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Sub Plate
The first order of business is to have something to
mount things on, and what I came up with is a "sub plate". This sub
plate will have everything mounted to it that operates the lock
mechanism. The size of the sub plate has to be smaller than the door but
larger enough to hold a bunch of moving parts. The size of the sub plate
is 8.700" X 8.700" X 1/2" thick and will be made out of
aluminum. I know this is an odd size but that's
what it worked out to be.
The pieces that I welded onto the back of the door frame
(that the door will close against) is 1/4" per side. Then I'll need to
make a box
that will attach to the sub plate, which will hide all
the moving parts, and I'm not exactly sure how deep that will be yet. I took
all this into account and added in a small amount of clearance just to
make sure. That's why I have an odd size for this sub plate.
The first thing I did was square the sub
plate, just like I did for the other large pieces.
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Next I cut the top and bottom surface's,
but only a clean-up cut, leaving my thickness at .480".
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I'll need to mount the sub plate to the door somehow.
But with the door only 3/16" thick, I won't be able to put threads in it
because they would end up going through it. What I came up with is to
use 'studs' in place of bolts.
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I plan on welding the studs to the door and having them
go through the sub plate and then use nuts to fasten it down with. To
make sure the studs are the right location, I'm using a 1/4" end mill to
make a shallow pocket in the door to locate the studs.
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Here's a close-up of what the pockets look like. They are .050" deep
which should work good for locating the studs.
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The studs will be made out of 1/4-20 socket head cap screws which is
good material. All I did was cut the heads off of 1.000" long bolts and
then faced and deburred the saw cut ends.
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I clamped them in place and then put four tack welds on
each one. However, clamping each stud turned out to be a challenge
because they didn't want to stay square. I had to straighten each one
after welding to make them straight, which took awhile to do.
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I drilled .257"diameter holes through the sub plate so
it slides over the studs. I didn't want the sub plate to move which is
why the holes don't have much clearance. The counter bores that you see
are to clear the welds.
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The counterbores are 3/4" diameter X 1/8" deep. Nothing fancy here but
it works.
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It fits!! But I had to tweak the studs a small amount more to make that
happen. No big deal really.
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For the time being I'll be using these nuts but later on I'll use
lock-nuts to fasten the sub plate down with. Now it's time to start
making a lockup system.
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