Carbon Fibre Laminations

[GrahameA]

Morning All

On two occasions I have read that Carbon Fibre laminations must have Glass Fibre laminations over them when building limbs.

Now this may sound stupid but, "Why"?

The lam is already a mixture of Epoxy and Carbon fibre unless there are issues with damage or failure it does not make sense to me.

[kimall]

Mate the stuff I have seen used on the bows is a matting type so would not be very wear resistant and would fray quickly I would think.I have seen other carbon fibre used not in archery but in motorbike mufflers and it was similar to fiber glass in that it seemed to be sort of encased in epoxy.It might be worth a email to one of the custom bowyers using it as I would also be interested to find out.
Cheers KIM

[longbow steve]

Hi Grahame, as Kimall said some of the product used is the woven matting which needs to be covered with glass but a reduced thickness of glass. The other product is like what Gilnockie is manufacturing and whilst it imparts amazzing speed due to reduction of material I have read it can be somewhat delicate, temperature affected and draw length sensitive.
Both carbon types are available from John Clarke. Steve

[Graeme K]

Hi Grahame

The main reason is that the carbon, especially unidirectional, is notch sensitive when highly loaded so small bumps and dings end up causing catastrophic failures. The glass is a protector but at the cost of performance.

GKL

[GrahameA]

Thank you Graeme. That clarifies the situation.

Hmmmm..... Should I grind down a 0.030 lam????? Will have to think about all of this.

[Graeme K]

Less glass the better -- 10 thou of glass seems to be about the norm.

GKL

[gilnockie]

I have used nothing but carbon on the back and belly of my bows for about five years.

I do not put a layer of glass over the carbon as it is not needed.

Most of the myths about about using carbon fibre on the back and belly of a bow are, I suspect, based on the vulnerability of a carbon fibre fly rod which has sustained a nick which causes the rod to fail under stress.

Carbon fibre laminates glued to a substrate, ie a timber or bamboo core, are as durable as glass laminates.

If you go to the leatherwall and do a search for carbon you will find numerous threads where questions about the durability and performance of carbon vs glass are debated. Many people doubt the benefits of carbon over glass. As far as I can remember I have not seen a posting by anyone who has shot a carbon composite bow who had anything but praise for them.

If you are looking for some evidence that carbon is superior to glass, look at FITA target recurves. None of the high end bows, and most of the lower level bows, use carbon on the back and the belly. Hoyt applies a thin layer of glass over the carbon, but it is white. I believe, but I have no evidence to support this belief, that the white glass is used to prevent the limbs from heating up in full sun.

So why do people express negative opinions, when they have no direct evidence to support them?

I honestly don't know.

Why do so few bowyers use carbon lams when the evidence is overwhelming that it will out perform glass?

My guess is that there are two reasons. First, carbon is not transparent, it is black. This means that a carbon back/belly bow will not show off the lovely exotic timbers which many American bowyers use. Second, I suspect that many bowyers have a set of patterns which they use to make a bow of a given draw weight and they do not know how to caclulate the dimensions of a bow of a given draw weight. Therefore they are unable to build a double carbon bow of a given draw weight without doing a lot of development work.

So what are the benefits of carbon lams on the back and the belly?

Carbon is stronger, lighter and stiffer than glass which means that you can make a limb which is thinner and therfore lighter than a double glass limb of the same draw weight.

A thinner limb of given draw weight, with stiffer material on the back and belly than glass, will recover faster than an equivalent double glass limb.

Because the carbon is stiffer and lighter than glass, in combination with a thinner and lighter limb, hand shock is reduced.

Because the limb is thinner, it bends (or draws) more smoothly, than a double glass limb of the same draw weight.

I believe that the only disadvantage of a double carbon bow is that it is black. Therefore it is the same colour as most other double carbon bows, unless you paint the limbs, which I have done.

There is one other potential problem with a black bow in a hot climate, be it carbon or glass. A black bow will absorb more heat than a white bow, or a bow with a light coloured wood or bamboo under clear glass.

This does not mean that a black bow will fail if used in a hot climate. Simply moving around will generate enough air flow around the bow to keep it cool. And any laminated bow will fail if left strung in full sun and still air for more than a few minutes. So susceptibility of carbon to failure because of heat is probably no worse than any dark coloured bow.

So much of what we are told about using carbon in bows is just plain wrong. I believe that the one disadvantage of carbon is outweighed by the advantages.

[GrahameA]

Hi Norman

I have no doubt of the superiority of Carbon (or Boron) over Glass strands.

My only question was why at least two supplier specified glass over the Carbon - it did not make sense to unless there was something I was not aware of.

Based on my limited knowledge at this time I would probably go for a very thin layer of glass over the Carbon - put it down to paranoia regarding things that fail. I have 3 set of limbs that are Carbon laminate construction, Nishizawa, Marksman and Samick. Each appears to have a glass layer over the Carbon - thus my reticence to go without such at this stage.

There is one other potential problem with a black bow in a hot climate, be it carbon or glass. A black bow will absorb more heat than a white bow, or a bow with a light coloured wood or bamboo under clear glass.

I would argue against that. My experience is that white bows will absorb just as much "Heat" and will rise to a similar temperature - it just takes a little longer. Both materials are finished with a Gloss finish and the reflectivity is very similar. When shooting in the sun for long periods the colour of the limb is not an issue.

(I have been in the situation whereby the temp was hot enough for a glass/timber longbow and an all wood longer both showed noticeable drops in their poundage due to their temperature and we where both putting our bows into the shade after every end. It was such an issue that I seriously considered building an insulated box to keep the bow in between ends which would have some ice in it to keep the bows cool. However, I have not shot in similar conditions since - but I do have the foam to build it. )

p.s.

Most of the myths about about using carbon fibre on the back and belly of a bow are, I suspect, based on the vulnerability of a carbon fibre fly rod which has sustained a nick which causes the rod to fail under stress.

I have several Carbon (High Modulus Graphite) Fly Rods Some of which are quite old. I have never had any HMG or HMG/Boron Rod fail in use. And they have been used hard in Tropical climates.

[gilnockie]

On two occasions I have read that Carbon Fibre laminations must have Glass Fibre laminations over them when building limbs.

Now this may sound stupid but, "Why"?

I suggest that you go back to your sources and make sure that they said "must have glass fibre laminations over them". There are many double carbon bows which do not have glass over the carbon. Check out O L Adcock's ACX longbows and Black Swan, among others.

I believe that the premise is incorrect, based on my experience and that of other bowyers.

Based on my limited knowledge at this time I would probably go for a very thin layer of glass over the Carbon - put it down to paranoia regarding things that fail. I have 3 set of limbs that are Carbon laminate construction, Nishizawa, Marksman and Samick. Each appears to have a glass layer over the Carbon - thus my reticence to go without such at this stage.

The next question is: why place glass over carbon? I can only surmise that it is to retard the absorption of heat and for aesthetic reasons. You believe that a white finish is not significant in retarding heat absorbed by bows. I built a double carbon longbow for competition for myself, and I gave it a white finish to retard heat absorption. My experience is that it worked. I belong to a target archey club and I do not recall seeing a modern target bow which does not have white limbs. What colour are your limbs? Are they a dark colour?

If you do not think that a white surface retards heat absorption, I guess we will just have to agree to disagree on that point.

I have several Carbon (High Modulus Graphite) Fly Rods Some of which are quite old. I have never had any HMG or HMG/Boron Rod fail in use. And they have been used hard in Tropical climates.

I too have several carbon fibre fly rods, and they have not failed in normal use. The issue is not the likelihood of failure in normal use, it is the vulnerability of a carbon fly rod which is damaged. A carbon fibre tube is vulnerable to nicks and scratches. Gold Tip used to place a warning on each arrow not to use it if it was damaged, yet the same warning is not placed on alloy arrows. I am suggesting that this vulnerability has given rise to the myth that a flat carbon fibre lam used in making a bow is vulnerable to damage if chipped or nicked.

In conclusion, you asked a question and I provided an answer. If you do not agree with the answer I provided and my reasoning, then so be it.

[GrahameA]

Hi Norman

I suggest that you go back to your sources and make sure that they said "must have glass fibre laminations over them".

Quote from book:

"It should be noted that ALL carbon laminations MUST be laminated with fibreglass backings and facings."
page 8 - I will send you a pm concerning the Author.

My experience is that it worked. I belong to a target archey club and I do not recall seeing a modern target bow which does not have white limbs. What colour are your limbs? Are they a dark colour?

As do I. Two white, one Gunmetal Grey

A selection of Limbs that are not white (dark coloured):
Hoyt 900CX black on side white on the other.
Hoyt G3
WinEX - Very Dark Grey
KG X-TEch
Sebastian Flute - SHC

[Mike-dy]

"It should be noted that ALL carbon laminations MUST be laminated with fibreglass backings and facings."
page 8 - I will send you a pm concerning the Author.

Post the names of the books and authors up here Grahame, the more info I can find on building lam bows the better.
There's plenty out there on selfbows.
Anyone recommend some books on Lamintated bow building?
Thanks,
Mike

[gilnockie]

Hi Graham

So according to your source my bows, OL Adcocock's and Arvid's from Black Swan should not be functioning at all.

It seems to me your source is mistaken.

[longbow steve]

Hi Mike, I found the Traditional bowyers encyclopedia offers up patchy pearls of wisdom.
Jack Harrison? has a book that I have flicked through that has some good info.
Pirates of Archery forum offers free, real world info . Steve

[alaninoz]

Is there any confusion here between a glass lamination and the resin matrix the carbon is embedded in? No idea myself, just asking. I happen to like the look on the wood (bamboo in my case) under the clear glass.

[GrahameA]

Good Evening Norman

At no point have I suggested that bows without the glass lams would not work. The question was why the need for the Glass to which I got a reply from Graeme K which seemed reasonable and was a person who has credibility with me.

The initial piece that perked my interest regarding the need for Glass Lams with Carbon laminations came from the Bingham Catalogue.

This is from Catalog 34, page 2 under Carbon Unidirectional Glass.
“Recommended for laminated Limbs with Bo-Tuff E Glass being used as skin glass”.

Now given Binghams have been around for 50 years producing materials for composite bows and are the largest supplier of bow making supplies in the world it would be reasonable to assume they know what they are doing and it would seem reasonable that there must be a reason for recommending E Glass skins.

The second time around was in John Clark’s Book on Longbows and the third time in his book on Recurves. In both case the word MUST was used

e.g.
"It should be noted that ALL carbon laminations MUST be laminated with fibreglass backings and facings."

page 8

Design and Construction of Composite Recurve Bows.
An Australian Perspective.
2nd Edition, 2002
J.Clark
ISBN 0731645456

John Clark is a long time well known Bowyer, the Author and Publisher of several books with regard to making Composite bows and arguably the largest supplier of materials for composite bows in Australia and that is a reasonable reason to take some note of what he says as far as I am concerned.

[Mububban]

Hmm, if the "must use glass" comment came from a retailer I'd suggest it was a liability/warranty thing for them. To reduce the number of careless owners bashing their bows around and then demanding a warranty replacement because the carbon "failed."

Coming from a bowmaking handbook.....it could still be for a similar reason. I'm sure a seasoned bowyer with years of experience could do things that you would never show a raw novice bowmaker, as without those years of experience and feel for the materials and processes, our bows would just fail.

My usual philosophy with teaching and learning is to teach the basics really well, and follow the rules. Then once you understand the rules and why they exist, you can experiment with breaking them gently and hopefully safely. But if you'd charged in straight up, spectacular failure could be the result. As well as a hospital visit depending on what you're trying to do

Just my thoughts.

[gilnockie]

I have no idea why Binghams and John Clarke recommend the use of glass over a carbon laminate. I could surmise that in both cases they want to avoid a public liability claim and therefore they favour a belt and braces approach. Therefore they recommend that glass is applied over carbon to prevent it from failing.

At the risk of repeating a remark I made earlier, there is a body of evidence that it is not necessary to apply a layer of glass over a carbon laminate.

If that evidence is insufficient and you want the theory behind the benefits of carbon vs glass, I suggest that you go to this link:

http://www.gurit.com/core/core_picker/d ... .asp?id=64

In particular, go to page 4 where you will find a series of graphs which clearly illustrate the properties of E-glass, S-glass and carbon fibre, among other materials. There is also a lot of interesting material on composites in general.

If your position is based on authority and experience in the relevant field, I will rely on Gurit, who own SP Systems. Here is their home page:

http://www.gurit.com/

So, I guess the issue is: why would anyone recommend that you cover a layer of carbon fibre with a material which is not as strong, not as stiff and heavier?

[GrahameA]

Norman

So, I guess the issue is: why would anyone recommend that you cover a layer of carbon fibre with a material which is not as strong, not as stiff and heavier?

Go back to the first post on this topic.

[gilnockie]

Now go back and read my first post where I wrote that it is not necessary to put glass over carbon laminates on the back and belly of a bow.