This blog started with an old safe I bought with unknown content and combination. It describes the process of opening, finding the origins, contents and mechanics of the safe.

The posts are closely relate to each other and should probably be read in chronological order. Therefore, if you are visiting this blog for the first time you might want to start reading with the oldest entry and work your way back to the present time.

Sunday, August 30, 2009

The Locking Mechanism

When reading my blog I noted that it really should be read chronologically since the individual entries relate strongly to each other on the same project. Maybe a blog is the wrong format for this project. Anyway, back to the safe.

I had a close look at the locking mechanism. First I removed the inside cover of the safe door by taking eight screws out. The back cover has been bent open once before to unlock the safe from within through a hole in the bottom of the safe. The paint has chipped of along this bent line and this is clearly visible.

This is the sign on the inside cover of the door.

Taking off the cover exposes the mechanics of the locking mechanism. The door is filled with some type of concrete for fire protection. A metal plate fixed to the concrete is holding the locking mechanism. In this picture the locking bolts are pushed out, the safe would be locked if the door was closed.

There is a grey steel cover over the main part of the combination lock with a small soft piece of metal holding an extra lock up (underneath the grey cover), which would engage if the small metal piece (called trigger) was broken. This is called a relocking device which is mentioned on this sign on the front of the safe:

The idea is that somebody forcing entry will trigger this by either breaking the little metal piece or melting it. The safe would then permanently lock itself and make it impossible to be opened without major mechanical force or very detailed knowledge about the relocking device. Note that in my safe the relocking device has been tampered with and is not installed properly any more. Simply standing the safe upside down would disengage the relocking device. Normally there should be a spring loaded pin in the pivot of the relock arm, that "dead-locks" the lever in place.

I assume that in a previous forceful entry this relocking device was triggered and had to be broken.

In above photo I removed the grey steel cover exposing the brass case that is holding the combination locking device. Next I removed the brass cover:

The brass cover is holding the wheel pack (see photo below). The pin on the top right of the cover presses on a release spring in the brass casing. Only if the brass cover is on the casing the lock automatically disengages when the nose enters the gate. The pin can easily be simulated by pressing the spring with a screw driver. I guess this is another device to make forceful entry into the lock difficult.

The combination lock is a Herring Hall Marvin manufactures lock. The wheel pack consist of three wheels called "hole change" type. Each wheel has holes in increments of 4. The top most wheel and the bottom wheel have even numbers while the one in between has odd numbers. A combination is set by carefully disassembling the wheel pack and putting the grey metal pins in the holes with the desired numbers. The bottom wheel corresponds to the first number to be dialled in the combination and so on. All wheels are different and have to be reassembled in the same order as they were disassembled, otherwise the desired combination wont work. It is therefore very important to test the combination with the door open before locking the safe. Here are some photos of the disassembled wheel pack. Note that the wheels are numbered from 3 the top wheel to 1 the bottom wheel to indicated their corresponding position in the combination.

With this type of lock the starting direction when dialling in the combination is important since the wheels don't have what is called movable flys. The gate and nose configuration is such that the lock will disengage entering from either way. This means that there are two slightly different combinations that will open the safe depending on the starting direction.

Judging by the size of the gates in the wheel pack and the fence (cylindrical in this case) I would guess that there is a tolerance of about 2 to 3 numbers. This means that one could be out by one with each number when dialling the set combination and still open the safe. This safe is in the first instance a fire protection safe and is not regarded as having a high security locking mechanism which explains this tolerance.

Now the interesting thing in my lock is that the numbers selected on the wheels do not correspond to the numbers that open the safe. This most likely indicates that the wheels in the wheel pack have been taken from a different type of lock. Since I have a working combination I know which number in my combination relates to what number in the wheel pack. I can therefore make a lookup table of corresponding numbers for this wheel pack. With this lookup table I can set my own combination. I will try this soon and report back.


  1. Your page here was very informative. I learned alot reading it. One thing i didnt find was setting a new combination. I was giving a safe similar to the one shown above with the same locking mechanism. The origanal owner didnt remember the combination but it was open. They was just goin to toss it, im fix it kinda guy and looked like a good safe. Didnt think it would be to difficult to reset the combo or figure out the old one after getting into the lock. Long story short i arranged all 3 pins in the wheel pack to set a new combo and right down the origanal locations. Before doing anything i did a little research on the web and i later realized after moving the pins that the page had been describing a differant style lock altogether. For the life of me i couldnt recall what numbers the pins were on. I know theres still has to be a way of determining where the pins should be. I hope you can possibly shed some light on this for me

  2. I sincerely enjoyed browsing your site. Informative, easy reading. I think I now understand the reason but the remedy still has me guessing. I have an antique safe similar to your pictures. Apparently I have triggered the relocking device. The handle spins, the combination knob seems locked. It has been a reliable safe until recently had to start forcing to open & close. Upon attempting to open, felt click and handle now spins 360. Turning it upside down didn't work either.
    Am I farting in the wind or is there a feasible way to get back into my safe?

  3. I inherited a safe exactly as show. The combination rotates freely but I do not know the combination. I tried to give the safe away here in Palm Springs but neither safe company wanted when I texted them a photo Trying to learn its weight so I can have it move to a scrap yard.