Any good how 2s on making large fiberglass panels without molds

[Jonny Hotnuts]

These are the best posts of all time.
Period.

[Unkl Ian]

We used Closed Cell Foam,vacuum bagged onto the inside of the panels,
while they were still in the mold,then another thin layer of 'glas over that.
Don't know the brand name,this was 30 years ago.

The main body shell was a very thin "viel" of 'glas,then two layers of mono directional carbon/'glas.No gel coat.The parts were translucent when they
came out of the molds.

Very stiff,where the foam was used,and VERY durable.

The guy doing the panels went on to do work for Al Holbert,
and at least one Indy car team.
---------------
Chopper guns are for production work,where speed
is more important than weight,strength,or durability.

[Loose Goose-Terry#1]

I went to the ACMA Expo in St. Louis this year and saw where the paper hexcel core and the Kevlar core material (both looked like a honey comb) was being used on the coaster cars built by the engineering students at the University of something-or-other (they say your memory is the second thing to go when you get old, LOL). Looked like some pretty neat stuff! The Kevlar core would probably work great wherever you might need some high rigidity. The students tested both and decided on Kevlar. The stuff I saw would only flex in one direction so if you need it to form a compound curve you would probably have to cut and piece it together. 

Terry

[hotrod]

There are some really good resources on fiberglass and materials but most of the books I have picked up are centered around boat building but the info is still very transferable.

Fiberglass and composit materials  by Forbes Aird, has some info on car body construction in it.
ISBN 1-55788-239-8  about $20


Paint and Body Handbook (HP books) Don Taylor and Larry Hofer (I don't have this book but it looks like it has some good info in it.)

Boatbuild Manual Rober M. Steward
ISBN 0-07-061376-1
pgs 58-72 deal with fiberglass etc.

Gougeon Brothers on Boat Construction (406 pages)
Used as a boat building text book.
West Marine sells the Gougeon Brothers epoxy products

Larry

[Unkl Ian]

Lots of info here: http://www.fibreglast.com/contentpages-Learning-Center-286.html


'Glas over Urethane foam:
http://www.rqriley.com/frp-foam.htm

[JimL]

I know this is really late on this ...what do you call it...string?  Anyway, here's some food for thought for anyone needing a semi-reuseable mold for custom shapes.  I've had really good luck using steel parts (various shapes from old roofs, hoods, fenders, gas tanks, etc) that are tack welded and sometimes hot glued together.  I reinfoce for stiffness with foamboard or wood, using hot glue.  I use a little Bondo for rounding inside corners, and build a fairly permanent mold that I can use more than once.  Most of the inside surfaces will be quite smooth, and you won't have much finish work to do.  There are so many great shapes in the junkyards, it seems too much work to do it myself!  You'll have a decent female mold pretty quick. Take your time waxing (I use a heat gun on the metal, for the first coat) and the parts come out ok.

Try this website (not mine) to see one of my simple steel molds.
http://home.brisnet.org.au/~jmiller/leinfam/seat.html

Regards, JimL

[Blue]

The best method I've seen is to use cardboard or masonite sectins to establish 2D contours and then spray foam and shape it.  Symetry can be had be doing one side perfectly, then making cardboard reference profiles every few inches in both width and length (span and chord).  Shape the other side to match.  The smoothness of the contour is what you make it and you won't need to do much bondo if you do a good job on the foam.

Now the good part.  Blow off the dust and cover the foam in 3M packing tape.  It sticks well and doesn't stick to resin.  Then lay up your skin over the tape.  You can pop the skin off after it cures and yank out any foam in the creases.  Then add any sub-structure you need.  No residual foam weight or bulk.

Have fun!

[1212FBGS]

Honeycomb coring material works best with prepreg materials... if you try to use honeycomb with a wet lay-up you will fill the holes up with resin... foam core works good on airplanes and boats but has a HDT (heat distortion temperature) of around 180f... Inside engine compartments can see temperatures of over 400f and will deform body panels (problem Sam Wheeler has on his body)...On the 3 Vesco bodies, the Ack attack body, and all my liner bodies I used a balsa wood sandwich core before vacuum bagging them
kent

[UltraCarbonFiber]

Here is a link that was posted on my composites forum about wet laying a door panel with nomex honeycomb nomex core and carbon skins.  It's a word doc that you can save as or open. 

http://www.turbomustangs.com/techarticles/pbcarbonfiber.doc

There are also a few tips on basicmold making at the beginning that may be of interest.

As 1212FBGS stated pooling with honeycomb can be an issue if you are not careful but it can be done as shown by the results in the above link.  Read the weight of the finished panel, it's incredibly light.  The key is wetting out the material on plastic and removing extra resin before dropping the last plies of fabric down.  One downside of a honeycomb is of course cost, balsa is cheaper.  Honeycomb may also be overkill because shaving ounces off a car for the salt might not be needed or wanted.  Also a friend of mine who runs a composites shop back in Indiana makes his own prepreg for some projects:  Here's a link on that: http://www.racingcomposites.net/unt?id=312 Obviously the mechanical properties won't be as good as real prepreg but sometimes it's "good enough" for the application without spending $60 lin yd on carbon prepreg fabric.  He also vacuum bags and oven cures the parts with diy preg.  Using this diy preg would also aid in constructing honeycomb core parts without the pooling problem.  He claims to be getting good results this way.  I am going to try this out soon just for fun. 

A good point was brought up about temps around the engine bay, resin selection is key there. Here is a supplier I use and a high temp laminating epoxy:

http://www.decomp.com/laminate/htr250_1063.htm   

Here's another supplier that makes a few high temp systems.  Once you go above 400f your resin selection really starts to diminish not to mention the hassle of post curing higher than 400.

http://www.ptm-w.com/index.asp?pgid=20

[1212FBGS]

The resin is not the problem.... the "core" wont take the temp.... the first resin you recommended only has a hdt of 375 and requires a 4 hour post cure at elevated temps... not a good selection..... and the ptm-w resin has always been considered a "hobby" resin and surely not for a big lay-up like a liner or car body
Kent
ps your first link on the mustang page wont open and the prepreg ling is asking for user log in.....

[UltraCarbonFiber]

The resin is not the problem?  At 400f you bet it can be a problem.  Use balsa and low temp resin and we all know what happens.  I was referring to your comment about "if you try to use honeycomb with a wet lay-up you will fill the holes up with resin... "  That was the problem you mentioned about honeycomb correct?  In case you missed it I didn't speak to the issue of foam core and it's associated problems. Although there are thermo formable foam cores that I know of that can exceed 400 f hdt.  Both Diab and Degussa make a product suitable for temps above 400f.     

Only has an hdt of 375f?  That was just two examples of a resin that could be used.  Not a good choice based on what, every engine compartment going over 400f.  Because you've built liners that went higher than 400f in their bays doesn't mean every situation requires higher temp resin.  Every high temp system I know of requires a post cure.  As far as ptm-w always being considered a hobby resin, how about the idea of using what works for the application instead of saying "hobby" resin is beneath you somehow.  We wouldn't want anyone using hobby products now would we, lol  Speaking of hobby did someone say Balsa?     Perfect example of a material used for everything from model airplanes to structural applications.  Many hobby products can be used just fine under extreme conditions.  Hobby products aint beneath me if they work.

P.S. the mustang page is a word doc and there is nothing wrong with the link, you didn't wait long enough for it.  For anyone that it doesn't work for I'll be happy to email you a copy, somehow I was able to download it.  As for the forum sign up yah I'll just post the entire post so you don't need to sign up. 

BTW, Kent why do you seem to have such an issue with my posts?  Just wondering what the deal is or maybe I'm not the only one you take issue with.  I haven't been around the forum long but already you've thrown a few rocks my way.  As I recall in my last post you pretty much said "how many times have I been on the salt"?  I guess you had some issues with me putting in an opinion on an alleged "500 mph motorcycle".  I was commenting about a news story and not any of the technical aspects of that project.  Anyway I get the fact that you have been involved in composites for as long time but you're coming off looking like a bad lawyer making arguments for the sake of argument.  How about adding to my post rather than taking away from it.  I have a little bit of experience and I'm trying to help someone out by contributing.  If I'm wrong I have no problem hearing it but be precise about why I'm wrong.             

[UltraCarbonFiber]

Here's the post about DIY preg I was telling you about from www.racingcomposites.net

An alternative to resin infusion is impregnating the fabric before laying it in the mould. A sort of poor man's pre-preg! It actually has some advantages over pre-preg as you can use whichever resin you want without having to have a huge supply of pre-preg. Also it drapes very well without having to have an autoclave for a good finish. If the cosmetics of the part is important I'd recommend curing the first two layers to get a void free surface, then lay the rest in one hit.
First make templates of the part from which the part will be made;



Cut two pieces of 4mils plastic sheet (visquine) and lay one on your bench;



Next, pour some epoxy on the plastic and spread it to a thin film;





Lay the fabric on the resin an use a squeegee (bondo spreader) to squeeze the resin through.


Add more resin and squeegee it through until you can't squeese any more off. This will give you a good resin to fabric ratio.Too much will cause problems ,including poor surface finish, voids, porocity and weak parts.

Place another piece of visquine on top and smooth out the wrinkles with a rag.





You can now cut the fabric up using your templates or put it in the deep freeze










After cutting out the shape, remove one piece of visquine and lay in the mould (the fabric, not you!)





When its in place, remove the other piece of visquine.



Using a brush, tease the fabric into place.

Then bag it as usual.