Re: hollow limb buildalong, session 7 (The End) added

[simson]

Some guys asked for a buildalong – I will try it.
I have done several hollow limb bows, some examples are posted here:

http://www.primitivearcher.com/smf/index.php/topic,34915.msg460154.html#msg460154
http://www.primitivearcher.com/smf/index.php/topic,34898.msg459925.html#msg459925
http://www.primitivearcher.com/smf/index.php/topic,38380.0.html
http://www.primitivearcher.com/smf/index.php/topic,41177.0.html
http://www.primitivearcher.com/smf/index.php/topic,35613.0.html

The tools needed are:





Hollow limb design only makes sense on high crown staves.
I have choosen a Laburnum stave, about 2,5  - 3“ in diameter and 66“ long.
After debarking I saw this would be not an easy candidate, very wavy and lots of knots. I run it through the bandsaw and this were we were at the moment:

Side profile



front profile










here you see the fungus inside the stave, some of the outer rings are intact, but the fungus did spread over the rings …..







My first thought: let it be firewood!!!

But anyway, it doesn't matter if this will became a bow or not – showing the process of hollow limb can be done on every piece of wood. Let's try it and don't expect a shootable bow ...

This are the disadvantages:
- very thin ringed
- not matching string alignment
- massive dogleg in one limb
- not matching reflex of the limbs
- severtal knots (not avoidable in layout)
- some holes
- a fungus inside, growing from the center pith outwards, but was not intelligent enough to do that growing in the same ring

This are the advantages:
- nearly no twist
- it's laburnum – one of the prettiest woods
- it's laburnum – one of the best bowwoods
- and it has everything what we call character – so it's a challange


the fungus has produced that bright spongy material, nearby is a dark brown which I think the tree has produced to stop the fungus - this is very hard and brittle (inlayed minerals?) and makes the tools quickly dull. The olive is the origin color of the heartwood, the white is the sap – this is the good stuff






on this little stave I can use mostly only the gooseneck scraper and the  'Geissfuss' (transl. word by word: 'goat leg') don't no how you call that wonderful tool





the result so far



will continue when I have time again …

[Zion]

I'll be real interested to see this turn out, are you going to even try to get to shoot?

[missilemaster]

Oh BOY!!! I'll be following this! Is the orientation of the hollow part of the limb the same as an ACS bow?

[Badly Bent]

Thanks for doing this Simon, gonna be very interesting to follow and learn from. Like the way you assess your woods
properties and your staves pros and cons to lay out a plan before starting. I'm learning already.

[Gus]

Yes Sir,

Thank You, I'll be watching...

-gus

[ssgtchad]

Your the man I'm making some popcorn now.  Thanks for or time.

[Carson (CMB)]

Is this really happening?   Dream come true! Watching closely.

[Del the cat]

Wow, Blimey... you look to be as foolhardy as me
We are gluttons for punishment... hope she works out.
V interesting project.
Del

[simson]

Zion:
Yeah, will try it - we will see a bow or firewood

Cody:
I think the advantages of the hollow limb design are: It will add additional strength to the bow, without more wood (fold a sheet of paper like the letter U - and it is stiff!). Will say it is mass saving. And, the flattening out alone will create a movement in the limbs. Much less wood and much less stress. The compression stress concentrates in the 'bellywalls' (at braceheight), while drawing the bow the hollow limb flattens out, the neutral plane  changes and the stress is contributed in a wider area the longer the draw. In other words the hollow limb design affects a much higher drawweight than a 'normal' designed bow (steeper f/d curve in the first inches of draw) I think this is a difference to ACS bows, the hollowed out here isn't that high and because it is a stiff laminated glass bow it cannot play with the flattening out advantage. The rounded shape of an ACS design saves mass and gets stiffer (sideways). This is good - but I'm talking about very deep hollowed out dynamic limbs! Hope you understand me, I'm hard struggling for the English words and grammar...

Badly Bent:
Too nice words from a master!

Gus, sgtchad, Carson:
nice you are interested

Del:
mmmmhhhmmmm ....... yes, that is obviously true

[simson]

I forgot to mention: laburnum = golden chain tree

Here we go again to session 2

This stave is by far not the best candidate to show the advantages of the hollow limb design, but it's an interesting challenge and the beginning is already done.

I do the hollow limb design normally only the best intact staves, so it is quite easy to chase an inner ring and follow outwards to the tip as a guideline. Usually I have then little work to do the taper outwards.

Not so here! The fungus has spread over the rings and destroyed the wood. I have to take off the complete bright spongy stuff, even if it 'hurts' an inner ring. This can cause stability problems (warping sidewards) or coming out of tiller, but I have to live with that. If one of the two belly walls gets too thin , it will be overstressed. I have to compensate that with slightly more thickness in the rounded middle.

A first floor tiller test shows heavy warping, as expected. To get that a bit better I cut off 2“ from the lower limb which has  a heavy curve sidewards.



Cut of 2” from the upper limb also.
Didn't get enough for string alignment, heating is nessecary – we that later!
For now continue hollowing out the limbs

here two pics of cutting in intact wood, results in nice long chips.






after working with the goatleg (don't know the right word):



after working with the gooseneck:



working out knots and holes to nearly the same thickness as the surrounding area:





here is a pic how it looks now:



here is a grain wave on one of the belly walls (problem again):



the same spot:



such areas must be carefully watched, hope I can take off wood here while tillering

marking thick spots and working down:







enough for today, here is the leftover of the second session (just the same amount as the from the first):

[Zion]

This really puts a new perspective on the whole process. I gotta say i'm most interested in how you will tiller it. Are you the only one that has come up with this? It obviously works haha.

[Thesquirrelslinger]

so are these things really fast?

[Newindian]

Something for the bucket lost, that's some pretty wood, I would think that this design would focus all the compression on the outer walls of the curve though

[IdahoMatt]

This is intriguing,  I will be watching this one....

[ssgtchad]

Simon I believe that tool your using is called a bent gouge. How many hours have you spent on carving this bow so far?