The tool I'd like doesn't appear to exist...

[rohare]

Hello, I may very well be demonstrating my ignorance with this question, but here goes.

I am engaged in a rather odd project and I am looking for a tool that would assist me with it. The project is to decode an unknown combination to a high security padlock. Don’t worry, I’m not a criminal! I am active in the locksport community which means that I pick locks and open safes as a hobby, and perhaps someday, competitively. The specifics of the project are, that I wish to discover the combination to a Sargent and Greenleaf 8088 high security padlock. This little beast is essentially a miniature safe-lock housed in a padlock body. Back in the 50’s and 60’s the US government used them on file cabinets containing classified and top-secret documents but they were disallowed at some point because they weren’t resistant enough to destructive attacks. Nevertheless they are considered very secure from non-destructive methods of opening to this day. I bought one without a known combination off ebay for a few bucks and have developed a theoretical method of manipulating it open. A few other people in the community have also proposed this method but I am not aware of anyone that has actually made an attempt to do so and documented it.

So that brings me to the metrology aspect of the project. What I need to accomplish is to apply a fair amount of force to the shackle such as one would do by grasping the padlock body with one hand and the shackle with the other hand and tugging (perhaps 20lb’s of pressure?). Then, without changing the pressure, I need to take a fairly accurate measurement of the inside “diameter” of the space between the shackle and the body. The key is repeatability. I need to apply a fairly consistent degree of pressure (though it anything can vary, it’s this factor more than others) between the shackle and the body, and take a measurement of the exact same spot on the shackle and the exact same spot on the body each time. I may need to do this several hundred times. The degree of accuracy I need is probably on the order of 1/32 inches or ½ mm. After each separate reading, I then need to remove the pressure to adjust the lock for a new reading.

I’ve already looked at calipers, but nothing I saw looked like it could withstand the pressure I need to apply. I’ve also looked at micrometers, but I’m not sure about their capacity for handling pressure either and I don’t want to drop hundreds of dollars on this project just to find out it won’t work either. The tool I imagine in my mind would be perfect would look like split-ring pliers with a dial indicator attached, but no such tool seems to exist. What I’ve decided will probably work best at this point is a hand vise to apply pressure and hold the lock steady, and a caliper to take the measurement. However, this is not ideal because the introduction of a second tool increases the likelihood of inconsistent measurement and increases the amount of time it takes to take each individual measurement. That time sure adds up when you’re taking hundreds of measurements.

So, my question is: Does anyone have a better idea than the one I just outlined? Thanks very much in advance for any assistance anyone can give me here.

 

[samthedog]

Why wouldn't you use 2 tools? I believe you will need to fabricate a tool for this job that will work in conjunction with a calliper.

Since the lock you are trying to open is a standard, then make a spreading tool like the one below:



Then use a pressure sensor:


http://www.meas-spec.com/product/Pressure/EPL.aspx

....either between the lock body and a jaw, or between the spreader's leadscrew and the point of contact in the "jaw sleeve" - the jaw on the left in the provided picture. This gives you the option to measure the flats between the jaws as you open them, and measure the pressure / force being applied. Pressure sensors are not hard to find and are not terribly expensive.

This gives you 2 advantages as it gives you a measurement reading between the shackle and lock body, and also gives you the required pressure to finally crack the lock. The pressure required is probably the better reading of the two as I would not expect the physical distance to change much, but the pressure reading would give you more information on what is happening inside the lock. When one of the tumblers is engaged and the correct number is dialled, then I would expect there to be a slight reduction in the pressure reading.

Paul.

 

[pestilence]

Wouldn't hanging a weight on the padlock and suspending it by the shackle give you a more accurate and repeatable pressure, plus you have the use of both hands. You could then use an inside micrometer to measure the space.

This is the answer. Suspend the weight from a split hook that goes in the shackle, leaving the center of the shackle open enough for a caliper to measure the apex of the bend so it's repeatable. Your tension will always be identical. You could even conceivably clamp the caliper to the shackle and the lock body using little parallel clamps. That would ensure the measurement is always from exactly the same spot. I assume you're watching for a change, so zeroing the caliper open initially would instantly show the relative difference.

 

[swatson144]

I'd start with like a HF cheap drill vice ~15$ mounted to a steel plate. Make soft jaws to hold the lock with the shackle over the fixed jaw securely. modify one of those grip builder exercise thingies to apply tension. measure movement with a mag back dial indicator etc ~ 20$ stuck to the mounting plate.

This will allow you to lay the vice on a table with the lock face up, zero the indicator apply repeatable pressure and see the movement. Then remove the spring and do your magic, reapply the spring and note any movement in the dial indicator.

It'd be useless with the lock in use but if it works it wouldn't be that hard to make a spreader with the indicator built in. Just more complex and expensive.

Steve

 

[rohare]

Wow! These are great ideas. I guess it just shows my lack of experience with these kinds of things. One thing I would like to take up is the idea of measuring pressure rather than distance. This was the idea I had to begin with, but ended up rejecting it in favor of measuring distance instead. My reasoning was that if I measured pressure, then the measurements would be of an action I was doing rather than a measurement of the state of the lock. For example, if I applied 20lb of pressure (say, with a weight) to the lock in a state where no wheels were in their correct position, I would get a reading of 20lb of pressure. If I then applied 20lb of pressure to the lock when one or more wheels were in the correct positions, the shackle should raise ever so slightly more than before, but wouldn't a measurement of the pressure still show 20lb? Is my reasoning flawed in this regard?

As for measuring the physical distance, even if the amount of change is very small I would be used to doing this. When manipulating a safe's lock, I routinely look for gradations as fine as 1/4 of the distance between dial marks. The really good guys glue a vernier scale above the dial marks and read 1/10 distances between the dial marks.

Based on the suggestions, and assuming that I my reasoning to prefer distance over pressure measurements is correct, how about this revised idea: I'll use a hand or drill vise to hold the lock steady and apply pressure. By usign a vise instead of a weight I realize that I am giving preference to a steady work enviroment over precise repeatability of pressure. This might be a mistake, but I think it's probably a good trade-off. Attached to one end of the vise will be a finely graduated ruler (1/32 inches or 1/2 mm gradations) that will extend past the other end of the vise. When the vise is in the as-closed-as-it-will-go-with-the-lock-inside position, whatever number is read on the ruler will be the zero point. When I open up the vise after having done some manipulation of the dial, the point where it stops opening will be be the reading of the shackle distance for those wheel positions. I can re-check the zero if I feel I neeed to just by closing the vise again. This has the benefit of a stable platform, using only one tool, measuing the same way repeatably, etc. It has the drawback of not having precisely repeatable pressure, but again, I suspect that is the less important of the various factors. How does this sound?

 

[Charley Davidson]

I can just see this guy now on a future episode of "I almost got away with it"

 

[pdentrem]

I have seen the inside of a couple safes over the years. I thought the bar will not drop until all the tumblers were in their proper position? Once the bar drops into the tumblers then there is movement. Right?
Or these file cabinet locks are a different beast?
Pierre

 

[cesium]

As for measuring the physical distance, even if the amount of change is very small I would be used to doing this. When manipulating a safe's lock, I routinely look for gradations as fine as 1/4 of the distance between dial marks. The really good guys glue a vernier scale above the dial marks and read 1/10 distances between the dial marks.

Based on the suggestions, and assuming that I my reasoning to prefer distance over pressure measurements is correct, how about this revised idea: I'll use a hand or drill vise to hold the lock steady and apply pressure. By usign a vise instead of a weight I realize that I am giving preference to a steady work enviroment over precise repeatability of pressure. This might be a mistake, but I think it's probably a good trade-off. Attached to one end of the vise will be a finely graduated ruler (1/32 inches or 1/2 mm gradations) that will extend past the other end of the vise. When the vise is in the as-closed-as-it-will-go-with-the-lock-inside position, whatever number is read on the ruler will be the zero point. When I open up the vise after having done some manipulation of the dial, the point where it stops opening will be be the reading of the shackle distance for those wheel positions. I can re-check the zero if I feel I neeed to just by closing the vise again. This has the benefit of a stable platform, using only one tool, measuing the same way repeatably, etc. It has the drawback of not having precisely repeatable pressure, but again, I suspect that is the less important of the various factors. How does this sound?

It sounds like you're trying to measure distances that are within the resolving ability of a normal scale or caliper. The problem is that these tools are normally for measuring something which is not moving, while it seems you would like to detect small motions of the shackle. The dial indicator recommendation is probably your best bet:

I'd start with like a HF cheap drill vice ~15$ mounted to a steel plate. Make soft jaws to hold the lock with the shackle over the fixed jaw securely. modify one of those grip builder exercise thingies to apply tension. measure movement with a mag back dial indicator etc ~ 20$ stuck to the mounting plate.
Steve

You can get finer grades of test indicators which have ticks at 0.0001 inch, or 0.001 which is more standard, and they are all spring loaded so they hold themselves against the surface (the 0.0001 have a lighter touch). There are magnetic versions, as well as ones on adjustable arms. Hold the shackle with some light elastic, set up the indicator, and then you don't even have to touch it. You may be able to see the smallest 'ticks' and things you may not have noticed before as you turn the lock, and 1/32" would be clearly apparent.

There are a variety of styles and setups. I would think that the arm of a test indicator, versus the probe of a dial indicator, would be easier to setup against the lock. I believe there is an importer marketing a kit with both, along with a base and some accessories, for under $50. I would not go with the electronic ones for this, just the mechanical dial.

 

[rohare]

It seems like several of you really favor the use of a weight. I just want to make sure I'm clear that after each reading I will have to remove the pressure from the shackle in order to change the dial. That's one of the reasons I was looking for alternatives. As for the dial indicator, I do find that intriguing. I think I'll try the ruler idea first since I'm already equipped and then buy a dial indicator if necessary. Thanks so much for all the great ideas everybody. I'm now able to take a crack at it and see how it goes and I've got some good backup plans in case it doesn't go well. And for those who are waiting to see me on a "dumbest criminals" show, don't hold your breath! I strictly adhere to the two cardinal rules of locksport ethics. 1) Never pick a lock you don't own or for which you haven't been given explicit permission by the owner. 2) Never pick a lock upon which you depend for security. This stuff is purely a hobby. Just think of it like trying to figure out the most difficult puzzle ever. :thinking:

 

[pestilence]

You can get a digital caliper or dial indicator capable of reliably reading .001 of an inch in relative distance for $10 with a coupon at harbor freight. There's no sense in messing around with rulers.