Hi,

Do you think it is possible to sharpen a carbon composite blade?
I would like to try to make a straight razor blade or a kamisori blade but is it possible
to sharpen the edge like a ceramic blade?
If yes what composite is the best performer for this application?
Carbon, Kevlar, twaron?
Gelcoat or just resin?

Thanks for your help guys.
Kind Regards,
Olivier

Yes you can sharpen the edge of a carbon blade, but it will never keep the edge for more than a few cuts, even i relatively soft material ...

... You will get the best results If you use only very fine weave low weight CF that is very densely woven (Like the EC Plain 130 gsm specialist) and A hard resin like EC IN2  .. You will need to use a mould that will stand up to compressing the edge area of the blade with high pressure. (And vacuum of course)

Also to make the blade keep its edge best, make the angle you sharpen it at , quite steep . do not try to make a very low angle like on a straight razor..

To make something really cool using CF, use a Titanium or stainless foil as the middle layer in the blade.   Such a blade will actually be practically usable .. even if the foil itself can not be hardened.

"Sapere Aude"... Dare to KNOW!

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

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

Thank you Dravis,

To create a high pressure on the edge area you will need to make a mould that can be mechanically compressed (By clamps, bolts  or the like) while also having a vacuum bag present..

I only make flat sheets or profiles this way, My mould consists of two 20 mm thick polished stainless steel plates.  I sandwich the fabric between them, do a wet lay-up - envelope bag the whole lot,  vacuum on via through-bag connector, then clamp the whole thing down with about 50 kg of lead bars ..
This gives a very high fibre to resin ratio. 

I simply grind the resulting "flat bar" into the desired shape, just like making a knife from flat bar stock..

I've never used foil for the cutting edge, but I have used 1 mm hardened knife steel sheet, ground to a rough shape, then sandwiched between CF fabric.

The same method could be used for the foil .. both methods require skillfull grinding of the blade ..

"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 :-)

Hi Dravis,

erm , it will look pretty, but thats about it ....

rather sandwich a layer of steel between the layers of carbon and then grind equally either side , so that you just have a steel tip 4-5mm exposed as Dravis already said

In order to use a compressor for adding pressure to a mould, you will need a pressure vessel, capable of sustaining the 7 -10 bar overpressure.  Not easily obtainable, nor cheap ...

I do know that you will not get a better result than with mechanical pressure (clamps or heavy weights)

The people I know who have experimented with binding prepregs to steel, do not get the same bond strength as with mechanically compressed vacuum bagged hand layups

Titanium is even worse, its extreme natural corrosion resistance comes from it forming an Titanium-oxide barrier layer, literally in seconds, upon exposure to air.  This happens in its micro-porous surface cavities, so even sandblasting it does not help.  The only way I know to bind Titanium fully to epoxy is to "sand in" the epoxy with my diamond sanding block, wetted in ready mixed resin and hardener, then quickly rinsing my sanding block and bonding while the epoxy is still wet, and preventing oxygen from reaching the TI surface.  This process can give you nearly the same bonding strength as with stainless steel.
Carbon-steel is much easier.

The laminates I have made were D-2 rust resistant tool steel 1 mm thick, hardened and sandblasted to ensure god mechanical and chemical binding for the epoxy.

You will nver be able to sharpen pure CF to straight razor levels .. the material is not fine grained enough.  You will need hardened steel or Beta-Titanium alloys to do that. Beta-Ti-alloys are like rocking-horse-droppings-- Only one Knifemaker has it it the perfect form (Mission Knives) and even Beta-Ti is is not hard enough to keep a proper razor edge.  Carbon steel (the stuff that rusts) is the only way.

Carbon-fibre "laminated" blades can be very tough and usable (and great looking!!) with either a stainless steel or carbon steel edge.  With a straight razor you hollow grind the edge, giving the blade quite a thick "spine" or back, this is a big advantage when using CF for the bulk of the blade-  The thin edge steel needs only to be exposed at the edge.

Stabbing knives can be made from pure CF, so some people carry them for "self defense" or as "last resort backups"  IMHO a purely stabbing weapon is an extemely poor type of "self defence" ..



"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 :-)

Your mould is build with two Stainless steal plates.

Yes, full vacuum is perfectly possible!  I lay up on a flat piece of vac-bag, wetting the CF thoroughly then fold over the bag, and seal the three remaining sides with gum tape, leaving a small piece of 5 mm aluminium tube going through the gun tape.   I then connect a vac hose through the catch-tank and extract all the excess resin, running it to a full vacuum with the flat bag between the two pieces of stainless steel.
Once I have good vacuum, i load up all my lead ingots (for bullet casting ... ) on top .. that's usually between 50 and 100 Kg of lead.  Since I usually have around 30 sq-cm.  of CF flat that's around 4 kg /sq-cm ..   When I want the finished laminate to be a precise thickness I add stainless steel spacer strips around the laminate, inside the vac bag.

You can probably machine out the female part of the mould, directly from the metal, which is what I would do I if needed a larger production run of precise CF smallish items.


 

"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 :-)

It would also likely be worth doing a full post-cure on whatever resin system you choose as that will increase stability and also make the resin slightly harder.  Also means if you work the blade a bit too much while shaping, the heat generated will be less likely to ruin the edge.

Also for those of you in the UK, you would be wise to read up on the specifics of knife law surrounding non-metal blades as during 2004 the Criminal Justice Act 1988 was modified to include "stealth knives" in section 141.  They have described a "stealth knife as:
 

"a stealth knife, that is a knife or spike, which has a blade, or sharp point, made from a material that is not readily detectable by apparatus used for detecting metal and which is not designed for domestic use or for use in the processing, preparation or consumption of food or as a toy"

  I have heard of some people adding metal strips inside the lay up but I am not sure if this is 100% compliant with the law, although it does seem that logically it would be fine. So if you are making anything, make sure you are complying with the law.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant