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Thread: plywood caravans
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7th April 2007, 08:17 AM #16
Around here somewhere I have a 1930's book of caravan plans, now, I haven't built one but I have repaired a couple of horse floats and I have repalced floors and tailgate ramps with ply.
I have used marine grade ply and I believe the difference is the integrity of the layers, no holes, cracks, joins or other flaws which helps achieve a uniform finish with added strength.
The second factor is the adhesive which is water resistant (not proof) which attributes to the longevity of the product.
When I used 1" ply for the floor I used the black stuff, I think that is exterior grade, and painted it with a thick rubbery material as horses do two things as soon as they get on board, and possibly repeat the performance during the trip, the tailgate was replace with marine ply, sealed with diluted PVA glue and then painted and had rubber strips attached.
For a caravan I would use a marine grade ply, seal and paint.
Todays caravans are still made of ply and hardwood frames, stapled together, they look as rough as guts until the pretty exterior aluminium sheet goes on and the window frames go in, the interior ply is generally a veneered (plastic) woodgrain or similar finish.Stupidity kills. Absolute stupidity kills absolutely.
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7th April 2007, 08:58 AM #17
'Course we don't agree Shane!
The use of lightweight timbers is a given (radiata here BTW!), it's the size of the scantlings that are commonly used. Both of the plans for campers that I've seen (as opposed to teardrop plans which generally have it sussed) are built like houses, with 2x4 studs.
We have a whole different engineering dynamic with a van, and I'm no expert, not by a long shot, but all we need to do is build a tea chest and put a door or two in it.
Modern Caravans do it, and a home builder can improve by miles using composite construction methods and basic materials... all you need to do is use two really light skins, and something to keep them apart... done really. I reckon insulating foam would do it admirably too, with a minimum of framing, but there you go.
cheers,
P
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7th April 2007, 10:38 AM #18
Shane,
Midge has got it right (again, why is it that we agree on so much?), those plans are overengineered by todays standards and avaiable technologies. To liken it to boat building, those plans would have you build your little dinghy with a heavy clinker hull whilst it's now possible due to modern glues to make a hull the same size that's much lighter, stronger and quicker to build.
Wandered into a local manufacturer of mobile homes/campervans a few years ago as I'd just been burnt for a few grand on a job and thought I might work for someone for a change. They were making a lot of their stuff in foam sandwich construction, very light and strong. Like midge said, just two skins with something to keep them apart. They weren't offering enough money for my liking so I didn't end up working for them, but that's another story.
I'm thinking sandwich panel: ply/foam/ply, bonded with polyurethane glue. I reckon I can glue up large panels on the shed floor by laying down the bottom sheet, applying glue, placing foam, applying glue to the 2nd piece of ply and fitting and then placing besser blocks all over the sandwich to provide the neccesary clamping. There will be timber battens already glued in place on the bottom sheet, right around the perimeter and others placed for any other required fixings. I'll probably use white coated cabinet backing ply for the interior, it's about 4mm and coated with what looks and smells like white gelcoat. For the exterior I haven't yet made up my mind. I do have a couple of rolls of woven glass and I was thinking of using very thin ply on the exterior and completely glassing the it once it's assembled, both for strength and for waterproofing.
Mick"If you need a machine today and don't buy it,
tomorrow you will have paid for it and not have it."
- Henry Ford 1938
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7th April 2007, 11:22 AM #19First On Race Day
And the first brock trophy goes to...............
and we got no "2" as well
A FORD driver.
ironic isnt it?
and if ya cant win on ya own merit punt em off!!!
holden cheater team!!!!!
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7th April 2007, 11:49 AM #20
I reckon you're spot on the money Mick.
I'd use the glass (over thin ply) to give a little more durabilty and dare I say it, puncture resistance. Now I know there are some on a particular boating forum who will choke on their Easter Eggs reading those words from Moi, but one of the differences between lightweight dinghy hulls and caravans is the momentum behind any collision with overhanging trees etc.
Large flat panels are really easy to lay up and fair, so I'd be with you all the way.
Another way is simply to adhere sheets of prefinished glass to the ply. I don't know where to get it buy Reiner Gudd does retail it at http://www.trikesaustralia.com/teardrop/
Cheers,
P
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7th April 2007, 07:29 PM #21
I dont think you would have too much problem getting a "plywood" caravan up to spec.
Afterall its only a trailer....... especialy if you can keep it under 1000kg GVM.
the question is..... wil it be a plywood (structured) caravan or more a plywood formed "fibreglass" caravan.
From my understanding the best way to get the strength is in combination with light weight is the timber and plywood framed fibrglass clad method.
I don't think anybody sensible would argue that the chasis should be conventional tubular steel.
with the modern electric brakes and some carefull consideration about weight. it should be possible to poduce a reasonaly light, strong and towable unit.
One of the big concerns is to keep the superstructure light and the weight low otherwise you will have to change your name to "Noddy".
Now if you are building a timber caravan for the fun of it..... you have to use curved laminated ribs somewhere..... I still remember the jig for making the laminated ribs for the roof of the old mans creation.
He called it the "banana bender".
the other thing is that these caravans were usualy simple affairs..... not these enormous multiwheeled condominiums that people call caravans now.
the kitchen facilities often didnt exist or they were on the outside of the caravan. Showers, toilets, dining tables inside.... bah humbug.
cheersAny thing with sharp teeth eats meat.
Most powertools have sharp teeth.
People are made of meat.
Abrasives can be just as dangerous as a blade.....and 10 times more painfull.
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9th April 2007, 01:35 AM #22
this is the old ply coming off
(an earlier posting shows the caravan before the demolition started)
this is the condition of the original ply on the roof
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9th April 2007, 06:59 PM #23
AHH the old moisture under the edge moulding trick.
Thats wahy I recon the way to go is to glass over the lot and forget the edge mouldings.
If you must use mouldings..... one word....... "sicaflex".
cheersAny thing with sharp teeth eats meat.
Most powertools have sharp teeth.
People are made of meat.
Abrasives can be just as dangerous as a blade.....and 10 times more painfull.
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13th April 2007, 12:06 AM #24
cute van,. what are you towing it with?
would look great behind an old FB holden (or an XM ford if you are that way inclined)____________________________
Craig
Saving a tree from woodchippng is like peeing in the pool;
you get a warm feeling for a while but nobody notices.
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13th April 2007, 09:31 PM #25
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13th April 2007, 09:41 PM #26
My 1958 FC Holden we will be towing the caravan with. I hope to have the van finished by Easter 2008 to drive across the Nullabor to attend the national vintage caravan get together and the FE,FC Holden Nationals (The FCs 50th Anniversary) The wagons modified, 202 motor ,disc brakes etc.
Picked up the plywood from Morgans,
4mm Imported Marine Ply, 5ply Pacific Maple, B.B.A Bond/WPS on label (and some 6mm to do some other repairs)
Now I've got to figure out making it all weatherproof and making it look pretty ( Bondcrete, Sicaflex and a good exterior paint )
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20th April 2018, 11:15 PM #27Novice
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Wow, must be the quietest thread on the forum.....
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20th April 2018, 11:26 PM #28
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21st April 2018, 12:06 AM #29Novice
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21st April 2018, 12:38 PM #30GOLD MEMBER
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The main difference between structural and marine grade plywood is the timber specie. Marine grade ply is manufactured from marine borer resistant timbers. The glue is the same in both. Therefore, unless you are intending to use your caravan as a submarine, there is little reason to go to the expense of marine ply. A lightweight timber with anti rot properties makes the best frame. These days that would include treated Radiata, but my favourite is Aust Red Cedar, if you can find it at a reasonable price.
When it comes to joining, I prefer to retain flexibility where ever possible, particularly at ply to ply abutments. There are plenty of good quality flex sealants on the market these days. Factor in UV stabilization when making the choice. Gusset frame joints where ever possible for added strength.
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