go ahead, call me crazy !

[noseoil]

Have to admit I'm a bit baffled as well about the wall buildup you're planning. The sticks glue to the inner edge of the frame (inside?) and the foam is outside the frame? Or is the foam on the inside of the frame & the sticks go on the outside to support the aluminum & serve as a backing block to screw the foam against from the inside?



A sketch is worth a thousand words here....

[dave campbell]

jeez i thought i was the baffled one !

sorry for keeping you on edge--this project has not seen pen and paper since the drawing i posted on page 1---- no time for sketches and such---all the planning is safely tucked away in my brain, to be chewed on as i fall asleep, wake up, and whenever anyone tries to converse with me. i usually just glaze over and say "trailer".

the wee logs are glued to the inside of the frame, along with a 1" strip of 1/4" ply-- to give me something woody to attach the inner finish. the foam is going on the outside.
i know it won't stand up to a stray lawn dart but i'll take that chance.

mystery sticks.JPG (88.44 KiB) Viewed 1704 times

i'm going to try self-drilling screws to hold the foam on, with a decent washer. the business end of the screw will be buried in the wood blocks. the layer of 1/4 ply on the inside of the blocks is not really crucial, but i thought it would be a more continuous surface to work on, and add a little more strength to the structure

side shot.JPG (36.94 KiB) Viewed 1704 times

[dave campbell]

just did a foam and washer test.

if i just go ahead and try to attach the foam with the screw and washer, it does work, but the foam has a tendency to split a bit as the washer compresses. if i remove a bit of foam first, then the washer and screw countersink nicely . now i am contemplating finding a different screw head with a lower profile.....

washer test.JPG (56.56 KiB) Viewed 1688 times

washer test 2.JPG (65.04 KiB) Viewed 1688 times

[dales133]

You should have no problems findi g a countersunk or wafer head to work.
Im using some at work to s rew battens onto steel studs
In a shorter version theyd be perfect.
8-10gauge countersunk with snap off hole cutters on the tip

[aggie79]

Very interesting approach!

Maybe the type of screws/washers that MtnDon used to attach the inner layer of foam on his CTC would work:
http://www.tnttt.com/viewtopic.php?p=1064643#p1064643

[OP827]

Excuse my interuption here with some constructive critique if I may. I do not see how this sandwich kinda structurally works together. If I was doing it, I would probably try to make the steel strips structurally work together with the aluminum skin. Maybe use stick tape (VHB or similar) or glue with some Sikaflex adhesive the aluminum riveted skin to steel strips, that would ensure no galvanic contact, but structural support. Then I would put the foam under it, maybe in between the wooden blocks and flash with foam thickness.

Unless the foam has a structural skin glued to it, something like canvas or FG cloth, it does not have ANY structural properties and can only serve as insulation mostly, but it is your build and decision. Just my 0.02. Keep it going!

[dave campbell]

hey thanks for the info aggie79 i will be on the lookout for a better system to attach this foam. pressure spread over a larger area would be nice, and a reduced screw head height. i did not give this idea much thought and jumped right to the screw/bolt and metal washer without really considering other options.

it absolutely poured (!!!) today so i stayed in the basement fabricating wheel well stuff.....

well start.JPG (68.83 KiB) Viewed 1618 times

well start 3.JPG (88.23 KiB) Viewed 1618 times

well start 2.JPG (74.9 KiB) Viewed 1618 times

[dave campbell]

Excuse my interuption here with some constructive critique if I may. I do not see how this sandwich kinda structurally works together. If I was doing it, I would probably try to make the steel strips structurally work together with the aluminum skin. Maybe use stick tape (VHB or similar) or glue with some Sikaflex adhesive the aluminum riveted skin to steel strips, that would ensure no galvanic contact, but structural support. Then I would put the foam under it, maybe in between the wooden blocks and flash with foam thickness.

Unless the foam has a structural skin glued to it, something like canvas or FG cloth, it does not have ANY structural properties and can only serve as insulation mostly, but it is your build and decision. Just my 0.02. Keep it going!

hey thanks for the idea and C.C

as cool as the cage looks in wee photos there are a couple of small moguls that need to be ironed out. the aluminum needs something backing it and i thought the plywood was
on the heavy side----the cage already rife with excess weight, using all that steel. i did not want to attach the aluminum to the cage without a layer of something under it, and on the inside i thought it would be nice to have some decent wood to muck around with interior stuff.

the wood block and plywood skin glued to the inside has actually given the steel cage greater strength than i thought it would. i am thinking that when i rivet the skin together, i will pin it to the cage, through the foam in maybe a dozen places ?two dozen ? who knows--maybe i can sika the foam to the aluminum as i go ?? or maybe the foam will gain some strength just by being pinned down between the skin and cage ?

[OP827]

Oh I see you are pinning the skin to the steel, and if you figure out a way to glue the aluminum skin to foam, that would work, but could be a challenge as aluminum is not an easy material to glue and thermal expansion is another one to check. I wonder what sealant/adhesive could do that reliably and not require air to dry since the foam and aluminum are not porous? Foam will most likely to be further prepared to be glued, it is covered with silicon lubricant and nothing will stick to it without sanding or such and also the strength of the joint is weak.

[pchast]

Plastic 'insulation Washers" sold in 500 quantity for about 25$ and use most flat head screws, drill screws,
etc.. Generally 1..75 to 2" diameter, they are used to install foam onto masonry and hold stucco etc.

[dave campbell]

Plastic 'insulation Washers" sold in 500 quantity for about 25$ and use most flat head screws, drill screws,
etc.. Generally 1..75 to 2" diameter, they are used to install foam onto masonry and hold stucco etc.

thanks i'll look into that----got to admit that my research has been on the side of minimum---head down and going for it. must take a step back and do some learnins....

Oh I see you are pinning the skin to the steel, and if you figure out a way to glue the aluminum skin to foam, that would work, but could be a challenge as aluminum is not an easy material to glue and thermal expansion is another one to check. I wonder what sealant/adhesive could do that reliably and not require air to dry since the foam and aluminum are not porous? Foam will most likely to be further prepared to be glued, it is covered with silicon lubricant and nothing will stick to it without sanding or such and also the strength of the joint is weak.

thanks for the info --- in my dream world the foam will not need to be glued to anything (except maybe the frame)---hopefully just pinned for all time between the aluminum skin and the cage.

today's update---- finished fabricating the wells and installed a few more straps in corners for wall backer.......just a few more wee tabs of angle iron here and there for wheel well walls and floor support

well done 1.JPG (78.53 KiB) Viewed 1524 times

through the wells.JPG (82.33 KiB) Viewed 1524 times

backer.JPG (96.49 KiB) Viewed 1524 times

[OP827]

[S. Heisley]

You might try double sided tape. It would be a cheap 'try' and it only has to hold the foam until the aluminum goes on. Then, the aluminum will hold it in place. Didn't you plan on riveting the aluminum to the frame?

[dirtsailor2003]

My two cents, on insulation, boat building and weird shapes, and things. I'd skin this frame on the outside. Run all my wiring , pipes, etc, needed in conduit. Then have the insulation shot on from the interior.. Closed cell, which doesn't transfer condensation. Then skin the interior. Expensive, yes. But when you're already doing the job you're doing on this build its well worth it.

[dave campbell]

You might try double sided tape. It would be a cheap 'try' and it only has to hold the foam until the aluminum goes on. Then, the aluminum will hold it in place. Didn't you plan on riveting the aluminum to the frame?

great idea--considering it. some of the tape out there is stronger than me and i'm afraid of (wrong placement=oh sh**) !

did some washer hunting today. thanks everybody for the occasional smack....these should work better

washer upgrade.JPG (47.52 KiB) Viewed 1457 times