5.21 ELECTRICAL (continued)
OPEN BARREL TERMINALS
The following text has been reproduced from
"The AeroElectric Connection "http://aeroelectric.
com/articles/matenlok/matenlok.html
Special thanks to Bob Nuckolls for allowing
us to reproduce this information.
Figure 1 is a closeup of the business end
of our Open Barrel Terminal Crimp Tool.
Note that pockets "C", "D" and "E"
have "butt-cheeks" formed into the
upper surface. These pockets
cause the end of wire grip wings to
curl over and dive into the approxi-
mate center of the wire strands.
Pockets "A" and "B" have a smooth,
circular shape used to shape the
terminal's insulation-grips into a
"bear hug."
Figure 2 shows a typical nylon
connector housing and a strip of
open barrel pins. This particular
connector is a Waldom/Molex
product purchased in a blister-
pak from Radio Shack. The
techniques described here are
typical for all connectors of this
genre.
If you wish to mount the
connector in a hole, the tabs
visible at the rear of the
connector housing can be
folded flat against the side of
the connector. Barbs molded
into the wings will slip through
the appropriate sized
rectangular hole and hold the
housing captive in the hole.
Check the original
manufacturer's data for
recommended hole dimensions.
Pins supplied in strips are intended for application by
automatic machine. The pins come in reels of perhaps
10,000 and feed into the side of an application machine like
a belt of cartridges into a machine gun. For our use, we
need to cut individual pins apart similar to what you see
here in Figure 3. Note that part of the material that joins
adjacent pins is left in place. It's too long in this view and
will be snipped off again later.
OBC-1 CRIMP TOOL FOR OPEN
BARREL TERMINALS
FIGURE 2
FIGURE 3
THESE TABS USED TO
"MOUNT" CONNECTOR
IN HOLE
Strip the wire about 3/32". Note that I've shortened the insulation grip
wings on this pin. These connectors are designed for automotive
applications where wiring insulation is MUCH larger in diameter than
for the same AWG size in aircraft wire. Left full length as supplied, it's
difficult if not impossible to get a proper "bear hug" on the wire's
insulation. See Figure 4.
Note shortened wire grip "wings". I've also shortened the stop tabs
but they will prove to be too long.
If left in as-supplied shape, the wire-grip and insulation-grip wings
tend to rotate the pin in the tool's dies as they close. This can result
in a poorly shaped crimp or even broken wings. Use a pair of pliers
to bend the wings into a "U" shape with sides parallel or even tilted
inward toward each other slightly. See Figure 5.
Now comes the fun part. Grip the pin loosely in pocket "D" with the
ends of the wire grip wings pointing toward the pocket's "butt cheeks".
Insert the stripped end of the wire so that exposed strands are inside
the crimp area. Close the tool while being watchful of dreaded "pin-spin". If things go as they should, ends of wire grip wings will do
a 180 degree turn and dive back into the center of the strands from both sides. You'll want to squeeze the tool with as much force
as you can with one hand. When you've got a nice LOOKING crimp, put a 5-8 pound pull on the wire to make sure it doesn't pull out
easily from under the wire grip. If it does, you need to squeeze harder next time.
Use tool pocket "A" to form the insulation-grip wings down onto the wire's insulation. You'll have to rotate the pin in the tool so that
the ends of the wings are pushed into the circular bottom of the pocket. As the ends of insulation-grip wings collide in the bottom of
the pocket - don't compress the tool any further. Take the pin out and use the end pincers of the tool to deflect the end of one
insulation grip down against the insulation. Return the pin to pocket "A" and rotate the pin in the pocket as you form the
insulation-grip wings down smoothly around the wire. The goal here is very different from the electrical connection. The conductor
strands need to be held very tightly while the insulation gets a only snug "bear-hug" as shown here. If you look at similar pins
installed on PVC insulated automotive wire, the fabricator may have turned the insulation-grip wings into the insulation not unlike
the wire-grip. I DO NOT RECOMMEND this on the aircraft wire - the insulation is too thin. For airplanes we want a simple, snug
support of the wire behind the wire-grip without penetrating the insulation.
Note also in Figure 6 how short the stop tabs are. Trim with caution as you learn how to deal with each style and size of pin. Cut the
tabs off too short and the pin will not be properly retained when installed. If the tabs are too long, the pin will simply resist insertion
into the back of the connector housing.
FIGURE 4
FIGURE 5
FIGURE 6
PAGE
REVISION:
DATE:
VAN'S AIRCRAFT, INC.
04/15/13
0
RV-ALL
05-23
FIGURE 1
