Mortise lock picking.
I decided to have a look at mortise lock picking, which sounds great in theory, but not so great in practice !. I was actually shopping for piano wire when I came across a 3 lever mortise door lock, for the noble sum of £5. I took it home, stripped it down and re-assembled a dozen times and was struck by it's simplicity, flimsy construction and I still have not worked out how, in a million years, the levers can line up with the bites in the key !. The lever stack just seems to flop around. Each lever is about 0.8mm thick and between the levers is a spacer wafer that is 0.5mm thick. There is an additional spacer on top of the stack, between the top lever and the case. All we have to do to pick the lock, is apply tension to the bolt and then raise each lever to the correct height and the lock will open !.
Tensioning the bolt.
The bolt is tensioned in the same way as the key does. Pressure is applied to the bolt in the direction that you want it to travel. The only problem is that the only way into the lock is via the keyhole and it is through this that both the tensioning device and the picking device has to fit at the same time. As far as I can ascertain, a much greater amount of tension is required, so the average tensioning tool has a 'T' bar to enable this torque to be applied.
The picking wire.
The job of the picking wire is to allow the operator to raise each lever in turn, in the binding order, until the release slot in the levers all line up, and the bolt can be withdrawn ... by the tension applied to it.
If we go back to the dimensions I gave in the introduction for the thickness of the levers and the spacers, it ought to be seen that the width of the picking wire must be more narrow than 1.3mm. So the operators task is to move the pick backwards and forwards in the lever stack, align the pick wire with the lever, then turn it to raise each lever in turn .... in the binding order. It is an act requiring delicacy and precision .... at least on my floppy £5 lock !.
The design of the tool.
So far I have seen three different design approaches for the un-curtained mortise lock tool. The machined 'co-axial' tool, a somewhat simplified version based on the Dangerfield design and ad-hoc versions of the above. Costs for the first two types may vary between £50 - £100 per tool. Some tools are sold in a 'raw' state which means they have to be 'adjusted' by filing to suit a single lock or lock type. The filing operation may mean that the tool will not work with other types of lock, so cost becomes a important consideration.
Most designs require a slot to be machined in the tensioning tool, to accurately locate the picking wire and this requires access to machine tools. It is possible to make this slot with a hacksaw or even a needle file and I have done so, but the end result will always end up inferior to the machine produced examples.
There is an even simpler design, consisting only of a filed down key and a picking wire made from piano wire. An example is shown below.
The idea does work and I have picked my mortise lock over a dozen times using this DIY tool in the last two days .... but one thing is sure .... there has to be a better way !. Points to note are that the tip of the pick wire has been ground flat and is curved. Since quite a lot of torque is required to tension the bolt to an opening state, the hole in the tensioner can accommodate a 'T' bar. Likewise the torque loading on the pick wire is also quite high and therefore at least two set screws will be required in the 'knob' to stop it slipping, on the wire. As you can see, if required there is plenty of space for even more set screws to secure the picking wire.
In my £5 mortise lock there was no spacer between the bolt and the bottom lever. The reason for this was that the lock used the same bite for both the bolt and the first lever !. However when we are picking, it produces a difficulty, because the picking wire only has to be a fraction out and it catches on the bolt. The tensioning pin also only has to be a fraction out, to catch on the bottom lever !. With the lock in a vice on the bench you can see this happening, but when the lock is mounted on the door, you are working 'blind'.
One possible solution is to treat the lever/ spacer pack as a composite 'sandwich' and use the outer edges of the lever pack, as their own reference points when positioning the picking wire. I am still thinking about this. It would overcome the limitations of the 'floppy' lever pack.
A DIY "Dangerfield" mortise picking tool.
Just to show it is possible to saw and file the slot for the picking wire, here is a home made Dangerfield type tool, for picking mortise locks. I started off by cutting the slot with a hacksaw and then opened the slot up with a needle file.
For the tension pin I drilled an under sized hole in the slotted torsion wrench and then hammered a pop rivet shaft into the hole. I had planned on silver soldering the pin in place, but found the force fit was good enough for the task.
A close up of the pins, shows how the tip of the picking wire is shaped, to smoothly address the lever The width of the tip must be narrow enough to pass between adjacent levers and spacers. On some mortise locks there is no spacer next to the bolt, because the lever and bolt use the same depth of cut and that further restricts 'picking room'.
Other mortise locks.
I have on the desk in front of me, some Chubb 9 pin brass keys. Now if the lock was the same quality as the keys ..... and of course it has to match the keys, from 'new' to 'worn' then I suspect that picking an expensive Chubb mortise lock would be a pleasure compared with my £5 pile of crap. However we have to examine the extremes in order to produce a 'universal' solution.
A Rotary mortise lock lever bumper. ?
This is just a reminder to me. It started off as a joke, but then developed into a subject for a brain storm session, which was unfortunately continually interrupted by someone wanting to discuss semantics'
An externally driven flail to bump the levers up in the same way as happens with a bump key in tumbler locks. The term 'bump' is as defined in the Oxford dictionary and is not dependant Newton's Third Law of motion!.
OK, just in case Barbarian passes this way, let's consider the flail. To prevent damage to the levers the flail 'fingers need to be of a softer material than the levers. Another requirement is that the flail must be able to pass through the key hole !. Ok let's go through the keyhole as see what we are dealing with !.
Here we can see the stack of three wafers in relation to the keyhole. If a flail was rotating clockwise it would strike nothing other than those components that have to move to open the lock, ie the levers have to move upwards and the bolt to the right.. The hinge pin for the lever stack, can clearly be seen at upper left. The bottom lever is small and hidden under the stack. Under the stack the bolt can be seen and the curved slot in it that the key would fit into, to move the bolt to the unlock position (to the right). So it may be asked, with the flail in operation, would the bolt be self tensioned ?. If we zoom out a little ......
We can now see the whole of the lever pack in relation to the keyhole. The completely independent handle mechanism can be seen on the top.
The original idea came from the anti-mine flail tank, which used rotating chains to explode the mines. We have to bear in mind that ours has to pass through the keyhole. My first thought was that we need a steel shaft, the end of which is bored to take five flexible flail fingers. So the working end of the flail would look something like an artists paint brush with five very thick bristles. When the shaft is rotated, centrifugal force forces the fingers into the shape of a disc. As the disc rotates the fingers bump the bottom of the lever pack, bouncing them upwards. When all gates have cleared the bolt, the bolt will open. Maybe I ought to have said IF all the gates cleared the bolt !. I can hear the arguments in your minds, but just ask your self one thing, isn't this the same as trapping the driven pin pack above the shear line, when bumping ?. The levers trap out in the binding order, so there is NO question that they ALL have to clear the bolt at the same time.
Why wouldn't it work ?.
It requires a certain amount of energy to strike the levers hard enough to cause the center of the gates to bounce above the bolt scear. This takes us back to Newton's laws again that says that Force = Mass x Acceleration. The flail fingers will have a relatively low mass compared with the levers, however we can compensate between certain limits by increasing the acceleration of the flail fingers, by increasing the rotation speed of the shaft. A limiting factor is the stiffness of the lever return springs. So to the question of would it work, I would say that no-one knows unless they try it. If anyone wants a starting point ... read Hatchers notebook on ballistics !.
I do not approve of cutting the bow off an old mortise key, chucking it up in an electric drill, in order to try this out ... unless you have good insurance !