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I think I made my lock un-bumpable


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#1 Bump123

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Posted 09 March 2007 - 10:06 AM

I was toying around with the whole concept of lock bumping, and newtons law of kinetic energy. So I took a lock that I have and bumped it, 37 out of 50 times.. Proving that the lock was very eaisly bummped. (Kwikset Deadbolt)

I then took it apart, luckly this lock had either an 8/9 pin in it, that I was able to replace with 2 other pins from another lock, (either 4/5 or 4/4 ) Don't really know, but I made sure they equaled the pin I removed.

I reassembled and tested with the real key. Worked perfect so I knew I had matched it up correctly. So I went to bumping.. and out of 50 tries, I was NOT able to bump the lock. I haven't tried picking yet. But to me so far this seems like a real easy and cheap fix as opposed to paying an arm and a leg for a lock thats classified as High Security and unbumpable...

Any comments suggestions, opinions are greatly appriciated.
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#2 Customer Support

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Posted 11 March 2007 - 01:39 AM

While I haven't tried this myself... I've already referred a few people to this post. Thanks!

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#3 BLK

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Posted 11 March 2007 - 09:27 AM

Something about this does not make sense to me. If the lock works with the same key as it originally did, then it should bump no differently.

A few questions:

Did you change anything other than the 2 bottom pins?

Did you change/replace any of the springs?

Did you lubricate the lock? Or wipe off any lube that was in the lock?

It sounds like you made the lock so that acts like it is master pinned. That does make it harder to bump, but it does not make it impossible--just harder.

I would like a better discription about what you did to the lock.
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#4 Bump123

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Posted 11 March 2007 - 09:52 AM

For lack of Professional terms I am just going to write it out as best as I can as I know.

The lock I worked with is a 5 pin lock (10 pins total counting upper and lower) The top 5 pins are all the same size when I opened the lock, the bottom 5 pins are different sizes. 1 out of the 5 bottom pins fit into either an 8/9 cut, (it was the longest pin) I removed that bottom pin and replaced it with 2 shorter pins from another lock that equaled its size.

You might be correct in saying that its still not un-bumpable but I guess I figured that before the modification 37/50 successful bumps, compared to 0/50 pretty much covered the basis.. at which point a window would be eaiser to break...

#5 BLK

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Posted 11 March 2007 - 04:41 PM

As far as physics is concerned, the top pin would be the only pin to move up above the shear line regardless of how many pins are below it.

As a point of clarification, KwikSet locks have 7 cut depths. I have not played with which bottom pins would have to be put together to make a 6 or 7 cut, but I may do that just to see which ones it takes for each. If the origingal key works, then the cut on the original key would have to be fairly close to correct for the new pin stack (fairly close is all it takes for KwikSet usually).

Solution: try filing down the cuts on the bump key you are using. I would only file it down a few thousandths of an inch, then try bumping the lock again.

Solution: transferring energy through an extra pin in 1 stack may take a harder hit on the key.

Could you take the lock apart, stack the pins as they are in the lock and take pictures to post to show what you have done? I have 40 or 50 extra KwikSet deadbolts laying around, so I may play with this to see if I can duplicate what you have done.

Aside: I bump locks that are master pinned a lot and do not have any more problem bumping them that with ones that are not mastered.
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#6 theopratr

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Posted 11 March 2007 - 06:03 PM

As usual, my money rests with BLK. However, I can see how your situation is possible.

As a Physics major, the energy transfer when using bump keys is an engaging look at a real world problem. By replacing a bottom pin corresponding to a depth 8 with two depth 4 pins, you simply introduce the possibility of the energy transfer being "messy", or simply inefficient.

When the peak of the key strikes the bottom most pin, the energy is (ideally) transferred in a vertical direction. This vertical transfer is most efficient if the angle of the peak on the key is forty-five degrees relative to the motion of the key. Any less than this may not "push" hard enough to jump the top pin high enough, and any more than this is transferring more energy in a horizontal direction, forward through the pins as opposed to up into the top pins. This is true regardless of the number of pins encountered before the top pin.

The most elegant representation of the motion that is occurring can be found with a Newton's cradle. (The five balls of similar mass suspended in series on wires.) When you drop one of the balls on the end, it impacts the remaining four balls, but only the last ball is pushed away. In a normal lock with a single bottom and top pin for each pin position, you have a Newton's cradle with only two theoretical balls... your key is essentially flicking the first ball, and the second one is springing away.

If you introduce another "ball", by replacing the single 8 pin with two 4 pins, problems can result. First, if you are hitting the bump key too hard, it's like tossing the end ball at the series. More than just the end ball will fly, because the impacting ball has more kinetic energy than it would by simply falling on it's own. However, conservation of momentum tells us that the top pin, which is of less mass than any other pin in the system, will still take the majority of the force and thus be sprung as normal, but the more massive top 4 pin will not receive a real high velocity, probably just enough to put it more or less on the shear line. Thus, the lock will not open. A lighter tap on the bump key will fix this.

The other possibility is that if your bump key has cuts that are greater than forty-five degrees, the forward energy in the pins could cause the top 4 pin to jump because the transfer was dirty, and jump just enough to cause the lock to bind. This could be fixed by perfecting the slopes on the key.

So in conclusion, from a physical stand point, the splicing of that pin should make no difference. In reality, however, an imperfect bump key would be handicapped by such a pin.

Sorry if my explanation was either over-simplified or rambling, I don't know what everyone's background is! I'll see if I can make a few pictures to explain myself.

Edit: When BLK says to file down your bump key a bit more, that is fixing the entire energy transfer problem. The 4 pin only hops a little, in either case, and if the resting position of the pins is a bit deeper, the top 4 pin hopping won't matter, as it won't reach the shear line.
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#7 BLK

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Posted 11 March 2007 - 08:34 PM

If you only lift one ball on Newton's Cradle, then only the last ball will be knocked away from the others and the others will stay in place. The same thing seems to happen with bumping, the peak on the key hits the bottom pin and knocks the top pin above the shear line.

Bump123: If you want to experiment with your lock, take out all but the modified pin stack and try bumping it. Then if you can bump that pin stack, add the pin stack with the next longest bottom pin in the original chamber so the key works and try to bump it. If you can bump that set up, then take out the 2nd pin stack and reset the pin stack with the shortest bottom pin in it in the chamber that matches the original set up so that the key works. Try bumping that set up. My guess is trying to bump the longest pin stack and shortest pin stack will be the most difficult...just my guess. When you get back to 3, 4 or 5 pin stacks installed the difficulty should increase with each add set of pins.

I tried to bump a lock on a house last week that my pass key would not open--the tenant had changed the locks. I finally pulled the core of an entry set and took the pins out and made a key that worked to gain entry to the house. The problem I had trying to bump it was, I think, do to the fact that there was a 6 pin beside a 1 pin. It doesn't take much to get the top pin over the 6 bottom pin above the shear line, but it takes a pretty good thwack to get the top pin above the 1 pin to make it that far. Add to the equation the force of the spring above the 6 pin pushing that top pin back down while the top pin on the other stack is still going up and you get a much smaller window of opportunity to have a clean shear line that will allow the lock to open.

It appears then that it all comes back to the force of the thwack and the tension of the turning torque on the key being just right to make Bump123's modified lock open.

Question: did you use 2 bottom pins in the modified stack or did you use a bottom pin and a master pin?
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#8 Bump123

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Posted 12 March 2007 - 06:05 AM

Bump123: If you want to experiment with your lock, take out all but the modified pin stack and try bumping it. Then if you can bump that pin stack, add the pin stack with the next longest bottom pin in the original chamber so the key works and try to bump it. If you can bump that set up, then take out the 2nd pin stack and reset the pin stack with the shortest bottom pin in it in the chamber that matches the original set up so that the key works. Try bumping that set up. My guess is trying to bump the longest pin stack and shortest pin stack will be the most difficult...just my guess. When you get back to 3, 4 or 5 pin stacks installed the difficulty should increase with each add set of pins.

Question: did you use 2 bottom pins in the modified stack or did you use a bottom pin and a master pin?



I will try and do that today for you, in hopes that I don't spend 30 minutes chasing springs again... (I know you all just got a visual, now quit laughing)

As for your question, I am a bit confused on what you are asking. I am not quite sure what a master pin is to comment on it. But to make things eaiser, I took apart 2 other deadbolts, both were generic unnamed locks, and took the pins out of them, which equaled 20 possible pins to work with, since 10 of them were top pins and all the same size, I didn't use any of those, I found 2 bottom pins which were I guess tapered off at each end, that matched the pin I removed, and used those..

Hope that helps..

#9 BLK

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Posted 12 March 2007 - 06:18 AM

I will try and do that today for you, in hopes that I don't spend 30 minutes chasing springs again... (I know you all just got a visual, now quit laughing)

As for your question, I am a bit confused on what you are asking. I am not quite sure what a master pin is to comment on it. But to make things eaiser, I took apart 2 other deadbolts, both were generic unnamed locks, and took the pins out of them, which equaled 20 possible pins to work with, since 10 of them were top pins and all the same size, I didn't use any of those, I found 2 bottom pins which were I guess tapered off at each end, that matched the pin I removed, and used those..

Hope that helps..


I have an appointment to get taxes done this morning and then off to work. But I have 2 houses to rekey this evening on the way home so I will try to duplicate what you have done with the bottom pins to see which pins you used to equal the longer pin. My guess is that it had to be 2 number 1 pins or a number 1 and a number 2 pin. I think that any longer pins would exceed the tolerance of the KwikSet plug and would not work.

By the way, if the springs don't fly everywhere once in a while, you aren't human. Try keeping one finger on top of the cap while you are prying it up so it doesn't fly across the room.
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#10 BLK

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Posted 12 March 2007 - 08:47 PM

The math does not work on this.
#6 pin=.0287" #7 pin=.310" #1 pin=.172" so 2 #1 pins=.344" or .034" more than 1 #7 pin. That is 1.5 cuts deeper. The original key would not work in your lock if it was more than .006" different--that is the nature of KwikSet locks.

Bump123, post pictures of the lock dissembled with the original long pin and the replacement stack of 2 pins and the original key. I think I have missed something here and need to see a picture.
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#11 Customer Support

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Posted 12 March 2007 - 08:48 PM

Hrmm... I'm going to take a look at my depth and spacing charts (not that I doubt you, BLK :D )

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#12 BLK

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Posted 12 March 2007 - 09:00 PM

The numbers came straight out of my KwikSet pin kit. The math is correct. I must have missed something somewhere...I will reread the thread, again.
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#13 Bump123

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Posted 13 March 2007 - 09:02 AM

The math does not work on this.
#6 pin=.0287" #7 pin=.310" #1 pin=.172" so 2 #1 pins=.344" or .034" more than 1 #7 pin. That is 1.5 cuts deeper. The original key would not work in your lock if it was more than .006" different--that is the nature of KwikSet locks.

Bump123, post pictures of the lock dissembled with the original long pin and the replacement stack of 2 pins and the original key. I think I have missed something here and need to see a picture.



I took it apart an played with it like someone suggested, except forgot to take pictures, however when I removed all pins except for the modified one, I was able to bump it, It took almost twice the thumping power of the hammer to bump it, the second I added a regular pin back to it though (now only have 2 pins the modified, and the stock, it became VERY difficult to bump but I was successful 1/10 times or so.. But once the rest of the pins were added back, it went back to impossible (for me at least)

Any ways, once again I will try and get some pics for you on this, But as for your measurements, not saying they are off, but the pins I used are NOT from another Kwikset lock, they were from some generic POS locks that were on my house when I moved in last year.. They don't have ANY kind of stamping on them... not even the word CHINA (thats how generic these locks are.. )

#14 BLK

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Posted 13 March 2007 - 11:09 AM

OK, if they are not STANDARD KwikSet pins, then all bets are off! I would still like to see pictures and if you could measure the pins to find out how long they are that would help also.

As you add more pin stacks to a lock, especially when the bottom pins vary greatly in length, the lock becomes harder to bump. The reason is, as stated above in an earlier post, the window of opportunity at the shear line is reduced a lot.
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#15 BLK

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Posted 08 April 2007 - 02:20 PM

This has been irritating me ever since this thread was started....SO, I spent 3 hours playing with the concepts in this thread.

I took a KwikSet single cylinder deadbolt with the original key and started overloading the pin stacks one at a time. Here is what happened:

I overloaded 1 pin stack with 2 #1 bottom pins and a .180 top pin and spring. It took 6 attempts, but it bumped.

I repinned the lock with the above pin stack and the other 4 original pins. It bumped in 2 attempts and the original key worked just fine. Although there was some drag on the plug from the excessive pressure from the overstuffed upper pin chambers. The plug had been marked by the top pins when I removed it and inspected it later.

I overloaded another pin stack (in addition to the one above) with 2 #4 bottom pins and a spring. The key worked fine and it bumped in 2 tries.

I overloaded the other 3 pin stacks, recapped it with top pins and springs in place and it bumped in 2 tries and the original key worked just fine.

I bumped it again and found only bottom pins in the plug when I took the cap off and removed the springs, top pins and extra pins used to overload the pin chambers.

Conclusions: Newton's Cradle theory does not apply. I have no idea how to make a lock bump proof. :confused:
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#16 bumber

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Posted 10 April 2007 - 02:44 PM

what if you put rubber or a spring BETWEEN two bottom pins that are+the spring=to the original pin length?? B/C the medium would in theory would absorb the impact but the origanal key would let it set the pins w/ a constant force!!
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