Making a lightwight box - foamboard?

[NoSpam]

I need to make a lightweight case to carry a strangely shaped guitar around, is foamboard any good for this? If not, is there anything else - or am I back to using plywood as usual?

[Owain]

fibreglass sheet?

Owain

[NoSpam]

I'll investigate, but I'm not sure that it would be any lighter than 4mm plywood. Is there anywhere to buy honeycomb board (like the stuff Ikea use, but 6 or 10mm?)

[Nightjar]

I don't know where you would buy it, but this is the stuff to make really lightweight items from, particularly if you laminate aramid or carbon fibre sheet on either side:

is used for racing boat hulls and, in PN2 grade, aircraft, so a boat builder (or Airbus Industries) might be able to help.

Personally, I would use aluminium to make the case.

Colin Bignell

[Peter Parry]

Get a lump of Cellotex/Kingspan and carve to shape. Clad in lightweight 3 ply to give abrasion/impact protection by cutting the 3 ply to shape and attaching it to the Kingspan using Polyurethane glue. Before gluing strip the aluminium foil from the outer surface of the board. If you spray the board and kingspan lightly with water the PU glue foams up and fills all the voids between plywood and core giving you a very strong and stable box.

[NoSpam]

Thanks Colin, this looks priocey but I'll investigate

[NoSpam]

Thanks for an intersting idea

[fred]

I'd be worried about the celotex shedding dust, also it's rigid so wont absorb shock too well (might be important if this is to be used as a shipping case.

A balance might be to use one of the common packing packing foams such as Plastazote. This stuff does give a bit so absorbs shock but think it would be stuff enough for Peter's hard shell idea to work.

The idea is to build it up thickness in layers but you can pre-cut the shape first which makes the sculpting much easier.

This is 20mm sheet, quite expensive but you might just get the full case out of one sheet:

connection, first hit, may be cheaper elsewhere.

[The Natural Philosopher]

actually a way that may work for you iof you have te patiemce is once again culled from the model aicraft knowledge repostiry.

Glue slabs of high density extruded polystyrene foam (floor insulation - generally blue mauve or pink) together (use epoxy) and use knife, wire brush and sandpaper to make whatever shape you want and then cover it all in epoxy resin and glass cloth. If teh epoxy resin is too expensive use a water based acrylic varnish - anything that bonds the cloth to the foam is good.

interior finish from crushed velvet of coirse :-) exteriors? its your choice but if the acrylic or epoxy is 100% sound then for sure you can use body putty and car spray .

a cheaper (heavier) alternative to the glass/epoxy/acrylic is to use papier mache over the foam. Wall paper paste and strips of newspaper or brown paper built up to about 3mm or so should suffice. That will then also take a spray paint finish.

Never forget that hand moulding is actually quite easy a thing to do.

If you decide that e,g, the papier mache is all you need, the foam can be washed out entirely with cellulose thinner post moulding.

[NoSpam]

My thoughts were starting to drift the same way. I used to own a share in an aircraft called a Rutan Long-Ez that was built using moldless composite techniques.

Papier mâché is an interesting idea - I haven't played with that since I was a kid. I've no idea how thick it needs to be for reasonable strenth, but I think it may be tough to get a decent flat surface finish. More food for thought!

[Nightjar]

I'd more or less forgotten it. It will be a lot cheaper than aramid honeycomb.

Colin Bignell

[The Natural Philosopher]

It is slightly tougher than MDF.. finish is no problem since it sands easily enough. and if you uses strips torn edged they can be layered fairly well. I did a plane like that - problem was a pinhole and the paint ate the foam through it.

but that was a single paper layer - if you use about 1/8" plus it is essentially a sort of wood and any way you finish wood will work.

[The Natural Philosopher]

I've sort of used the brown paper over foam a couple of times and it is a good finish ..the thought came partly from laterally thinking about laminating glass and partly out of thinking of all those moulded fibre cases one has over the years.

[Andy Dingley]

Friend of mine did it for a musket case. Considerable waste of time and effort. Loads of layers to make it strong enough, and it's a long time drying between layers and an even longer time afterwards.

Fibreglass would have been quicker and easier.

The mould was expanded polystyrene blocks, stuck together with copydex and shaped with a rasp. Take it out afterwards with some acetone.

[Thomas Prufer]

I made a form-fitted toolbox insert using polyurethane foam, see below.

Worked well...

Thomas Prufer

[Nospam]

Thanks Thomas. Did you find that the foam caused the cardboard sides to bulge outwards? Was much heat generated while the foam cured?

[Nospam]

Thanks Thomas. Did you find that the foam caused the cardboard sides to bulge outwards? Was much heat generated while the foam cured?

[NT]

:

Nice one. Could we put that on the wiki? I don't know if you've got any pictures.

NT

[Nospam]

Sorry about the earlier multiple messages, this is what I intended to write:

Thanks Thomas! A couple of questions: Did you find that the foam caused the cardboard sides to bulge outwards? Was much heat generated while the foam cured? What is an "injector pump" in this context?

[Thomas Prufer]

Not much, not more than the weight of the foam. The box was open on the top, so the foam could expand freely, without building up pressure. Also, I moistened the box.

I'd say no, but I didn't test the middle. I foamed and left, because of a) the urge to touch and feel and fiddle and b) because the damn stuff won't come off, ever, short of using an angle grinder, unless you catch it immediately with acetone...

Thomas Prufer