Ozbow

I think we've done this before but i can't find it.

Does anyone find coloured glass gives a higher weight bow than clear glass for the same thickness core stack?

Cheers... Rod

Right now the technical terms are escaping me but Coloured Glass is a different Construction, something to do with the Fibre Count. A few FPS means nothing anyway. If it where me I'd be looking for Performance with lighter Lamination;s like Bamboo instead of something pretty and heavy like Bubinga under clear Glass. Of cause the unstrung Profile is the real Clue. I cant remember hearing that Clear Glass gave appreciably lighter Draw Weights, just adjust Draw Weight when Tillering.

regards Jacko

Rod you might find that clear and coloured are actually different thicknesses. In general coloured glass finishes in an even number ie; .030- .040 etc whereas clear is for example .043. Once i just picked up the relevant pieces of glass and incorporated them in my stack using stated measurements. Now I mike every piece and make calculations accordingly as there can be wild variations within one piece like a '.040' piece being .38 at one point, .037 at another and even .040 at yet another. This can explain why 2 bows made with 'same' stack dimensions can vary a lot.I have actually resorted at times to laying pieces on bench and judiciously sanded some of the discrepancy out.With recurves, as little as .001 of thickness can be 1# weight variation. i just made a takedown using similar stack to previous build and look like coming in 8# over weight and this was with careful measurement of all components. The only variable as i see it was it came for a shipment of new glass, which by the way ,the clear is at least acceptable.

Thanks for your input Perry and Bob. I need to sit and think on this a while.

Cheers... Rod

Hi Rod,

This topic has arisen a couple of times and my email to Elmont Bingham and reply as follows.

If you wish to read the post the link is; http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=10356

I may be wandering a little off the topic but the following email to Bingham's was prompted by a post from Kimall regarding clear Bo-tuff. I experienced a similar situation where clear glass appeared to yield lower poundage.

From: Greybeard [mailto:greybeard@pcsol.com.au]
Sent: Wednesday, September 15, 2010 5:44 AM
To: 'Bingham Projects Inc.'
Subject: Bo-Tuff clear glass.

Hi Elmont,

I have a question regarding Bo-Tuff clear glass.
For the given thickness of the laminated core of a bow does clear glass i.e. .043 ULS yield a lower performance/draw weight than coloured glass of .040 ULS?

I am led to believe there is less glass fibre in clear glass. If there is a notable difference is there a percentage value that I should build into the core of a bow?

Regards,

Daryl.

Hi Daryl,

Thanks for your e-mail. Thickness for thickness, they are the same. The same limb thickness with black will yield the same weight as the same limb thickness with clear. The black glass is harder, not stiffer.

Sincerely,
Elmont.

Upon checking the thickness of some clear glass I had in stock some was 10% under thickness. As my digital vernier callipers have not been certified as 'accurate' I can not dispute the variation in thickness as stated.

A problem that I encounted when using hard rock maple for core material was that for a given core thickness with each new supply I purchased I could be plus or minus 5# of the targeted draw weight.

Daryl.

Uls coloured glass comes in at .040 nominal and ULS clear is .043 nominal.Both vary wildly in thickness even using a 'dodgy' set of calipers as the percieved error would most likely be constant