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question of keys

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#1 gopostal


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Posted 08 November 2007 - 03:44 PM

I bought the 11 key set and I have been having a lot of fun with them. My question is I have a masterlock to play with and it is very hard to bump. Is it normal to file the first peak down to the size of the others to make it work better? I can consistently hear pins set (3 or so) every bump but it won't open. If I make copies and file the first tooth will it help? Also is it best to file all your copies so that the teeth are all evenly sized?

If you are feeling especially generous I have read the forums and it says to take a "little" off the end and shoulder (.5mm I believe?) to practice MM. In laymans terms what constitutes that width? Is it as wide as a penny?

Thank you guys for following up on the questions posed here. I have always been fascinated by mechanical things (wanted to go into robotics as a teenager) and this is just a blast to play around with.

#2 theopratr


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Posted 08 November 2007 - 06:59 PM

I generally like to file the first peak down the match the rest of them, and I strongly believe that for minimal movement the success rate is much higher. I could get into the mechanics of why, but it's a long drawn out story that I will post someday.

The long and the short of it is: I find it very easy take a normal bump key, with the larger front peak intact, and take a bench grinder to it. Very carefully match the angle of the other peaks, and grind the key down along that axis until the first peak is the same size as all the others. (See illustration.) The finish by doing the same thing to the bottom of the key, to make it look pretty and fit the keyway in a similar fashion as the original.

Posted Image

*Red and blue lines are approximate first and second grinding bounds, from a qualitative perspective.*

Although the tip has been shortened, don't touch the shoulders. This is a method of pull out, although it could also be applied to minimal movement. With the key fully inserted, shoulder to the face of the cylinder, the pins are in their respective valleys, so there's no problems with pins resting on peaks. When you're grinding, make sure to match the angle of the tip of the key to that of the other peaks on the key, this way your new first peak is an effective bumping surface. Also, make note of where the actual point on the tip of the key is, and try to grind the bottom to make the new point approximately similar.

Also, for reference, .5 mm is a hair less than half of the thickness of an American penny. For minimal movement, you should be filing between .5 mm and 1.25 mm off - just enough so that the fully inserted key has the pins just touching the face of the peak behind them.

#3 gopostal


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Posted 08 November 2007 - 08:16 PM

I cannot thank you enough for such a detailed reply (with diagrams no less!). You thoroughly answered my questions.
Me before: :brickwall:

Me now: :bow: