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

[blacksmithden]

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.

Since he's planning on repeating this exercise several hundred times, rather than measuring it each time, would it not be more practical to make up a go/no go gauge ? Take the measurement of the closed lock with pressure on it...then make up a gauge that's a few thou over. It would be a LOT faster than trying to measure the distance every time.

 

[Codered741]

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:

Maybe instead of using an actual weight, use something that will create pressure, like a pneumatic cylinder. Mount the cylinder to a substantial weight, say 10-15 pounds more than you want to exert, and use air pressure to fine tune the exact force applied. If you use a sensitive pressure gauge, and a small bore cylinder, you should get repeatable, accurate pressure, as long as you don't run out of air. Make sure that the cylinder stops mid stroke, and you should be good to go!

I would think that a Dial indicator would be the best tool to measure a change in distance. You should be able to create a mount that maybe clamps to the shackle and measures to the body of the lock. Just make sure that it is square to the body for best results.

 

[pestilence]

Since he's planning on repeating this exercise several hundred times, rather than measuring it each time, would it not be more practical to make up a go/no go gauge ? Take the measurement of the closed lock with pressure on it...then make up a gauge that's a few thou over. It would be a LOT faster than trying to measure the distance every time.

My previous suggestion before this was to clamp the caliper to the parts and continuously read the distance. He doesn't sound like he has the machinery to make gauges and he also doesn't appear to know how much the relationship between the parts will vary. He was talking about using a ruler presumably because he thought a dial indicator or a set of calipers would be expensive.

 

[cesium]

Since he's planning on repeating this exercise several hundred times, rather than measuring it each time, would it not be more practical to make up a go/no go gauge ? Take the measurement of the closed lock with pressure on it...then make up a gauge that's a few thou over. It would be a LOT faster than trying to measure the distance every time.

Probably not a normal go/no-go, because he's looking to see the motion, not measure a distance against a reference. The exact length could be different every time, but it's when the motion occurs, in relation to where the dial is on the face. Therefore, if he had machining capability, some type of lightweight taper could be put into the shackle, like a bar of teflon. It would drop under it's own weight if the lock moves.

 

[rohare]

Geez guys, you all have come up with more ideas than I know what to do with! I'm going to try the vise and ruler bit first since it's easy, I already have the materials, and it should have adequate accuracy. Again, I'm assuming that 1/32 inch is adequate accuracy.

If this is not easy enough to read or does not have the necessary accuracy I will rig up a dial caliper. I have a cheap one from a previous project or I could borrow a precision one if necessary. This will work if my theory (based on study of the patent drawings and text, plus pictures of disassembled locks on the internet) is correct.

If my theory is flawed, then I'll move to pressure readings instead of distance readings. Now I just need the lock to arrive in the mail... anic: