Post For Tim Baker ( Sinew)

[Tim Baker]

Another:

[Bob Barnes]

one I'm waiting for the sinew to get dry... 

[sleek]

That is interesting tim. Especially that top one. Do you plan on leaving the levers full length? The triangular braces, are they going to stay that bulky?

[Tim Baker]

Badger:

I'll put together a tentative stat and test list and brainstorm it with you.

Putting the touch-up sinew on that test bow tonight.

[willie]

Putting the touch-up sinew on that test bow tonight.

Cool, how long has it been taking sinew to dry when applied in small spots?

[Tim Baker]

willie:

"... how long has it been taking sinew to dry when applied in small spots?"

Almost as long as for a just-senewed bow. Water from the glue soaks down deep and takes a long time to travel back out.

sleek:

It's the same bow in both photos. They're from 10 years ago. Yes, the outer limbs were kept that long, and did a bit of energy storing; they were tapered to near zero before testing. Despite a very fat FD curve it shot as slow an especially poor D bow. Theory and hope is no match for reality.  A bamboo version did as poorly. They were quickly trashed.

Here'a a photo of both, and a 3-point F/D curve for each. Lesson learned: F/D curves can be poor predictors of performance

[Tim Baker]

The bows

[willie]

Tim,

any ideas why they under performed?

[Tim Baker]

willie:

" any ideas why they under performed?"


One reason is the same for why recurves so often shoot slower than well-made straight bows: Outer limbs store a tiny fraction of total energy while outer limb mass eats up tons of it. Another: The huge % of limb devoted to retroflex put crushing strain where most of the energy is stored and hysteresis is very high in such overstrained wood. It was an anti Mantra bow. 

And in the looks department it was an anti Bob Barnes bow--see six posts above.

[sleek]

Tim, im wondering something and that never goes well, but here goes...

Your goal is to stress the sinew out as much as possible to get gull use of it. But the way they reflex horn bows isnt possible with wood bows because the wood cant handle that much compression ( can it? Is it really being compressed if its stretched first then bent back to normal shape? ). So perhaps you can reflex a woden bow with sinew the way a horn bow would be, then slowly heat the belly ( this works from my experience ) with a heat gun, work the belly with heat, and apply pressure to flatten the limb out. A damp rag to wipe the heat iff the back helps. That would stress that sinew out, but still allow the wooden belly to bend at full draw without failing.

[Tim Baker]

Sleek:

Elevating the sinew will allow it to be even more strained than on an Asiatic composite, if desired. Reflexing is still important, and the fact that sinew in this design is storing such a high % of total energy means that the belly doesn't have to do much tension work, so it can be much thinner than otherwise. Being so thin it can be pulled into far larger reflex than conventionally. For example, the bow can be tillered backward to full draw then elevated sinew applied. Even though thinner than a conventional belly it's full thickness is free to do the compression work

[Tim Baker]

A fun and maybe dumb idea: One or more versions of the experiment bow here will be given a poor-man's horn belly:

When a puddle of hide glue is allowed to fully dry it's surprisingly horn-like. If applied in successive coats to a bow belly the bow becomes substantially stiffer. And since hide glue is about as elastic as horn it should be able, like actual horn, to carry much or most of the compression load and store much or most of the compression energy, protecting the wood belly in the process.

If the belly, now core, is an especially light wood, when then pulled into reflex and sinew backed, an especially light and high-stored-energy bow should result.

I'm just starting to play with this. Maybe others would like to also, and report their results. A dumb part of the idea is that hide glue is prey to moisture, so a glue belly would need special protection.

Glue can be brushed on, but only thin coats result, hours of drying time needed so the new coat won't melt the earlier one. One way to speed the process and insure thicker and more uniform coats is to set a mostly-open-space fiber mesh down and saturate it with glue. It's not paleo, but to speed testing, a separated, gossamer thin strip of toilet paper does the job, several now-thicker coats allowed at the same time. The wood fiber is maybe 5% of each layer's mass, does no work itself and prevent no work from being done.

Questions and comments and arguments welcome.

Side view of 1/2” thick redwood bow limb, the thin brushed-on dried glue belly at top.

[Tim Baker]

Transparent dried glue belly.

[Tim Baker]

A speedy way to apply the glue is via squeeze bottle, like mustard or ketchup comes in. Keep it in the fridge between sessions.  50 points to the first person to identify that black material beside the bamboo.

[BowEd]

50 points to what?It's bahleen.You can do better than that....lol.Nifty squeeze hide glue bottle.Your hide glue belly is made of cologen though.Horn is keratine.Be interesting to see how much compression it will take though.