Tips & Tools with Fred Stutzenberger – Part 14
Tips & Tools #14 Inletting the Lock Plate
“Inletting the lock plate is an exacting and, if it’s the first time you’ve done it, exhausting job. The worst job is inletting the plate.” (Peter Alexander) Peter’s description sums up the task but don’t let that deter you from doing a good job because the lock is the first area of interest when someone picks up your rifle. If your lock inlet is nicely done, it says a lot about your rifle in general like your front yard says about the perception of your house. So be careful, be patient and be gentle with yourself even if your best-laid plans slip a bit awry. Just so you can visualize how your completed mortise is going to look, study Fig. 1 a bit. At the rear of the mortise is the hole for the wide and tapering sear arm. Moving forward, there is the cutout for the sear, bridle and tumbler then the rear lock bolt, mainspring mortise and forward lock bolt hole. That is a summary of what every flintlock mortise will have with minor variations.
Three cautions before you start. First, if you are mating the plate to a swamped or tapered barrel, remember that the tail of the lock will be angled out from the centerline of the rifle. Be sure that you have enough wood to accommodate that angle. You don’t want to start inletting only to find that you run out of wood at the rear of the panel. For example, on the Jäger rifle I am using as an example here, the barrel has a lot of swamp in its dimensions; the distance between forward panel surfaces is 1.815”. The distance at the tail of the lock is 1.935”. That makes for a nice architecture and avoids a slab-sided wrist, but it can be a real problem if you got too chisel-happy when you took off wood from the lock area prior to inletting the plate.
Second caution: the tightness of inletting the plate. The first few rifles I built had plates inlet so tightly that eventually removal and replacement of the locks for cleaning pulled out slivers of wood from around the mortises. You see that on old original rifles frequently. Much of that was caused by inevitable shrinkage of the wood. Ideal inletting allows the lock to be hand-removed with little effort yet has no big gaps that scream “Novice!” More on that later.
Third caution: the position of the plate obviously determines the position of the lock. The pan/bolster line should lie along the midline of the side barrel flat (cover the flat with Magic Marker black or diemaker’s layout dye and scribe your centerline). On big-breech swamped barrels like the one on this Jäger, the lock can be mated a little lower than barrel centerline to accommodate lowering of the wood along the barrel channel walls to decrease that “too much wood” look. The back of the lock’s flash fence should ideally mate up at the back of the barrel, but if it is moved a little forward of that for better positioning of the touch hole, that’s fine too. Use an adjustable carpenter’s square to mark the location of the bottom of the barrel then the 3/16” thick web between barrel bottom and ramrod hole and finally an extra 1/8” on the panel to mark the belly line of the stock. Leave that wood in place…you just want to know where things are going to be (hopefully) as you continue work on the stock.
The lock I use as an example in the inletting protocol was developed by Larry Zornes Mold & Gun Shop. It was patterned after a lock designed by Francois á Luneville, French Royal Armsmaker, in the late 17th-early 18th Century period when the French flintlock began to displace the German wheelock. The development of the characteristic Germanic Jäger (the ancestor of the American Longrifle) followed as a response to the introduction of the French flintlock into Germany beginning in the 1680s. A decade later, the flat surfaces and facets of the Bérain style flintlocks appeared in Germany, rapidly following their development in France2. Predictably, this lock has both French and Germanic characteristics (Fig. 2). Many of the Jägers from that period (such as those by Caspar Zelner of Vienna3) had similar locks. This is the first time I have inlet this lock, so it will be a new experience for me as well as for the reader.
As for any lock, after the lock panel is smoothed and at a true 90° to the top flat of the barrel, the first order of business is to inlet the lock bolster. To do that, authors usually blithely say something to the effect “…use an X-Acto knife to scribe its boundaries…” I’ve never figured out how you can get under the plate to do that scribing around the bolster corners and along its bottom surface when it is clamped to the panel. So I just level up the plate to the panel by taping the first appropriate piece of wood I find lying around to the inner surface of the plate (Fig. 3). That levels up the plate to the panel surface. Coat the mating surface of the bolster with inletting black, clamp the assembly in the correct position and give the plate a good whack with a wooden mallet. Voila! The outline of the bolster is blacked in on the panel (Fig. 4). Fill in any little skips with a pencil to complete the outline. Cut the outline deeper with your inletting knife and gradually and carefully chisel out the mortise level by level. As you get close to the barrel, remember that the edges of razor-sharp wood chisels can be ruined by hitting metal (and chisel marks on the side of the barrel don’t rate as artistry either).
Once the bolster is inlet, the plate will set flat on the panel ready for inletting (Fig.5). Cut a deep incised line around the edge of the plate, angling the knife in a bit and staying as close to the edge as possible. Then go around again and again and again. You want that incision definite and deep (Fig.6) to avoid any chip-out during wood removal.
The next step is crucial to good inletting of the lock. You want the surface of the lock plate mortise inner surface to be parallel to the side barrel flat and 90° to the top barrel flat. I set my barrel stock assemblies up on my drill press and a roller rest to support the barrel end (Fig. 7). I usually use an inclinometer, which is nothing more than an angle finder with a magnetic base (available at any building supply store) to level the assembly precisely. A good spirit level should work just as well. Remember that you are leveling on the side of the barrel, not the panel. This is important when inletting locks to swamped barrels. I have a milling table on my drill press, but my quill stop to control drill depth is somewhat “vague” so I do a couple “locating cuts” to see where the quill stop should be set for the bottom of the plate mortise. If you are removing the wood with a chisel, make your calculations as to how deep the plate mortise should be by measuring the gap between the bolster and the barrel flat. I measure the gap by using numbered series drill bits; for example, if a #23 bit just slides between bolster and barrel, then the plate must be inlet 0.128” into the lock panel.
Remember what Peter Alexander said: “The worst job is inletting the plate.” Now that the worst is over, move on to T&T#15 and get the innards of that lock inlet and working freely in its mortise.
1. Alexander, Peter. The Gunsmith of Grenville County. 2002
2. Gusler, Wallace B. and James D. Lavin. Decorated Arms 1540-1870. Colonial Williamsburg Foundation and University Press of Virginia, 1977.
3. Shumway, George. Rifles of Colonial America, Vol. 1, 1980.