Drilling for the sear bar.

[Uncle Alvah]

On my first build, I have inlet the lock plate, drilled for the lock bolt and now am at the point of drilling for the sear bar. Seems straightforward enough but figured it wise to ask advice on here. I could not find where Recreating the American Longrifle covered it.

[Chowmi]

Uncle Alvah,
I've only done one, so take this for what it is worth (not much!).

If you want to be precise, you need to do two things first.

Figure out your sear travel. It will move from full cock to hammer down.  Assemble your lock, and then mark where the sear sits with the hammer down.  Then cycle the lock through half and full cock and mark the furthest point the sear moves to.  (Might be at half cock, full cock or partway between).  Then you have all positions marked on the back of the lock.
Now disassemble the lock.  If you want, you can make a tracing of the back of the lock plate, with the sear positions on it.  This may help later on.

Next, put the lock plate into the inlet (lock dis-assembled).  Stick a sharp pencil through all the holes in the lock plate, you will need this later for the internals inlet anyway.  Specifically, draw a circle where the sear screw goes through.  Then, take the lock plate off.  Now you know where the sear will sit.  You can place the sear (upside down) onto the wood with the hole for the sear screw lined up with the circle you drew.  Now you know where the sear bar is and the arc that the sear will travel.  Next, you just need to refer to the back of your lock plate, or the tracing you made to determine where on the arc the sear moves when you action the lock.  That will define the hole that you need to drill.  Does that all make sense?  You are using the screw hole to place the sear on the wood, and then using the sear to figure out where the hole goes. 
On some locks, the arc is easy to eyeball because the lowest point is super close to the bottom of the lock plate.  Others, not so much. 

Next, make sure you drill it deep enough so the tip of the sear bar does not drag on the bottom of the hole, but no deeper.  Hold your drill bit up against the sear and see what depth you need.  Mark the drill bit.  Obvious, but don't drill so far you go through the side panel!! 

I can't remember what drill bit size I used, but the travel of the sear will tell you the minimum size. 

It's easier to do than it is to describe.  If that doesn't make sense, let me know, I will draw a picture. 

Cheers,
Norm

[retired fella]

what chowmi said.  One added point concerning depth.  Some sear bars can be cut down once your hole is drilled and trigger installed as a final adjustment to keep it from dragging on wood on the bottom side.  Do Not  drill deeper than it needs to be.

Keep at it, you'll get there.

[Uncle Alvah]

There does not seem to be much difference between full/half/down positions as to where the sear sits, it moves very little when the hammer is being retracted, and once at half or full cock, is pretty much the same place, as show by the bottom line. The upper line is the upper limit of sear travel by pushing it with my finger.
Or have I completely misunderstood the process?

[sqrldog]

UA
Go to  Contemporary Collecting  look at the Bivins rifle on page 3 there is a picture of the lock inlet on the Bivins rifle. May help with your question. Tim

[Chowmi]

There does not seem to be much difference between full/half/down positions as to where the sear sits, it moves very little when the hammer is being retracted, and once at half or full cock, is pretty much the same place, as show by the bottom line. The upper line is the upper limit of sear travel by pushing it with my finger.
Or have I completely misunderstood the process?

Uncle Alvah,
it depends on the lock, but you also have to consider the movement of the sear In between the full, half, and hammer down cock positions.
I'm sitting here with a Chamber's Round Face English lock, and as it turns out, the highest point that the tail of the sear hits, or travels to, is as it moves between hammer down and half-cock.  So you need to document the full movement of the sear, not just the place it sits at each end position.  Your lock may or may not show the same movement pattern, but you need to figure out the extremes of the sear movement. 

I just re-read your description, and I guess I would say that if you have captured the full movement of the sear, then you are good to go.  Sounds like it doesn't move much.  Just double check and then drill. 
If you drill a hole that is too small, you will find your error when you get all the internals inlet, and it doesn't work properly.  That is the safer way to go.  You can always go bigger.
 If you drill a hole that is too wide, you have taken away wood that doesn't need to be gone in an area that needs strength!   

Cheers,
Norm

[PPatch]

Hi Alvah;

You've gotten some good advice so far, I will try and help a bit.

Remember your build sequence; Lock mortise to the point of all internals being inlet including the sear bar hole being drilled. Next you will want to do the trigger bar and internals. Obviously the lock and triggers function together and you will need to be very positive with the trigger placement relative to the sear bar.

Looks like you have the bar located on your lock plate, the hole goes immediately below that. You can always make it deeper if need be, the way to tell is to blacken the tip of the sear bar and test fit it into the mortise, if the tip leaves a spot then you need to go a bit deeper.



That is a late Ketland lock, yours is a Chambers/Siler if I remember correctly, but the hole is in about the same location. I use a 3/8ths forstner bit for the hole and am very careful of the depth.

I, and others here, also drill another hole coming up from the trigger plate that intersects with the sear bar hole. I use a 1/4" bit for that. This second hole is drilled immediately below the small bolt hole between the trigger slots.





This second hole allows you to see the sear bar by looking into it, and this aids you in locating your triggers. Note in the photo that the trigger bar is being inlet from front to rear, it is done this way so that you don't end up with a gap at one end or another of your trigger bar which WILL happen on a curved surface.

Go slow, be sure.

dave

[Uncle Alvah]

So then in your second picture the hole up to the sear bar hole has not yet been drilled?

[PPatch]

So then in your second picture the hole up to the sear bar hole has not yet been drilled?

It has been drilled, note the dark spot in the trigger bar slot I am inletting, and it is drilled directly beneath the sear bar and off a bit to the lock side of the bar inlet. If you use that small hole between the trigger slots as your guide you will do fine. At first, of course, you must determine where to inlet the triggers, this takes a bit of fiddling around and do put your thinking cap on before starting your trigger bar inlet. I do the "fiddling" with the whole trigger assembly, once I have the location I remove the trigger insides and begin inletting the trigger bar, remember to file a slight chamfer on the bar before inletting.

dave

[Uncle Alvah]

So the hole is drilled up through the stock, but not through the trigger bar itself?

[PPatch]

So the hole is drilled up through the stock, but not through the trigger bar itself?

Correct, once you know where to drill remove the lock entirely. you are only drilling deep enough to intersect with the sear bar hole, no further. You do not touch the bar at all and it should not be in in the bar hole when you drill.

dp

[Uncle Alvah]

Now I'm with ya, thanks! I was thinking that there was a third hole to be located and drilled through the trigger bar in addition to the two shown.