If I had a “real” shop, I’d have machinery for dealing with metal… a brake, and roll bender. Since I don’t own either of those (and they are the sort of thing you need a 18-wheeler to deliver), I had to improvise. Flat sheet metal (at least the 0.063″ aluminum) just doesn’t like to conform to a curve. The spring force it exerts is really high.

Note: We are now in a “long retrospective” mode since I finished the trailer to the point of usability over only 5 days (this was day 2) so Adrian and I could use it over the break.  In fact, it is hard to remember when stuff happened. I basically finished as much stuff as I could before running out of clamps, or space or both each day. I’m going to blog it all, but it probably isn’t in anything like the order it actually happened in.

Improvising a “Roll Bender”

A roll bender is 3 rollers that you feed a sheet of metal through over and over again. The result is a smooth radius curve. You can even bend it all the way around and make tubing out of it.

What I had was a couple of saw horses, some 2-by material, clamps and a time constraint. You saw this in the last post, but I want to actually talk about it here.

This set up is NOT perfect. It is possible to get light creases in the metal, especially near the edges if the board you use to press the metal down extends all the way to the edge.

You’ll notice that center of the metal is being pressed down with a short 2×6 with a longer piece over it (not in contact with the metal) for the clamps to grab. The wider board (2×6) seems to be less likely to crease the aluminum also.

The fundamental problem (besides being slow and frankly terrifying) with this improvised bender is that you have to release it to move the metal. A roll bender allows you to feed sheet metal through continually bending it smoothly the entire way. That would be great, but wasn’t in the time budget (it’s possible I could have found somewhere in San Diego that had one I could use or that I could pay to do it).

Cycling it (i.e. bending it more then less then more, fatiguing the metal) helped too. In the end, I had enough bend on it that I didn’t have to force it. It was approximately there, at least in the middle of the sheet. The edges were more of a problem sense I could slide far enough through to catch them.

Gluing and Screwing

Because the aluminum is very springy and my radius were not exact, I ended up adding screws to the curved pieces. It isn’t ideal, but it solved the problem. I put screws along the top and bottom edges. The sides are not screwed. More on this in a future post.

I use a hole spacing tool (officially called a Rivet Fan Spacer, used for airplane work) to ensure even spacing. The vice-grips keep the spacing from changing. For quick use, it isn’t needed. The fan spacer is pretty stiff to change, but I wanted the same spacing over weeks. I set this up and locked it down. All the screw spacing on the trailer is exactly the same that way.

Clamping the top involved lots of 2-by material, straps and shims.

I managed to lock myself out of work on the inside of the trailer with a strap back across the doors (mounted in the this picture even though I haven’t blogged that yet).

The boards over the top of the trailer are to keep the straps from crushing in the roof.  The walls are quite strong, but the center is just 1/8″ plywood over insulation in most places.

I also used similar glue (carpet in the center and construction adhesive on the edges). The results are acceptable, but by no means perfect.

Back on the Horse – Rear Hatch

The rear hatch metal has a simpler bend than the front nose. It has a radius bend in the center, but is mostly flat on either end.

With a little work (OK, a lot of work), I got this:

It isn’t perfect, but the shape is pretty close. I also added a bunch more 2-bys to my inventory and a bunch more clamps (+24, so 40+ now).

Take 2 of the rear hatch cover used a combination of carpet adhesive on the field, polyurethane construction adhesive on the edges, and screws on the top and bottom edge to hold things down.

I also ended up putting a few counter sunk screws along the middle of the bend on the outside edges to keep it from pulling away.

I had to add a small (1.5″) strip of aluminum along the bottom edge to make up for the hatch being slightly larger than the material I could purchase.

Door Two Too

Door one got finished previously, but door 2 had to get wrapped up. Being flat, it was simple. Carpet glue, clamps, weight and wait, router, done.

Cutting aluminum this way with a router makes a TON of shiny aluminum shavings. I tracked them all over the house over the week or 2 I worked on this. Roomba to the rescue.

That’s it for now.