[ASK][Glue] Sinew Plate of Grozer's Biocomposite Bow

My opinion/suspicion is that the sinew does nothing in Grozer's biocomposite bow.

Fiberglass is 40x as stiff as sinew and any bowyer will tell you that the outer-most parts of the bow do most of the work. Since the sinew on the biocomposite bows have fiberglass on top of them, it stands to reason that the sinew is doing almost nothing. The only thing the sinew does is change how the bow looks (and doubling the price).

If you look at all the bows unstrung, the biocomposite bows aren't any more reflexed than the laminates so even if there was any extra flexibility in the limbs from the sinew, his bow design isn't taking advantage of it.

thank you for your reply.

Now, the image is becoming clear :)

I did not know they put fiberglass layers in-between the sinew, core, and horn (^^" not work hard enough), thank you for the information.

However, why so many users claimed
their biocomposite bows are soft and more smooth than others?
psychological effect? lol

Mule wrote:

My opinion/suspicion is that the sinew does nothing in Grozer's biocomposite bow.

Fiberglass is 40x as stiff as sinew and any bowyer will tell you that the outer-most parts of the bow do most of the work. Since the sinew on the biocomposite bows have fiberglass on top of them, it stands to reason that the sinew is doing almost nothing. The only thing the sinew does is change how the bow looks (and doubling the price).

If you look at all the bows unstrung, the biocomposite bows aren't any more reflexed than the laminates so even if there was any extra flexibility in the limbs from the sinew, his bow design isn't taking advantage of it.

:) :)

In a wood/glass composite bow, the fiberglass -- .030" thick to .060" on each side -- supplies 88% of the power and the wood laminates and other things between the glass supply on 12%.

I've sure some of the reports are biased by marketing hype. It also depends on what previous bows the reviewers have been shooting...

My impression is the the biocomposite is mostly marketing hype trying to lead uninformed buyers into believing that Grozer is doing things "the old way". Putting horn or sinew between fiberglass is, IMHO, a waste of time, energy and resources (and the buyers' money).

In these days,
I am still thinking about the function of the Horn and Sinew Plates.
Mr. Csaba should not risk his reputation.
He must apply them for some reasons except for better looking and making a fortune.

I agree that Fiberglass layers play the most important role in this structure.

The concept of Lamination is to
integrate various materials to build a perfect bow.
So we may analysis this structure in a different way rather than stick ourselves
in the Traditional concept (horn for pressure, sinew for tension).
[he may conduct a correct process for modern materials and processes with wrong theories.]

Despite additional Weight contributed from the Sinew ans Horn Plates,
it is softer and faster than those bows manufactured by Grozer Csaba
(according to Grozer's video, and I tend to believe in the statement of this bowyer).
The Soft should be attributed to the additional two layers.

Probably, the Sinew & Horn Plates can be considered as
part of the bow-core. We may not directly used the concept of Horn bow into
modern process, even thorough what people are doing is to build a
bow with similar characteristics of traditional Horn Bows.

Mr. Csaba has made a lot of efforts to improve his products.
I am looking forward to hearing new products from his website, still~

it is softer and faster than those bows manufactured by Grozer Csaba
(according to Grozer's video, and I tend to believe in the statement of this bowyer).

Yes they're faster because they're heavier bows, note the poundage:

Laminated L2 Tartar 39# bow: 210 fps
Laminated L6 Sarmatian 43# bow: 217 fps
Laminated L7 Turkish 45# bow: 226 fps
Biocomposite Assyrian 56# bow: 237 fps
Biocomposite Assyrian 61# bow: 243 fps

The video showing the FPS measurements and in every test they use the same 26 gram arrow. Of course if you shoot lower gpp the bow is going to shoot faster..

Mule wrote:

Yes they're faster because they're heavier bows, note the poundage:

Laminated L2 Tartar 39# bow: 210 fps
Laminated L6 Sarmatian 43# bow: 217 fps
Laminated L7 Turkish 45# bow: 226 fps
Biocomposite Assyrian 56# bow: 237 fps
Biocomposite Assyrian 61# bow: 243 fps

The video showing the FPS measurements and in every test they use the same 26 gram arrow. Of course if you shoot lower gpp the bow is going to shoot faster..

Agree with that. :)
Even though I would like to say this test is not accurate
(different types of bows may result in different results),
the above list is truly convinced...

Hughlin; Mr.Gr?zer has already risked his reputation, even with his "finest" bows, where he has been caught cheating and telling lies about the construction. Take a look at this:

http://198.170.107.188/phpBB2/viewtopic.php?t=2689

Also, take a look at this picture, which shows a broken bio-composite, where you can see the glass fiber underneath what was said to be horn, but which obviously is not:

[external image]

I would not buy from anyone dishonest.

oh :shock:
thank you for your information, again.

I have at present one of the so called “biocomposite” Turkish bow “short” by Grózer (47 1/2” long, 40# @28” = @ 29 3/4” AMO). The fiberglass layers are ca. 0.02” - 0.03” thick, and these are in a direct contact with the wood core, i.e., the structure of the limbs is: a plate of the biocomposite polymer called “pressed horn” /glue, fiberglass, glue/ the wood core /glue, fiberglass, glue/ a plate of sinew soaked by some suitable modern glue. Owing their internal rather than external location, I think that these thin fiberglass layers may only have a function of strengthening of the core, rather than a real dynamic action as supposed by Mule and KenH. The dynamic action should really be done by the sinew plate and “pressed horn” plate, I think.

I performed some interesting experimental measurements regarding this bow, measuring the speed (V) of arrows of a different mass (m): m1, V1; m2, V2; etc., all at an equal draw length (28” AMO in the present case), and I applied the general method I always use to determine the virtual mass and other important parameters of the bow. The method (which is perfectly general, for any bow) is as follows:

One plots the values of Y =1/(V×V) vs. the values of m, and obtains a series of experimental points that lie on a straight line, Y = A + B m. The values A and B can be found by regression analysis, and many graphing programs are able to do this, thus providing A and B and the relevant ranges of uncertainty. The theoretical meaning of A is the ratio m°/(2E), where m° is the virtual mass of the bow and E is the total kinetic energy (arrow + string + limbs etc.; i.e., the total energy expended when drawing the bow, W, minus the energy lost by hysteresis, E’). In its turn, B means 1/(2E). Thus, A/B equals m°, the virtual mass of the bow under examination. Furthermore, 1/(2B) means E, and thus, if one has previously determined the value of W from the area of the plot of drawing strengths vs. drawing lengths, one obtains also the energy lost by hysteresis, E’ = W – E. Furthermore, A also represents the value of 1/(V×V) in the limiting situation of an arrow of mass zero, and thus, the square root of 1/A provides the maximum theoretical speed the bow in question is able to reach.

Well, the results I obtained when applying this method to the “biocomposite” Turkish bow “short” by Grózer were as follows (m in grains, V in ft/s): 538 gr, 146 and 145 ft/s; 481 gr, 156 ft/s; 320 gr, 184 and 183 ft/s; 262 gr, 197 ft/s;
A= 5.00175E-6 +/- 1.21673E-6 B = 7.75604E-8 +/- 2.86298E-9
m° = 64.5 +/- 18.7 gr
V(lim) = 447.1 +/- 46.1 ft/s
E = 38.84 +/- 1.49 J
E’ = W – E = 45.5 – 38.84 +/- 1.49 = 6.7 +/- 1.5 J

We observe that some results are unusually good, in particular the virtual mass is very, very low (64.5 +/- 18.7 grains), and the limiting value of V is really high (447.1 +/- 46.1 ft/s), although the composite ottoman flight bows may overcome 500 ft/s (results obtained by analyzing the Karpowicz data reported in http://www.atarn.org/islamic/akarpowicz ... _tests.htm).
In conclusion, my “biocomposite” Turkish bow “short” by Grózer is a very honest bow!

A 0.030 lamination of glass is still about 40 times stiffer than the wood and likely even more so than a lamination of real (?) sinew or 'horn plate'.
The core would not be 'strengthened' by any glass layers glued to it. The wooden core in a glass bow is simply there to act as a 'spacer' between the glass lams. The core is then adjusted in thickness for required draw weight.

For my part this discussion (on biocomposites) is much more simple:
Is it a fiberglass bow? = yes
Is it a good bow? = maybe
Is it a bow made in the traditional way from traditional materials? = no
Can it shoot as fast or faster than a traditional bow? = pound for pound it would not surprise me.
But I really think it should not try to masquerade as a bow made from natural materials.

mikekeswick wrote:

A 0.030 lamination of glass is still about 40 times stiffer than the wood and likely even more so than a lamination of real (?) sinew or 'horn plate'.
The core would not be 'strengthened' by any glass layers glued to it. The wooden core in a glass bow is simply there to act as a 'spacer' between the glass lams. The core is then adjusted in thickness for required draw weight.

I can agree, it is very possible that the two thin glass layers play an important role in the dynamic behavior of the bow in question ("Biocomposite Turkish bow short"). However, to my opinion both the "biocomposite" polymer layer named "pressed horn" by Grózer and the layer made of sinew soaked by a synthetic glue (a polyhurethane binder, I think) play in their turn an additional, non-negligible dynamic effect. As a matter of fact, the thickness of the fiberglass/wood/fiberglass sandwich in this bow seems me to be too thin for 40# draw strength to be reached by this bow, if one supposes that the additional biocomposite polymer layer and sinew + binder layer were only decorative. I have measured, the more accurately as I was able, the thickness of the different layers in my bow: I find 2.80 mm (0.110 '') the wood core; 3.40 mm (0.134 '') the glass + wood + glass wool sandwich, i.e., tee two glass layer taken together are 0.60 mm (0.024 '') thick; 2.60 mm (0.102 '') the pseudo-horn layer; and 2.10 mm (0.083 '') the sinew plate. The entire thickness is 8.30 mm (0.327 ''). Whether such a lamination is really preferable, or not, than a simple lamination made of a slightly thicker wooden core and two (possibly, slightly thicker) fiberglass layers, so as to reach the same draw weight, I do not know. No doubts, however, that the bow exhibit a very low value of the virtual mass, ca. 65 grains, which never I have found in other bows (values lower than 100 grains are extremely unusual). The lower the virtual mass, the higher becomes the efficiency with lighter arrows. Of course, it is also possible that such a low virtual mass is merely the effect of the moderate length of the bow (47.5 ") and that a fiberglass/wood/fiberglass bow of equal length and draw weight can have an even lower virtual mass. Only experimental determinations (graphs of 1/ (V×V) as a function of the mass of the arrows, in order to determine the virtual mass, as described in my previous post) can solve once and for all these questions in scientific terms.