Mini SIPs As A Foamy Technique

[mezmo]

Hi all Foamlings...

I thought there was already a thread on this, and looked, but
didn't see one so, "Here One Is" now:

This will probably be my approach when I get around to
doing one. 'Thought it'd be good to corral info on them in
one place, so here goes the first post:

Here is an interesting design for an expanding Pontoon Craft
that uses self-built plywood-foam-plywood SIPs:
http://www.elasticat.com/

And this page gives his method of plywood-foam-plywood
composite construction, using fiberlass and epoxy as exterior covering:
http://www.elasticat.com/compositepanels.html

- - - - - - - - - -

The following info is from some earlier posts I did on various different threads,
just cut and pasted to here for the info/links:

I think SIPs are a good idea and I will probably use a form of them
whenever I get to build. [Too many house projects are a priority
at the moment.] For a larger size construction, I'd seriously look
into them. I consider them a Foamie variation.

Anyway, check out linuxmanxxx's post/builds.
Here's the link to them:
search.php?st=0&sk=t&sd=d&sr=posts&author_id=11546
He is using a small scale version of them and gives details on how he did them -
they'll be a reference for me in the future. He uses them in his business:
http://www.microcampers.com/ Just browse through them until you reach one
that pertains to his SIPs and then click on the thrtead title if you need context.

Here are some links to a SIP builder with a difference. [compared to those
SIPs that are used for house construction.] They are in Washington State,
and make many different kinds/thicknesses of them. Quite an interesting product.
http://www.superhoneycomb.com/
http://singcore.com/
http://singcore.com/tiny_index.html
http://media.designerpages.com/3rings/2 ... ing-homes/

Here are a couple links for them being used:

A gal in Washington State is building a tenwide Tiny House, using them:
http://mytinyabode.blogspot.com/

And her Dad is using them to remodel a vintage Airfloat TT:
http://www.everyonecandance.com/Airfloat_Process.html

- - - - - - - -

I've also been wondering about a variation on the Mini-SIP that'd use
the stitch-n-glue boat building method. http://www.boatbuilder.org/
With that I'd basically build the inside walls of 1/4in plywood with the S-n-G
method, frame any/the openings perimeters and the outside edges
with the appropriate size 1x wood or such, and then glue in the foam
[most likely in the appropriate shaped/sized pieces vs a large sheet]
to cover the outside of the interior 1/4in plywood walls and thus help
insulate [an uninsulated trailer is a poor accomodation in my personal
view] and fill out the form of the body of the trailer. Any seams and gaps
would be minimized while applying the foam pieces, but any remaining
can be filled in with one of the canned gap filling foams, and then all
that'd be faired out with some kind of fillers to try and make a smooth
surface for the outside skin. After that, I'd probably go with either a
fabric and glue and paint or fiberglass cloth and epoxy as the outside
skin. It all depends on costs and if I could even tolerate the fiberglassing
fumes. [Epoxy is supposedly less "fumey" than the polyester type, but I
do have allergy problems with some chemicals, so it'll remain to be seen
if that could even be a possibility.] Some kind of foamcoat is another
alternative too, but they are more expensive than the old-time fabric-
glue-paint method.

Cheers,
Norm/memzo

[GPW]

Sips are sure a good idea , the only problem is the quality of materials used ... I’m trying to get away from using plywood altogether ... Thinking more along the lines of a Thick chipboard replacing the plywood ... Lighter , cheaper , easier to waterproof/paint , and doesn’t de-laminate by itself in our notorious Humidity ... Easier to repair too, damages being more localized... as with those mini frozen Turkeys ... Just an alternative SIP really ...

Thing too with wood/foam/wood SIPS , you don’t save any weight really ... Two sheets of 1/4” ply , plus the weight of the foam and glue and you’re in the weight neighborhood of a 3/4” sheet of standard plywood ...

[KCStudly]

Two sheets of 1/4” ply , plus the weight of the foam and glue and you’re in the weight neighborhood of a 3/4” sheet of standard plywood ...

Oh yes but much stiffer!

[GPW]

Yeah , but how stiff do we need it ??? ( know I’m setting myself up with that one ... )

[mezmo]

One of the many aspects of the Foamie that I especially like is the
automatic built-in insulation it provides. But foam doesn't lend itself to easy
structural joining in-and-of-itself, so you have provide that otherwise.

A personal choice of mine will be to have a birch plywood interior
surface/finish for my miniSIPs. Plywood can be argued against, but if quality
plywood is used and known preventative methods are used to protect it from
moisture, I don't see any problems in using it/and wooden components
for some of the structure and finish. I can agree with the view of eliminating
as much wood as possible in a build, but that does have a cost, in material,
time, and in build method. We just need to make the mix of it all fit our
time available, skill-level [or willingness to learn them] and available budget(s).
Aluminum tubing/channels/extrusions and even the fiberglass or other
composit equivalents can be substituted for structural wooden pieces. Exterior
and interior skins/surfaces can also be provided by FRP/aluminum sheets/plastic
laminates etc. - not to mention, the canvas/glue/paint method and the commercially
available foam coats and urea bedliner types of paintable/sprayable coatings.

1/4inch plywood has the benefit of being generally available and moderately
reasonable in cost. The thinner 1/8inch plywood can be used too but it's availability
is not as widespread. Just know what you are getting in it, and get a quality piece
of plywood when you get it. [just be sure it actually has at least three plys
of equal size - when seen looking at the side of it - I caution that, as I had to get
some for a home project, and some of the "plywood" in the 1/4inch area consisted
of a single thicker middle layer with extremely thin top and bottom veneers - for
appearance sake only - and which is totally structurally useless. It's just another
example of a cheap "modern" material.] I've never dealt with marine quality plywood,
but the more I learn about it, the more it seems to be worth the extra cost it entails,
but that's just my view on it - everyone can reach their own conclusions on that. And
suppliers that deal mainly in plywood ['specialty'] or some other source, like cabinet
making shops or local lumberyards or marine component suppliers, seem to be the
best sources of higher quaility plywood. I am continually dismayed at what is available
as plywood at the various"Home Centers".

Part of the miniSIP approach is to adapt how walk-in freezers are built to the Foamie
method. They use miniSIPs-like composite-panels, generally of bonded aluminum/metal/
composite sheeting:foam:aluminum/metal/composite sheeting construction, joined by
various methods. Cam-lock, tongue and groove, etc., are a couple of them. But the one
that I think is most adaptable for our purposes, would be some variation of attaching the
mini-SIPs together at the intersecting edges/corners with exterior and interior moldings
or extrusions. [Note: Similar panels are also used by insulated door and garage door manufacturers and some modular sunroom manufacturers etc..]
http://www.refrigeration-equipment.com/ ... anels.html
http://www.metalpanelsource.com/permatherm.html
http://www.americanwalkincoolers.com/insulation.html [interesting foam discussion on
XPS-Extruded Polystyrene on this page.]

Don't forget that Winnebago used "Thermo Panels" that were made of 1/4inch plywood,
a structural foam, and an external aluminum skin all bonded[glued] together for their TT
and Motor Homes in the 1960s-70s+. I've never seen any detail on how they joined them
together, bit they must have used some kind of perimeter framing on the panels - since
screwing/ mechanically joining foam to foam isn't the strongest of connections at best. A
lot of the modern day European TT makers are using a variation on them.

The European caravan/RV manufacturers seem to be leading in this lighter-weight approach.
A variation on one of the following approaches seem to be applicable for our purposes:

This manufacturer uses the method of "joining extrusions", produced on their own
proprietary machinery to make the curved shapes they need.
http://www.baileyofbristol.co.uk/
http://www.baileyalu-tech.co.uk/
http://www.baileyalu-tech.co.uk/the-alu-tech-design.php

Here is another approach, where the mini-SIP style panels are all bonded/glued together with the new super strength structural adhesives. The whole entire unit is bonded together without
using fasteners.
Main website:
http://www.elddis.co.uk/
http://www.elddis.co.uk/why-choose-eldd ... nstruction
An interesting 5min+ video:
http://www.caravantimes.co.uk/video/ind ... 381771.htm

So, all this is, is where I'm coming from on using the miniSIPs approach. It seems to be a DIY-doable and possible way to get a lighter weight, strong and insulated TD/TTT/RV/Tiny House...
And don't forget, I also mentioned the stitch-n-glue plus foam and then some kind of applied
"softer" exterior covering [fabric-glue-paint/foam coats/urea-or-bedliner] variation. [Lets
give that a wacky name, and call it an 'accumulated pseudo miniSIP' ["APM"], due to it not
being glued up/assembled all at one into panels, but it is rather, built-up over time, into what
approaches a miniSIP.] That seems another possible approach, to give me the interior
surface/finish that I want, and get the Foamie benefits, while still using Foamie methods, but
also avoiding one of the Foamie technique's pitfalls - that of the foam warping when applying the covering to one side at a time, for example.

Cheers,
Norm/mezmo

[GPW]

No Rules eh !!! Build it like You want to ... If it works , tell us .... If it doesn’t work , PLEASE tell us !!! ... The only way we learn is by doing ...

[Bogo]

Here is another approach, where the mini-SIP style panels are all bonded/glued together with the new super strength structural adhesives. The whole entire unit is bonded together without
using fasteners.

Actually the structural adhesives have been around a few decades... Many car bodies are now glued together. Over the years it has become much easier to use them.

Main website:
http://www.elddis.co.uk/
http://www.elddis.co.uk/why-choose-eldd ... nstruction
An interesting 5min+ video:
http://www.caravantimes.co.uk/video/ind ... 381771.htm

On that video. Notice the keyed construction. Not only does it increase the bonding area, it also provides mechanical keying against shear forces and it should help some with pealing forces. Looks like the keys are plywood. I'd use a Baltic birch for its consistency. Where a curved key is needed, they could be formed out of thinner plywood laminated up over a mold. They would only need to be close in shape. To make the groves, use a router. For the glue, it would need some gap filling properties to make up for imperfect routing and key shape. Note, it would be best if the key strip fit tightly in the grove. For even more bond area, multiple keys could be used. There is a limit to the practicality of using more as the joint may get stronger than the wood at the edges of the panels.

Looks like in the SIP panels they are using wood strips around the perimeter. That is what the keying is routed into. This would allow getting rid of the perimeter frames I was thinking of using. I like that as it makes going to a curved roof much easier. No need to bend an L extrusion into a large complex curve. For making the SIPs, I'd build the panel up, and fully finish all the edges. Then I'd route the grove for the key, and finally glue the panels together. Fully finishing the edges will mean the sealed surfaces extend under the edge of the glue joint to the key way. That will help prevent water getting into the perimeter wood. The wood edge pieces could be all sides sealed with epoxy resin before being built into the SIP panel.

[Bogo]

This manufacturer uses the method of "joining extrusions", produced on their own
proprietary machinery to make the curved shapes they need.
http://www.baileyofbristol.co.uk/
http://www.baileyalu-tech.co.uk/
http://www.baileyalu-tech.co.uk/the-alu-tech-design.php

No extrusions are needed. Just a fabricator with a long slip-roll.

This is a quick detail for the box corner I designed, for a hard sided pop up, showing both the lifting top and the base in a 3D cross section. Lifting top has the curved corner for the outside and a angle for the inside. The base has both inside and out as angles. The red pieces are delrin plastic glides, and likely need to be thinner to prevent binding. The panels are 1" thick AL/foam/AL composite panels. Their skins will be on the order of .032" thick. The outside curved corner can be formed from a 1/8" thick AL plate on a slip roll or bent using a press. No need for a custom extrusion of that shape. The panels will be glued to the outside corner pieces first. Then the inside corner angle irons will be glued in place to finish off the corner. The inside angle irons are not welded to the frame. They are only glued in place.

Since then I figured out how to make fittings for the corners to glue the corners together rather than have the frame welded together. Using plate aluminum and standard metal hammering techniques they could be formed. It would also be possible to use a press to bend the aluminum plate between male and female dies. I favor pressing them, but it could be fun designing the dies due to spring back. The aluminum will need to be a slight bit over bent so when it springs back it goes to the desired shape.

[KCStudly]

Super accurate dies are not required. It's not like a casting or extrusion.

Usually in a press break the the upper die has the radius (or other shape desired, sometimes under size) and the bottom die is left more open (oversize), then the depth that the press operates through is adjusted to get the desired shape, accounting for spring back.

So for a large radius, as above, the upper die might be made from a piece of round bar with a piece of flat bar weld on lengthwise to attach it to the press (like an upside down letter ' i ') with the round bar having the radius desired (say 1-1/2 inch, or slightly smaller for a 3/4 radius). Then the bottom die could be a wide V or two half rounds (like the letter ' B ' laying on its left side). So long as the gap and depth of the valley in the V or B is a little wider than the upper die plus twice the thickness of the material being formed, the press can be made to travel past 90 degrees to account for spring back.

So long as the dies are relatively straight and uniform, and they don't have nicks or sharp edges that would mar the face of the material, getting a good 90 deg part would be fairly easy with a good press break.

p.s. Small world. Karl (my shop buddy) just bought a huge hydraulic CNC press break at auction. Look for pic's soon on my TPCE build thread!