angib wrote:Interesting. Is the build method to assemble the core and then laminate skins onto both sides, plus fair the outer skin?
Sort of a hybrid buildup - vacuum form and bond inner skin on the roundovers and sidewalls, inner skin on the floor panel, assemble the sidewalls to the floor panel, form, tab, and inner skin on top, locate and insert hard points for fasteners, then skin the entire exterior.
I don't have a better word for it than "top", but when I say that I refer to the panel that sweeps up from the floor in the front and ends up connecting to the floor in the back.
Lightweight is good, but if you're building 5' x 12', it sounds like you want to fill up the inside which raises two issues:
- you need to build the interior cabinetry as light as the exterior;
- you have to not put anything in the interior cabinets.
Fully agreed!! There will be minimal "stuff" inside for a number of reasons, most having to do with this trailer being a multipurpose hauler. I'll be using it to travel a Fall tradeshow circuit we do, haul long skinny telescopes and mounts to dark sites, and serve as a basecamp for kayaking trips.
The focus on an ultralight trailer is to allow payload while not stressing my Subie too much.
I think the structural side needs to be looked at again. Just by gut feel, a 1-1/2" core in the floor seems total overkill - the unsupported areas of the floor are not that big even with a simple triangle chassis and this is not a house where you can walk on the floor. The floor does not support the body - it's the sidewalls that do that - the floor just stops the occupants falling out.
I'm thinking of the floor as a torsion box panel. 1-1/2" is only a few dollars and three pounds more than 1" and adds a great deal of intrinsic strength and torsional stiffness all by itself.
On the other hand, 1/2" core for the sides and roof sounds pretty thin. Core thickness needs to reflect panel width (that is, the lesser of length or width) and for the roof that's the 5 foot width. In contrast a kayak has 'panels' only 8" wide - giving bending moments only 1/50th as big. 15oz is generous as a skin weight but core thickess matters much more. 3/4" core feels more sensible to me.
When I build kayaks, the panel thicknesses are 3MM (plus 4 or 6oz. skins). I talked this over with some folks I work with in the marine industry, and most of them suggested 1/4" would provide adequate rigidity - they were wondering why I was building so heavy...
For hatch rims and door frames, practicality says wood inserts are best. Wood (or an expensive alternative) will also be required at attachment points like where the body bolts to the chassis.
Default "hard point" will be either a high density urethane foam plug in place of core material or a section of cells cut out and replaced with epoxy putty. I was thinking it would be nice to mold a "S" form into the door and sidewall to make a more water-resistant seal, but if it's not necessary I'll skip it.
I don't think the hatch needs any rim - trailer hatches screw/bolt down to a flat surface so it just needs a wood frame instead of the core, to screw/bolt to/through. For the doors, the easiest thing might be to let a wide wood frame (maybe 1x4) into the core material, laminate both sides and then cut along the centre of the wood, leaving a laminated-in wood frame in both the sidewall and the door blanks.
Nice and elegant solution for the door! Thank you! Sometimes I'm resistant to seeing the forest *or* the trees...
As for the "hatch", I was thinking more of the galley hatch, so the question of keeping water out still stands...or maybe just let some water in but use no wood inside the galley area and let it drain out again?
The rounded profile on the roof-to-wall joint sounds like pie in the sky to me - this is maybe 100 times more difficult than the hatch and door question. I don't think it's even worth thinking about - just go for a regular square joint.
Nope - going to do it the hard way.... I've done fun stuff of this particular genre before - all I need is a good female mould and a source of vacuum to pull the core down with. Throw a bit of heat on it, let it cool, then bag a skin onto it and it won't even spring back when unmoulded. I also want the form rigidity of the curved sections for supporting roof racks...
I haven't used this core material so I don't know how much in-plane stiffness it has. If one skin could be laminated to the core and then the result bent around the relatively large curves of a teardrop, the work saved would be enormous as the second skin could be restricted to the outside where it's so much easier to work.
Almost exactly the plan, actually! I'll have to test how it does without kerfs, but the panels can be successfully kerfed for tight radius curves.
by Thomcat316 » Fri Jan 14, 2011 9:28 am 
Can't help with the molding but I sure hope you post lots of pictures. You can be sure lots of us are wanting to do something like this.
