On another thread
http://americanlongrifles.org/forum/index.php?topic=24569.0 , some of us recently talked about books that are useful for new builders. I think Peter Alexander’s book won the most votes. (It is my favorite among those currently available. I think it’s a great book.) However, there is one area where I think new builders using that book could use a little more instruction. That’s in the area of layout for lock inlet when you aren’t starting with a plan already drawn up by an experienced smith. This topic is important for some new builders working with a slab. It is also important for those working with precarved stocks that do not have the lock inlet carved. Since some precarves don’t have the lock positioned very effectively, it is becoming increasingly popular to order the carved stock with the barrel mostly inlet, but the lock not inlet. That allows the builder more flexibility. But it also means that he/she need to have a more complete understanding of mechanical and aesthetic layout requirements than they would have otherwise.
Basically, what we are describing here is a situation where you are left to draw out the lock-position plan yourself. It’s pretty much common sense, but if you haven’t done it before, it can be helpful to helpful to have a good diagram to show you what you are after. Alexander does talk about this on page 67, but he doesn’t provide an especially good diagram. (or, perhaps I should say that he doesn’t do so in the 2002 edition. Other editions may improve on this.) Anyway, it’s a problem easily enough remedied! Here’s a diagram.
This diagram is from a rifle my son and I have been building together. .45, 13/16 straight barrel. small Siler with a revised profile. (Overall a fairly lightweight, comparatively inexpensive build. I mention that only to say that that’s the kind of build many new builders are looking for.)
[To save the image full size, put your mouse over it, right click, then select “save picture as”.]
The first thing I want to point out is the red line on the layout paper. That red line is the outline of the stock slab (so it marks the max options available for the slab we were using.) The basic layout issues for most flintlock longrifles will be similar to those shown here, but note that the actual forward-backward position in relation to the curve of the wrist will depend somewhat on what school you are representing. If building with a precarve, some of those factors will be predetermined by your pre-carve shape, and on the trigger assembly you will be using.
In looking at the layout plan, also note that I have dropped the touch hole down below the center of the flat, and that the tail of the lock sit in the lower half of the wrist (and that the curve of the lock guides your eye into the wrist). Finally, note that these choices mean that the forward lock bolt was not centered on the forward lobe of the lock. That is not a problem. Provided the bolt passes through good metal, it can otherwise be positioned a bit higher or lower. From perspectives of both design and mechanics, the other issues are more important, and so the bolt position in relation to the lobe should at best be a secondary consideration.
That said, I should also mention that if using a swamped barrel, this issue of forward lock bolt placement is easier to manage and the lower flat of the barrel hangs low enough that this is usually a non-topic. But many cheaper kits (and cheaper builds in general) use straight barrels, and that affects overall layout. The bolt must pass through the web between barrel and rod hole, and it must pass securely through the front lobe of the lock, but it doesn’t have to be centered in that lobe. If you are using a narrow gauge, straight barrel, you may need to adjust vertical position of the bolt in relation to the center line of the lobe. But remember that the final product will have the end of the bolt filed flush and hidden behind the frizzen spring, so no worries if it sits slightly higher than center.
Here’s a photo of something I find very, very helpful when doing layout work. It’s a “lock plate profile template”, cut out of soft plastic (from a large peanut butter jar). Note that the template has sear arm and touch hole positions marked clearly so that they can be positioned optimally when using the template to draw up your layout. Having a template made of see-through material helps you position the template accurately in relation to other lines already drawn/sketched on your plan. I find this much more effective for carefully measured layout than just using the actual lock plate.
This template shows the touch hole in “sunrise” position. If you wanted to use “early dawn” instead, you would accomplish that by making your template with the touch hole dropped down just a fraction deeper into the pan. Note that you do
not need to raise the lock further up on the side of the flat. From a design aesthetics perspective, it is much better to drop the hole down, rather than raising the lock up.
Before actually doing your layout, be sure to check the lock main spring in relation to the lower flats of the barrel. You don’t want the main spring to hit the barrel. With most locks it’s not a problem, but it can become a problem with large barrels and small locks. It can also become a problem if you position the lock too high on the side of the barrel, or if you pull the front lobe of the lock up too high (as might happen if you mistakenly assume that forward lock bolt absolutely has to pass through the center line of the lobe.) So before cutting wood, check to be sure that the lock position in your plan is not going to create a conflict between mainspring and barrel. (The red mark in the photo shows the area that you have to check, to be sure that it’s not going to conflict with the barrel.)
If there is a conflict, then you may need to drop the touch hole lower. Some builders may be concerned that with the touchhole dropped lower on the flat side of the barrel tube, the lower position would create a longer/deeper touch hole. That’s true, but it’s not a problem. As this next diagram tries to show, the difference in length is really minimal, and furthermore, coning from the inside or use of an insert will virtually eliminate any difference in the relative length of the two touch hole positions.
[NOTE: The next two paragraphs and photo of springs are a revision added after the original post, in response to helpful comments from Bob Roller and WadePatton.]
Some new locks come with cast springs that have not yet been tuned, and it is perfectly acceptable to contour the top limb of the spring, cutting back the corner and beveling it where it may hit the barrel. The following photo shows three springs (Davis, Siler, and a lock cast from an old original Maslin). Note the shoulders of the top limb. The top limb of the Davis more square than is necessary. It could easily be reduced. The shoulder of the Siler comes from Chambers already rounded back somewhat, but not beveled. And the Maslin shows how the spring may look with the shoulder rounded back and with the edge beveled.
The top limb of the Davis and Siler shown could easily be filed back in a manner similar to the Maslin. (If you file the spring, file with the axis as much as possible and polish out your file marks to help reduce chance of breakage.) I should mention that builders have different opinions about filing the bend. You will note that the original Maslin limb was filed back, but the bend was not reduced. Personally, I prefer to stay out of the bend, and thus leave it as strong as possible. But I don’t hesitate to file back the top limb, and will do so even if only so as to be able to leave wood between spring and barrel. (Leaving a web of wood between the two helps keep powder residue and moisture from getting into the lock via the barrel channel.)
Some builders will position the barrel and then try to position the butt and lock in relation to the barrel position, as if the barrel was somehow the anchor. I find it much more helpful to think of the string of relationships from a purely sequential
mechanical perspective, and when doing layout, that means I start with length of pull and move forward. On the slab, it means I start with the butt and try to determine what I want to show most (curl, burl, etc.), then move forward from there. The following sequence determines the mechanical relationships:
1. The butt is determined (quite obviously) by the end of the board. So, if building from a slab, the tail end of the slab is the real anchor. (In building with a precarve, the barrel position may have been partially determined. But even then you may still have some flexibility to move it back further, or down deeper. So don’t automatically assume that the barrel “anchor” can’t be adjusted.)
2. Trigger position is dependent on length of pull. So determine length of pull first, then sketch in a trigger.
3. Sear arm position is then determined by trigger position.
4. Horizontal touch hole position in relation to overall layout has then become a function of sear position, since sear and pan are on either end of the same chunk of steel.)
5. Horizontal (forward-backward) position of the barrel in relation to the lock is then a function of position of the pan. The pan determines the touch hole, and the horizontal barrel position is determined by where the touchhole will work best in relation to the breach plug.
6. Vertical position of the touch hole on the barrel is then determined by the combined relationship of pan position and barrel height (up and down) and (also, but with more variability) in relation to the web of wood left between barrel and rod hole. (The forward lock bolt must pass through that web.)
Keep in mind that the horizontal position for touch hole (and thus the position for the barrel, as well) are determined in part by what sort of touch hole you will be using. In general, the hole should be as far back as possible without interfering with the threads of the breech plug. In some old rifles, the hole did cut the threads, or even pierce the plug itself, but that option creates additional mechanical and cleaning issues that most contemporary smiths prefer to avoid. If using a straight, simple touch hole, then the barrel can move further forward (so that the touch hole is very close to the plug face). This can help overall wrist and lock panel geometry. However, if coning or if using an insert, then the barrel must sit further back by an 1/8” or so. This is required in order to make room for the additional material removal required in these techniques. Most contemporary smiths don’t want the cone or the threads of the insert hole to interfere with the plug threads.
This issue is shown in this next photo, which shows a straight .45 barrel with the front of the beach plug marked by a line and the touch hole and insert diameter sketched on with a marker. (I’ve drawn the lines oversize so that you can see them easily.) Note that that the position of the touch hole is lower than the centerline.
Once you determine the mechanical relationships, you can then work on the aesthetic and architectural elements, such as where these parts need to fit in relation to the curve of the wrist, the position of the tail of the lock in relation to wrist height, the shape of the lock panels, the amount of wood to leave here and there, etc. Those are all important architectural elements, but note that they are aesthetic issues, and thus secondary to mechanical issues. If you mean for your rifle to be a working tool (rather than a movie prop or a non-functioning museum mockup), then you will do well to keep mechanical relationships the primary criteria during layout. Aesthetic design will then follow in its proper place.
Finally, when you work out those details for the lock placement, you are then ready to draw out a design for the rest of the fore stock. (Try to avoid thinking of the lock panels as sitting on the fore stock. Instead, think of the fore stock as
flowing out of the panels. The eye is drawn to the lock and lock panels, so that’s where your eye starts look first.) When you have sketched out the fore stock and the location of the rear entry hole in relation to the barrel, then use a straight edge to draw in the rod hole in relation to the lock. If working with a slab, then the location, depth and angle of the rod hole are somewhat optional. You can position the hole up or down as you wish, provided you leave enough of a web between barrel and rod for the forward lock bolt to pass through. If, however, you are working with a precarve with predrilled rod hole, then you will need to determine where it sits as you received it.
You can measure the exact depth of the inside of the rod hole by drilling some small holes in the bottom of the barrel channel and into the rod hole, then using a feeler gauge to check depth of the hole (in relation to the top of the fore stock rail.) Here’s a photo of a simple feeler gauge you can make for this task.
Keep in mind that you do not have to leave a thick web of wood between barrel and rod hole. It only has to be thick enough for the lock bolt to pass through the web. So, if you think it is too thick on your precarved stock, then you can consider whether or not you want to deepen the barrel channel, so as to drop the barrel down deeper. But do keep in mind that dropping the barrel deeper may simultaneously require you to raise the position of the touch hole. So don’t cut wood until you are sure that the new arrangement would be better than the one you started with!
Hope this is useful.
Whetrock
PS: Here is a thread on related topics that may be of some help:
discussing barrel position etc in relation to lock on kit guns
http://americanlongrifles.org/forum/index.php?topic=24016.msg230715#msg230715
