Ozbow

Hi guys. Just want to get some advice as to whether the attached piece of timber is okay to make a bow out of. It's an unidentified eucalypt and you will see from the photos it has a bit of a bend at one end. I've marked a line at 70 inches which shows that the bulk of the bend is not a problem. Possible steam remedy? Apart from that it is very straight. I've also got a pic of the end grain which is at a bit of an angle. Is it acceptable as is or would it be necessary to adjust the angle of the back to be perpendicular to the grain?


Above image shows grain from straight end.


The above shows the grain from the bendy end with the line across at 70 inches from far end.


Above shows end grain at an angle.

Note I haven't made a bow as yet. I'll likely get a bamboo board soon to have a go at that also.

Thanks, Indie.

indie wrote:Hi guys. Just want to get some advice as to whether the attached piece of timber is okay to make a bow out of.

Indie,

The only way to find out is to make a bow from it. Do you know the history of the piece of timber?

Generally I reduce the board to a size that will comfortably accommodate the bow style. Quite often when reducing a board internal pressures/tensions are released and the timber will move.

I let the timber sit for a few days and if it hasn’t moved I mark out the bow.
For durability you could back the bow with pole bamboo.

Daryl.

Thanks Daryl. The timber was given to me by my brother-in-law, I'll ask if he knows the history of it but as he described it to me as "an unknown eucalypt" I don't think he'll have any further info. I'll cut it down and let it sit. Any thoughts on the end grain direction?

And yes, I'm keen on some bamboo backing.

If the end grain orientation runs true for the length of the board you may be able to have the grain either horizontal or vertical if the board is thick enough.

Backing the bow should overcome this issue. Note the grain run off in my Brigalow bow.
Daryl.

Cheers Daryl. I've edited the last pic to show the growth rings in black and what I expect is the optimal line for the back of the bow in red. This would get the growth rings at 90deg to the back. Would it be necessary to do this? Will it work fine with the growth rings at around 60deg to the back if I just make the current face the back of the bow? I suppose the other option is to chase a growth ring but that's my least desirable method. Thoughts?

Indie, is the board thick enough to cut a flat bow as indicated by the yellow lines?
Daryl.

Daryl, the entire board measures 90 x 35 so it could be a bit tight. If the bow blank ends up being 45 x 12 I need a 36mm board if it's cut at 30deg.

Indie, it is probably better to cut the board on the flat and back the bow with pole bamboo, hickory, sinew or other suitable material.

Daryl.

Looks like some kind of Vic ash, or Tassie oak. If it is, then its not good for bows, get a proven species. Sorry to disappoint you, but don't waste your time and a nice board that could be used for another project.
Hamish

Hamish, can you elaborate as to why they're no good? I've checked density for those species and they look okay at mid to high 600's. Elastic modulus also seems okay. I'll weigh the board and try to work out it's density.

Thanks.

immerse the timber lengthwise into water, do not totally let go. Mark where the water level got to. Divide the wet length by the dry length and multiply by a thousand. This will accurately measure the number of kilograms per cubic metre.


Hamish, Tasmanian Oak is a trade name for a number of similar appearing species, not a species name.

Kevin

Tassie Oak etc. Myself and quite a few other bowyers have tried it. Despite being overbuilt by normal standards, 76-80" long, flat bellied, bending through the handle the wood develops compression fractures, if you look at it harshly. In reality the timber I tried several times from different boards, chrysalled during tiller checks with a long strings. I have yet to experiment with a another timber that performs as badly in compression(I avoid trying timbers that are already known to be poor candidates for bows, so there are probably plenty of timbers out there equally or more unsuited.)

Unfortunately for us Aussies, the Bowyers Bibles wood density theory works better for woods from the Northern hemisphere. Many of our woods despite having a high density, or good stats for rupture etc, don't equate into good bow woods. Brittleness in tension,or and poor resistance in belly compression are quite common(there are plenty of exception though). Many of the stat's given are only relevant for static purposes, like beams in building.

We have some good local timber but most aren't easily available commercially, or in the quality to work in a self bow. For English longbows with round bellies Desert acacias, saffronheart work well.flatbow timbers -some eucalypts like ironbark and spotted gum will work but even then I find them a bit to touchy to invest my time in unless limbs are 2" or so wide.

The only thing that might be in your favour is on the end grain I can't see the distinct banding of growth ring like structures common to Vic ash etc. This could just be the way it was cross cut, if done roughly obscuring the end grain clearly. It could be a harder type of eucalypt, but the face grain looks just like Vic ash to me from the photo's.

Hi Kev, Haven't seen you for a while, hope you are doing well. You are right about the trade name thing. I never actually said they were species, but I see how my very average communication skills could have implied that, when I said to try a proven species. I probably should have said proven timber, or tree etc.
Hamish.

I understood what you were saying/trying to do.
I just thought that your knowledge and experience in this area is so great that it would be a pity to diminish it in any way such as possibly causing a little bit of "blurring".....never mind me it the TAFE teacher coming out. I just think that it is hard enough for beginners [me being one] when incorrect common names are used. Bootle is a fair reference and reasonably available. For me it is my bible wrt nomenclature. Pretty hard comparing results and insightful input if we are not talking about the same stick. Trouble is most of the timber sales points have very limited knowledge of their product other than the details on their goods delivery receipt.

Love the things you share about making selfbows. I dips me lid.

Kevin