Screws and Countersinking

I have written any times about the need to use screws instead of glue in a flight simulator cockpit.  In essence, the width of an assembled cockpit structure is usually far wider than a standard 900mm wide door.  So if you want to transport it, it has to be disassembled. That means: no glue.

So what is so special about inserting screws when building a Flight simulation Cockpit?

  • Screws have to positioned optically correctly (= accurately) since  they are visible when looking at the exterior “skin”.
  • They need to be evenly spaced because they actually are supposed to simulate rivets.
  • They need to be deeply countersunk in order to enable sanding of the flat panels into curved panels.
  • They also need to be deep enough so that after sanding the paint can flow onto the screw-head depression and thereby give the impression of a rivet that would be found on a real aircraft’s skin. (Sorry, you cant use an actual rivet simply because the structure might have to be disassembled !)

The first step in accurately positioning a screw is to drill a hole for the screw first. While it is tempting to just quickly ram in a screw with a powerful battery screwdriver, please resist this temptation. You will never get nice even screw positions, and you are quite likely to weaken the wood or even split it along the grain. Instead, get into the habit of carrying out the following steps:

Use a vernier caliper in conjunction with a metal ruler and a propelling lead pencil.

Pic of Propelling Pencil
An inexpensive propelling pencil (0.5) is much easier to accurately mark off a cross on wood than a standard wood pencil which constantly needs to be sharpened.

 

Pic of metal rule
Metal rule with engraved gradations. With the lead tip of the propelling pencil, the exact position can be “felt”.
Pic of Vernier Caliper
Vernier Caliper – this can be a cheap plastic one, although a metal instrument with a digital display is really useful when working in awkward spaces in low light. A caliper enables you to easily construct a line parallel to an edge. It is also handy to mark off evenly-spaced cross  lines.
Pic of an Awl
Use an awl with a wooden mallet to create a 2mm deep indent precisely at the marked cross. A large nail filed to a sharp point and a metal hammer will also work.

Once a series of accurate crosses have been drawn, use a  wood drill-bit to drill a hole to a depth of about 75% of the screw length (from head to tip). Measure the major diameter (distance from one side of the outside edge of the thread to the opposite edge) of the screw thread with a vernier caliper and choose a bit diameter that is about 50% of this distance  for soft wood and 70% for hard wood.

Then use a countersink bit to create a deep funnel for the screw head:

Pic of countersinking stages
The stages between countersinking for flight simulator cockpits and no countersinking at all.

Finally drive the screw in firmly but be careful not to drive it too deep – it’s easy to do with modern cordless drills and soft wood.