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  Author    Fiberglass Repairs  (currently 704 views)
Posted on: June 19th, 2015, 19:17:24 Quote Report to Moderator
Baby Member

Posts: 17
Hello Forum:
I have the subframe fitted and removed.
It seems the hole in the floor will not interfere with the subframe bolts.
The previous mid engine builder made an aluminum plate for the front
subframe bolts to attach.  It's pretty nicely made, heavy duty and
would give me a place to attach a simple roll bar hoop.
I think I will leave it in place.

I went to Fiberglass Depot ( not kidding real name).
I found fiberglass material that is a thick layer of matt and two layers of tri-axial cloth.
They use it on the bottom of hulls where you need high strength.
It is supposed to build 1/8" per layer.
I have done several tests of resin to harderner.
Think I got it worked out.
I had a tendency to add too much hardener and it went off too fast.
I am going to sand the edges for a 1.5 to 2.0 inch taper.
Got an air sander that works great.
Going to make an mdf wood form from the underside and coat it with form release.
I will put on a layer of matt.
two layers of cloth.
and then remove the forms so I can see thru it better.
I will use the three layer material to build up the thickness.
and end up with matt on the last layer to get it the right thickness.
I was going to put two layers of 2" wide FG tape top and bottom
and then 4" wide layers top and bottom.
It should be super strong.

I may put some foam or wood strips across the floor to add rigidity.
Not sure i will need that after is all built up.
Probably do it anyway.
That would tie the patch to rest of the adjacent floor....

Only thing I am concerned about not is the shock towers.
They were cut off so the coils springs could sit higher....
I need to build up the rear shock towers.
Do people make "monte carlo braces for their cars"
Would it be possible to get the dimension from the floor to top of shock?

Also they cut holes in the fender wells for cooling and so the tire did not rub.
or that's my guess.

It's going to be a tricky job to fix.
compound shape and nothing to bond to on the outside finder.
I was thinking about making a fiberglass angle that is bonded
on first then drill holes so that the form has some way to attach.
I 'll do this repair last so my FG skills will be better.

just talking to myself now....
Do you celebrate Father's Day this Sunday?
Or is this a Yank holiday only?

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Richard Porter
Posted on: June 19th, 2015, 22:05:51 Quote Report to Moderator
Medium Member

You can't have Windows without pains.

Location: Maidenhead, UK
Posts: 124
Fathers day is getting very commercialised over here now. When my dad was alive we never bothered with it.
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John Dickens
Posted on: June 20th, 2015, 11:06:31 Quote Report to Moderator
Big Member

Posts: 449
Use melamine faced board instead of mdf. Resin will not stick to it even if you are less than thorough with the release agent.

If you are in a warm climate 1% hardener will be fine.

Use polyurethane foam rather than wood to make stiffening ribs. Word swells if it gets damp.

Don't try to laminate two layers of woven fabric together. They will not bond strongly enough as they do not amalgamate in any way. You are relying on the strength of the resin alone to hold them together. If possible there should be a layer of csm between two layers of woven fabric.
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Posted on: June 23rd, 2015, 15:56:06 Quote Report to Moderator
Baby Member

Posts: 17
Thank you for the advice.
melamine is a great idea.

Funny you don't like wood.  Mr. Marsh's feeling will be hurt.
I have worked on boats and the older ones used lots of wood stiffeners.
Foam is probably better. I just like the idea that wood adds strength and rigidity.
Hmm how about aluminum?  I have lots of scrape around.
small round tubes, small square tubes even channel.

Sorry csm is that matt?
Short pieces of fiberglass put together in randon layers

So your saying do not put cloth layers over cloth layers.
Go matt, cloth, matt, cloth etc etc

I thought the matt was for the outside layers as it sand and finishes smoother.

Thanks again
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John Dickens
Posted on: June 23rd, 2015, 20:42:05 Quote Report to Moderator
Big Member

Posts: 449
The real strength and stiffness comes from the fibreglass box section formed over the wood, foam or whatever, not from the material used as the former. If you use foam (or paper rope) you can add strength exactly where you want it with only a very small increase in weight.

CSM stands for chopped strand matting. The random array of short fibres held loosely together by a PVA size.

If you are using epoxy resin then you can safely bond together layer after layer of woven fabrics as the resin is strong enough to bond them securely and permanently. If you try the same thing with polyester resins the bond is not strong enough and the layers can de-laminate. Personally I would not bother with woven fabrics at all in the main laminate. I would however sandwich Kevlar tape in areas of high stress such as bolt holes or hinge placements.

This Austin Healey lightweight rally spec boot lid which I made a while back shows the sort of thing you should be looking at.
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