11'6" three berth ply/foam/aly composite caravan

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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Fri May 05, 2017 6:14 am

Going to make some progress this weekend. :worship: All I have done in the last twelve days is fit the bearings and hubs, put the wheels and suspension on the chassis and fit the towing coupling. And make one half-wall.

Chassis on wheels (at nine am). It's autumn here, as you can see from the low sun and the fallen leaves.

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close up of the suspension; Australian Trojan Duratorque half-axles, 1500kg. Probably too sturdy :thinking: Will change them for lighter later if it turns out that way, have to see what Erin wants me to put inside. If she wants a running machine, a wood-burning stove and a walk-in freezer (and who wouldn't? 8) ), well, 1500kg may be about right.

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Before galvanising I made bolt holes for fixing down the deck (will be fixed with @20 bolts and 30 tek-screws), made arrangements for brake hoses, made conduit holders for the trailer lights and tabs for other fixings :thumbsup: .

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So happened that beside the chassis this morning were three things I built previously; front to back, a tractor tray (angle iron from an old bale elevator), a 13hp Honda powered log splitter that I designed and built which has given eleven years of service (has a lifter built on, it is in the transport position in the photo), and the tractor boom pole.I have a FEL (front end loader) for the tractor, too, but it isn't fitted yet, I have to fabricate a sub-frame. I need to put the FEL on to lay down the new drive on which to build the shed in which I originally intended to build the caravan. :lol: I may not die with a fortune but as things are going I should have a very decent to-do list to leave someone. :lol:

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Hope to cut and mount the floor and start the front and back walls this weekend. But my plans are the best joke God heard today, as my friend says. :)
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Fri Feb 02, 2018 10:22 pm

Well, best laid plans. Since May 2017 been in Humerica, Britain and at work, h'aint been building caravans thats for sure. :roll: Started again last two weeks.

Epoxying the 4mm marine ply to the inner walls with a home made vacuum press. The green stuff under the plastic is garden screenshade which I used in place of breather material, works great. The yellow lumps are squashed sponges, "poor mans vacuum gauges". The entry into the bag is a plastic tank plumbing fitting. I bought the professional tape sealant for the making the vacuum bags but it is too tacky and I cannot reuse the bag (can't remove the tape without tearing). I have eight or ten runs to do. Also, the professional vinyl I got was not tough enough for my handling. So I am using plain old 125micron polythene and farmers poly tape, kinda like thick four inch masking tape, for three sides, as I can get the tape off without tearing the poly. Achieving about 1-3psi with a one hp motor. Have a 3hp motor and could probably get to five or more psi of vacuum with the larger motor and some fiddling with the tape and closing up every whisper but at even 2psi I have the equivalent of nearly 4 US tons press on that table, doubt I need more. Some people use paint cans or sandbags, why not, but the big boys do it this way (although they do it much better than I do, no doubt :thumbsup: ).
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Takes about an hour to put epoxy on foam and on ply, line everything up and get the bag closed. Preparation is cleaning plus 40grit sanding both glueing surfaces. Epoxy is roughly one third colloidal silica by volume, maybe a bit more. Here's the vacuum pump and motor which I rigged. Pump is from a dairy and can take a six hp motor, I tried 3hp, 1/2hp and 1 hp, settled on the 1hp as sufficient. Swapped pulleys to get ratio I wanted. Nice and quiet. Nothing automatic and not tank so works three hours per epoxy job but barely gets warm.
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The motor came off a quality old compressor. I had torn the wires off and lost the capacitor when I scrapped it. Six wires and no diagram (well, none that I could understand :thinking: ), quite a bit of head scratching before I wired it up. Right first time, however. If you are from OSH, shut your eyes....the wiring is crude but safe, I don't let anyone near the pump when there is power to it. It's on an rcd and it is well earthed.
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Here's another view of the vacuum table
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Last edited by hossesdad on Tue Feb 13, 2018 1:27 am, edited 2 times in total.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Tue Feb 06, 2018 8:01 pm

I am putting the ply on the last half of a side wall, ie, the fourth run. Made a new bag. The corners are done by cutting out a roughly right-angled piece (you can see it just below my chopping board that is used to store the little bits of tape used for tacking the cover)
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The corners are finished by cutting off a piece of double sided tacky tape, the length being the height you want the corner to be
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and sticking it in place. Surprisingly effective and easy. Worth doing because when I didn't do it this way, there were a lot of wrinkles and they are hard to airproof.
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The rest of the edges are done with ordinary poly tape, unless a pleat is needed in which case another piece of double sided tacky tape is use. I cut enough tape before I start taping and store it on the wall. When you pull poly tape off the roll it stretches, hanging it lets it settle down.
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The caravan has 50mm of insulation and a solid build because we will use it when skiing, amongst other things, and the weather can be hectic. Here is Ebi skiing last year
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Mon Feb 12, 2018 5:51 pm

made samples of prepared aluminum glued to prepared foam under pressure, then tore them off. All held well. However, Gorilla Glue and Loctite MP5000 were patchier and required less force to lift; we could barely get the epoxy off and it had brought up a thin equal layer of foam all over. Epoxy required big screwdriver to get if off, I could tear open a tin with about the same effort. However, the torn-off samples can be read in different ways, so here they are.

Gorilla Glue
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Loctite MP50000
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Epoxy

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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Tue Feb 13, 2018 4:39 pm

All the pieces except the roof are assembled and the inner ply epoxied to them. At the front in the photo is the lower front, made up of bits, which will be behind the interior galley and loo when built, so joins don't matter so much.

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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Tue Feb 13, 2018 7:12 pm

Now I am routeing grooves outside the panels for 12mm x 50mm treated ply strips for fixing the aluminum. I am not going to drill or do fixings for two years and see if the epoxy holds the aluminum as it should. Thermal expansion is the threat, i guess. The strips are set 100mm (say four inches) in from the edges of the aluminum sheets.They will be epoxy coated before being glued in...that will seal in the treatment. I understand building regs allow aluminum flashings to rest on treated timber provided timber is painted or coated. Screws are a different matter but that is for later.

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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Wed Feb 14, 2018 6:18 am

here is a sample of the composite material that I prepared for stress testing. Supporting the ends I could just break it with my body weight.I waxed the ply (gaboon marine ply) and I think it has come up a nice colour. Mix of beeswax and canuba oil. Our hallway is panelled in matai (NZ hardwood) waxed with the same stuff, looks terrific. It has lasted ten years without polishing.

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Re: 11'6" three berth ply/foam/aly composite caravan

Postby HarleyCamper » Mon Feb 19, 2018 10:32 pm

Great build! Certainly following. I think this is the first galvanizing I've seen. Maybe that's just because I'm a Noob.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby Flatworm » Wed Feb 21, 2018 1:24 pm

Nice job. Great to see another kiwi here.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby OP827 » Fri Aug 10, 2018 6:59 pm

I will be following your build with interest, came across your build while it was mentioned in discussion about wall design. I had similar challenge with building wall sandwich panels, but you did it "big boys" way :). I must say that people from Australia and NZ are very inventive and handy, just by looking at yours, Flatworm and other kiwi and oz builds here and then commercial caravans sold in your country like Eco-tourer, Kimberly etc. Thanks for sharing and good luck with your build!
My foldable foam trailer build: http://www.tnttt.com/viewtopic.php?f=50&t=61344
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