Spotted Gum question

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ed · #1 Post by ed » Tue Jul 25, 2006 4:48 pm

Hi again. I didn't get to see the replies to this question so I will post it again and hope people are kind enough to answer it once more....

Though I am cutting back some spotted gum I bought as a post, to one of its growth rings, I wonder if it is normally necessary. The wood is extremely dense and seems to have little loss of strength between growth rings anyway. How likely is it to split if it was just to be cut to shape and ignoring shaving the back down to one growth ring?

I ask mainly for future bows, I am already cutting this one back - damn hard work though.

GrahameA · #2 Post by **GrahameA** » Tue Jul 25, 2006 5:56 pm

Hi Ed

IMHO - I would try and get back to a single ring. I have had a few that have decided to fail and it always seems to start with a feather lifting where a ring was cut. But then again I am pretty poor bowyer - and I am serious when I say that.

Part of the issue is how heavy a bow you are building. 40lb seem to be the point at which problems start below that you can do all sorts of things and when you go over 50lb tread carefully.

Glenn Newell · #3 Post by **Glenn Newell** » Tue Jul 25, 2006 6:23 pm

Ed our Aussie hardwoods while they do have growth rings that is not the true grain, to find the true grain you need to split the timber as sleeper cutters use to do, it's a waste of time working down to a growth ring with spotty and other hardwoods, spotted gum does not have the separation of of latewoods by the pulpy earlywood as northern hemisphere timbers have so you wont run into trouble there. The biggest problem with spotty is the location where it was grown, it needs to be cut west of the Great Divide, west of Chinchilla is best, anything that comes from the coast is useless for bows. When you make a self bow out of our hardwoods just make sure that there are no sudden run-offs of the grain you can usually sight it. Don't leave any square edges on the bow limb, round them off well and this will deter splinters from lifting on the edges...Glenn...

ed · #4 Post by ed » Tue Jul 25, 2006 6:46 pm

hmm ok, that sort of leaves me wondering what I am even doing! hehe.
Ah well, I am looking at over 50#, in fact more like 70# so I suppose I could back it to make it a little safer. No problem with compression then for spotted gum?
This peice is cut square so I can see some grain run off at the sides. When I get down to the one growth ring I will see if there is room to follow the grain the whole way or if I will have to compromise.

Has anybody tried backing it with bamboo? Rough it out and then tiller after the glue up? I have some Selleys urea formaldehyde that should do the job. I have also seen selfbows backed with denim, but read that raw silk strands is better - like where do you get that!

I am happy to experiment a bit with the bow a bit. Not unhappy if it ends up being too short for me but long enough for some 28 inch draw shorty. I can always give it away. Anyway back to carving it out again - too late to stop carving for that growth ring.

greybeard · #5 Post by **greybeard** » Wed Jul 26, 2006 8:50 pm

Hi Ed,
I you are contemplating backing the spotted gum with bamboo a lot can be learnt from Dean Torges book or video 'Hunting The Bamboo Backed Bow'. If you can't get a full length stave out of the post take twins out of the post and 'Z' splice at the handle.

Daryl.

ed · #6 Post by ed » Wed Jul 26, 2006 10:35 pm

thanks. I will have to look up the book. I am hoping to get a 76 inch bow out of it, less than that might be a worry for 32 inch draw, 80 would be better. Hadn't thought of Z splicing it but sounds like a good idea.
no chance to work on it for a bit as I will be in Sydney....

greybeard · #7 Post by **greybeard** » Fri Aug 25, 2006 9:22 pm

Hi,
While cutting spotted gum floorboards for laminations some of them took a twist as they came out of the table saw. I took the offending laminations to the supplier and they were most helpful in explaining the problem. The board had been cut from as section of log that probably had a natural bend in it and that board contained late and early growth running through the board. Hopefully the photo illustrates the problem?
I have raised this point to assist those wishing to make selfbows out of milled boards as a change such as this when removing wood from the belly (and releasing tension) could be disastrous in a selfbow.
Daryl.

ed · #8 Post by ed » Sat Aug 26, 2006 1:07 am

too late to scare me Daryl

already have a board glued up and handle going on tomorrow. Will not be unhappy if it doesn't work out great though - so long as it doesn't bend like your peice!!

little indian · #9 Post by **little indian** » Tue Aug 29, 2006 10:26 pm

What is it about east of the divide spotted gum
that makes it unsuitable for bows?
and how do i tell the difference at the hardware shop?

greybeard · #10 Post by **greybeard** » Wed Aug 30, 2006 7:09 pm

Hi little indian,
I am not an expert on timbers but it would appear that timbers grown on the eastern side of the range are usually in a higher rainfall area and grow more quickly. Timber from west of the range being generally drier area seem to produce a more dense timber. Weight and tightness of grain in the timber should give an indication. For preference I deal with a timber yard rather than the local hardware as the timber merchant seems to have more knowledgable staff.
Daryl.