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?

in message <[email hidden]>, Alan Braggins

(') said:

Simon Brooke said:

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

Quoted message said:

Jon Senior <jon_AT_restlesslemon_DOTco_DOT_uk> wrote:
> 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?

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.

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.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; IE 3 is dead, but Netscape 4 still shambles about the earth,
;; wreaking a horrific vengeance upon the living
;; anonymous

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
http://www.cfsnet.co.uk/acatalog/CFS_Catalogue__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

http://www.cfsnet.co.uk/acatalog/CFS_Catalogue__FIBREGLASS_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) http://www.jasmine.org.uk/~simon/

;; 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) http://www.jasmine.org.uk/~simon/
;; 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