you start, see if the holes in the door for the knob are going to line up.

Get a chisel the same width or narrower than the mortise. Note the chisel is beveled on one side only. That side should face the wood you want to remove, the flat side the wood you want to keep. You may be able to do this without a hammer, use the chisel to shave small amounts of wood off the top and/or bottom of the hole. See above about the holes in the door for the knob.

If the plate does not fit the shallow recess in the edge of the door, put the lockset in and mark your line with a corner of the chisel. Remove lockset.

Now take the chisel and set it on that line straight on - i.e. level with the floor, bevel towards the wood to be removed. Tap it with a hammer to create the end of the recess. A little too deep is better than a little too shallow.

Now you can lay the chisel vertically flat on the face of the door and shave out the wood working from the hole towards the mark you created.
posted by rudd135 at 7:27 AM on July 4, 2021 [1 favorite]