Message-Id: <3.0.3.32.19981023053706.006e74f8@mail.digital.net>
Date: Fri, 23 Oct 1998 05:37:06 -0400
To: lancair.list@olsusa.com
From: John Cooper <heyduke@digital.net>
Subject: Hard points
In-Reply-To: <36300896.19A9@CPro.co.za>
Mime-Version: 1.0

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>Have anybody considered using round pieces of phenolic for hard points.
>It sure would be simpler to drill a hole with a hole saw into pre-preg,
>than to cut a square hole with a dremel.

Yes, this is the way to go. Cut out your 1/4" phenolic on a drill press
using a 7/8" hole saw with a 3/16" pilot. (I cut halfway through from one
side, then flip it over to finish the cut.) This will leave you with a
little "button" which is 3/4" diameter. Use a file to remove the flashing
on the circumference of the button. Then using a 1/2" counterbore (a plain
drill will work), relieve the pilot hole on one face so the head of an
AN-3-XX bolt will fit down into it and not protrude up beyond the face of
the button.

There are several ways to install the hardpoints:

1. Inlaid from the back (easiest).
2. Inlaid from the front (where you can't get to the back side or don't
want to mess up the surface there)
3. On top of the core (where you don't want to cut into the skin or need a
raised hardpoint).

Method 1 & 2:

Then with a 3/4" hole saw, cut thru the skin and core of the area where you
plan to install the hard point. Cut thru ONE SIDE ONLY (except for the
pilot hole). Remove the skin and core with screwdriver or something.

Rough up the head and neck of your appropriate-length of AN-3-XX bolt and
sand the faces of the phenolic with 80 grit paper to remove all shininess.
Sand an area around the hole on the side where you will be applying the bid
tapes. Flox the hardpoint into the waiting hole, and apply two-bid over the
side where you cut the hole. If you are using "Method 2" and need to cut a
hole in your bid tapes, use a leather punch.

Method 3:

Prep the button, bolt and skin as above, but use structural adhesive to
stick the button onto the skin where you want the hardpoint. (You will have
to analyze whether the surface you are bonding to has enough plys to carry
whatever load you intend the hardpoint to carry - add more glass if
necessary.) Make a fillet of structural adhesive around the perimeter of
the button. (The phenolic sticks better to the structural adhesive than to
the flox.)

The next day, when the thing has set up, grind a nice smooth radius around
the top edge of the button, and grind off any excess structural adhesive,
being careful not to cut into the fiberglass underneath. Apply two or three
bid over the top of the button. (Cut a hole in the center for the bolt
using a 3/16" leather punch). In some places where the load was light, I
omitted the bid tapes over the top.