Best Selfbow Design? - Page 2 - Graybeard Outdoors
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post #11 of 11 (permalink) Old 01-27-2017, 02:49 AM
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Join Date: Dec 2008
Location: SE Qld Australia
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Originally Posted by flmason View Post
So how does the wood relate to the design?

That could be a really good thing to know.

True, "Handy" isn't what I'm getting at, but rather performance.

I do not live in the USA but Australia so I will limit my answer to just a few oversea's Timber Species I have used in the 25 plus years I have been making Selfbows. There are literally hundred's of Timbers you can use to make Selfbow's. I'll leve it too you to do further research. This is a very complicated question and I will try to keep things as concise and brief as I can.

Different Timbers have different Properties. A Selfbow is a Bow made from a Single Piece of Wood. A Selfbow's Back is under Tension, that is it stretches, a Selfbow's Belly is under Compression.

Different Woods are strong in Tension, other Wood's are strong in Compression and others still have a good balance of both. Mass is also important as too much mass out at the Limb Tips add's weight where it is not needed and slow's Cast. You must take these qualities into consideration when choosing what Design to use with a particular Species of Timber.

When you read of Bows that are Backed with Timbers such as Hickory it is because Hickory is strong in Tension and makes for a good Backing. Then you get something like Juniper which is strong in Compression and not as good under Tension. Together these 2 Timbers are a good Combination for a Laminated Wooden Bow. I note that many Cultures around the World also developed Sinew Backed Bows. Sinew is enormously strong in Tension. Back a light Wood that is strong under compression such as Juniper or Yew with Sinew with a shorter Pyramid Limb, even a Recurved Limb and you will get a Bow made from natural Materials that performs very well indeed.

Back a heavy Wood such as Hickory or Osage with Sinew, while it will make an excellent Bow it will have more mass in the Limbs using the same design as the lighter Timber it will have excess Mass in the Limb and probably Cast will not be as good.

Now Sinew can pull a Bow into Reflex just as you can Glue a Timber Backing on a suitable Timber and then pull it into reflex. Once Clamped on a Jig to hold correct profile the Laminated Bow will also hold the Reflex you pulled it into.

Why reflex a Bow - In general term's the further a Bows Limb Tips are in front of the Riser / Handle the more string tension the Bow will have when Braced for a given draw weight. Recurves generally shoot have better Cast than a Reflexed straight limb design because they have more string tension at Brace height for a given draw weight

Timbers such as Hickory also are relatively strong in Compression and can be used to make excellent Selfbows. But Hickory is also a relatively heavy Wood so you must chose a design that allows as light a Limb as possible. Hickory is a poor Timber to use for an English Longbow design as they have a D cross section which is best suited to Timbers of lesser mass such as Yew. The D Cross Section also concentrates compression forces as the Belly has a narrow D shaped down it's length. Yew Sap Wood is particularly strong under Tension and the Yew Heart Wood is particularly strong under Compression. It is therefore excellent for the English Longbow's D Cross Section.

Hickory's qualities are best suited to a long Pyramid Limb Design which has a Lenticular and sometimes a Rectangular Cross Section. The Timbers I mostly use in Australia are similar to your Hickory and Osage in that they are relatively heavy. Our Timbers are stronger and have tremendous Tension and Compression qualities to go with their extra Mass. Therefore these Timbers in my experience are better suited to a long narrow design.

It really is an enormous question, I hope that I have cleared thing's a little. Dig Deeper, there is a lot of information out there. I recommend that if anyone wants more information or clearer answers to register on the the Primitive Archer Website.

http://www.primitivearcher.com/smf/

regards Jacko

"To my deep mortification my father once said to me, "You care for nothing but shooting, dogs and rat catching, and you will be a disgrace to yourself and all your family."

Charles Darwin
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