Hatch Ribs, Hatch Skin, Electrical Progress

In the previous post the first hatch rib had been placed in the mold.  Two days ago we removed it from the mold and placed the second rib.

Here you see both outside ribs.  These are both 8-ply, making them 2" thick.  They will have a rabbet created around the outside edge on one side that will be 1/2" deep to receive the skin.  Next we will create two center ribs 1-1/2" thick to allow for the skin. 

A test was created for the proposed skin, comprised of a layer of 3/8" x 3/4" white oak tongue-and-groove bead board (without the additional beading) and a layer of 1/8" birch plywood on the outside.

For the purpose of the test we didn't bother sanding the saw marks off the inside surface of the slats; this was more a functional test to gauge stiffness and assembly technique.  The two plywood sides were patterned on the sharpest point of the curve.

Here you can see the individual slats with tongue-and-groove detail, and the 1/8" birch applied.

The test revealed several things:

1. The 1/8" birch ply is necessary to enhance stiffness, although it does not make the hatch rigid.  Therefore we may need to add some lateral bracing inside the hatch.
2. The milling will be time-consuming, as we will require approximately 140 slats, each 5' long, for about 700 lf.  The process involves ripping a 3/8" slice from 8/4 oak stock, then ripping that slice in two to produce two slats.  Sanding will be necessary on one side to remove saw marks.  Next, the groove edge is milled on the router table, followed by milling the tongue edge.
3. Assembly requires spreading glue along the length of the tongue on both sides, putting a spot of glue on each rib, placing the slat and nailing with the pneumatic nailer.  Then the glue must be wiped.  Therefore the assembly must be done in such a manner that both sides of the hatch are fully accessible.
4. Securing the plywood can only be done where it crosses a rib, then at the top and bottom edges of the hatch.  The issue is that we must have a joint since the plywood sheets are 5' and the overall length of the hatch is approximately 7'.  This will necessitate applying the beadboard to the 5' point, then applying the first sheet of plywood, which can now be clamped along the entire edge where it will join the other sheet.  Afterwards, the balance of the beadboard can be applied, followed by the second piece of plywood.  We still have the issue of securing the edge of this piece where it joins the other sheet, but managing this with only one loose edge instead of two will be easier.

Yesterday we pulled a bundle consisting of three plastic sub-ducts, three #10 wires for the rear DC circuits, and a pull string through the conduit from the electrical cavity to the rear of the trailer.  It took two attempts.  The original approach was front-to-rear.  The corrugated sub-duct builds up resistance at every turn in the pipe, and it was too difficult to get it to make the last turn to the vertical.  

The second attempt worked from the rear forward, and was more successful.  Still, after making the last turn to the vertical inside the electrical cavity, it became very difficult to pull.  We got it to an acceptable point and decided to stop there.

In this front-to-rear conduit we have:

1. Three #10 wires for the DC circuit - positive, negative and chassis ground
2. Three sub-ducts, one to carry the trailer clearance light circuit, one to carry the speaker wires for the radio/cd/mp3 player, and one spare

Today is an off day, owing to the wet weather.  Recall that the trailer is being built under a "party tent" and the main work table is under a temporary garage structure.  When it rains, the cement floor inside the temporary garage can become flooded, and working with anything electrical while standing in water is ill advised.  Likewise, the saws and router table must be used without any cover, and rain prevents their use.

Sean is continuing the wiring.  My next steps are to sand the vents for the top of the electrical cavity, install them in the cover, and polyurethane that cover and the two lower doors for the electrical cavity.  I have also procured the latches for the four doors and will install them as convenient.  

We can remove the second rib from the mold tomorrow and lay up the first inner one.  When the four ribs are complete, they need to be surfaced and cut to fit, then joined to the top and bottom hatch edges.  I will need to procure the additional 8/4 oak for the beadboard, after which we will need at least a full day if not more to mill it.  Then, finally, the hatch can be fully assembled.

Since the hatch is projected to weigh about 100 pounds, we are thinking it would be advisable to have some kind of spring-loaded assist to lift it.  I don't believe conventional gas struts will be adequate.  If any readers have thoughts on this, or specific parts to suggest, please leave a comment.  And, thank you in advance!