How to Cut Carbon Fibre Sheet and Carbon Fiber Parts (Technique & Safety)


Welcome to this Easy Composites guide to cutting,
shaping and finishing carbon fibre sheet and carbon fibre parts. The idea of this tutorial is to cover some
important safety information and also to explain the best techniques for cutting this material
and then shaping and finishing the cut edges. This guide should provide helpful information
to anyone who needs to cut and finish carbon fibre parts whether they are untrimmed original
parts that you have made yourself like this, stock carbon fibre material – like this sheet
– that you’re cutting to make your parts or existing carbon fibre parts, like this seat-post,
that you need to cut to shorten or adjust. This tutorial is made up of the following
sections: Firstly, an explanation of what carbon fibre
parts are made from Some important safety information when cutting
carbon Tools and best techniques for cutting
The best tools and techniques for shaping and finishing edges, and finally…
Protection for cut edges If you’re unfamiliar with carbon fibre it’s
useful to understand what this material is before your start working with it. Carbon fibre parts are actually ‘carbon fibre
reinforced plastic’ which is to say that they are a composite material made from a plastic
(normally a cured resin) which is reinforced by carbon fibres. It’s important to understand
this because both the resin and the carbon fibres present both their own risks and considerations
when cutting the cured composite. When cutting or shaping carbon fibre parts
it is important to follow good safety practices. If you do so then cutting this material can
be made perfectly safe. The weight of evidence to date from studies
specifically into the dangers of working with carbon fibre overwhelmingly suggest that it
presents similar risks, and should be protected against in a similar way, to working with
other dense materials like hardwood or fibreglass. In addition, some resin systems may produce
toxic smoke when cut using high speed machines. The main risks are irritation to skin, eyes
and lungs caused by fine dust particles and danger from splinters and sharp edges of the
cut laminate. If you’re using high-speed cutting tools then there are the risks associated
with that sort of equipment. One final risk comes from the fact that carbon
fibre dust is electrically conductive, although in practice this is more of a risk to your
electrical tools and equipment rather than yourself. All risks and irritation from carbon fibre
dust can be significantly reduced by working in a well ventilated environment and ideally
with some localised extraction. In a workshop environment that might working with a positionable
extraction arm like this. Or even working on a down-draught table like.
Now these will draw dust down into the filter before even gets a chance to be airborne. But, if you’re working at home or doing more
infrequent jobs then something as simple as a vacuum cleaner, like this, positioned on
the table as near to where you’re working as possible with do the same thing and suck
up dust as it’s being created. Carbon fibre dust itself is NOT toxic however
fine particles of it can irritate your lungs in the same way that cutting materials like
hardwood can. The plastic element of carbon fibre parts
is most commonly a thermoset resin such as epoxy, polyester or vinylester. Of these,
epoxy resin specifically can produce toxic dust when cut using high-speed cutting equipment
and because it is often difficult to know which resin system has been used in the manufacture
of a part we would always suggest assuming that high speed cutting could create hazardous
or toxic dust and so take appropriate precautions. To safeguard against both risks, as well as
extraction or good ventilation, we always suggest wearing a respirator when cutting
carbon fibre. So, let’s take a look at the different types
of respirator that are available. We’d suggest avoiding disposable nuisance masks like this;
they don’t really have any guaranteed protection factor at all and don’t offer a good level
of fit either. Instead, for occasional use a P1 mask like
this is a good starting point. For improved protection a P2 dust mak like
this filters out finer dust particles and a valved example, like this one, is much more
comfortable to wear for long periods of time. For prolonged or regular use you might want
to look into a re-useable respirator like this one. These tend to offer a much better
fit ensuring that dust can’t find its way around the mask. Again, look for P2 stamp
even a P3 rating which safeguards against high toxicity materials. The next safety consideration is your skin.
There’s two risks to your skin when trimming carbon fibre parts; the first being cuts from
the sharp edges and the second from irritation caused by the fine dust. If you’re cutting down ready made carbon fibre
parts like, which could be a seat-post for example then you’re very unlikely to encounter
any sharp or dangerous edges but if you’re trimming freshly demoulded carbon fibre parts,
like this, then exercise great caution because the edges of the laminate where it goes thin
can be absolutely razor-sharp and give you a nasty cut. Skin irritation from the fine dust particles
is very common when cutting or sanding carbon fibre. This irritation is most likely to affect
your hands — particularly in-between your fingers — and your forearms. Thin surgical gloves, like these, can be worn
to keep the dust off your skin but for heavier trimming operations we would always generally
opt for a disposable full suit as well. If you do get carbon fibre dust on your skin
then wash it off with cold water not warm or hot water. This will avoid opening your
pores and making the irritation worse. The last piece of safety equipment we would
recommend is eye protection. If you’re only fettling or making small adjustments
to a carbon fibre part by hand then there is very little risk to your eyes but for any
heavier cutting or power tool use then safety glasses, like these, offer a good basic level
of protection or alternatively, for heavier trimming operations then a set of goggles
like these is recommended. There is nothing particularly difficult or
unique about cutting cured carbon fibre. Many people assume that it cannot be done without
expensive specialist tools but this is not the case. Better, more appropriate tools will
make things quicker and easier but, if you are careful and go about it the right way,
you can certainly cut carbon fibre with fairly standard tools. As a general rule, when cutting carbon fibre
you want the cutting surface for the tool you’re using to be as fine as possible. A
finer cutting surface will splinter and fracture the laminate much less than a coarser cutting
surface. This means that the best blades to use don’t in fact have teeth at all, instead
they either have a fine grit on their cutting edge like this Perma-Grit hacksaw blade, or,
like this slitting disc, which is made of a ceramic material which always gives it an
abrasive surface at the cutting edge. If you don’t have a cutting tool with an abrasive
edge then you can still use toothed blades but you will find that they may chip and splinter
the laminate more when cutting. If you do use a blade with teeth then you
want the teeth to be as fine as possible. This means using blades designed for metal
rather than those designed for wood in tools like hacksaws and jigsaw blade. In all cases, when you cut carbon fibre you
should always cut ‘wide of the mark’ compared to exactly where the finished line should
be, you’ll cut a bit past that, so that you can rub it back using a sanding block or abrasive
paper. In doing so, if there has been any chipping or splintering of the laminate during
cutting this can be rubbed away leaving a smooth and accurate edge, which we’ll demonstrate
after. So let’s now take a look at how a range of
tools cut a range of different types of carbon fibre material. So, we’ve got a good spread
of different types of material including an easy to cut foam core panel, some solid prepreg
carbon fibre sheet, a laminated part, a pultrusion and this seatpost to cut down, and then a
range of tools. Some of them are more appropriate for cutting different types of material than
others but we’ll work our way through and demonstrate which ones are better and what
sort of cut you can expect. So, because we’re onto the actual cutting
of the carbon fibre now we need to pay attention to our safety gear so we’ve got respirator
and goggles and then we’re just going to use a cutting surface so that we can hold the
materials and be able to saw off the edge and into space over this downdraught table
so we use a piece of foam for that. Here’s the various bits and pieces that we’re
going to be doing the cutting demonstration on. We’ll just put the seatpost and part to
one side and concentrate first of all on these two sheets. So, start by just marking out a simple shape.
Of course, this is only for demonstration purposes so we’re not paying any particular
attention to the measurements or the shape or accuracy when marking these out. First of all we’ve got the prepreg sheet.
This is pure carbon fibre, 2mm thick and we’re going to be cutting it first of all using
a hacksaw, a normal hacksaw, with a metal cutting blade in. Just starting off gently,
along the cut. A metal cutting blade actually does a really nice job on a prepreg sheet
like this. It wouldn’t be as good if we’d got corners to get round or a tight shape
to follow particularly but for straight lines like this then you can see the metal cutting
blade making light work and a nice smooth cut on this prepreg sheet. So, looking at the cut edge on this one now
you can clearly see that’s done quite a nice job, there’s really very little finishing.
We’ve cut a little bit wide of the mark, like we said we would, and we can rub that back
later using a block. Moving on now to the next tool; we’re using
a Dremel. Now, this is a Fortiflex Dremel so it has the motor remoted and then a flexible
shaft making it very easy and lightweight to handle. And, we’ve got a Perma-Grit tungsten
carbide abrasive wheel in the Dremel and this is probably the most professional way to trim
carbon fibre parts. If you’re doing it regularly, like on our manufacturing side, then this
is the way that we’d be trimming all manner of complicated shapes and as you can see the
Perma-Grit wheel makes extremely light work of this rigid prepreg sheet and we’ve just
cut wide of the mark again so that we ca tidy up these edges afterwards. To be honest, you
can probably go closer than that with the Dremel and a good level of accuracy. So, sticking with the solid 2mm prepreg sheet
we’re going to demonstrate a way that you can use a hand tool to take out this middle
detail instead of the Dremel that we’ve just shown you. First of all we need to drill a hole through
the sheet so that we can get a rodsaw through into that centre detail section so we’re using
a perfectly normal rechargeable drill here and the drill bit again is a perfectly normal
metalworking drill bit. We’re going to leave this and show you all
the way through the drilling process. It does take a bit of time but this does demonstrate
that a normal drill bit will drill through prepreg sheet like this without too much difficulty.
We’d probably choose to use a pedestal drill to make slightly lighter work of this but
normal hand tools like this will do the job. That’s just going to leave us with a slight
amount of burring around the hole. If we take a look at the other side as well again just
a bit of burring. If we were trying to drill really neat holes rather than just opening
up a hole for the tool then we’d file that back to tidy up the edges. Opening up the rodsaw now so that we can thread
it through the hole that we’ve just created and allow us to cut out this centre section
and just latch that back into this. Now these Perma-Grit rodsaw files are fantastic
for quite detailed shapes; getting inside of cuts like this. They do make reasonably
slow progress; you’ve got quite a few mm of cut and that obviously slows things down but
you will get there in the end so they are a useful tool to have in your collection for
detail like this; if you’re cutting switches out of a panel. You can obviously get in and
tidy up all of these edges. The nature of the rodsaw means that we’ve
got a wobbly edge, particularly one’s a bit smoother than the other, depending on how
difficult it was to get a position on the sheet whilst we were cutting it. This edge
has got a bit of wobble on but we’re going to take that off later using a file and smooth-up
that edge. So, in marked contrast now to the hand cutting
that we’ve just been doing with the rodsaw, we’ll get on a good quality mask and safety
goggles for this one because we’re demonstrating using and angle grinder with a slitting disc
in to cut this solid 2mm prepreg carbon fibre sheet. Now, an angle grinder like this will make
extremely light work of even the thickest solid carbon fibre laminate. It really needs
to be straight lines you’re cutting; it’s not much use for detailed or curved surfaces
so trimming complicated parts is out but for straight-cuts like this, this really is a
fantastic tool. You need to excercise care because it’s a powerful tool but it does cut
very quickly and leaves you with a very smooth edge with no burring at all. So for our next demonstration we’re going
to be using a foam cored carbon fibre panel. This is a single layer of carbon fibre either
side of a structural closed cell PVC foam. We’ve got a gelcoat on the panel as well which
makes things interesting in terms of chipping at the laminate. Now, because of the foam
core construction you can see that the drill makes much lighter work, as will the other
tools, but it does leave this chipping and fraying at the edges. We’re going to demonstrate
a range of different jogsaw blades in the jigsaw cutter, starting with the most appropriate
which is a Perma-Grit tungsten carbide gritted blade so it doesn’t have teeth instead it
has this tungsten carbide gritted surface, now that stops any chipping and fracturing
of the laminate and allows us even on this foam core panel, which as we say has got the
gelcoat which would be prone to chipping and delaminating; we can cut that very nicely. So, moving on to a metal-cutting blade; this
is slightly less appropriate but will still make a decent job of the cutting. Now, a metal-cutting
blade has got much finer teeth than a wood-cutting blade and that means that when we cut, although
there is a small amount of chipping that happens, it’s kept to a minimum and on a solid carbon
fibre laminate you’d probably see very little chipping at all. So, moving on finally to the third type of
blade. This is a wood-cutting blade and not one that we would recommend although we will
demonstrate it and if you wanted to you can still cut carbon fibre laminate with a wood-cutting
blade although it will fracture and chip at the laminate significantly more and certainly
on this foam core panel where we’ve got the gelcoat that’s going to cause problems. Looking
closely at it now you can see this size of the chips that are being taken out of the
laminate. It makes quick progress but it’s really not the ideal cutting blade at all
and you can see the fractures making quite a jagged edge. If we compare the inside cut on this piece
which was done with the Perma-Grit blade then we’ve got the outside edge on this one was
cut with the metal-cutting blade; there’s just some small fracturing there, and then
finally if we look at this edge which was cut with the wood-cutting blade you can see
a lot of chipping and a lot of fracturing down that edge. We’ve demonstrated there using a jigsaw to
make straight cuts but of course one of the main advantages so using a jigsaw is the fact
that it can make a very nice job of curved, detailed sections like this and so there’s
certainly a place for using a jigsaw particularly with the right blade in, like a Perma-Grit,
and it will leave you with a nice edge on a cut laminate like this. Earlier we demonstrated how effective a Dremel
with a tungsten carbide wheel could be when cutting solid carbon fibre sheet laminate,
well, it’s even more effective when you’re cutting contoured shapes like this actual
carbon fibre part where you’ve got a detailed edge to trim to and quite a 3D shape to the
part. We’ll demonstrate now typically how close we would cut when trimming a part like
this. With a steady hand and using the thumb as a guide on the part itself we can be within
a fraction of a mm of the finished trim-line and that of course leaves us with much less
finishing and fettling to do on the parts. A Dremel like this making very light work
of the slot that needs cutting at the top of this vent and if you look at the finished
that we’ve got there’s really very little fettling to do afterwards, just a fraction
of a mm to take off this part. Next we’ll demonstrate cutting some pultruded
carbon fibre tube. Now, because of the fibre orientation running length-ways down the tube
this does pose some interesting problems when cutting. We’ll just demonstrate using the
angle grinder with the slitting disc on this pultruded tube. We’ll make a fairly careful
cut through, you’ll see that because all of the fibres are running length-ways down the
tube they’re very much prone to fracturing. One solution to this is to rotate the tube
so that the slitting disc is always cutting down, down through the material, rather than
potentially splintering off at the bottom. If we take a look at that cut, compared to
the one earlier you can see that’s much smoother and cleaner. Following the same principle using hand tools,
if we just mark up this tube. Using a hacksaw what we do is cut a small incision all the
way around breaking the fibres at the outide of the tube, keep rotating with the hacksaw,
once we’ve gone all the way around we drop down gently with the blade. By cutting in
this way when we pull off the masking tape you can see that we’ve got a perfect finish
and we’ve eliminated any danger of splintering or fracturing the pultruded tube. Another example of where we might want to
use this technique is cutting down this carbon fibre seat-post. A bike seat-post like this
will make use predominantly of unidirectional material so we want to be careful again of
fracturing in the same way that we were with the pultruded tube so we’re going to make
an incision – a light incision – all the way around the outside of the tube where we’ve
marked it off with the masking tape. Being careful to cut through all of the fibres,
all of the reinforcement on the outside of the tube – just a very shallow cut, and then
when we’ve done that we’re going to cut down through the material – through the tube itself.
Again we’re using a metal-cutting blade in a hacksaw, just cutting it by hand, as you
can see with no special tools, no special equipment, just following this good practice
we can make a very nice job of cutting through. So just being careful to cut off that material
that’s holding it at the top and as you can see, the cut edge is very nice and smooth
with no fracturing at all. Now that we’ve got the first cutting operation
done on these various samples of carbon fibre material it’s time to finish the edges by
rubbing them back with an abrasive block so that we can get the final contours. In the
case of the parts like where we were using the jigsaw with the wood-cutting blade, where
it’s chipped and fractured at the laminate, we’ve got a reasonable amount of rubbing back
to do on those edges. Now, we can do that using either something like a Perma-Grit block
or another form of sanding block or we can just make a sanding block by just wrapping
some abrasive paper around a piece of foam or wood. Sanding these cut edges is going
to be another dust generating operation so on with the respirator or dust mask. Starting
off now using a Perma-Grit block this would be our favoured way of finishing edges. The
block has two sides; a course side and a fine side, so we’ll start off using the course
side of the block and very quickly even on this solid 2mm prepreg sheet then flick the
block over and use the fine side just to finish that edge and leave that really quite nice
and smooth. We’ve just rubbed back both of those edges on this part that were cut using
the hacksaw and in no time at all they’re as they should be. So we’ll look next at the foam core panel
that we cut using the various different jigsaw blades where we’d got quite a lot of chipping.
Using a Perma-Grit block again starting with the coarse side and then turning the block
over and using the fine side makes incredibly light work of finishing an edge like this
even when we had quite a bit of chipping. Now of course if you don’t have a Perma-Grit
block don’t worry – you can make a perfectly good sanding block by wrapping a piece of
abrasive paper – in this case we’re using a piece of 120 grit – around a piece of foam
or wood and that will leave the carbon fibre sheet with a nice smooth finish as well. Sticking now with the 2mm prepreg sheet but
returning now to take a look at the detailed section on this inside of this part that we’re
making, something like a Perma-Grit square file like this is absolutely fantastic for
getting into these detailed areas particularly into corners and things but there’s also a
range of alternatives including flat files such as this or traditional files designed
for metalworking would also be appropriate but would cut a lot slower than a Perma-Grit
file. So you can see that a Perma-Grit sanding block on contoured edges like this trimmed
part makes very quick work of radiusing these edges and then with the flat edges and corner
radiuses out of the way we just go round the whole perimeter of the part using some rolled
up 120 grit wet and dry paper. For this area where we’ve got the slot we’re going to use
a flat file again like we used earlier – this will allow us to keep the edge flat rather
than introduce any wobble while we rub it back and then just using the square file up
in the corner allows us to get to that difficult hard-to-reach section. Then, finally, again
just using some wet and dry like we’ve used earlier allows us to put a very final finish
to this seatpost that we cut back earlier. The 120 grit paper that we’ve been using to
finish all of these edges had left them all with a really nice smooth finish. If you do
need an even finer finish, for example if you want to polish the edges up to a gloss
then you can do so by using a 240 and a 400 finer grit papers. The final consideration for our cut carbon
fibre parts is whether or not we need any protection for the cut edges. 9 times out
of 10 we would leave an edge exactly as it is and for most applications that would be
perfectly fine, however for harsh environments such as a marine environment then we might
want to protect the edges against water ingress. One way to this would be to lacquer the finished
parts in which case the lacquer will coat the edges and seal them but as an alternative
you may wish to use some epoxy resin around the edge to seal the cut edge. We’ve mixed up just a tiny batch of epoxy
because there really isn’t much that’s going to be required. You could use just about any
two part epoxy laminating resin for this edge sealing but particularly any resins described
as epoxy coating resins would be very suitable because they’ll always cure with a nice clean,
hard finish. Just using a lint-free wipe to wipe it carefully around the edge of this
part leaving it with a glossy, smooth, sealed edge. I hope you’ve enjoyed this Easy Composites
guide to cutting and finishing carbon fibre sheet and carbon fibre parts. The important
things to remember are that with some basic safety precautions cutting carbon fibre can
be perfectly safe and that secondly you don’t really need any really need any particularly
specialist tools or equipment in order to achieve a good finish. Some of the equipment
that you have seen, like the Perma-Grit tools, are available on our website and we also have
an excellent range of carbon fibre sheet, angle and section so if you do fancy having
a go at your own carbon fibre project do check us out.