I want to make a flat sheet (or rather block) of carbon fiber that is 3cm thick? It's not a big block, roughly 7x7cm. I can only imagine infusion would be pretty useless for this as vacuum will have hard time pushing down that thick of a sheet so I'm thinking wet lay up and put something really really have on top to compress. What say you? Also, most importantly, how many layers do you think i'm gonna need to build that kind of thickness?

Anybody? I'm most likely to be using 285gsm 4x4 twill if that''s of any significance 

Hi,

Normally I get around 1 mm thickness from 4 layers of 200 gsm twill ..

I would simply do a test ... Cut out 10 7 x 7 cm pieces of your 285 gsm cloth compress it in a vise between two pieces of steel plate/ other hard material, and measure the distance between the two plates... I guess you will need the plates to press the "stack" anyway   Make it 8 x 8 cm or a bit more to be able to remove the outside "fuzzy" edges ..

Add layers until you get the desired compressed thickness ...  add epoxy ...  cure ... Done 

I make quite a lot of cloth "micarta" for knife handles, using both Epoxy and Polyester... I have two 20 mm thick stainless steel plates to compress it between.

I lay up blocks of about 1 cm thickness ,,, a couple of layers, then soak with resin, then more layers.. .e.t.c.  

It all begs the question:    Why make a 3 cm x 7 x 7 cm CF "block" ....  The same block in hard aluminium will be as strong and probably lighter...

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Because I want to make a watch case from the block. The watch case itself will be 44mm but I need the block to be substantially bigger

I disagree with the weight point. aluminium is about 2.7gm/cm3 where as carbon is 1.6-1.8 gm/cm3 depending how processed so its extremely unlikey unless very very resin rich that the same volume alloy block was lighter.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

As a very general rule with vac bagging, I read 200gsm is between .25 and .3mm thick

With regards to the weight point, I think you're right Warren, but I was thinking more in terms of strenght vs. weight in a complex shape, and as it turns out thats exactly what "StanTheMan" wants to carve out of his CF block.. 

personally I would make the watch case as a "forged carbon" part..  I.e., shredded CF with Resin stuffed into a metal mold, and precision cut pieces of very fine weave prepreg CF for the top and bottom layers.

Use high pressure "workshop hydraulic press" and heat the mold with an oil heating system.

I'm working on such a setup to make CF / Carbon Nanotube rifle-scope mounts.  They will have molded in threaded Titanium studs for the assembly screws..

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

I like the forged carbon idea, easy to make a part in the end but the tooling and set up could be expensive relative to other ways. But the forged thing would great.




You could also lay up a 30 000g stack of pre preg carbon and sandwich it in between two metal plates. Simply clamp or press and cook. You might make a block that did 3 or 4 parts so with allowing for some trimming it could be 100mm x 300mm.

At 1000g per mm

30 000g of 200g pre preg cloth is about 150 layers of material. $80 per sqm

30 000g of 300g unidirectional is about 100 layers. $40 per sqm

I assume you might be CNC shaping the block?




To do 100 or 150 layers of wet laid carbon would be a super sloppy mess and a PITA to do.

With the pre preg you may also need to clamp it and heat it a bit (60 deg for 10min) along the way with so many layers. Maybe do this de-bulk every 5000g?