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

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

Postby hossesdad » Wed Feb 15, 2017 9:05 pm

Opening a thread for my build. Title says it. My thread on foamies about composites: http://tnttt.com/viewtopic.php?f=55&t=67807
Work has started, pictures tonight.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Thu Feb 16, 2017 4:14 am

I have built stuff using an angle grinder to cut steel. I treated myself to a cold saw this time and (although a cheap one) it beats the grinder hands down for speed and tidiness. In this photo I am ripping some old 2" by 3/16th equal angle into flats to make tabs for bolting the floor to the frame. That cut was done in about thirty seconds. I build my own sawhorses, the one in the picture was done last week.

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I'm using 3/4" treated ply for the floor and scarffing it as boatbuilders do. I used an 8:1 angle. Here are three sheets of plywood lined up and planing has started.

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Planing took about twenty minutes of machine time, maybe, certainly not more. The work is in the lining up and tidying up afterwards. I did this partly because I wanted to practice scarffing for a different project. If you have never done it, you are aiming to get straight lines in the veneer edges and a smooth slope from the marked top to the bottom. You can do sheets one at a time but this is quicker. Scarffs nowadays don't have to be very neat, epoxy glue fills a lot of gaps.

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Scarfing can also be done with a router or a circular saw, though you will need a 7" cut on the blade to scarff 3/4" ply at an 8:1 angle.

I am building the trailer myself. I am planning on galvanising the frame ( galv costs about 3x paint for .25 effort and x5 durability) so I am cutting steel and drilling drain holes. (Galv needs at least four 7mm drains on each closed frame member). I have cut the frame rails and drilled for the torsion axle mounts. Welding will begin this weekend. Haven't welded for a while, wish me luck. There will be photographs.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby rruff » Thu Feb 16, 2017 2:54 pm

hossesdad wrote: Scarfing can also be done with a router or a circular saw, though you will need a 7" cut on the blade to scarff 3/4" ply at an 8:1 angle.


You used a hand planer to scarf? Scarfing always looked esoteric to me, like something only a real craftsman would do, so of course I never considered it. ;)
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Thu Feb 16, 2017 4:36 pm

rruff, nice to hear from you, I am no craftsman either. I will let you know how this scarf goes together and how long it took when the glueing is done. The advantage of a scarf is that it allows a natural flex. I am pretty sure it doesn't matter in a small caravan floor but it is only an hours effort for a better job. If I had saved the time, I would only have wasted it drinking coffee.

Couple of pointers for anyone trying it. (1) make sure the plywoods best faces are face-to-face in your stack, so that when you join them all the good faces are on one side (I had to cut up pieces of paper and number them, sad isn't it?). (2) A master boatbuilder says to screw the planks together and to a backing sheet using heavy screws with long shanks and short threads. Nine holes to be epoxied is a small price to pay for squeezing out the warpage. (I used afew panel pins to get the alignment right before I put in roofing screws)
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby rruff » Thu Feb 16, 2017 6:52 pm

Looks good to me! :thumbsup:

Do you have experience using epoxy? I wondered if it would make sense to use a silica thickener. I've seen it recommended for gluing but don't know if straight epoxy is better.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby swoody126 » Thu Feb 16, 2017 9:29 pm

hossesdad wrote:...

Couple of pointers for anyone trying it. (1) make sure the plywoods best faces are face-to-face in your stack, so that when you join them all the good faces are on one side (I had to cut up pieces of paper and number them, sad isn't it?). (2) A master boatbuilder says to screw the planks together and to a backing sheet using heavy screws with long shanks and short threads. Nine holes to be epoxied is a small price to pay for squeezing out the warpage. (I used afew panel pins to get the alignment right before I put in roofing screws)


#1. YES, mark your panels BOLDLY in pencil

#2. YES, screwed to an under panel before even mixing the POX. the screw holes ARE insignificant

#3. make darn'd sure to use a good straight edge when aligning the panels for screwing

#4. use a lot of waxed paper under the process, a blue tarp might be in order. Pox will stick to any/everything

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

Postby swoody126 » Thu Feb 16, 2017 9:45 pm

rruff wrote:Looks good to me! :thumbsup:

Do you have experience using epoxy? I wondered if it would make sense to use a silica thickener. I've seen it recommended for gluing but don't know if straight epoxy is better.


POX is a just coating until it is thickened

thickened it becomes a great gap filling bonding agent

wet both surfaces w/ unthickened POX b4 adding the thickening agent you choose

tape the areas you don't want POX'D and once the job is done and b4 the POX cures remove the tape to save yourself a LOT of clean up

the WEST SYSTEM folks have a huge amount of information on this process

there are some fine commercial thickening agents

many successful boatbuilders simply use WOOD FLOUR(not saw dust)

DUCKWORKS BOAT BUILDING SUPPLY has several offerings in their EPOXY line

their DWX is much less sensitizing than most out there

ALWAYS USE NITRILE GLOVES

use VINEGAR to clean yourself up

take your time and HAVE FUN

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

Postby hossesdad » Fri Feb 17, 2017 11:08 pm

Swoody, first class advice, will take it all. You know your stuff. I am going to screw the boards upside down to two straight 2x4's when I glue them up. I wlll take the 2x4's off when it is screwed glued and bolted to the frame. The lot will weigh but I have a tractor with boom pole. I mean to work on saw horses, not the ground, so I will be able to observe the good faces, too. It's much better when you can access both sides.

Here's my epoxy stash, hiding in the unused sauna for a year. (Those prices are NZ dollars, but we do pay high for a lot of stuff)

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By the way, Swoody, I have a nearly finished boat to a John Welsford design, he's a Duckworks associate. His opinion is that "scarfing is easy peasy" (exact quote).

Today I built another sawhorse. Took maybe forty minutes. Not my design. The advantage is you can cramp all around the top on that overhang, and when the top is cut to bits in a few years, take off the legs, turn it over, screw the legs on again and, bingo, fresh top.

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Heres some noodle modelling for OSH (yes, there are earplugs in those ears)

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I was cutting steel with the coldsaw today when rain stopped play and sent me inside. It has stopped now. More later.

Good luck with your builds, or, if you have finished, happy travels.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Sat Feb 18, 2017 1:58 am

rruff, not much experience with epoxy, some work on a stitch and glue boat. Learning by making mistakes and covering them over. Made a fibreglass canoe called the Tirpitz once, it was so overweight it would have passed for a recreational submarine. :oops:
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby rruff » Sat Feb 18, 2017 12:34 pm

swoody126 wrote:POX is a just coating until it is thickened
thickened it becomes a great gap filling bonding agent
wet both surfaces w/ unthickened POX b4 adding the thickening agent you choose


Thanks, swoody!

I'm playing around with laying up fiberglass on foam (XPS). The foam needs to be heavily textured to get decent adhesion, and I figure I might as well use an epoxy-silica paste spread on to fill the texture before the layup. Saves some weight and cost, and seems like it ought to work. What do you think?
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby Sheddie » Sat Feb 18, 2017 9:12 pm

Welcome from a fellow kiwi :shake hands:
Good luck with the build :thumbsup:
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Sun Feb 19, 2017 12:41 am

Sunday started fine.

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I used a simple jig I made to cut steel with the cold saw. Just a scrap of ply. Spent time getting it just right last week.

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This is a long piece I cut, then turned one side. It's a good test of the angle.

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Caravan will weigh @2000lbs. The caravan will be 2200mm wide, the main rails 1585mm apart. (sorry, my calcs are in mm). I had to decide today how many cross members to use. Everything in this pic is 2 1/2" x 1 1/2" x1/8th tube. The torsion axle halves mount to the two central cross members which are effectively the axle, the a-frame mounts to the front two (furthest away). (The main rails are on their sides in this photo and nothing is in quite the right place).

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I tested the flex in the floor before deciding on what size steel to use for the other cross-members. This is me between jumps. If I had known you would be looking, I would have tied my laces.

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I settled on ripping 2 1/2"x 1 1/2" tube in half to make three 2 1/2" x 1 1/2" unequal angle iron lengths for the (counting from the far end, which will be the front) third, sixth and seventh members. The sixth and seventh members will be under the beds.

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Rain stopped me then. I put it all under cover and will get the welder out tomorrow (I have a few spare days allocated to this either side of a business trip)

Nice to meet you, Frank, will be a pleasure to chat. Love your build, I had noticed it before.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Tue Feb 21, 2017 2:09 am

Cut outriggers today.

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I like jigs. I made one for trimming the outriggers with the cold saw.

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Tapered outriggers all on one rail.

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Did the bevel and gap welds first

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Checked a few. Seemed okay

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So I welded everything.

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But when I knocked off the slag some of the fillet welds had slag inclusions! A problem with 6013 at low amperages, it seems. Upped the amps by 20 and did some practice runs on scrap. Much better.

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Will redo some of the t-joints tomorrow. There is heat shrinkage in the rails, too, but I will be able to push it out when I do the cross-members.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby hossesdad » Tue Feb 21, 2017 2:37 am

Is there a welder here who can suggest the best rod for 1/8th" tubing? I am running out of 6013 and would try anything that might be more sure-fire.

Also, is this thread too slow? I could skip a lot.
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Re: 11'6" three berth ply/foam/aly composite caravan

Postby KCStudly » Tue Feb 21, 2017 11:36 am

Thread's good, you're doing fine.

I like 6013 stick for what you are doing (not the cleanest steel stock and welding outside). Match stick diameter and heat range to material thickness regardless of alloy.
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