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.

The Origins and Contents of the Safe

After some research on the internet I managed to reconstruct most of the details of how the safe ended up being on an internet auction for me to buy.

In 2000 an American couple bought a holiday home in Christchurch, New Zealand, bringing the safe with them. She tragically died in a car accident in 2006 in Texas. A relative then investigated the safe (which apparently led to the drill holes next to the lock) and wrongly declared it empty. The husband returned to New Zealand in 2008 and got an auction house to auction the contents of the house. This included the locked safe. A local antique dealer bought a number of items, including the safe, on this auction. He tried two locksmiths to open it and eventually gave up, not wanting to spend more money on it. He then listed it on TradeMe a New Zealand internet auction site similar to eBay, where I managed to buy it.

When I finally opened the safe it was full to the brim with things. Most of it were documents, family photographs and other family mementos. Besides that there were two sets of US silver flatware and a collection of bead necklaces.

A few days ago I managed to contact a son of the previous owner. Many of the documents in the safe related to him. He was very pleased to hear that some items thought to be lost were still in existence. He asked me to send him the family photos, mementos and documents, which I did yesterday. He gave me some further background to the safe. It has been in his mothers family since they bought it in an auction in 1977. He still remembers the last combination it had, which is different from the one it has now. He thinks its likely that his mother had the safe opened at some stage due to loss of the combination on her part.

My next plan is to have a closer look at the lock by taking off the inside cover of the safe door. I will report about that as soon as I find the time.