I'm posting this here because I think others may benefit.

In your composite construction Alan, what type of foam core are you using? Aircraft spruce has styrofoam, polystyrene, polyurethane, divinycell, and last-a-foam. I'm making my dash/instrument cover, which is very curvey, so I'm thinking polyurethane is best for its workability and since it's 3x cheaper then last-a-foam. Comments appreciated. Oh, and what type of epoxy are you using?

So far I have not used any. However, in order to save weight and increase rigidity especially on the hinging rear end, I probablly will.

I'm actually laying up with polyester resin so some of the foam choices will not be available to me...like you I'll have one eye on cost.

I'd guess Syd and Shug could throw a lot of light on this topic....

Listening in with great interest. Fill'er up with knowledge please...

Graber

Hi There,
Dad (Syd) won't be back until Easter, or after. He's off reworking the engines on a big motoryacht, or so he tells us. More like an excuse for getting away from us, and drinking a lot of Rum

The foam he uses here, as core, is Airex PVC boatbuilding material. It is available in different densities. He has also got ali and aramid fbre(I think) honeycomb here somewhere, but he uses that stuff only with the hi tech material in the autoclave or with vacuum. He uses other stuff for patterns, but mostly mdf.

You'll have to ask him again when he comes back for more specific info. He'd go off his nut if I said more than he would, as he keeps his methods to himself mostly,so it's not worth the aggro for me to say too much.

Cheers,
Ian B.

you chaps tried asking here http://www.fibreglast.com/fibretalk.php


or for an article see

http://www.fibreglast.com/contentpages-Guidelines+for+Sanwich+Core+Materials-164.html

[Edited on 25/3/04 by timf]

Fiberglast Forum.

Nice one! THANKS!

Looks like I have some reading ahead of me.

http://www.fibreglast.com/contentpages-Learning-Center-286.html

[Edited on 3/25/04 by sgraber]

Excellent resource links, thanks guys. Think I'll post that link on my site too.

Related to this topic is an excellent book from Aircraft Spruce:

MOLDLESS COMPOSITE SANDWICH
HOMEBUILT AIRCRAFT CONSTRUCTION
by Burt Rutan

P/N 13-11600 $14.500
A step-by-step construction manual for the beginner in working on composite aircraft designs. If the steps are studied and followed carefully, a first time builder can work confidently with these materials. Profusely illustrated.

Good thread...good links...

Most of my GRP experience is with simple single skin stuff...used paper rope etc., but not much else...

We can all learn something I guess...

Just finished watching the "Mike Arnold AR-5" tapes on fibreglass construction. I must say they are probably some of the best videos on the subject I have watched. I have played a lot with different composite construction techniques including mouldless epoxy, polyester moulds, vacuum bagging, sandwich construction. Most of this has been on relatively small scale (I used to design and build RC Airplanes in my youth). I definately picked up a few tips from his videos that will help me.

For non structural stuff I like to use "blue foam", in the US its the pink stuff you can get from Home Depot. Its pretty easy to work with and nice to hot wire cut and shape. I plan on making my body buck using this. Given the shape of my car I can hot wire cut a large portion of it using templates. The only problem with this foam is that you can't use polyester resin over it otherwise it melts. One solution is to use glass and epoxy and then some form of filler. Alternatively, you can spray it with household emulsion paint. You can then use polyester over it. I have decided to make a scale model of my bodywork using exactly the same technique I will on the fullsize buck.

For structural stuff I plan on using something called ATC Corecell foam (http://www.atc-chem.com/Core_Cell/Core_cell.asp). I have some samples of this and its unlike any foam i've seen before. For its weight it has very good compressive and shear strength. I plan on using this stuff to make my splitter, diffuser and front crash box. I will use a combination of carbon, S-Glass and epoxy. The plan is to vacuum bag this stuff. You can use this foam directly with polyester which is nice. For my bodywork, I was planning on using a combination of chopped strand glass, glass fabric and 1/8" corecell in strategic places. From my past experience, its amazing how much lighter/stiffer you can make parts with careful use of even a thin core.

[Edited on 26/3/04 by ProjectLMP]

quote:

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Originally posted by ProjectLMP

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KB, Forgot to ask, what are you planning on making?

i spent a whole day at work reading this site when i only wanted to look up one thing.

quote:

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Originally posted by sgraber
Fiberglast Forum.

Nice one! THANKS!

Looks like I have some reading ahead of me.

http://www.fibreglast.com/contentpages-Learning-Center-286.html

[Edited on 3/25/04 by sgraber]

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quote:

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Originally posted by ProjectLMP
KB, Forgot to ask, what are you planning on making?

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If its non structural, I'd definately go with the pink type foam you can get from Home Depot. Way cheaper to get it there than through some specialist place. I am assuming you are making a one off so mouldless construction would be the way to go. Even if you decide to make copies later you can take these from a mould produced from the original. I highly recommend going epoxy. Its a bit more expensive but given the size of the part the resin isn't really a huge cost factor. The longer setting time really helps especially if you haven't done much of this stuff before. Also the lack of smell always helps (especially with the significant other!). Probably 3 or 4 layers of bidirectional glass is all that is needed plus some local reinforcement for attachment points. In the past I have inset small aluminum plates into the foam before glassing over it. That way you can tap them for fitting bolts etc. If you want something a bit more cosmetic, the last layer can be carbon fibre. When dry, rough up the surface and paint on two or three coats of epoxy to fill in the weave. Finally, wet sand and then spray with a clear coat. A couple of pointers I have picked up while playing with this stuff are

. The pink foam is easily worked with normal sanding tools, hot wire cutters, dremel tools and routers

. If after rough sanding you switch to wet and dry and sand wet you can get a really nice smooth surface and the paper doesn't clog as much

. If you have a complex part with many compound curves, switching to a fabric weave called harness satin helps. This is more drapable than biaxial cloth and stronger.

.Inhaling fully cured epoxy dust isn't too bad for you (although not recommended). However, partially cured expoxy is very nasty stuff to inhale. Some epoxy can take weeks to fully cure unless elevated temperatures are used.

Steve, hows the body design coming along?

One of the idea's I am toying with is to make by buck directly over the chassis. The bodywork would split in 3 places and I was planning on making the buck in 3 seperate pieces. The idea would be that I could take the complete buck off the chassis when complete without destroying it. Each piece would be an exactly replica of the final body panels except a lot thicker. I've done something similar with model aircraft in the past but on a smaller scale and it worked really well.

I am thinking the whole buck will be made from pink foam pieces glued together in sections. I will hot wire cut the basic side and top profiles where possible and then do the compound curves by cutting and sanding. By building it up from smaller subassemblies you can create complex shapes and also save foam by making sections hollow.

After getting an accurate profile I was then going to put a few layers of glass over the foam to strengthen it. I would either seal the foam and use polyester resin or just use epoxy. If you use cloth instead of chopped strand mat it doesn't take nearly as much resin so epoxy may be viable from a cost perspective.

The next step would be to use drywall compound to get the final shape.

Then spray on a thickish layer of primer surfacer and wet sand and polish (similar to Alan's technique).

Its sort of hard to explain in words. I am going to make a scale model using exactly the technique highlighted to prove the concept and also develop my body shape.

Anyway, enough of my ramblings.

quote:

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Originally posted by ProjectLMP
Steve, hows the body design coming along?

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Hey check out the nice composite middy body the kids at Western Washington U are doing for this year's FSAE.

Go here and scroll down:

http://fsae.com/eve/ubb.x?q=Y&a=tpc&s=763607348&f=125607348&m=25210205111&p=2


Sigh, I wish my memories of school were like this...

They made a bespoke BEC V8 for their car a few years back as well.

http://dot.etec.wwu.edu/fsae/v30/v30pics.html

Big fun does come in small packages.

Cheers, Ted

[Edited on 27/3/04 by andkilde]

Just picked up on this thread cause the gogglebox has been down with a pesky virus for a couple of days. For Small scale stuff I use polyurethane foam slabs. Airex and Nomex core is the norm on some of the boat Hulls I have had to repair, mostly with Epoxy resins and Kevlar cloth. Carbon has a bad reputation in some boat hulls most builders only use it in small quantities unless its an out and out speed machine End grain Balsa is still popular in a lot of boats. Another product I have used very widely that I dont see a lot of people use is Coremat, very good stuff for layering in say a car panel using CSM to add stiffness. Quite cheap
but you have to watch the weight as it acts like a sponge with poly resin.
Shug.

[Edited on 27/3/04 by Hugh Paterson]

quote:

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Originally posted by andkilde
Hey check out the nice composite middy body the kids at Western Washington U are doing for this year's FSAE.

Go here and scroll down:

http://fsae.com/eve/ubb.x?q=Y&a=tpc&s=763607348&f=125607348&m=25210205111&p=2


Sigh, I wish my memories of school were like this...

They made a bespoke BEC V8 for their car a few years back as well.

http://dot.etec.wwu.edu/fsae/v30/v30pics.html

Big fun does come in small packages.

Cheers, Ted

[Edited on 27/3/04 by andkilde]

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All I can say is WOW!!! I saw all the machine work involved and started to think that they had to have blown their $8500 budget on the engine/tranny alone, not to mention all the other custom machined parts. I'm sure that they did all the work in house but still, wow!!!!

Any of us could build an engine like that, all it takes is a CNC mill and some drawing skills. What makes an enormous difference though is the engineering necessary to make it live. That's where the skill and $$$$$$$$ comes in.

I haven't seen it, but I hear there's a photo on that site of a bent connecting rod. I was also told the engine was never even in competition... What a shame.

As far as the original question, see my post in the bodywork section, or clickey here

A buddy who knows all about composite techniques felt most people have forgotten about the advantages of clay. He points out these days most publications advocate the following moldless construction.
1. Start with a big foam block.
2. Cut to rough shape.
3. Start sanding (making lots of dust.)
4. Fill low spots with smelly toxic epoxy.
5. Sand with finer grit - more dust.
6. Spray with smelly messy toxic paint to find and fix contours.
7. Repeat.

His point was, by using the "old" clay method:
1. Start with block of clay.
2. Start sculpting.

All other issues are avoided. No dust, no fumes, no sanding, only sculpting.

I thought he had a very good point.

He wasnt stoopid, but I looked into the amount of clay I would have needed, and it would have been alot, at least for my use, (insert appropriate light bulb) unless I built a substructure than molded the clay around that!