2nd February 2010
I thought that it was time to make a bump hammer from Delrin. I had been hesitating because never having bumped a lock, I was not sure exactly what was required in terms of weight, springiness, and handle length.
This is about life size. The handle is far too long (14"), but I will not cut it to size until I have had some practice.
The bump keys came in a set of three, each cut to different depths. On arrival the bump keys had sharp rough edges, so the first thing I did was to 'clean' them up and remove all burrs. I later found I had under done the cleaning and had to do a bit more, especially after key three got jammed in the lock
I practiced on an un-mounted generic Yale type cylinder lock. Having watched all of the Youtube video's on bumping, I at least knew that the big mistake most beginners make is applying too much pressure to the key when hitting it. This traps some pins, prevents them from 'flying'. I found I needed so little pressure, that there was very little feedback from the key and sometimes I did not know that the lock had opened, until I tried to pull the key out for the next strike !. There is definitely a knack to the process, how hard to hit it (not very), how much torsion to apply to the key (not a lot) and which of the three keys to use. I have numbered my keys ... one is the deepest cut. Two is the medium cut and three the shallowest or widest key. I had most success using key two. Key one does not feel as if it is making much contact with the lock pins. Key three I actually managed to get stuck in a new lock !. When key two was inserted into the lock, it actually felt 'right'.
I then moved onto the lock that is mounted on the letterbox jig and failed to open it once !. I am not sure of the reason. It is a new lock and so is the night latch plate on the other side of the door. I am wondering if they have not yet worn enough yet and perhaps the mechanical loading of tail from the night latch plate to the cylinder plug, may actually be stopping the plug from rotating freely, when the pins clear the shear line. When I get time, I will dismount this lock and see if it can be bumped in the hand.
I did try some grommets and springs to push the key out automatically for the next strike. I mangled a few springs and the grommets on their own were not to successful, so I going to have to find something that does work. It would have helped if there was a should on both sides of the key. I have a spare blank so maybe I will hand cut a 999 bump key and modify it to give reliable auto ejection. I need a 'home made' one for the test rig anyway.
7th February 2010
Results are improving !. The first thing I realised was the head of my bump hammer was too heavy and was 'following through' when the key was struck. So I have made another out of Delrin, with the head half the thickness ....
Length 280.0 mm. Head 10.0mm thick.
In front of the hammer is a set of three bump keys from Lockrus. They differ only in the depth of cut. I have been practicing with them on two no-name tumbler cylinder locks A and B. A opens using key 2 and key 3 opens lock B. Lock B was a lot more 'difficult' to bump and I had to refine my technique somewhat. My big problem was that I was applying too much torsion to the cylinder, very little is required, literally a feathers touch.