Monday, March 27, 2017

Tips & Tools with Fred Stutzenberger – Part 16

Tips & Tools #16. Lock-Sideplate Connection

In T&T #15, the lock mortise was completed. The flintlock is usually held in its mortise via two substantial bolts ranging in size from #10-32 TPI down to #6-40 TPI. On the opposite panel (called the “off side”) the bolts pass through a sideplate that can range from a graceful, lacy work of art down to nothing more than a simple washer. Whatever the aesthetic considerations, it matters not one bit from the functional standpoint, but the sideplate does offer the opportunity for embellishment on the off side of the stock.

T&T#16-Fig.1

Fig. 1
The top three cast brass sideplates were commonly used on American Longrifles. The bottom plate was cast from a French design of the late 17th Century.

The one non-negotiable factor in choosing a sideplate (other than suitability of style) is whether it will fit the lock in terms of hole spacing and size. Some commercial castings are “adjustable” within pretty broad limits to accommodate a range of lock sizes while others are rigidly set with bolt holes already cast into their patterns (Fig. 1). The Zornes lock on our Jäger rifle is over 5.5” long, so the shorter sideplates in Fig.1 were not long enough to accommodate the lock’s bolt spacing. French hardware designs were widely plagiarized by German, English and Dutch arms makers1, so the French fusil sideplate was chosen for style and because the bolt hole distance fit the lock (Fig. 2). Of course, just like any other casting, it will take a bit of handwork to get it ready for inletting. I started by countersinking the bolt head locations with one of my homemade countersinks designed for this specific purpose (Fig. 3). Even if a bolt has to be installed a little crooked in the hole to avoid an obstacle, it still will not be noticeable with the head nestled in the countersink. However, there is some planning we must do to mate-up the sideplate with the lock while keeping the forward lock bolt out of the way of the barrel and the ramrod. Both can pose obstacles if not planned for carefully.

T&T#16-Fig.2

Fig. 2
The bolt spacing of the sideplate mates nicely with that of the lock. I make my lock bolts from a scrap lot of hex head bolts that were discarded from the Clemson University machine shop.

T&T#16-Fig.3

Fig. 3
My countersink tool allows recessing of the bolt head to conceal canting of the bolts.

The big uncertainty at this stage of the project is the position of the ramrod hole. The Jäger rifle used as our example has a heavily swamped barrel, so the bottom of the barrel channel will get lower toward the breech end. The first step is to establish the rear bolt hole in the lock plate. In our lock, the rear bolt position was suggested by the shape of the bolster that extends far enough back to avoid interference from the breech plug lug (why didn’t other lock makers think of that?). The hole through the bolster was drilled with a #23 bit for threading 10-32. The plate was placed in its mortise to use as a pilot for cross-drilling through the stock. That hole was then clearance-drilled with a #9 bit for the 10-32 bolt.

T&T#16-Fig.4

Fig. 4
These two tools made from scrap serve as accurate gauges of depth.

At this point, I ran into a problem. I had rough-shaped the Jäger stock over twenty years ago, inlet the barrel and then put the assembly away up in the rafters. Now when I measured the barrel-to-ramrod clearance, it was 0.295”, a full 0.100” more than I wanted. So I have to shift my attention to get that reduced before moving on to install the front lock bolt. Using my fore end shaping rig described in the next section, I reduced the barrel/ramrod web from 0.295 down to 0.192” at the point of the entry thimble. I used a combination of two little homemade depth gauges (Fig. 4) to make those determinations. The top gauge is made from 3/8” mild steel rod. The 1/16” diameter cross pin is held to an easy interference fit by a set screw. With the barrel in place, the gauge in placed in the ramrod groove with the pin in a hole drilled through the web. The pin is pressed down against the barrel while the rod is pressed down in the ramrod groove. Measure the length of the exposed pin with your dial caliper to determine the barrel/ramrod web. The lower depth gauge is made from ¼ ½” flat bar stock. It has been drilled for a 1/16” length of drill rod held by a screw from the side. Place it across the sides of the barrel channel at the breech end with the pin contacting the bottom in the area where the front bolt will pass then move the gauge over so that the pin will indicate the channel depth on the outside of the stock at the same point. Compare those distances to give yourself a close estimate of the distance between the channel and hole. After the hole is drilled, you can also put a diagonal line of 5/64” holes across the bottom of the barrel channel to show you where the bottom of the ramrod hole is. That will tell you how much wood you can take off the bottom of the stock.  Of course, if the ramrod hole comes out into the trigger mortise, that will give an indication also. If you do not use some reliable measuring device to determine the positions of the barrel bottom the barrel/ramrod web thickness and the bottom of the ramrod hole, you are flying blind when drilling the forward bolt hole and shaping the bottom of the stock.

In T&T#17, more detail will be given about the shaping of the fore stock and the ramrod hole. So perhaps you might want to get #17 under your belt before proceeding.

References

1.Shumway, George. Rifles of Colonial America, Vol. 1, 1980.

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