Who said you cant use fibreglass sheet?...

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hunterguy1991
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Who said you cant use fibreglass sheet?...

#1 Post by hunterguy1991 » Fri Jun 27, 2014 7:15 pm

Hey all,

Interesting little clip for you all to critique. While doing a little research on youtube for a steam bent bow I'm currently working on I cam across this... It is a takedown recurve with limbs made of steam bent red oak and fibre glass sheet. He goes over he method of constructing the limbs (albeit a little questionable) and then shows a shooting of the finished bow.

Now while some parts of this are painful for me to watch (and I'm sure will be for you also) as an archery and armature bowyer, I find the materials used interesting, especially since I have been steered away from them in the past by members, most notably the fibre glass sheet.

I feel that if a proper construction technique be devised and a little more care taken in the construction a really good thing could result. The bow seems to be a fairly fast shooter going from the video and at his advertised 35lb...

https://www.youtube.com/watch?v=xfH9LY9Fjwo

Something for you to ponder at least... I myself am seriously considering a trying a bow using the sheet both back and belly.

Straight shooting,

Colin

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Re: Who said you cant use fibreglass sheet?...

#2 Post by greybeard » Sat Jun 28, 2014 1:34 pm

“Who said you can’t use fibreglass sheet?...”

Colin, I do not know of anyone who has made that statement.

Perhaps the question should be; why commercial bowyers and bowyers in general do not use woven fibreglass cloth.

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

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Re: Who said you cant use fibreglass sheet?...

#3 Post by hunterguy1991 » Sat Jun 28, 2014 2:13 pm

Daryl,

Perhaps I should have chosen my words more carefully... but on several occasions I have been told not to bother with the fibreglass cloth as a backing, for various different reasons, most commonly, it will over power the timber.

This is in fact not the case as his bow shoots just fine, better than fine in my opinion.

Now I also think that a decent finish could be attained with the cloth if more care was taken in its application. The use would allow more novice bowyers, such as myself, to create heavier draw bows without the need for costly power tools (band saws, linishers etc) that will run well over 1000 dollars to purchase and set up.

Just my 2 cents on the subject anyway.

Colin

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Re: Who said you cant use fibreglass sheet?...

#4 Post by GrahameA » Sat Jun 28, 2014 3:19 pm

Afternoon All
greybeard wrote:“Who said you can’t use fibreglass sheet?...”

Colin, I do not know of anyone who has made that statement.

Perhaps the question should be; why commercial bowyers and bowyers in general do not use woven fibreglass cloth.

Daryl.
I would concur.

Looking at the Video the chap is using Fibreglass Tape not strip that he purchased off the internet as a backing material.

If people want to use "Fibreglass Tape" as a backing - "go for it". People have been using other materials as a backing for a few years. e.g. "Dry Wall" tapes. There used to be a buildalong on manufacturing your own Carbon laminates years ago.

However don't expect to get consistent results unless you use techniques that give a level of consistency to the application. IMHO just buying a strip of manufactured material from whoever will give a more consistent result.

And choose an appropriate design for your bow so you do crush the core material / wood.

My $0:02 worth. Backing ELB style bows with Epoxy and Fibreglass tape from your local Boat Supplies shop can be fun ... and frightening when the bow lets go.
Grahame.
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Re: Who said you cant use fibreglass sheet?...

#5 Post by greybeard » Sat Jun 28, 2014 4:37 pm

hunterguy1991 wrote:This is in fact not the case as his bow shoots just fine, better than fine in my opinion.
How will it shoot after 10,000 arrows?
hunterguy1991 wrote:The use would allow more novice bowyers, such as myself, to create heavier draw bows without the need for costly power tools...
Of the heavy draw weight war bows found on the Mary Rose none were backed.

One test you could do is to coat a strip of the woven glass fibre with the epoxy and let if fully cure and then carry out bending tests. Do the same tests on Bo-tuff ULS fibreglass and note the difference.

Tom Jennings, Bowyer;
“Today's modern bow is made up of laminations of wood and fibreglass, the wood serving as a neutral core or spacer between two laminations of fibreglass.
Actually it is the fibreglass that does the work of the bow, carrying 88 percent of the load while the wood core carries only 12 percent. As you increase the spacing between the two fibreglass laminations by using a thicker core, you automatically increase the strength of the bow by the square.”


Colin build some bows with the woven glass fibre and post the results, I am sure there will be interested members.

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....

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Re: Who said you cant use fibreglass sheet?...

#6 Post by hunterguy1991 » Sat Jun 28, 2014 7:15 pm

GrahameA, the guy in the clip clearly states that he is using fibreglass "cloth" which is 85% unidirectional... this is not tape.

However, I do agree with you that the glass strips from Binghams etc work far better that what he is using since that is purely what they are designed for and will result in a much more consistent and probably stronger final design.

Daryl, as for your comment on lasting thousands of arrows, I would not expect a bow made from a 15 dollar board and backed with fibreglass cloth from a hardware store to last for 10 000 shots. That would be unrealistic I feel.

As for the Mary Rose bows, were they not backed?... As far as I'm concerned they in fact were backed, and they were backed by the best natural backing available, the high tensile strength, natural sap wood of the Yew tree!!

Piece of my civil engineering knowledge here, you may already know this but here goes... The natural growth of a tree promotes a natural tensile stress within the sapwood layer around the tree and a natural compression in the heartwood. Where the two meet is a natural "zero" stress, neutral plane. This is why when a tree trunk is split directly in two along its centre line it has a tendency for each side to bend away from the cut.

Colin

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Re: Who said you cant use fibreglass sheet?...

#7 Post by GrahameA » Sun Jun 29, 2014 12:01 pm

Morning.
hunterguy1991 wrote:GrahameA, the guy in the clip clearly states that he is using fibreglass "cloth" which is 85% unidirectional... this is not tape.

However, I do agree with you that the glass strips from Binghams etc work far better that what he is using since that is purely what they are designed for and will result in a much more consistent and probably stronger final design.
You missed the point.

You can buy fibreglass sheets (similar to Alsynite), cut them into strips and use them in bow making. What the chap is doing is backing his bow some tape and epoxy (or Polyester). Which is different.

As an example you can get a sheet of fibreglass, cut it into strips and layer them in a mould/press to make a bow which is different to backing with a strip or backing with some cloth/tape.

You can also purchase fibreglass structural/engineering shapes and use them for building bows. The next bow built from GRP/CRP sail battens will not be the first.

There is a whole of world of GRP bows that people can play with it they want to.

(I have this desire to play with building my Expoxy/Graphite Laminations.)
Grahame.
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Re: Who said you cant use fibreglass sheet?...

#8 Post by Dennis La Varenne » Sun Jun 29, 2014 10:13 pm

Hunterguy 1991,

I have a goodly number of the American NFAA magazines called 'ARCHERY' dating from 1945. In them, there is repeated reference to the use of woven fibreglass as backing and facing. It was all the rage at first because it was the only kind available and my guess is that it was made similarly to the woven and resin impregnated Fortisan which was developed during WWII and applied as backing for the most part. Later, it was found that the woven glass tended to break down due to the friction of the crossed woven fibres against one another resulting in the fibres being severed. This meant that the whole reason for using fibreglass began to fall apart because it was not reliable. It could not maintain it structural integrity with repeated bending. It was not until much later that a unidirectional fibreglass called Conolon and produced by Eichholz came into production that the problems encountered withwoven fibreglass began to be overcome.

Because the fibres ran only lengthways, the problem of the horizontal fibres cutting the lengthways fibres disappeared with no loss of performance and a considerable increase in durability and reliability. All this was worked out in the mid to late 1950s and references to the problems experienced in using woven glass recur in the questions to the technical editor in that magazine.

If I had the time, I could source the reference from those magazines where the problem is discussed, but you would need to have access to them yourself to verify those references, so you will have to take my word on the matter. It would mean perusing 50 to 60 of the earliest editions of ARCHERY to find them again unfortunately and then to scan them to post on this site for other's reference as well.

Gordons Plastics persisted with woven fibreglass until the late 1960s I think it was. It came with an adhesive paper backing over the gluing surface, but I do also know that Bear Archery made their own linear glass back in the 1950s and dispensed with woven glass for reasons that their catalogues from that time do not mention.

This YouTube fellow has not discovered something new. It has all been done decades before he was born. Remember the aphorism about those who do not learn from history . . . or are simply ignorant of it through no fault of their own.

By all means, have a go at this material and test it hard to see what happens for yourself. I can only pass on what I have read from magazines published when I was in primary school. My brother in law was a racing kayak and canoe maker who used the same material in his boats. It was fine for that purpose because the amount of flexion in the hulls was minimal compared to that in a bow.

Regards,
Dennis La Varénne

Have the courage to argue your beliefs with conviction, but the humility to accept that you may be wrong.

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Re: Who said you cant use fibreglass sheet?...

#9 Post by Nezwin » Sun Jul 27, 2014 1:46 pm

Colin,

My 2 cents...

I've worked with a lot of composites since I was a kid in my Da's workshop and have experimented with a few different techniques for backing bows. My first bows were backed precisely like the guy in the video - bidirectional cloth impregnated with poly or epoxy resin. He mistakenly refers to it as 'unidirectional' - it's not, it's bidirectional weave. He also says it's impossible to get out all the air bubbles - it's not, you need to use a roller.

The method he uses worked okay for backing lams, in that it stops splinters rising and creates a homogeneous layer on the most highly strained element of the beam/limb. However, it doesn't really perform a lot of structural work. The fibreglass itself is not strained enough to be considered well within its Young's curve, so the majority of the desirable properties of fibreglass are lost.

Compare this to a length of Gordons Bo-Tuff - Firstly, the Bo-Tuff is pre-stressed, allowing the fibreglass to really do a bit of work. Secondly, the Bo-Tuff is thicker, giving it s greater SMoA and more of the work done by the limb being performed my the glass/resin matrix. Thirdly - the Bo-Tuff is true unidirectional glass (there isn't even evidence of the minor cross weave used in commercial unidirectional cloth, suggesting to me they either remove this prior to lay up or have it supplied in single strands), negating the internal friction within the matrix that Dennis has rightly described.

As mentioned above, I have used this method before and it has worked well to seal off the back of the limb, but I am now experimenting with commercial unidirectional cloth prestressed in a form to make a lam, then ground to a desirable thickness with a drum sander (God bless the Men's Shed!). Results have been mixed but I'm getting there, time being the largest constraint at present. If you plan to go down the bidirectional weave route (and I encourage you to experiment and see what results you get) don't plan on getting the smooth finish you would have with Gordons - this requires the glass & resin to be cured in a smooth form. If you're laying up directly onto the limb the weave will reflect through the resin and it is quite unavoidable without significant efforts made (and it would be easier just to make the glass lam separately in that case!).

Hope it's of help in some way!

Neil

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Re: Who said you cant use fibreglass sheet?...

#10 Post by hunterguy1991 » Sun Jul 27, 2014 8:16 pm

Nezwin,

A few things,

First, no idea where you discovered that Bo-tuff is prestressed, I cant find any information anywhere that says it is, and I find it hard to believe anyway since if it was it would hold some shape... as it does not, I'm sceptical.

Second, why would you want something that is going to be put in tension under load tensioned before its loaded? That is just getting you closer to yield stress when the bow is loaded/drawn, which will result in set... not good. If anything, you would want the back of the bow put in compression initially to reduce the stress when drawn... Ie a prestressed Beam.

Third, Modulus of Elasticity, MoE has nothing to do with a materials thickness, it is a material property. The level of stress within a material varies with thickness, more thickness, more stress to achieve the same bend... ie, getting a heavier draw weight with the same timber, increase the thickness of the limb.

Having said that, I am curious to see some of your work with the glass and epoxy backed bows if possible... you said it was a while ago but are any of them still around today? if so could you post photos please?

Should I eventually get into laminated bows, (down the track I will) I will be using the Bo-tuff glass on back and belly for sure.

Cheers for your thoughts, hope to see a few of those bows you have made!!

Colin

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Re: Who said you cant use fibreglass sheet?...

#11 Post by rodlonq » Mon Jul 28, 2014 9:59 am

[quote="Nezwin"

As mentioned above, I have used this method before and it has worked well to seal off the back of the limb, but I am now experimenting with commercial unidirectional cloth prestressed in a form to make a lam, then ground to a desirable thickness with a drum sander (God bless the Men's Shed!).

Neil[/quote]

Neil,

It is commendable that you are having a go at making your own unidirectional bow glass. It would certainly be very satisfying to use your own backing/facing in a bow, which would more than offset the labour component of making it. I am interested to know how it is working out for you from a cost point of view. If you are going to the trouble to make a form for it you must be planning to make a reasonable quantity. How does it stack up against a bulk order from say Binghams, if you include the cost of abrasive belts for the drum sander as well. I assume you are attempting to make clear bow glass?

Cheers... Rod

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Re: Who said you cant use fibreglass sheet?...

#12 Post by rodlonq » Thu Jul 31, 2014 5:04 pm

Colin,

According to Gordon's brochure Botuff has "pretensioned" unidirectional fibres. I imagine this would result in the resin matrix being under compression surrounding the tensioned glass fibres in the cured product. Have a look at http://www.gordoncomposites.com/downloa ... loads.html in particular the GC-70-ULS.pdf.

I think the reason the fibres would be pretensioned is because it seems most resins are 2-3 times stronger in compression than tension (e.g. http://www.smooth-on.com/tb/files/EA40.pdf ). Therefore, pretensioned glass fibres would ensure the resin (initially in compression) does not suffer tensile failure. This is analogous to pretensioned reinforcing in concrete structures, due to concrete having massive compressive strength and very little tensile strength. If the steel in the lower part of a concrete beam were slack, the concrete would crack under tension before the steel took up the load.

Note the ULS glass has a woven inlay (scrim) to give it lateral strength. I believe this is why it seems most bowyers prefer it to the cheaper UL glass without scrim. I know I double check I have ULS before hitting the submit order button.

I think you may have misread Neil's reference to SMoA (second moment of area) to read MoE. I can't see where Neil mentioned MoE but the SMoA definitely has everything to do with material thickness.

I hope the above references are useful.

Cheers... Rod

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Re: Who said you cant use fibreglass sheet?...

#13 Post by hunterguy1991 » Thu Jul 31, 2014 8:00 pm

Its possible that your theory is correct about the glass fibres. Personally I feel it is more analogous to a insitu poured concrete beam. The only ore tensioning needed in the fibres is to hold them in the correct plane as the resin is poured.

As for the analogy to a prestressed concrete beam, again I suggest a insitu poured beam which can be designed with slack steel reinforcement yet takes load before the concrete cracks. There is no such quantity as second moment of area... What you are referring to is the second moment of inertia or a cross section's 'Ixx' or Iyy depending on the axis of bending. Yes I do agree that it does depend on thickness of the section greatly.

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Re: Who said you cant use fibreglass sheet?...

#14 Post by rodlonq » Fri Aug 01, 2014 9:15 am

hunterguy1991 wrote: There is no such quantity as second moment of area...
mmm.... yup, thats just a label for the same thing mate.... http://www.engineeringtoolbox.com/area- ... _1328.html

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Re: Who said you cant use fibreglass sheet?...

#15 Post by Nezwin » Sun Aug 03, 2014 10:27 pm

rodlonq wrote:It is commendable that you are having a go at making your own unidirectional bow glass. It would certainly be very satisfying to use your own backing/facing in a bow, which would more than offset the labour component of making it. I am interested to know how it is working out for you from a cost point of view. If you are going to the trouble to make a form for it you must be planning to make a reasonable quantity. How does it stack up against a bulk order from say Binghams, if you include the cost of abrasive belts for the drum sander as well. I assume you are attempting to make clear bow glass?
Rod, from a cost point of view it's probably relatively similar to buying Gordons lams, but as you said, there's the satisfaction element. The form is just a length of c-section with some 'plugs' ground to seal each end, with a small pad of rubber to grab the fibreglass threads, ensuring they don't move when tensioned/stressed and that it can be 'locked' into this prior to applying the resin. I rang up Gordon's and asked them about their Bo-Tuff and they explained it all to me, quite happily too. Nice guys. Once the resin has set I release the clamps on the 'plugs', remove the lam, grind it to thickness and trim to width. They're nominally clear, although the lateral weave is visible - I assume Gordon's use individual threads as opposed to the commercially available product. A patient man one day might pick them out prior to applying the resin. Or, a bit of dye would cover it, for the mean time. As they are, the grain beneath glass is visible, I'll see about some pictures some time. It's been a while since I had time to get into the shed.

Hunterguy 1991, sorry if I came off as critical - honestly, I can't encourage you enough, I really was just making the distinction between glass cloth backing and fibreglass lams. Good luck!

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Re: Who said you cant use fibreglass sheet?...

#16 Post by GrahameA » Mon Aug 04, 2014 8:01 am

Morning.
Nezwin wrote:.... The form is just a length of c-section with some 'plugs' ground to seal each end, with a small pad of rubber to grab the fibreglass threads, ensuring they don't move when tensioned/stressed and that it can be 'locked' into this prior to applying the resin. I rang up Gordon's and asked them about their Bo-Tuff and they explained it all to me, quite happily too. Nice guys. Once the resin has set I release the clamps on the 'plugs', remove the lam, grind it to thickness and trim to width. ...
What you have described is essentially the same process/procedure used for small production of Carbon Laminates. Heaps of personal satisfaction, no great savings of cash. (Just in case some gets the urge. IMHO I would seriously look at wide range of what is available in commercial product before having a go at making your own.)

Thanks very much for your comments and in my opinion you were not critical.
Grahame.
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Re: Who said you cant use fibreglass sheet?...

#17 Post by Nezwin » Mon Aug 04, 2014 8:25 pm

For those interested...

Here's the glass I'm using -
IMG_0013.jpg
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With an old bit of standard cloth for comparison -
IMG_0014.jpg
IMG_0014.jpg (114.72 KiB) Viewed 7042 times
Here's the polished side of the finished result -
IMG_0015.jpg
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And the ground side -
IMG_0008.jpg
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This particular piece is untrimmed, hence the slightly tatty edges to it.

Here's the finished product -
IMG_0009.jpg
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IMG_0012.jpg
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These were both failed experiments (?), or rather, a case of too much improvisation and not enough patience. Accordingly, the glass is pretty knocked up from a lot of careless moving around, nor has it been finished with a matte sealant, so it still has the gloss. However, you can clearly see the grain through the glass as it turns transparent once it has been glued. You can also see the thin lateral weave, which I think should be able to be removed prior to adding the resin, when I get a chance to try again. As I also mentioned, some dye would cover it, so I might look at some dark green or black maybe. If the clear ones work out well, a bit of stain on the lam beneath the resin could bring out the grain just nicely...

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Re: Who said you cant use fibreglass sheet?...

#18 Post by rodlonq » Wed Aug 06, 2014 4:52 pm

That looks the goods mate, top effort.

Cheers.... Rod

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Re: Who said you cant use fibreglass sheet?...

#19 Post by Dennis La Varenne » Wed Aug 13, 2014 11:08 am

After my earlier post expressing my concerns with using woven fibreglass, I remembered a bow I have in my collection which is backed with woven fibreglass which has been glued to the surface using an epoxy compound. Here is a picture of the back surface.
IMG_2551.gif
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Of no particular relevance to the topic, here are some pictures of the bow itself. It is a novelty bow made with sympathy to the Tolkien book 'Lord of the Rings' and is the bowmaker's interpretation of an 'Elven' bow. It is just on 72" long with recurved ends which are glued on like siyahs on Turkish bows and has some interesting carving. It is also very broad at close to 2 inches and has just on 1 inch of set with the nocks on the same plane as the back of the handle area.
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Dennis La Varénne

Have the courage to argue your beliefs with conviction, but the humility to accept that you may be wrong.

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HOMO LVPVS HOMINIS - Man is his own predator.

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Re: Who said you cant use fibreglass sheet?...

#20 Post by hunterguy1991 » Wed Aug 13, 2014 12:00 pm

Nice looking bow Dennis!!

Any braced shots of it? curious to see what it looks like...

And the more important question, does it shoot?

Colin

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Re: Who said you cant use fibreglass sheet?...

#21 Post by Dennis La Varenne » Wed Aug 13, 2014 6:31 pm

Colin,

Here is a braced picture of the Elven bow. :biggrin: I have hung it upside down. The downward pointing upper limb has a positive tiller of 3mm. I put an arrow shelf on it this evening once I worked out where it likes to shoot from. The arrow shelf is a small 15mm flathead nail. It draws 52lbs@28in, but I can only get it to 26in so far. But it shoots fine with 40-45 spine arrows around its 1 1/2 inch wide handle. If I could get it back to 28in. it would be pretty impressive.

I will have to round the edges off a bit though because I can feel fibreglass fibres catching my skin if I slide my hand along the limbs. The fibreglass layer looks very thin - certainly less than 1mm, and it takes an extra 1/4in. of set after unbracing to 1 1/4 inches but comes back to 1 inch after resting. It was made by Rudderbows a good while back and had 40lbs@28in written on it in pencil under the lacquer. He was a bit out with his weight, or perhaps it has dried out more since he made it. I bought it as a curiosity more than anything else.
IMG_2564.gif
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Dennis La Varénne

Have the courage to argue your beliefs with conviction, but the humility to accept that you may be wrong.

QVIS CVSTODIET IPSOS CVSTODES (Who polices the police?) - DECIMVS IVNIVS IVVENALIS (Juvenal) - Satire VI, lines 347–8

What is the difference between free enterprise capitalism and organised crime?

HOMO LVPVS HOMINIS - Man is his own predator.

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Re: Who said you cant use fibreglass sheet?...

#22 Post by Nezwin » Fri Aug 15, 2014 3:47 pm

Dennis La Varenne wrote:I will have to round the edges off a bit though because I can feel fibreglass fibres catching my skin if I slide my hand along the limbs. The fibreglass layer looks very thin - certainly less than 1mm, and it takes an extra 1/4in. of set after unbracing to 1 1/4 inches but comes back to 1 inch after resting. It was made by Rudderbows a good while back and had 40lbs@28in written on it in pencil under the lacquer. He was a bit out with his weight, or perhaps it has dried out more since he made it. I bought it as a curiosity more than anything else.
That's a beautifully made bow, Dennis. I've been curious about static recurves for a while now, so the braced image is very interesting to me. Re: thickness of the fibreglass layer, I'd say that it's just a single layer of cloth laminated directly onto the back of the bow, efficient in keeping splinters from lifting but not substantial enough to do much of the work as the limb bends. Still, a beautiful piece of work there, I can't wait to get my own static recurve shooting!

Dennis La Varenne
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Re: Who said you cant use fibreglass sheet?...

#23 Post by Dennis La Varenne » Fri Aug 15, 2014 4:45 pm

Thank you, Nezwin. I never thought of it a beautiful; just curious about its shootability with the concern that all those humps along the belly would interfere with its tiller, but it works fine. I just wish I could draw it out to the full 28" to see what it is really capable of.

The siyah is a simple matter of a scarff joint onto the end of a straight limb so far as I can see. The glue surface is 70mm long and tapers in width from 15mm at the nock to 23mm where it feathers into the limb proper. There is no sign of any kind of dovetailing or pinning of the joint. I suspect that the fibreglass matting helps secure the glue joint.

Rudderbows is making a static recurve now - a recent addition to his line. He is calling it his Mongolian style bow. Here are some pics. It is Hickory like most of his range, and costs around $US135.00 plus shipping as I recall.

If you look very closely at the second picture, you can just make out the scarff joint which I have labelled. The feathered end of the joint is whipped with a light cord.
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Dennis La Varénne

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Nezwin
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Re: Who said you cant use fibreglass sheet?...

#24 Post by Nezwin » Thu Aug 21, 2014 8:53 am

Thank you, Dennis. Those pictures are some food for thought. My own attempts at static recurves have been with short siyahs, or wedges, laminated between two lams, much as one would with the riser in a trilam. When I get something completed (and up to a displayable standard) I'll post some pictures.

Neil

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