Post by wisconsinjoe on Apr 10, 2020 10:07:03 GMT -8
On my scratch build, I'm considering using square aluminum tube stock (1.5" x 1.5" x 0.25" wall thickness) instead of 2x2 or 2x3 pine (1.5 inch thickness) to be used as roof rafters. I'm looking for greater strength to combat roof sagging. Also, I may want to scab on some wood to act as a receiver for fasteners, perhaps gluing the wood to aluminum. I can't find any simple engineering charts to help me figure this out. Is this how modern trailers are built? Does anyone have insight on this?
I don't have an answer for you, but for my scratch build/rebuild I added more roof rafters than the original had. The original didn't have any sagging, just pleeeenty of water damage and rot. I copied the original rafter profile, as they had a crown cut into them. 2.5" wide, 2.5" tall at the walls, but they increased thickness to 1" at the center. I like that I don't have to worry as much about water setting on the top, and I didn't have any problems getting the roof vent or the skins installed.
The rafters were cut down from 2x4 boards on a band saw. I can't remember how we got the curve, I think I just traced the curve from and old board. But a long piece of string and some trial and error (or actual math) would work.
I used aluminum square tubing for my Aljo, then sistered wood alongside. The aluminum was smaller and didn't have a lot of strength. (1/2 x1/2) Shasta used angle iron in some trailers but had the same amount of wood rafters. Very few of my trailers have had 2 by rafters, most were 3/4". Whatever you decide on, be sure to pad the metal well on top to prevent roof rubs.
Post by dragonwagons on Apr 10, 2020 22:27:02 GMT -8
On one of my rafters I used a piece of U shaped Aluminum, and wrapped it around the board on both sides. I also used something closer to a 1x4 instead of the 1x2 that was originally there. I also used poplar instead of pine. I ended up only doing this to one.
On the rest I just placed two larger sheets of 3/8 plywood down the center on top of the rafters to create a crown to the top of the roof making it slope towards the side to help the water run of instead of pool, even if the trailer is not level. It also makes my roof strong enough to walk on (in that area). It was much stronger overall, small amount of weight and much easier than adding the U channel, and added the much needed crown to the roof.
Some, modern trailers are built with an engineered truss, with a plywood sheet, on top. So mine is more of a mix between the old and new.
I used aluminum square tubing for my Aljo, then sistered wood alongside.
How did you sister the wood to the aluminum? I'm considering using 1.5 x 1.5 inch aluminum with wood 1x2s sistered. Considering using contact cement to join wood and aluminum. Do you think it would provide significant added strength?
When I replaced the roof on our Friendship, I noticed a significant sag on the roof rafters (rough 1x3s on their side. I sistered straight wood to flatten the top, but don't think it is a long term solution.
I built a 20 foot canned ham trailer from scratch. I used 1inch square 1/8 wall box aluminum tube for the roof rafters spaced 2 feet apart. It worked out real well. I used self drilling screws to attach the inside paneling and also for any of the aluminum on the outside. I thru bolted them to the side walls. I also have a small rear door that is framed in the same aluminum. My son built a whole trailer from scratch using aluminum which he tig welded together.
Joe, I drilled thru the tubing and screwed thru into the wood rafter. 1 1/2 angle should add a lot of strength. I didn't have the option of going thicker, as I used the original skins and roof. I also padded the tubing, raised the roof vent and laid Reflectix insulation over the rafters and tubes.