How to address “sticky” mortise lock knobs

One of the problems endemic to people with houses more than 100 years old is inevitably the sticky mortise lock knob. This is probably a lock on an original door with a crystal glass knob but it could also be brass. When you turn the knob the latch doesn’t spring back out. There are a lot of possible reasons for this and I have pontificated at great length elsewhere online about this but I am going to explain the most common problems and solutions right here.

First I will list the problems that can be fixed without taking the lock apart. Number one problem is people overtightening the knob because nobody likes door hardware that feels flimsy, it seems natural that the knob shouldn’t wobble around on the door. Usually these knobs are screwed onto a spindle. You screw the knob on and then tighten a set screw at the base of the knob to hold it in place. You or your family may have inadvertently overtightened your knob when this set screw loosened, allowing the knob to turn independently of the spindle. Sometimes people spin the knob the other way and it loosens. Then the door doesn’t open and they call me in a panic.

This problem can be solved by screwing the knob onto the spindle only tight enough that the latch still springs back when the knob is released. If you tighten the knob more than that, the friction of the base of the knob against the rose (plate on surface of door) will be greater than the force of the spring inside the lock and the latch won’t come back out. (I never thought I’d use anything from honors physics. Thanks Mr. Elder, you are a peach!)

Once you have found that optimal sweet spot for your knob then tighten the set screw. If you are a type a personality and want to do the job right/don’t want to ever think about this again, buy something called threadlocker in the blue color and put a small dab on the set screw before screwing it in. This prevents the screw from backing out and loosening which may be what got you into this mess in the first place.

Ok so that covers the most common and easiest fix. That eliminates maybe 75% of you. On to the next most likely problem: alignment of the spindle within the lock. We have already examined the problem of friction between the knob and the rose, or “base plate” for those not familiar with door hardware terms. Other variables can cause excessive friction or wobbling in your lock too. The two main problems here are overtightening of the screws holding the mortise lock in place and misalignment of the rose or base plate on the door.

The mortise lock when installed should have the hub centered perfectly in the door between the two holes in the metal plates on either side of the door. If your door has no metal plates then that is a problem. Originally there probably were plates but some helpful person decided they were unnecessary and, well, here you are! Turns out they are necessary to support the knob and keep it from wobbling around.

Back to lining up the holes. If you look through the holes in those plates on your door, it should be a straight unobstructed hole through the lock. If it is not then you need to take some cardboard or something and put it behind the lock when you screw it in. You need to make it so that when the screws are tight, the lock’s hub is centered with those holes. The idea is that the spindle will spin without rubbing against anything.

Maybe the lock isn’t the issue though. Maybe the roses are too high or too low. Maybe they aren’t screwed into the door at all! Many times when people call me to look at these locks I take the rose off the door and find a perfect circle of little holes drilled into the wood at intervals because over time the holes got stripped and people rotated the screw holes on the rose for fresh wood. After 100 years of handymen and weekend projects, there isn’t any fresh wood left! Then it is time for either a different rose, plastic wood filler, or an entirely different solution like rivnuts or some other esoteric fastener.

Sorry I got off on a tangent. The main idea we’re on is making sure the roses are installed in the right spot. A lot of times they aren’t. To find out where they should be installed I like to take all the screws out of the rose and then tighten the knobs so that they are snug; don’t overtighten or you may distort the shape of the rose which brings us back to one of the earlier troubleshooting steps.

Once the knobs are snug and assuming the door is perfectly flat and free of paint ridges that the roses might slide into, we can assume that the roses are optimally placed. The screwholes may not line up with where they were originally and there may be a different color of paint showing. Unfortunately there is a decision to be made: will your antique lock work properly or will your door have some unsightly paint from yesteryear peering out? If you choose to have a properly functioning lock, stick a sharp object into the screw holes to mark where you need to put the screws.

Now you remove the knobs and drill pilot holes. These holes need to be smaller than the screw and they shouldn’t go into the body of the lock. I know that one is the very definition of a pilot hole and the other is also obvious but I’ve seen some stuff, okay? Make sure that the screws aren’t longer than the hole they are going into. These screws are usually really short which is why the holes always get stripped out. Ace Hardware has a great screw selection and even have antique brass and oil rubbed bronze finish wood screws in the appropriate sizes. I like the Maple Leaf Ace Hardware for my fastener needs.

We have now covered the easy fixes. On to the harder ones.

Sometimes knobs and/or spindles have stripped threads. This causes overly muscular or determined people to turn the knob past where it is necessary to open the door, and can also overtighten the knob. The solution, aside from removing caffeine/television/twitter and other stressors from your housemates’ lives, is to replace the knob and/or spindle. I mentioned Ace Hardware a little bit earlier. They also sell mortise lock knobs and spindles. These work in most interior mortise locks. They probably are inappropriate for exterior mortise locks and may cause a big problem if used instead of a split spindle.

The Ilco mortise knob set comes in either glass or brass finish. The brass one is made either of a very weak metal or plastic, I’m not sure which. The glass one may also be made of plastic. There are more expensive options but nobody wants to spend $120 on one of these doorknobs. If somebody does I have some actual crystal glass doorknobs to sell you, new.

Follow me into the weeds and we discuss opening the mortise lock. There are lots of reasons inside an old lock that the latch might not spring out. The latch might be bent from abuse, there may be some foreign object or broken spring blocking it, there may be paint on it because painters frequently don’t bother to tape off locks and just paint right over them causing the bolt to stop working unless you pay me to take it apart and clean it.

There may also be a broken spring. People are forever mailing me locks with broken springs. The two most common kinds of spring are the coil spring which wraps around the latch and the flat spring which either directly forces the latch back out or acts on a lever of some kind at the top of the lock connected to the latch.

The coil springs are stocked at Ace Hardware. The flat springs are used by gunsmiths. They can also be taken out of old windshield wipers or street sweeper blades found in parking lots if you want to fix it on the cheap. Usually the shape of the spring can be determined from looking at the broken pieces of spring inside the lock. Oftentimes these are missing after some enterprising individual from the past removed them when trying to fix the lock. You may find a bent paperclip or rubber band in its place if you’re lucky. In this case either deduce the shape from the features of the lock or mail it to me.

I hope that this information helps you fix your lock. Many of you are spending more time at home due to the Covid 19 pandemic, drop me a line with comments related to this and I may update it in the future.

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Bjørn Madsen

I am the Seattle locksmith you've been looking for. High Quality work at a reasonable price delivered in a timely fashion.