Attempting to build the world's quickest UK road legal Elan

[nalesutol]

Very similar to fibreglassing apart from:

Much more expensive cloth and resin.
Takes a lot longer to cure.
A lot harder to rub down imperfections.

You can vacuum bag fibreglass, which will give you a lighter and stronger part.

If you can lay up fibreglass you can lay up carbon fibre the same way.

[blackpopracing]

How does the vacuum bag make it lighter - does it use less resin?
Just been doing glass again forgot how itchy it is!

[nalesutol]

Ah, yes, carbon doesn't itch :-)

You lay up carbon, then a layer of peel ply. This is used to create a textured surface on the laminate ideal for secondary laminating/bonding or to act as a porous, removable barrier between the laminate and other bagging consumables. Being a porous layer, peel ply allows the vacuum to bleed trapped air and volatiles out of the laminate.

Next layer is a perforated release film (controls the amount of resin squeezed out of the carbon), followed by a breather/soaker layer which absorbs the excess resin squeezed from the laminate and allows the air to be sucked out to form the vacuum.

Then everything is placed in an airtight plastic bag and the air removed with a vacuum pump.

So, you use the same amount of resin as you would if simply wet laying, but the excess is sucked out, so the finished item is both stronger (layers pressed together and excess resin removed) and lighter.

[blackpopracing]

Thanks for that, I've learnt to use less resin and an ally finned roller to compress the layers and work the resin in, works well & strong but can still get (very) heavy compared to your weights.

[nalesutol]

Most of my panels are two layers. If you use a 200gm/m cloth you need the same weight in resin if you are simply laying up. ie 50/50. So a 2 layer sheet of carbon would weigh 400gms of cloth and 400 grams of resin = 800gms per square metre.

If vacuumed, you can reduce the cloth/resin ratio to 60/40 which means you only use 270gms of resin, reducing the panel weight to 670gms per square meter and it is also stronger.

The trick is to only use enough resin to fully cover every strand, be it glass or carbon. Any more just increases weight and reduces strength.

On a one metre square of carbon (or glass) a vacuum bag exerts a total of over 21,000lbs of force on to the panel = 9.5tons!! A little bit more than you could manage with a roller :-)

[blackpopracing]

Wow!that's impressive! No wonder CF is so strong.

[nalesutol]

Well, the strength is really in the material. You can do the same with fibreglass (vacuum bag). It will increase the strength but nowhere near to that of carbon.

When you look at carbon closely, it is made up of thousands of fibres in each strand. A 3K cloth, for example, has 3000 fibres in each strand! These are continuous fibres running the whole width and length of the cloth. They are tightly packed so it is very important that the cloth is completely infused with resin, which is another reason to use vacuum.

This is just one strand:

[nalesutol]

Worked on CF centre console last night. The ends will be trimmed to fit the dash and rear panels once they are in place. Photo is a little grainy due to low light conditions.

[daniboy123]

I've just read through this thread, what a superb thread thanks for sharing, I had no idea CF was possible DIY style like this!.
Once the car is complete will you need some kind of engineers report given all the changes that have been made?.
Have you carried out any destructive testing of your CF work to give you peace of mind everything is as it should be?
Once again great stuff and keep us posted

[nalesutol]

Hi and thanks for kind words.

Yes, there is a strange mystique around carbon fibre. I guess because when it was first available it was considered exotic and it was very expensive.

It is still quite expensive but it has become a DIY material now, even down to prepreg carbon.

I don't plan to get an engineer's report as I am confident that the work done is more than adequate. Suspension mods were designed by a race car builder and fabricated by an experienced race car welder.

Although some of the carbon is used to increase structural stiffness, none of it is safety critical so no plans for testing.

[daniboy123]

The reason I ask is that a lad building a car up in the same bodyshop as me had to strip it back down again and document the build with photos then get an engineers report before it could be made road legal. I wasn't sure if it would be the same for yourself.

[daniboy123]

This was due to the amount of modifications he had made to it, it works on a points system I believe but I guess the trick is not to declare everything at once.

[nalesutol]

If it passes its MOT then I will be saying nothing :-)

Worst case scenario is having to get an IVA, or whatever it is called now, and ending up with a Q plate. Don't want that, but not the end of the world.

Yeah, points system...I think I can muster 8...........possibly :-)


Get a vehicle registration number

DVLA uses a points system to decide what registration number to give a radically altered vehicle.

Keep the original registration number

Your vehicle must have 8 or more points from the table below if you want to keep the original registration number. 5 of these points must come from having the original or new and unmodified chassis, monocoque bodyshell or frame.


Chassis, monocoque bodyshell (body and chassis as one unit) or frame - original or new and unmodified (direct from manufacturer) 5
Suspension (front and back) - original 2
Axles (both) - original 2
Transmission - original 2
Steering assembly - original 2
Engine - original 1

Get a ‘Q’ registration number

You won’t be able to keep your vehicle’s original registration number if one of the following applies:
it has fewer than 8 points
it has a second-hand or altered chassis, monocoque bodyshell or frame
there’s evidence that 2 vehicles have been welded together to form one (ie ‘cut and shut’)

Your vehicle must pass the relevant type approval test to get a ‘Q’ prefix registration number.

[blackpopracing]

Jul 15, 2016 18:20:12 GMT daniboy123 said:

This was due to the amount of modifications he had made to it, it works on a points system I believe but I guess the trick is not to declare everything at once.

Makes no difference. Your friend had to pass IVA, I'm having to do the same thing on mine now.
The 'engineers report' was the IVA test.

[daniboy123]

He seemed pretty concerned about it and like I say had to document all his work then points system decided what happened with the cars registration. Just curious.

[Darkspeed]

Jul 14, 2016 10:32:55 GMT nalesutol said:

......On a one metre square of carbon (or glass) a vacuum bag exerts a total of over 21,000lbs of force on to the panel = 9.5tons!! A little bit more than you could manage with a roller :-)

Lets do some maths - you are talking about a whole 1m area at the full 1000 mbar atmos.

If we take our little roller and say that one paddle bar will be in contact with the laminate at any one single point in a rotation and that each bar is 3mm x 75mm - 0.000225 m2 and we exert a force of say 750g on it. (Yes I did a test on my scales )which is a very light application - and we do that all over our 1m square laminate - that square metre has been subjected to a total compressive force of 3333kg 3 tonne - if I used just the weight of my arm 5.2kg on the laminate - 23,111 kgs 23 tonnes that's twice your vacuum bag.

The hard part is the equivalent time under pressure - the all important work done area under the curve. - I think before you could have rolled each mm2 for 8 hours the resin may have cured - LOL - although we only get to roller for maybe an hour max before initial cure.

Do not underestimate the roller and arms effectiveness in laminate consolidation Especially if you use a satin glass cloth which uses far less resin and can take a good rollering.

[nalesutol]

Agreed, the vacuum only exerts 14.7lbs/sq in (actually, slightly less as a complete vacuum isn't possible with DIY pumps. They only state 99.995% vacuum :-) ) and this figure is easily exceeded by human hand, but only for a fraction of a second over any particular point.

However, the vacuum is exerted over the whole area for the full time the resin is curing which is around 1-2 hours for a fast hardener and 12 hours for a slow hardener (not possible by hand), including all the nooks and crannies that are difficult to roll (the corners produce the most resin excess).

If you are determined and have the time (hours) to spend constantly rolling, then you will get a pretty good job (providing you are also using cloth to soak up the excess resin) but still not as effective as vacuuming. I lay up, bag, push the on button and go and do something else :-)

You can do a pretty good job using the clothes vacuum bags and a domestic vacuum cleaner, so the cost isn't high to start off with. Use the fast resin so the vacuum needs to be held for only around an hour or so. As soon as the excess resin is hard to the touch you can switch off.

[Darkspeed]

I used to work with ultra high vacuum and the best piston type pumps were what we used to get the vacuum down to a stage where we could switch on the turbo molecular pumps and mercury diffusion pumps - Back then Cyro vac's were just getting started.

The best aspect of the vacuum is the ability to really push into the corners which is really difficult with a hand lay-up as well as the wicking out of the excess resin which is laborious with a hand lay-up.

Carbon does seem to have come down in price - like for like cloth is only three times Glass now - but its the Epoxy resin that is still very expensive by comparison with Poly.

Better get back and work on my own thread rather than clogging up yours

[nalesutol]

When you compare how many layers of carbon you need compared to glass the cost is even nearer. As you say, though, the cost of the resin is painful.

That's OK, I can always return the favour :-)

[nalesutol]

A little bit more work to the rear interior panels.