Tuesday, November 18, 2014

Plywood joining and dust making

Plywood was on sale at Windsor Plywood in Vernon, including their Baltic Birch, which I'm going to use for most of the trailer body and skin.  I didn't have a vehicle large enough to get the wood home (my trailer frame is still under construction), but the discounted prices covered delivery to the safety of my garage, which saves me a ton of work.

The nice thing about Baltic Birch (besides being quite a nice plywood to cut and finish) is that it comes in 5' x 5' fun-size sheets.  That's really handy for, say, a 5' wide camping trailer.

Now I can start making a mess!

This is a little dangerous: I have to resist the temptation to just start hammering the whole thing together until I see the frame.  There might be little imperfections to adjust for, or some as yet unknown reason to perform a redesign.

I started joining the plywood into 10 foot sheets.  I need to do 2 x 1/2" external walls, 2 x 1/8"internal walls (on the other side of 1" foam lamination), 1 floor, and 1 wall template.  I'll save the roof skins for later since they'll be unreasonably long and awkward.

Here's the template, my practice piece, in 1/2" standard:

I looked into doing a scarf joint, which seems to be the way that boat-builders and other fancy people join plywood, but that seemed like a lot of sanding.  I opted instead for a 6" lap joint, which was quite easy to cut out with a router.

After fine-tuning the depth to 1/2 the sheet thickness, I ran 3/4" dados.  I put the whole operation on the floor and knelt on a straight template board to make the cut.  It's important to get all the material out with each pass, because the router won't have a sheet to ride on once the next row is cut.

This whole process makes a tremendous mess.  After doing 2 sheet joins, I was knee-deep in coarse sawdust.

Here's a closer version.  The joining 2' 6" sheet was cut the same:

Aaaaand here we are clamping the joint using every heavy thing within reach.  The glue is Titebond III and in my experience it makes an alarmingly strong wood joint.

Here's the finished 4' x 10' plywood sheet, good as if I'd bought it that way:

I repeated the process for a sheet of Baltic Birch without incident.  The only thing different was the clamping method: I decided to use small screws to hold the joint instead of a pile of all of my belongings.  I'll probably take the screws out later, as they really don't add much strength to the joint:

For the 1/8" wood, I intend to use a butt joint with a 6" backer.  The backer will recessed into the foam core.  The join will be at the foot area of the cabin where it joins the galley, in pretty well the least obvious area of the trailer.

Sweeping time ...

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