Going Dutch

Simon Brooke said:

in message <[email hidden]>, Ian G Batten

Quoted message said:

Jon Senior jon_AT_restlesslemon_DOTco_DOT_uk said:

Seen it in the flesh. Looks quite nice, though there's
an awful lot of CF for a city bike. What with there only
being two in the world

I don't think there's any intrinsic reason why carbon-
fibre, using pre-preg, should be any more labour
intensive to work with than fibre-glass, and given
volumes the capital requirement (autoclaves and such
like) would be amortised.

You don't _need_ autoclaves for carbon fibre. You can vacuum-
bag it perfectly effectively with perfectly ordinary
polythene sheeting and a domestic vacuum cleaner.

Building kayaks from glass, you don't even need that, just
roller the resin into it. Volume production considerations
will be different, but could a carbon fibre one off piece be
done the same way, or is vacumm bagging the minimum amount
of equipment needed?

Simon Brooke said:

Alan Braggins(') said:

Building kayaks from glass, you don't even need that,
just roller the resin into it. Volume production
considerations will be different, but could a carbon
fibre one off piece be done the same way, or is vacumm
bagging the minimum amount of equipment needed?

Going a little beyond my knowledge here, but to get the
best strength/weight ratio with carbon fibre you need to
squeeze as much resin (and, obv, air) as possible out of
the composite as it cures. If you don't do this you will
get a composite with too high a ratio of resin to fibre for
optimum strength, and it'll be heavier as well and may have
air voids.

My scout troop's old kayaks were about three times the
weight of the ones we built, and had air voids visible in
places when chipped (which the newer ones didn't - one
advantage of translucent gelcoat was you could see they
didn't - they didn't chip the same way either). But that was
just resin rolled well in vs. resin slapped on thickly.

Quoted message said:

So you _can_ do CF without vacuum bagging but you don't get
the benefits in terms of strength and weight unless you do.
GRP benefits from vacuum bagging too. Vacuum bagging isn't
at all difficult and is now a very standard technique in
custom boat building.

Thanks. That's roughly what I expected, but it's good to
hear from someone with some experience. (I like the look of
your "biplane" catamaran design, by the way.)

Simon Brooke [email hidden] opined the following...

Quoted message said:

You're not comparing like with like. Chopped Strand Mat
has virtually no structural strength because all the
fibres are short and by definition they aren't aligned
with the direction of maximum stress. Even woven glass
cloth is not in the same league as CF because the tight
radius of the fibre in the weave greatly reduces its
strength (although woven cloth is good for abrasion
resistance). It's only when you get into unidirectional
glass that you start to get a material with serious
strength properties, and the difference in price between
unidirectional glass and CF cloth is not that great.

Please visit cfsnet.co.ukCFS CataloguOpen ↗
e__FIBREGLASS_MAT___FABRICS _10.html and tell me which of
the FG products corresponds to what you are describing, or
quote prices for the CF supplier you have considered. I
can't find anything remotely like the similarity in price
that you claim.

Jon

Simon Brooke [email hidden] opined the following...

Quoted message said:

Going a little beyond my knowledge here, but to get the
best strength/weight ratio with carbon fibre you need to
squeeze as much resin (and, obv, air) as possible out of
the composite as it cures. If you don't do this you will
get a composite with too high a ratio of resin to fibre
for optimum strength, and it'll be heavier as well and may
have air voids.

If you use a good core foam, you can achieve this by
_carefully_ wrapping the CF with PVC tape (Sticky side out)
which has been perforated before hand. The resin will
squeeze out through the holes in the tape.

Jon

in message <[email hidden]>, Jon Senior

jon_AT_restlesslemon_DOTco_DOT_uk ('') said:

Simon Brooke [email hidden] opined the following...

Quoted message said:

You're not comparing like with like. Chopped Strand Mat
has virtually no structural strength because all the
fibres are short and by definition they aren't aligned
with the direction of maximum stress. Even woven glass
cloth is not in the same league as CF because the tight
radius of the fibre in the weave greatly reduces its
strength (although woven cloth is good for abrasion
resistance). It's only when you get into unidirectional
glass that you start to get a material with serious
strength properties, and the difference in price between
unidirectional glass and CF cloth is not that great.

Please visit

cfsnet.co.ukCFS Catalogue FIBREGLASSOpen ↗
MAT___FABRICS

Quoted message said:

_10.html and tell me which of the FG products corresponds
to what you are describing, or quote prices for the CF
supplier you have considered. I can't find anything
remotely like the similarity in price that you claim.

It's hard to find the prices for this sort of stuff online
quickly, but
e.g. UK Epoxy are selling biaxial glass fabric at UKP67.90
for ten metres at 1.20 metres wide or just under
UKP6.00/m^2, 450gm/m^2. I haven't found in a quick
search anyone selling either unidirectional or triaxial
fabric in the UK. <URL:http://www.epoxy-
resins.co.uk/Shop/glasstape.html>

To compare, CFS are selling carbon fibre cloth in ten metre
lengths at UKP14.65/m^2, 200g/m^2 <URL:http://www.cfsnet.co-
.uk/acatalog/CFS_Catalogue__Carbon_Fibre_Fabric_35.html>

So the carbon is a bit more than twice the price but as
you'll use less epoxy to wet it out it works out in the end
about twice as expensive.

Obviously this is not a direct comparison because I haven't
been through the tech specs and looked at the strength
properties of these two examples (and I'm not really expert
enough to anyway) but it's indicative. Carbon fibre is
expensive, but it's not scarily expensive exotic material.

--
[email hidden] (Simon Brooke)
jasmine.org.uk~simonOpen ↗

;; single speed mountain bikes: for people who cycle
on flat mountains.

Simon Brooke [email hidden] opined the following...

Quoted message said:

It's hard to find the prices for this sort of stuff online
quickly, but
e.g. UK Epoxy are selling biaxial glass fabric at UKP67.90
for ten metres at 1.20 metres wide or just under
UKP6.00/m^2, 450gm/m^2. I haven't found in a quick
search anyone selling either unidirectional or
triaxial fabric in the UK. <URL:http://www.epoxy-
resins.co.uk/Shop/glasstape.html>
=20
To compare, CFS are selling carbon fibre cloth in ten
metre lengths at=20 UKP14.65/m^2, 200g/m^2 <URL:http:/-
/www.cfsnet.co.uk/acatalog/CFS_Catalogue__Carbon_Fibre-
_Fabric_=

35.html>

Quoted message said:

=20
So the carbon is a bit more than twice the price but as
you'll use less epoxy to wet it out it works out in the
end about twice as expensive.
=20
Obviously this is not a direct comparison because I
haven't been through the tech specs and looked at the
strength properties of these two examples (and I'm not
really expert enough to anyway) but it's indicative.
Carbon fibre is expensive, but it's not scarily expensive
exotic material.

Shame. I was hoping that you'd have a cheap source of CF
rather than an=20 example of expensive GF. ;-)

When I can justify the costs I will have to get some CF to
play with,=20 but I suspect I'd need to look at throwing
about =A3100 to get enough to=20 do anything useful with.
Maybe if I can't get some steel tube of the=20 right OD to
make an extending boom, I'll take a look at it!

Jon

in message <[email hidden]>, Jon Senior

jon_AT_restlesslemon_DOTco_DOT_uk ('') said:

Simon Brooke [email hidden] opined the following...

Quoted message said:

It's hard to find the prices for this sort of stuff
online quickly, but e.g. UK Epoxy are selling biaxial
glass fabric at UKP67.90 for ten metres at 1.20 metres
wide or just under UKP6.00/m^2, 450gm/m^2. I haven't
found in a quick search anyone selling either
unidirectional or triaxial fabric in the UK. <URL:http://www.epoxy-
resins.co.uk/Shop/glasstape.html>

To compare, CFS are selling carbon fibre cloth in ten
metre lengths at UKP14.65/m^2, 200g/m^2

<URL:http://www.cfsnet.co.uk/acatalog/CFS_Catalogue__Carbon-
_Fibre_Fabric_35.html>

Quoted message said:

Quoted message said:

So the carbon is a bit more than twice the price but as
you'll use less epoxy to wet it out it works out in the
end about twice as expensive.

Shame. I was hoping that you'd have a cheap source of CF
rather than an example of expensive GF. ;-)

Yebbut, if you're considering carbon at all it's not to
replace rubbish GRP, it's because you're pushing the
strength/weight limits of less expensive composites. So it
only makes sense to compare carbon against the top
engineering glass or aramid fabrics... unless you only want
carbon for pose value, of course.

--
[email hidden] (Simon Brooke)
jasmine.org.uk~simonOpen ↗ ;; Generally Not Used ;;
Except by Middle Aged Computer Scientists

Simon Brooke said:

Yebbut, if you're considering carbon at all it's not to
replace rubbish GRP, it's because you're pushing the
strength/weight limits of less expensive composites. So it
only makes sense to compare carbon against the top
engineering glass or aramid fabrics... unless you only want
carbon for pose value, of course.

And if you do only want it for pose value, you can
probably buy carbon fibre patterned stickyback plastic in
the sort of place that sells big chrome exhaust trims and
windscreen washers with blue LEDs. And I suddenly feel
tempted to decorate a bike frame with some, but I shall
probably resist.

Simon Brooke [email hidden] opined the following...

Quoted message said:

Yebbut, if you're considering carbon at all it's not to
replace rubbish GRP, it's because you're pushing the
strength/weight limits of less expensive composites. So it
only makes sense to compare carbon against the top
engineering glass or aramid fabrics... unless you only
want carbon for pose value, of course.

I know... Having taken another look at it, I was considering
CF as a possible material choice for the swing-arm of Senior
Recumbent Version
2. It would go some way towards compensating for the initial
choice of shock (Astonishingly heavy steel sprung
thing!). I may stick to steel for the time being but the
option definately remains.

Jon