Broach for fitting hammers

mooncoon

mooncoon

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One of the fiddly jobs in assembling a lock kit or building a lock is filling the square hole where the hammer or #### attaches to the tumbler shaft. A few months ago, I picked up an idea from the ALR site, that I thought was worth passing on. The tool is a home made broach made out of drill rod and the temper drawn to about dark brown. In use I drill a round hole the diameter of the dimension across the flats of the tumbler shaft and then hammer the broach into the hole. I advance one or two teeth at a time then remove and check for fit and drive the broach in a bit deeper. The broach allows me to get a perfect fit in 10 or 15 minutes. Important to drive the broach from the inside of the hammer which leaves a slightly tapered hole. I also have to file the corner notches to get the broach started but after that, all cutting is done with the broach. For dimensions, the broach illustrated is made from 3/8" drill rod and is about 4" long

cheers mooncoon

Broachb.jpg
 
H Wally said:
Neat! Did you cut the teeth freely by hand, with a lathe/mill, or jig?

Also, is there a specific angle aimed fore on the teeth or just "sharp"?
Click to expand...

I milled the taper then just made a cross cut every 1/8" or so with a hack saw and filed the teeth sharp and pointing away from the big end. I use a brass hammer for driving the broach in either direction (you need to hammer it back a bit to remove it).

No special angle on the teeth; probably the closer together and finer makes them cut smoother. I use a bit of cutting oil on the broach.

I used to have a hard time filing the hole square and tight but the broach keeps the square lined up correctly and slightly tapered and gives you a good fit.

I have come to think that the way that gunsmiths made locks and guns quickly and economically in the good old days was by using a variety of hardened filing templates and gadgets like the broach which allowed them to make very repeatable pieces very quickly

cheers mooncoon
 
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