Question for any Engineers or Materials Scientists out there

kennym · January 20, 2021, 03:53:58 PM

Roy, I think that is a smelly gear...

Roy from Pa · January 20, 2021, 04:41:32 PM

Flem · January 20, 2021, 05:57:53 PM

Thats Italian for the smell of a hockey rink.

avcase · January 20, 2021, 06:22:53 PM

Quote from: williwaw on January 20, 2021, 03:32:23 PM
you will have to find that out by trying, I suppose. It would be interesting to compare the density of formica to glass.

Flem, I read some where you have noticed density of laminates (glass/resin ratios) make a difference. Can you share more of your observations? Is it just the belly lams that it makes a difference on?

My father made me a laminated ash bow with Formica on the back and belly when I was a child. I still have that bow. For what it is worth, here is a quick comparison of mechanical properties. In terms of material properties, Formica is not much different than some of the high density tropical timber used to make bows.

Unidirectional
Glass Formica
Density 117.5 lb/ft^3. 84.3 lb/ft^3
Flexural Modulus 6.0 Mpsi 1.9 Mpsi
Flexural Stress. 111 ksi. 21.2 ksi

Stagmitis · January 20, 2021, 07:39:41 PM

Dang Flem look at those numbers! Maybe a craft paper core(Ie:wood) sandwiched between a linear carbon over an S2 cloth...

I wouldnt discount the binghams carbon core. I would bet its one in the same as a carbon backing just sanded on both sides.

One of the best carbon backs I made for my hills started with .30 linear carbon whittled down in thickness and backed on both sides with S2.

Flem · January 21, 2021, 09:05:36 AM

"Flem, I read some where you have noticed density of laminates (glass/resin ratios) make a difference. Can you share more of your observations? Is it just the belly lams that it makes a difference on?"

Willie, If I we are talking about the same post I made, I had observed that Gordon's is stiffer than my homemade laminate using my tensiometer. But my observation about Gordon's resin to fiber ratio was WAY wrong. I read the description to suit my theory. Sometimes we need to carefully read all the information being presented before we respond with what we think we know is set in stone. Guilty here.

I'm going to start calling you the Gopher, you do some digging!

Charles, you got some crazy ideas

.
I was wondering about that carbon also. I was thinking maybe it was material that had surface blemishes and they did not want to bin the stuff.
What was the total thickness of the carbon/S2 back? That sounds strangely familiar........

Stagmitis · January 21, 2021, 09:47:09 AM

From what I recall it was around .034 total. .020 Carbon, two different thicknesses of S2. Call me crazy but I also prestressed the laminate at glue up

williwaw · January 21, 2021, 03:36:59 PM

Flem,

From reply 81

Quoteall that unidirectional fiber is overkill on the belly of a bow

and from reply 70

QuoteI'm thinking the laminate we put on the belly side is not optimal. We use a laminate that was obviously designed to placed on the bow's back

Please allow me rephrase my question a bit.
What observations of your finished bows support these theories?

Flem · January 21, 2021, 04:09:39 PM

No observations, just theorizing.

avcase · January 21, 2021, 06:07:25 PM

Quote from: Stagmitis on January 20, 2021, 07:39:41 PM
I wouldnt discount the binghams carbon core. I would bet its one in the same as a carbon backing just sanded on both sides.

Yes, this carbon is the same. I'm using Gordon's .030" unidirectional carbon as a backing strip on a 120#@30" deflex-reflex longbow for the US Flight Championships this coming September. These are just one-off bows, yet designed to be durable enough to serve equally well as the regular hunting and stump shooting bow when not used for flight.

I wish I could find a source to get this carbon in .050" thickness.

Alan

Longcruise · January 21, 2021, 06:42:30 PM

How about grinding a strp to .020 and combining with a .030?

Stagmitis · January 21, 2021, 06:47:42 PM

Alan, glue two strips together and equally sand both sides until you get .050.

Stagmitis · January 21, 2021, 06:49:38 PM

Duh!!! Didnt see your post Longcruise

onetone · January 21, 2021, 07:21:43 PM

If using carbon I typically use two .014 uni-carbon lams on the back side of the limbs. That works well in my experience but may not be optimal in flight bow design due the added weight.

williwaw · January 21, 2021, 08:25:41 PM

Quote from: avcase on January 21, 2021, 06:07:25 PM
I'm using Gordon's .030" unidirectional carbon as a backing strip.....I wish I could find a source to get this carbon in .050" thickness.
Alan

With .050 carbon on the back, how much strain do you calculate will be on the belly?

Flem · January 24, 2021, 10:31:27 AM

"Are you not able to obtain Gordon's GC-70-UCL for a backing material? I recently bought and used this for a back on a longbow design.

Alan"

I have been holding out, hoping you would share your source. But it would seem from your last post that this source has disappeared?

avcase · January 24, 2021, 02:13:05 PM

Quote from: Flem on January 24, 2021, 10:31:27 AM

I have been holding out, hoping you would share your source. But it would seem from your last post that this source has disappeared?

I am using the unidirectional carbon that Bingham's sells. It is the same as the Gordon's unidirectional carbon that I bought in previous years for backings.

Flem · January 24, 2021, 04:34:25 PM

If I ever get around to making some test laminates, I will send you an .050" Finished on one side.
As long as you don't tell anybody where you got it.