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similar grey colored Loctite epoxy, then sanded smoothe and
painted, or not - to your liking. A new set of holes must be drilled
for the sear/selector pin at the proper locations using the side
plate layout dimensions. The trigger pin holes are close enough
to work as they are for the SMG trigger parts set.
On the bottom right side at the trigger slot there is another
smaller slot in line with a hole and a detent relief. This is the
mounting hole for the SMG safety. In the unlikely event that the
production semi model gun does not have
this slot and detents, they will have to be drilled and cut if the
safety is going to be installed. It is usually ignored.
As the forming die is to the making of the frame, so is the
drilling jig to the making of the trigger group holes. In this
design, the sear stud hole is used to align the frame to the rest
of the trigger group holes. It is really only time saving if you
have several frames to drill. It is again, the perfectionist's tool.
All of it should be fashioned from hardenable tool steel like oil
hardening 1/4" flat stock found in any tool supply house. Mail
order tool sales companies are a part of the source lists found in
the back of the book. Practically all of them stock O-1 precision
ground flat stock. O-1 is an oil hardening tool steel that will not
wear after heating and quenching in oil, which hardens it and
this explains the 'O' in O-1. Most machine shops will have
scraps of O-1 they will most likely part with for a small part of
what you can expect to pay a tool supplier. Of course, then there
won't be that excellent piece of scrap left over to make a hunting
knife. Other types of tool steels can be used sucessfully, too. A2
is an air hardening tool steel, and W2 hardens by quenching in
water. D2 is a tough die steel that is intended to be hardened in a
controlled air environment, but will oil harden as well. Care must
be used if this is done however, as it becomes brittle enough to
shatter if struck a hard blow.
Three pieces, four inches long are necessary. Two of them are
1/4" by one inch. The other one is 1/4" by 2". The flat thickness
used to determine the distance from outside bottom of the frame
to the correct hole placement height was .075". No tolerance is
necessary. If the tab forming block made for the forming die is
held to exacting 'slip fit' dimensions, it can be used as a gage to
set the inside distance between the sides of the jig for their
attachment to the bottom piece. As is visible in the drilling jig
print, the two sides set on the bottom plate, flush to the bottom
of the frame. If the frame is formed cleanly enough, the sear stud
hole can be transferred from the bottom of it to the bottom piece
of the jig. Or, be trusting, and use the blueprint. It works. USE
THE SIDE LAYOUT TEMPLATE FOR THE SIDE PIECES of the
drilling jig. Remember that these locations are from the BOTTOM
of the frame and include the flat thickness. The SIDE PLATE
TEMPLATES are to be used for both the direct placement of the
trigger group holes and the drilling jig holes.
Begin by marking one of the one inch wide pieces in the upper
right corner, 'right', and the other in the upper left corner 'left'.
(Or, R and L) These will be the outside surfaces of those pieces.
From this point remember that the dimensions for the right side
plate are given with the zero at the bottom right. The dimensions
for the left plate are given from the bottom left. These
dimensions are the same, just headed in opposite directions.
The height dimensions are established using the nominal flat
thickness of .075". So long as the flats are within .010" either
way from that there will be no problem. If the thickness is more
than that, you will need to add the difference. Only the hole
sizes will vary. See the drawing set numbered 7 through 9.
Drilling them with a clean sharp drill should be enough. It isn't
necessary to ream the holes to size. In fact, after hardening, it
could cause some problems. A drill just about always makes a
slightly larger hole. (plus .001" to .003")
To finish the jig, the metal should be flame hardened taking care
to only bring it into the red color spectrum before quenching in
oil (Using the recommended O1 flat stock ). Old motor oil from
an oil change works fine. All pieces should then be polished to a
silver finish (It needn't be a bright finish) and slowly reheated
preferably in a piece of 4" wide channel iron, playing the flame
on the channel instead of the O1 metal, until it takes on a little
tan (light straw, in the heat treat business). Dark brown or blue is
a little too much, but if these colors appear only at the corners
or as streaks through the O1, it will still be hard enough to be
servicable. At this point, leave it alone to cool as it will. DO NOT
QUENCH IT WITH WATER!!! It should leave a light tan with
brown streaks through it. With some care, this process can be
done on the kitchen gas stove. It may be possible on an electric
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