I have a metal door with a privacy mortise lock with a thumbturn.

I can't drill any new holes outside, we must use the existing hole for the door knob and deadlock.

I have to replace the existing mortise lock system to a separate single door knob lock set and a separate single cylinder deadbolt.

It means also reconfiguring the doorjamb (it is currently configured to the installed mortise lock).

Inside, the metal door has holes for the mortise and they would have to be covered somehow since the new door knob and specially the deadbolt won't be in the same position as the current door knob and thumbturn.


  • To make sure I can reuse the holes on the outside, what is the standard (or at least the recommended nowadays) distance between the door knob and the keyed deadbolt?

  • After removing the current mortise lock system, which is big, it will leave a considerable empty space inside the door, after installing the new door knob lock set and the single cylinder deadbolt. What do you suggest to fill it with? In fact, I think I need to fill it before I even install the new knob and deadbolt, correct?

  • Inside, because it uses mortise lock system with thumbturn, the hole where thumbturn is installed is not aligned with the outside hole (by design of the mortise lock). I will have to drill in the exact same height so I can install the single cylinder deadbolt. That will leave the hole of the thumbturn open. What do you suggest to close it, remembering it is a metal door?

I had a locksmith just emailing me saying this can't be done, but he was not specific as to why. Maybe because you can't really close existing holes in a metal door? That seems the most difficult part to me. Or because removing the current mortise lock will leave just too much space inside the door?

Thank you for any insights!

  • I want to better understand your requirement for not drilling holes in the metal door. Are you intending to remove at a later date without leaving a trace? Do you not own this door? Also, why are you converting from mortise to cylindrical lock? Why can't the solution be as simple as buying a mortise lock with an integral deadbolt (preferably the same brand) and reuse all the existing holes? I feel like you're overcomplicating/overthinking this. – Dotes Jul 10 '19 at 22:56
  • @Dotes Thanks. I can drill holes, but only the inside (apartment). Facing outside can't be modified due to building policies. I own the door, and I don't need to remove the modified lock later, it will stay. One of the reasons to go to traditional cylindrical lock is to later be able to install a smart lock (not compatible with mortise locks), but it's also my personal preference (prefer simpler stand-alone locks over all-in-one mortise). – igorjrr Jul 11 '19 at 2:07
  • I believe there are a few smart mortise lock sets available. – Alaska Man Jul 11 '19 at 5:16

I can't think of a way to do exactly what you want to do.

I haven't been able to change a mortise lock prepped door to accept a cylindrical lockset without using a remodel escutcheon plate that wraps around the 3 sides of the door.

Since your comment says that your end goal is to be able to install a smart lock, I'd suggest looking at commercial access control systems instead of the typical residential smart lock solutions available in retail stores.

The two most common ways to electronically open a door is with either an electric strike, or an electric lockset.

Electric locksets require special electric hinges and also require you to drill a hole from the strike to the hinge, so it's pretty difficult to do on site if it's not already prepped at the factory. You said that it's a steel door, so if the door is hollow it's much easier than in a solid core wood door.

Electric strikes are the easiest way to retrofit smart lock functionality on to existing doors with mortise locks. You don't even need to disassemble the lockset, all the work is in the frame. Basically the strike plate on the door frame opens and closes to allow the locked door/lockset to open when energized.

The user interface of the access control system is typically a PIN keypad or an RFID tag reader, but fingerprint might be available too.

Instead of using a normal deadbolt, you'd pair the electric strike with an electric drop bolt style deadbolt that goes on the top of your door and door frame.

  • Thanks. What about cutting a wood piece of that completely fills the space where the mortise lock used to be, install the new door knob and deadlock latches in this wood piece, then insert it into the door where the mortise lock used to be? Wouldn't that be doable? – igorjrr Jul 11 '19 at 21:42
  • @igorjrr I thought you couldn't drill any holes in the outside of the door. You usually need at least a 2-3/8" hole for a cylindrical lock, and you currently wouldn't have that with a mortise lock, so you'd need to drill it, but you said you can't. – Dotes Jul 11 '19 at 21:46
  • So I did not express myself correctly, I'm sorry! What I wanted to mean is that I can't change the current configuration/positions of the holes, but as long as the new keyed lock takes up the space, it is fine, so increasing the hole a little bit, and installing the new keyed lock is OK because it will still be in the same position and look just like before (just a little bigger lock I assume?) – igorjrr Jul 11 '19 at 23:04
  • @igorjrr Your largest potential issue will be getting something to screw the cylindrical latch in to, but if you're okay with the aesthetics of a wood filler block inside the metal door that you can see from the latch side, then it might work if you can find a way to get wood in there and also secure it. The correct way would be to have a commercial door technician field weld in a cylindrical latch mount into the steel door. It's likely that a brand new door would be less expensive and be guaranteed to work, so they would probably steer you towards that solution. – Dotes Jul 12 '19 at 12:27
  • Also if you're going to put wood in your door, you might want to check on the building code in your area. Typically corridors in multifamily buildings require non-combustible materials to be used, highlighted by the fact that you have a steel door most likely for the same reason. I'd purchase non-combustible wood for the filler block just to be safe. That's wood that's been specially treated to prevent it from burning, typically available at places that supply/sell commercial drywall, insulation, and steel studs – Dotes Jul 12 '19 at 12:38

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