Fibreglass, Carbon Fibre, Paper Mache - The composites chat thread

[Roman 13,893]

Yeah if you can get say 10mm radius it makes life heaps easier 

But about say 3mm radius is doable but gets tricky 

[flyingbrick 9,293]

yeah that is honestly the best way if its possible. A 10mm radius would do wonders for how that turns out.

Also, don't cut the CF too close to the edges as the over-hanging material adds valuable weight to pull the material around.

your plug looks great so far! Don't bother getting the finish too perfect because its largely irrelevant to how the outside visible face will look.  Just make sure you wax and PVA it more than you think you need to.

Edit. 

Fuck you, roman.

 

[CorollaGT 259]

Wax bottle said 5-7 coats for first time use so will get my Mr Miyagi on! Guess more sanding is tonights plan then ha

[Roman 13,893]

This stuff can be handy too 

https://www.fibreglast.com/product/3M_Super_77_Spray_Adhesive_1404/adhesives

Normally for holding stuff in place while you sort out vac bagging for infusion etc, I'm not sure if it sort of dissolves once epoxy gets on it
 

[kws 4,487]

If i wanted to make a mould and copy this spoiler, what would be the best way to do it? Its currently a big solid slab of foam rubber. Would be looking to make carbon versions eventually but probably start with fibreglass for cost/practice. The basic shame seems fairly simple. Fill the cracks, coat it in something and then lay fibreglass to make a mould? A bit like this I guess

Ideally I want it to have a flat base, and hollow. Would it be best to make it in two pieces, the top/sides and the bottom and then adhere them together at the end? This would make it easier to affix studs into the base if I wanted to.

 

[Roman 13,893]

Is there a demould line on the part from when it was made originally? The tricky part will be making sure youve got enough draft angle to pull the part back out okay. If you follow the original lines it should be no surprises 

[kws 4,487]

I dont believe there is a demould line, but the donor I have is a good 35 or so years old, been painted and a bit haggard. Originals are very hard to come by, and the reps you buy from the UK are apparently shit.

[Roman 13,893]

True, probably need to be quite careful with your approach to making a mold from it then too. 

I'd first consider making one from 2 part polyurethane closed cell expanding foam

Not the shit in a can but buy some of the good stuff. 

Wax up the wing fairly liberally box up the perimeter then pour it on.

As that way if the mold doesnt release it's less likely to damage the original part getting it back out. 

And prob try it first on something similar to get a feel for it.

I've had more than 1 thing that never came back out of a mold...

[Roman 13,893]

This is my scheme for a base plate for my trumpets. 
Trumpet just sits on/around an internal sleeve. 
Just smoosh some chopped up cf in the bottom and fill it up with epoxy so it hopefully self levels decently on the top side.
Then bust the filament back out (or dissolve if needed) and hopefully have an OK flange that's decently strong. 


Also I've always found it a pain in the ass to get the portions of epoxy right for fiddly small amounts.
However I've just got a pair of wide nozzle syringes. One is 20ml and another that's 5ml 
So with a 4:1 ratio I just need one full syringe of each and it's exactly right.
Much easier!

[Roman 13,893]

Ok the chopped up carbon idea was good/bad.

Because it was going into a tight space and i was sort of draping it in there with a plastic knife. All of the fibres orient the same way. So it broke very easily perpendicular to this direction as its only the epoxy holding it together. Will try again another time but be more concious of fibre direction. Probably would have been better with less resin.

I think this will be great in some cases and a good use of scrappy left overs.

[NickJ 3,914]

54 minutes ago, Roman said:

Ok the chopped up carbon idea was good/bad.

Because it was going into a tight space and i was sort of draping it in there with a plastic knife. All of the fibres orient the same way. So it broke very easily perpendicular to this direction as its only the epoxy holding it together. Will try again another time but be more concious of fibre direction. Probably would have been better with less resin.

I think this will be great in some cases and a good use of scrappy left overs.

I forget which resin combo you were on but some of the adhesive tech resins will show an increase in toughness after an elevated post cure.

Can you not make the flange as a seperate plate and bond it to the runner?

[flyingbrick 9,293]

7 hours ago, Roman said:

Ok the chopped up carbon idea was good/bad.

Because it was going into a tight space and i was sort of draping it in there with a plastic knife. All of the fibres orient the same way. So it broke very easily perpendicular to this direction as its only the epoxy holding it together. Will try again another time but be more concious of fibre direction. Probably would have been better with less resin.

I think this will be great in some cases and a good use of scrappy left overs.

Kinda sounds like your bits of cf were too large? I mean, you could chop it up real small, mix it with resin in a cup and then kinda spoon it in

[Roman 13,893]

They were say 5-10mm long

 

But as you stir it they all form longer chains and it drags out of the pot so it still ends up very directional if that makes sense. Not great in quite tihht spaces

[CorollaGT 259]

Had a go last night at doing the upper half. Decided to just do two layers to feel things out incase I screwed up prep work and it wouldn't release... 

But it's off safely. Few errors and some flaws but learning as I go

[CorollaGT 259]

Used some of the 3M Super 77 rarher than resin to hold the first layer in place. Boy oh boy that stuff is tacky! Have to be careful haha

[CorollaGT 259]

Still to do a third layer to hide a few mistakes, a good resin coat to sand / clear plus some tidying up but it coming together. 

[CorollaGT 259]

[Roman 13,893]

Nice work!

[flyingbrick 9,293]

Yeah that's epic. Don't worry about minor flaws! It is hand made after all! My bits anyways have a few spots where the weave has been high and iv rubbed through to the layer below. I actually like it, keeps it honest. 

[87creepin 205]

Has anyone tried to make a coolant overflow bottle? I want to do one as there's bugger all room in my engine bay (and bugger all for intake piping + filter). Would probably have to be able to withstand temps of the hot coolant + engine bay. 

This polymorph stuff looks like it could be worth a try using as a mold material?

https://hobbyking.com/en_us/esun-polymorph-hand-moldable-plastic-250g-bottle.html?queryID=826ea9d05e567fda145397744300bd71&objectID=52809&indexName=hbk_live_magento_en_us_products

I wouldn't worry about looks, except for the top thats visible really.