I asked elsewhere, now i'll ask here

[RogHodge]

The background, building a 5x8 foam/ply hybrid. Walls are 1/4 ply with 1" foam exterior. Roof 1/8 ply with 1" foam. All encapsulated by canvas/glue/paint shell. The shape is basically the same as the 'ultralight'

The question, spar size- if any. The roof ply will be glued and stapled to the wall ply, preliminary tests seem to indicate good holding power. The foam ply combo is quite stiff, so if the roof ply is bent to the curve of the profile- do I even need spars? My thought is to go without, thinking the curved ply is the real source of strength. The interior 'spars' serve mainly as a cosmetic cover for the joints.

Any thoughts? Please.

[mikeschn]

If you can pull that off, I'd love to see your build photos.

Mike...

[Junkboy999]

How do you plan to bend and hold the plywood. The spars are the main part where the plywood is bent over and fastened. I don’t think the walls of a camper himself would be a secure enough spot to hold the play while you bend it.

The front of my little woodi TD had two places where the ⅛ plywood was supposed to be glued to the spars. When the guy rolled the plywood around the top and clamped the sides, it bowed outwards in the middle of the plywood.

Now for woodworking we take a 4 - 7 thin 43th veneers and glue them together in a clamped down shape template or a vacuum bag to make rounded faces for tables and dressers. If you can get 3 sheets of barrel wood ( bendable plywood ) 1/16 and glue them up in a press shape to dry. cover the back in foam and then canvas and glue, that sound rock solid.

[RogHodge]

http://www.tnttt.com/viewtopic.php?f=21&t=56056&p=1016857#p1016857

Please join us for the discussion at the URL above

[GPW]

Rog , I don’t think you need spars with the rolled plywood ... that’s a very strong structure... Just thinking you could make some Temporary wooden frames to fit inside the cabin to better facilitate the bending bit if you anticipate a problem .... once attached , you could remove the frames from the inside ... That would be easy

Do we need a drawing ?

[RogHodge]

I think I may have pre-launched on the roof. As others have mentioned there is to be I eternal structure which will provide additional security for roof attachments. I will have a small shell near my head, support for a fan, which may be covered by a trolly type cover, and then the galley structure. With a little judicious planning I may be able to avoid mid roof spars but have a few key points to assist the process.

We now return to our regular program already in progress

[Mary C]

Ok, so if I lean on your side wall will it hold? just thinking I would put spars in to help make drive in the side to side, sway not cause the twisting effect in the wind. The spars are like the walls in the house with the ceiling, when they make the roof they put in cross angles to keep the roof from twisting in the wind. Spars in the TD framing will assist in the resisting the twisting. Just my thoughts I don't know if I said it right engineeringly right but the wind and the road bumps and could make it come apart. Spars to me are put in places to strategically keep the building up. I may be all wrong but this is how I see it. Like your skeleton of you body, It is what holds you up. Hope this helps.

Mary C.

[GPW]

QUOTE: “ but the wind and the road bumps and could make it come apart “ ... Seems we’ve heard this before ...

[kudzu]

In teardrops I thought the spars were, in large measure, a place to attach the wood roof & help keep it in it's curved shape. Since I know almost nothing my thoughts don't really count but...

[GPW]

K’, Everybody’s thoughts count here...

[Mary C]

I recant, I missed the part about the foam being one inch and I guess the attaching the ply roof with staples didn't help me stay understanding like I have said I learn by seeing. I sorry, but to a degree I would still have some type of horizontal spar in the making for the twisting................. Just me. I will sit down and shut up.

Mary C.

[atahoekid]

I agree with you, Mary C. I too would put in roof spars. I think spars 24" apart would work. Nothing too big, just 1 x 3"s would work. That's what I would do, but to each their own.

[RandyG]

I saw the pics of what you're trying to do and I think the spars will not add that much strength. The curve itself will be much stronger for the walls but for the roof it may give in extreme pressure. I like the idea Gpw thought of, for the bending for installation. Is there a forward bulkhead?