Useful attributes for local timbers

[rodlonq]

Gidday All,

I have decided I would like to have a go at a three layer ELB with horn nocks. Aiming for around 55# @28" from say a 70"NTN bow.

I have a few boards to select from but I don't know much (if anything) about the useful characteristics of them to know how to use them. I originally bought them to cut up for lams and riser parts for composite bows but now have an itch to try an ELB.

Could you fellas/gals please advise what the most appropriate use is for each of the below boards, particularly with respect to an all wood ELB.

Red Tulip Oak 225 x 25
Queensland Silver Ash 75 x 40
Queensland Maple 100 x 50
Spur Mahogany 75 x 50
Queensland Walnut 75 x 25
Black Wattle 125 x 25

Boards1.jpg (129.59 KiB) Viewed 1526 times

As far as colours go, I would like silver ash back, spur mahogany core and Qld maple or red tulip oak belly. Problem is this may be the worst combination from a structural qualities point of view? I would imagine the same principles would apply in selecting uses for these boards in composite bows as well?

Any comment on the usefulness of these boards would be most appreciated. Thanks for looking.

Cheers...... Rod

[greybeard]

Hi Rod,

You will need to evaluate the mechanical values of the various timbers.

The back lamination will need to have elastic properties, the belly lamination compression properties and a core being able to withstand both forces.

A flat laid bow should be easier to tiller than one with built in reflex. Reflexed ones tend to bring in their own set of problems. Tapering the core has advantages as you do not run out of belly material when bringing the bow to tiller.

Do not be afraid to use a gut feeling. Nothing ventured nothing gained.

http://www.ozbow.net/phpBB3/viewtopic.p ... 782#p95782

Daryl.

[GrahameA]

Evening Daryl, et al

[quote="graybeard] A flat laid bow should be easier to tiller than one with built in reflex. Reflexed ones tend to bring in their own set of problems. Tapering the core has advantages as you do not run out of belly material when bringing the bow tiller.

Daryl.[/quote]

Hmm...... May I suggest the preceding is veer good advice. Do not reflex the bow!

Grahame - who has suffered at the hands of bow with just a little reflex ...... Aaggghhhhh........

[perry]

I caution about the Queensland Silver Ash for a back or belly lamination. It is not great under compression. I have never seen it fail when used to make Selfbows under tension though. Makes good Arrows. I have seen Silver Ash Selfbows and every one of them failed under compression with massive frets, though some did hang in there for dear life.

The only other timber there I am familiar with is Black Wattle and generally it has good tension and compression capabilities. It is a reasonably dense timber so as the belly of a tri lam it may work well. Like the others say - make one and see.

I have only used it in Selfbows and it was like most Aussie timbers - Dense. I have shot a Hill style bow that had black wattle laminations and while it shot well mass was an issue.

regards Jacko

[rodlonq]

Thank you Daryl, Grahame and Perry.

It is interesting when you start looking for properties of different timbers that tensile strength (yield strength under tension) never seems to rate a mention. Perhaps it is too variable? I have found values for MoR, MoE and ADD from Yoeman's chart (thanks mate) for some of the timbers and what could be cousins of the rest (dangerous assumptions going on here ) for which I am thankful. I was hoping some of the fellas on here had experience with how these timbers go when you bend them. I will be patient and hopefully the blokes who have an answer will get a chance to read this thread sometime soon.

In the meantime I think I will try a flat bow from a spotty gum floor board for my young bloke to use over the holidays. I don't have time at the moment to make his composite bow.

Cheers....... Rod

[UPTHETOP]

Hey Rod interesting project will be good to see the out come especially from local timber. Will catch up soon and talk tackle.

Cheers Wayno

[Flatliner]

Jeese Rod it looks like you raided my timber rack . Out of those timbers I wouldn't use the Maple (too soft very low modulus of elasticity and crushing strength) the spur Mahogany may be doubtful too, the grain length may be a bit short. I don't have data on the QLD walnut but I use quite a bit of it and I think it is an excellent bow timber, my educated guess is it's figures would fall some where between the Tulip Oak & the Wattle in the chart below.
Hope this helps, it's out of "Wood in Australia by Keith R Bootle, excellent book!

Rob.

...................... modulus of ..... mod of ............ max .............................. Janka
timber ................ rupture ..... elasticity .... crushing strength .....impact ....... hardness

Silver Ash, dry;............ 92 .......... 13 ............... 52 ...................14 ............ 5.0
QLD Maple, dry; .......... 77 ........... 10 ............... 44 ...................11 ............ 4.7
Red Tulip Oak, dry; ......126 ............15 ................ 61 ..................15 ............ 9.0
Black Wattle, dry; ....... 124 ............18 ................ 41 ................. 39 ............ 9.2

[rodlonq]

Wayno, Looking forward to our next chat mate.

Rob, Thanks for the data and the reference to Keith's book. I will be sure to look it up

Perhaps the Spur Mahogany and Queensland Maple will be alright for riser materials in composite bows, or even veneers under clear glass?

My interpretation of the figures below for an ELB is I should use Black Wattle for the back (because it has high MoE and hardness to resist damage), Red Tulip Oak for the belly (for its high rupture and crush strength) and perhaps the Silver Ash is OK for the core with good crush strength and a nice contrast in colour. Am I on the right track fellas? Thanks.

BTW I cut out a 64" spotty gum board bow along the lines of the flatbow in the old Popular Mechanics article on here. I got it all smoothed over and ready for its first look the the tillering tree and thought I will give it a good clean up and inspection for remaining saw or rasp marks. When I blew it down with compressed air I found a check on the back of the bow about half way along the top limb. It was about 2" long and about 1/4" in from the side. It ran out to the side of the limb at the end and was about 3/16" deep at this point. The other end seemed to finish at a small pin knot. I floor tillered the bow to exercise the wood during shaping so I flexed it again and the check opened up a fair bit. I don't reckon it would have survived tillering so I ran it through the band saw and by the time I resanded it the whole length of the bow was about 5/16" narrower. So now it looks more like a deep cored, narrow long bow. I am still going to tiller it for the exercise but only to 26" for a youth bow.

Cheers....... Rod

[Flatliner]

Sounds like a reasonable combo to me Rod but you gota remember I'm a composite bow man so I'm a little out of my field (and maybe a little out of my head too ) so I would be waiting for a second opinion if I were you.
I was also thinking it may be a good idea to select back cut sections out of your boards to maximize the strength characteristics and minimize the tendency of quarter cut timber that doesn't have really strait grain to twist to the side when it's bent.
Rob.