Countermilling Plug/Housing Chambers

[xeo]

In the past I have created some frankenlocks with threaded plug chambers to add pick resistance. I used drywall screws or any other screw with sharp threading to do this. I would just screw it in as hard as possible then remove it.

I'd like to do this professionally (cleanly) to some locks. The drywall screws distorted the tops of the chambers which then required sanding. I would like to add deep threading/countermilling to both the plug and the housing.

What size taps would I need to use on a standard chamber size such as that of a Schlage/Kwikset/Sargent? Is using a tap the best method for this or is there something better?

[jeffmoss26]

A 6/32 tap should work. That is what I use for the tops of plugs when I screw up (ha ha) the top strips.
8/32 is what Medeco uses on their cylinders as the pins are larger in diameter.

[xeo]

The plan is to tap all the way down through the housing then add set screws. What size/threaded screws would I need to purchase?

[jeffmoss26]

I use 6/32 x 1/8" set screws since they are the shortest available. This way I do not have to cut the springs, just use shorter top pins.
As I stated in chat, with a standard tap you have over 1/2 inch of depth to work with on the tap.
With a bottoming tap, you have over 3/4 inch of depth to work with.

[Don]

Follow Jeff's advise on screw size.
Check here for some advise on the correct way to tap a hole : http://www.wikihow.com/Use-a-Tap

as stated in the link .. lubrication is VERY important for clean threads and to prolong the life of your tools.

[jeffmoss26]

Not to go against proper advice, but I have in a pinch simply forced the setscrew into the top of the lock. The brass was soft enough so it worked, but not well.
I do not recommend doing this, unless you HAVE to.

[gnarus8429]

Yup Jeff is right on the screws. Depending on the lock you maybe able to get away with no drilling. If the top is a metal strip type just pull it off and tap the chambers with the 6/32 tap. I got mine at ACE hardware all by itself for a reasonable price. If it is a plug in the top of the chamber drill a very small hole in the center of the plug, put a small wood screw in it and pull that out with pliers. Then you can tap the chamber. Much cleaner,faster, and easier to make look good. I would also consider cutting the springs if you don't have shorter driver pins. It makes all the difference in the world when it comes to getting the original resistance in the lock. I messed that up for quite a few locks and had to go back and redo them. Threading the chamber too deep may result in the spring / driver pin not moving freely in the chamber and result in it hanging up in some instances. Not sure on that one but, it just a thought.

[elbowmacaroni]

true... as long as the screw is a harder metal than the cylinder you can tap with a screw... although the deeper you go, the more difficult it will be to turn and create more threads. For the purpose of set screws, as long as you're using steel set screws it shouldn't be a problem though. As for doing the entire chamber, that migt be a bit trickier. You could always use a screw where the threads are just barely larger but the body of the screw is quite a bit thinner and you should be able to go the full length of the plug chamber using just a screwdriver to run it through.

[the lockpickkid]

The set screws I have are heat treated, haven't tried to thread them in without threads, but they are strong and I bet they would do it just fine.