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.
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.