I apologize in advance, I have a feeling this may get a little lengthy.
If you have figured it out or found your answer elsewhere, congratulations! If not, here are a few things I've observed in my experience. I do encourage NDE by picking, but there's nothing wrong with learning any and all other techniques in my humble opinion. If anyone notices something I am completely incorrect about, please feel free to point it out. Thanks.
Hope you don't mind, I used your picture to reference so it'd be easier to understand.
The areas of modifications on the tip and shoulder previously discussed are highlighted in YELLOW
When you file down the tip and shoulder, you will be "bumping" with the key fully inserted. CAUTION: filing the tip & shoulder too much will allow the key to travel too far. Making a copy prior to filing is recommended. Approximately between 0.25 and 0.5 mm (.010-.020" or 1/64-1/32") Usually works, but feel free to experiment. When testing if you have filed off enough, push the key in all the way to the shoulder. When you let go, if you can see/feel the springs push the key back out, that's usually enough. If you push it in and it stays there, you have probably gone too far.
*NOTE* Sometimes with a master padlock, your key will feel stuck and you think you've filed too far. Or, it doesn't seem to go in enough, and you will file more off than you have to. This is usually due to the head of the key getting stuck, shown in BLUE
With this method the pins will contact the key on the RED
(fig 1) areas as shown. To find the correct amount of tension when bumping, you have to listen/feel the pins. Place light tension on the key and strike it (one time only). Release tension and listen/feel. (Ideally when you let go of the key the pins should reset automatically without you having to turn the key back.) If you can hear pins resetting, good. Try it again. Keep striking/resetting until you have a feel for the amount of tension you need to set some pins.
I find that particular amount of tension is a good starting point for many locks that I have bumped, but that's just my opinion. Once you have a feel for that tension, instead of resetting, try to maintain it for the next few strikes. Occasionally on a stubborn lock I will use the pull back method in conjunction with this one. Also, occasionally you can successfully bump a lock and not even know it. I was practicing on a kwikset lock with a homemade bump key, and just couldn't get it to work. Out of frustration I began to take the key out to take a break . . . and it turned! Here's more on that and the "pull-back" method . . .
When using the pull-back method, I'm sure you know you pull back one click and the pins will contact the key on the red
(fig 2) areas as shown. For the most part, that larger "bump" on the front of the key shouldn't be a problem, but if the last pin (or any of them for that matter) sets at the lowest point, you can see why the pull-back method may have a problem. In figure 1
, the pins will only travel approx. the height of the lowest possible set (shown in green
). Whereas in figure 2
the distance travelled may push the pin(s) higher than the point at which they are supposed to set. You can file down the front bump and/or the rest of the grooves deeper to combat the low-set pin, but make a copy first
! You risk ruining your bump key.
As far as the kwikset key, I can honestly only speculate. But I believe that I had filed the shoulder & tip too far. Even though the lock was successfully bumped, because the key was in too far it was pushing the bottom pins up, preventing it from rotating. Pulling the key back allowed the bottom pins to drop off their contact points (fig 1, in red)
and turn the cylinder.
Hope this helps. Let me know if anything was unclear or confusing.
"When two people in business always agree, one of them is unnecessary." -- William Wrigley Jr.