Creating A Bump Key - A Couple Q's

[Svensontini]

Hi Guys,
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I'm experimenting with bump keys and I have a couple questions on their creation.
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From what I've gathered, bump keys can be created by hand filing, using a code cutting machine, or a duplicating machine utilizing depth and space keys.
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I'm most interested in using a duplicator and depth and space keys as I would imagine it would be easier and more accurate than hand filing, and I have easy access to a duplicator.
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The first step is to use the depth and space key for the deepest cut in the keying system for your particular keyway and cutting all cuts to that depth.
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This leaves you with a key that has a large triangle left at the tip though and I've seen references to filing that last bit down to match the rest of the key. If cutting a five pin key and you have depth and space keys for a six pin key, I would imagine that last bit would be cut the same as the rest, but would leave a little bit of the key extending out. If cutting a six pin key with a six pin depth and space key, I would think you could pause after the fifth cut and reposition the depth and space key back one position and then make the last cut.
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At this point, it's a bump key. There's some improvements that can be made though.
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I've seen references to filing that last little bit extending from the tip off as it keeps the key from hitting the back of the keyway in locks with a closed back in the keyway. I have also seen references to making the cuts about .010" deeper as it may help when pins of the maximum lenfth are in the lock.
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Using the bump key at this point is a little more labor intensive as you have to manually pull the key out one click for every attempt, and it can damage the face of the cylinder due to the shoulder bashing into the face.
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It seems that most these days are putting some sort of bumper on the key. This accomplishes two things, it keeps the face of the lock from getting beat up and if the bump attempt wasn't successful it returns the key to the proper position for another attempt automatically, so you can rapidly try again. Veterinary castration bands are often recommended for making the bumpers. O-rings, water faucet washers, actual coil springs, etc. can also work.
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So the next step is to file the shoulder down so the bumper can sit up against the bow (don't install the bumper(s) just yet though).
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Next, insert the key fully, then pull it back one click and mark the key blade right at the face of the cylinder (use a fine point Sharpie pen).
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Next is to find a bumper, or a combination of bumpers that comes right up to the mark on the blade. My thought here is that keys file easily and the castration rings are cheap and come in big bags (about $5 for a hundred), so just use castration rings and file the bow until you get the proper distance.
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Does this sound correct, or am I missing something?
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A question comes to mind about using them. Everything I read says that you just need a slight rotational tension so you don't bind the pins, however I would imagine that between the compression of the rubber and the friction between the rubber and the lock face that there's a little rotational resistance...so would putting some lube on the lock face just prior to starting be a good idea?
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Any and all tips, comments, suggestions, etc. would be most appreciated!

[Svensontini]

It looks like the way to deal with the tall bit at the end of the blade is to cut the key with a half step offset.
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A Kwikset KW1 has .150" between the center of the cuts, so a half step is .075". So, when setting up the duplicator inserting a .075 top pin, or maybe a 5/64" drill bit, between the indexer and the shoulder of the guide key should do the trick.

[Svensontini]

Hi Guys,
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I played with making a bump key today. I used a Corbin Russwin six pin 981 keyway key and 1-1/8" drilled six, pinned five mortise lock to test it on.
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I can confirm that moving the key blank over a bit is how to keep from leaving a big triangle at the end of the key. I thought a half a space would do it, and that's right at 5/64", but when I used a 5/64" drill bit that last triangle ended up smaller than the rest. I cut another one and used a 1/16" drill bit as a spacer and it's much closer to the rest. Next time I'll dig a feeler gauge up and get this dialed in perfect.
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Once I got the key cut I removed the shoulder all the way up to the bow of the key. I just put a blank in for the pattern key and turned it and the key being cut around backwards so I could cut right up to the bow with the machine rather than filing, it worked fine.
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Once I'd removed the shoulder I found that two castration rings were spot on for the distance to the face of the lock.
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I decided to give the new key a go. I also picked up a Harbor Freight 3311 vacuum vise, so I mounted the cylinder up in it, which was easy because of the rubber padded jaws. It's a spiffy little vise for the money!
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OK, so I used a tension wrench as I only have to hit my fingers a hundred times before I learn there's a better way. I put some tension on it and gave it whack with my spiffy new Brkhage bumping hammer...nada, nothing, wasn't budging. OK, we'll try again...nuthin'! I whacked the crap out of that thing, and still no joy! I was wondering if the rubber jaws were absorbing some of the shock, etc.. In frustration I gave it a half hearted whack...HEY! it turned! I tried again, with just a tap...HEY! It opened! I did it several more times, I need to practice, no doubt, but I usually got it in a few taps. I found if it was being stubborn that varying the tension usually got things working. It turns out you don't need to mushroom the end of the key! LOL! I guess the vise/tension wrench just let me be a little more zealous, usually fear of whacking my fingers keeps me in check! LOL!
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I didn't take anything off the end of this key, I may next time I play with it. I think I may try deepening the cuts just a tad also.