Post For Tim Baker ( Sinew)

[Tim Baker]

willie / Springbuck:

"Rolling bridges" wouldn't exactly roll; they'd only have to roll some small part of an inch. To test if rolling or toggling bridges would be more efficient [by reducing friction against stationary bridges] short lengths of wood pole, of the same diameter as bridge height, could be set temporarily under the backing just long enough for a test, the regular bridges removed for the test. When braced, the downward force of the backing would hold the rolling test bridges in place long enough for testing.

Springbuck:

Your fabric spacer idea is worth serious thought. Likely some configuration of different fabrics and glue will do the job, so it's now a serious candidate. Thanks, even though I hate it that you thought of it first.  For me at least, every part of the bow must be paleo-legal: could reasonably have been made before the metal ages, and woven fabric was around a few thousand years before the copper age.

" What are you doing toward the tips?  Does the cotton peter out in thickness?  Are you binding down the three layers together, or adding more glue to really secure the whole thing at the tips?  Or is it just the same sandwich with exposed layers all the way to the ends?"

For this first test version the cotton and sinew taper somewhat in thickness from working grip to near tips. Much of the tiller comes from the largely pyramid front view. On future versions the spacer and backing will taper to zero a few or many or many many inches from the nocks, narrow wood beyond that, for low outer limb mass.

[Tim Baker]

The cotton in place

[Tim Baker]

Maybe a better sense of how it rises above the bamboo ridges:

[Tim Baker]

Second try

[Tim Baker]

With two ounces of sinew:

[Tim Baker]

Lots of open spaces in the cotton layer, so possibly lighter that a wood spacer.  This sparsity of glue worried me that it might not hold together even through the drying process, so wrapped it tightly. Same for the sinew. Both held together though once dry, wrapping removed, then braced and drawn.

[PatM]

Do you have a moisture protection plan for this bow going to Mojam? 

[Tim Baker]

PatM:

For the first mojam my bows arrived in a plastic container; they weren't taken out till the day we did the tests. Probably a good plan for this bow too. Hard to believe that was almost 20 years ago.

[Bob Barnes]

Tim, It would be really nice if you could accompany Steve to MoJam this year for the anniversary and flight shoot...    

[Springbuck]

willie:  "Twisting the sinew into small bundles, letting them dry some, then sticking down with a glue ball and binding with twine seems like a way to control the tension in different parts of the back, perhaps varying the shrinkage and resulting reflex to create the reflex profile desired?"

      Willie, I think it could do any or all of the above, but I just recently worked with sinew for about the 4th time ever, and I have a thought on that.  I was helping a guy repair a lifted back on a Miwok bow, and learned all over how hard it is to handle sinew.  I see lots of guys combing it out in little bundles, even tying similar-sized bundles together, etc.

"The most difficult part of the operation...."  from the article.  It's one thing to say a Klamath bow had several courses of sinew on the back and another to understand how the hell the guy did it without sinew stuck to everything he owned and made the bow anything other than butt ugly.

  Maybe this account of the Native guy twisting sinew into bundles wasn't to imprve performance, etc.. perhaps simply a way to make them easier to handle.   

 Sinew strands get everywhere, stick to everything, half the bundle goes on the bow, half stays on your hand.  If you are grabbing bundles out of a bag or out of a bunch you always have too few or too many, or too long or short, etc.... .....  So, like, maybe gather similar-sized bundles, add a little glue, twist em up till they stick together and lay them aside. An 8" bundle has maybe one and a half or two rotations, tips tapering out to rat-tails, nothing like a double reverse twisted two ply sting or anything.

 When you have enough, size the back of the bow and lay the now tacky bundles on, adding glue as needed.

  Conjecture, but method is important.  Devil is in the details.

[Springbuck]

PatM said: " Why not curl the bamboo up like a Korean Bow before sinewing?"

   I guess I was assuming that was next....     Knowing what I know about Tim.

[PatM]

Sinew doesn't HAVE to be that finicky to work with.

  The comment about curling the bamboo up was a bit of a trick question.

[sleek]

PatM said: " Why not curl the bamboo up like a Korean Bow before sinewing?"

   I guess I was assuming that was next....     Knowing what I know about Tim.

I want to know the maximum bend bamboo can take before compression failure. Of course, that has too many variables, so is there a standard chart that has compression limits for wood?

[Springbuck]

  willie:  "Is "energy wasting" the same as  "not getting it's full potential?"

   I kind of think it is.  I, like you, don't think it is a good idea to stretch things right to the limit, but.......

   I'm pulling some numbers out of the air, here, but..... Say we want a sinew back for a 50 lb bow.  Since sinew can stretch almost 10% of its length, you can take "X" amount of sinew and pull it 8% of its length to get the 50 lbs.   OR, you can take "2X" amount of sinew and stretch it 4% of it's length.  Something like that.

Sinew is heavier than wood. 

[PatM]

It's also generally said that sinew works best with woods like Juniper but wouldn't exceptionally stiff wood force sinew to stretch more?