LOCATING THE LOCK SCREWS

[Zonie]

After answering a PT from one of our members I got to thinking that maybe some of you folks would like to see how I locate my lockplate screws.

The question in the PT was, "Do you drill the lock screw holes thru the lock plate?"
Here is my answer"

I always drill completely thru for both holes.

In fact, I use the thru holes to locate the holes that go thru the wood. My reasons, especially with the rear lock screw hole is as follows:

There is a very small area of bolster where this rear hole can live without interfering with the bridle, the tumbler or the mainspring and this area is the small surface that stands proud of the inner face of the lockplate. It is important that the screw is located in this small area such that it won't 'break out' of one of the sides thereby creating partial threads.

I locate this hole by taking the diameter of the screw threads (.138 for a #6 or .164 for a #8) and dividing it in half. To this, I add .030 so I end up with the number .099 for a #6 or .112 for a #8 screw.

Setting my dial caliper to the proper number and applying some inletting black or using a black felt tip pen to the small raised bolster face I use the edge of the bolster to guide the tips of the caliper and allow the other jaw to scribe lines in the black markings.
Where the marks meet, or in the area between where the marks are if they don't meet I center punch a small dimple. I then use this to pilot the drill bit in my drill press and drill USING THE PROPER TAP DRILL thru the plate.

For the forward hole, after determining where the ramrod hole and the bottom flat of the barrel is I know the "up/down" area the hole has to be.
Then by temporally placing the mainspring into the lockplates mainspring hole I know where the screw cannot be. By the way, this is rarely in the center of the lobe at the front of the lockplate. After determining the front hole location I drill the thru hole USING THE PROPER TAP DRILL.

With this completed I place the lock into the locks mortice and still USING THE PROPER TAP DRILL use these two drilled holes as a "drill jig" to guide the drill as I drill back thru the stock so the drill bit breaks out the far side.

You can do this with the barrel in place or with it removed but sooner or later you will have to install the barrel and once again, using the rear screw hole as a guide, drill thru the metal of the breech plug that is in the way of the screw hole. This hole thru the breech plug tang extension will have to be enlarged later. I usually use a 1/4 inch drill bit to enlarge this hole thru the metal.

Now, with the lock plate removed from the stock, use the CLEARANCE DRILL for the screw and enlarge the holes thru the stocks wood. This should be done with a 5/32 (.156 dia) drill for a #6 or a 3/16 (.187 dia) drill for a #8 screw.

Put the lock plate back into the mortice and using the clearance holes thru the wood to guide it, start the tap into the lockplates tap drilled holes. This should be done with a "tapered tap" not a "bottoming tap". A tapered tap is the standard kind that everyone buys from the store.

Turn the tap with the tap handle while applying some forward pressure against the lockplate until the tap has rotated about 1-2 turns. Then back the tap out by unscrewing it.
This may be done without lubrication.
Repeat this with the other screw hole.

With the lockplate removed from the stock, start the tap into the partially tapped hole using finger pressure only. The tap must pick up the started thread. If you have one, a drill press will keep the tap perpinducular to the lockplate but if you don't, just trust the threads you started and the thru holes you made when you started to align the tap.

You MUST use a good THREAD CUTTING OIL to lubricate the tap or you will break it so, lube up the tap and hole and thread the holes by running the tap in 2 turns, then backing it out one turn. Repeat this, adding lube until the full body of the tap will run freely thru the lockplates holes.

To locate the sideplate, drill a clearance sized hole thru the plate at the rear location trying to center it up as good as possible with the shape in the area.

Place a screw thru this hole and thru the rear lock screw hole.

Place a clearance sized drill bit thru the front lock screw hole from the lock side allowing the tip of the drill bit to protrude slightly thru the stock.

Now, swing the sideplate around the rear screw and across the pointed tip of the protruding drill bit. The tip of the drill will scribe a line on the inner surface of the sideplate.

Measure the sideplates width in the forward area and divide it by 2. Set your calipers to this number and using the side of the nose of the sideplate scribe a line that crosses the curved scribe mark that was made by the tip of the protruding drill bit.
THAT IS THE LOCATION to drill the forward screw hole for the side plate.

Have fun.

 

[Zonie]

Well, as fate would have it, the guy who asked the question came up with another twist to doing this.

It seems his sideplate was pre-drilled when he got it.
Because of this, one cannot arbitrarily locate at least one of the holes in his lockplate so, here's my answer for those of you who bought your sideplate from someone who thought they knew more about building your rifle than you did.

It also applies to those of you who bought one of those fancy sideplates with cast features and circular bosses for both of the screws.

If you have one of these fancy cast sideplates with circular ends on it for the lock screws first check to see if the center of those bosses are spaced correctly for your lock and have a chance of locating the screws in the right place on your lock.
Then, drill a hole in the center of each round boss and do as I describe below.
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The pre drilled sideplate may cause a problem if my method is used.

For the life of me, I can't figure out how someone who makes a sideplate can know where the best locations for a lock bolt is.

I guess if I were to be using a predrilled side plate my method would be to first locate the rear lock screw hole in the bolster like I described.

After this hole had been drilled I would place the sideplate onto the outside of the lock plate using the tap drill in the rear screw hole as a pivot for the rear screw hole in the side plate.

Then, I would rotate the sideplate up/down to best fit the front hole with the mainspring/top of the ramrod location and bottom of the barrel location. (You should have drawn the top of the ramrod hole and the bottom of the barrel flat onto the side of the stock after doing careful measurements to determine where these two features are).

Hopefully the front side plate screw hole will be in a location that doesn't interfere with the ramrod hole/bottom of the barrel/mainspring.

Once that location is determined then mark it and drill the tap drill sized hole as I previously described.

If there must be a choice between having that forward screw interfere with the ramrod hole or the bottom of the barrel, locate it so that it will interfere with the barrel. You can always file a clearance groove in the lower barrel flat.

 

[Birddog6]

Just a note........ some of those predrilled sideplates are made specifically for a certain lock, so you should ask if it is for the lock you are going to use.
Nutherwords one made for a large Siler will be spaced differently than one for a L&R classic or a English lock or Germanic lock, etc.
Now some you can put the front bolt where ya want it as you just shorten the sideplate, but the ones with the bosses for the screws are normally made for a specific lock, or the ones I have used were that way.
And I have had them where the lockplate was not long enough to get the screws where I want them, thus I lay it on a blank piece of 1/8" sheet brass (or iron if that be the trim) and scribe it, then move the front over & scribe it again to get it to the length you need.

Another thing I will mention, Before you take the mainspring & Frizzen off the lock, take a Exacto knife, turn it over & take the tip of the blade & scribe a line around the Front of the mainspring, and the same on the Front of the Frizzen.

It is best to have the front lockscrew Under the frizzen spring so it is hidden, but in Front of the mainspring, cause if it is not the mainspring will block you lockbolt hole.
:redface: Some locks you have allot of room in front of that mainspring & others you have just enough for the screw, so be sure before ya drill.

Keith Lisle