Monday, March 27, 2017

Tips & Tools with Fred Stutzenberger – Part 13

Tips & Tools #13. Finishing the Lock

In #12, the disassembly of a flint-type lock was discussed. Of course, if you have opted for a percussion lock, most of the same protocol applies, only simpler because you don’t have the frizzen and spring to contend with. Just remember with a percussion lock that there is nothing to break the fall of the hammer when it is out of the gun, so be careful. If you simply must test the fall of the hammer, put a piece of ½” diameter dowel into the cut-out in the bolster where the drum would normally be; that will absorb the shock of the hammer.

OK, back to the flintlock. There is much to do before you are ready to inlet. First, familiarize yourself with the name of every part of the lock. Since the first part of the lock to be inlet is the plate, let’s start there. The interior surface of the plate might have some scuffmarks (Fig. 1). That’s where moving parts are rubbing. In the example, the toe of the tumbler is scuffing the plate. The tumbler has a bearing ring on each side of the axle (Fig. 2) that is supposed to keep the tumbler from scuffing the plate and the bridle. In this case, a tiny amount of material has to be carefully removed from the tumbler toe (I use a diamond file followed by polishing with fine grit silicon carbide paper). While you are working on the tumbler, polish the axle that rotates in the plate (Fig. 3) and both sides of the fly (Fig.4). If your lock is a late period model, it will probably have a stirrup (Fig. 5); make sure all rough surfaces are cleaned up, particular the cross members that contact the mainspring and the tumbler. Carefully polish the contact surfaces of the sear nose and the tumbler notches with a triangular Arkansas stone. Be sure not to alter their geometry.


Fig. 1
This plate shows a scuff-mark where the tumbler toe is rubbing.


Fig. 2
Bearing rings on each side of the tumbler are supposed to keep the tumbler from rubbing the plate.


Fig. 3
The tumbler axle operates under a heavy load and needs to be polished for smooth rotation.


Fig. 4
The fly must be smooth on both sides and its tip to operate properly. Don’t get confused, this is a left-handed lock.


Fig. 5
The whole force of the mainspring rests on the cross members of the stirrup and will cause a lot of friction if not smooth.

Polish the inner surface of the mainspring if it is scuffing on the plate. A sure way to highlight scuff areas is to coat the inner plate surface with a Magic Marker, reassemble the lock and cycle it a few times with a piece of wood in the cock jaws. After polishing the required surfaces, smooth and polish the edges of the plate and establish a bit of draft to ease removal from the mortise as it progresses. That will make inletting a lot easier. Be sure to smooth the top of the bolster behind the flash fence. Scratches there (Fig. 6) will likely pull out splinters of wood from the lock mortise during the ins-and-outs of inletting. Fig. 7 shows the parts that needed polishing on a new Jäger lock.


Fig. 6
This bolster badly needs a bit of draft filed into it followed by smoothing.


Fig. 7
Here are the tools used on the parts that needed some attention in this Jäger lock (I forgot to put the mainspring in the picture). Note also that I knurled the head of the jaw screw on the cock…not authentic, but sure gives a good grip. Also, I kicked up some burrs on the inner face of the top jaw to hold the flint better.

On the lock exterior file and smooth the mold parting lines that invariably show on the cast parts. The frizzen is so hard that a diamond file (see suppliers) is required there. When using abrasive paper, use a Popsicle stick to back up the paper. The screws on many locks extend through the plate, creating an unfinished appearance. Shorten those screws and sand them to a pleasant rounded appearance (Fig. 8).  In T&T #14, we’ll get into inletting the lock.


Fig. 8
Lock screws look a lot nicer if there are no exposed threads showing. Compare the rounded ends to the rough-cut end.


Brownell’s Inc., (800-741-0015) for diamond files and Arkansas stones

Enco Manufacturing, (800-USE-ENCO) for a wide range of abrasive papers and polishing cloths.

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