Lower Left Wing - Wing Walk Plywood Glued On

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I expected more spring back after forming the plywood.  The wing rib capstrips had more spring back.  In this first picture the plywood is just laying on the rib.  The lightest clamping holds it in place so nailing the plywood down should get a good glue bond.

The first step is to layout where glue goes on the plywood.  This is easily done with the plywood clamped in place. 

I use a mechanical pencil all day, every day, but for tracing around the wood members a regular wood lead pencil works better.  You do need a pencil sharpener.

You need to layout the topside as well to know where you can place nails.  It can all be done with a straight edge.

Because I bought plywood too short to do the walk in one piece I need to make a 10:1 splice.  I'm locating it at the aft spar, where the bend in the plywood is the least.  It also works out nice for clamping the joint since the aft spar is 1 1/4" wide and a 10:1 splice in 1/8" plywood is also 1 1/4" wide.
The plywood was cut 12" wide and I want an accurate joint. The first step is to square up the sander table and level the saw table to support the end of the plywood, 48" long.

I placed a straight edge along the face of the belt sander and drew an extension line on the saw table.  I placed the table where I could conveniently make a 3" rise to a 30" run for my 10:1 angle.  I drew a line for the angle and clamped a guide block on the back of the line for the plywood to rest against controlling the angle.  You've got to love math and geometry.

The start point is marked on the sander table for locating the edge of the plywood.

I drew a 1 1/4" line on the plywood as a check on how even the sanding is across the board.

I cut a piece of 2x4 as a push block and square it to the sander so it can rest on the table while gently pushing on the plywood. 

The long edge needs to be sanded smooth.  The wood is being sanded very thin and slight bumps in the block will affect the straightness of the finished grind.

To keep the plywood tight against the angle guide I clamped a block on the table.

The block just has to be snug.

You can see it held the plywood against the guide just fine.

A very gentile touch is needed.  As you grind you want to watch the edge of the plywood and put slightly more pressure at either end to keep it straight across the board.

The grind is finished when the edge is just feathered.  I cut the aft section of plywood to length after grinding and fitting it all on the wing so I could experiment with this grinding process if needed

After doing the aft portion I used the same process for the forward section.

I did the direction of the splice so the aft portion is on the bottom and glues to the spar.  The forward section is on top.  The idea was that the aft portion is in tension if you step on it so it needs a firm grip to the rear spar to help take the tension load.  The aft end of the forward section just needs to stay down.  Hopefully the joint is well enough done that it also carries some of the tension load.  I'm also going to mark most of the aft portion as no step to reduce the chance of someone breaking it with a heavy step.

The 2 pieces were clamped in place so the aft portion could be marked for cutting to length.

To clamp the joint while the glue sets I've ground a slight curve on a piece of 2x2.  The ends are about 1/32" below the center so the center will be pressing tight on the joint while clamping near the ends.  You can see that if you clamp one end the other end has about a 1/8" gap.

Glue must be applied to both the frame and the plywood.  I mixed up 24 grams of glue for each section.  It worked out about perfect.  I did 2 separate batches so it would be as fresh as possible for each.

I used my long and short spring clamps along the trailing edge where I couldn't nail.

The clamp block at the joint worked well.  I got a very even amount of glue squeezed out along the length of the joint, indicating even pressure.

Every where I could 3/8" nails were paced about 3/4" to 1" apart.  Using the Great Neck Brad Nail Driver really speeded up this process.  I worked from the trailing edge forward nailing.  As I nailed I placed clamps at each end of the support members to assure the plywood was tight.

The nail pattern at the leading edge blocks is tighter and I clamped the edge to help assure it stayed tight while the glue set.  I know,  the wood was a perfect fit so why all the stress, that's just me.

This was one of the most satisfying projects on the wings.  It really went well.  It took about 2 1/2 hours to do all of this.  Once the glue is set I have a little trimming on the edge of the plywood.  I must not have had the rib perfectly flat.  It's very close.

I'm really happy with this.