Tonka is Not So Good

[Marc St Louis]

Tonka is a SA tropical hardwood that is very heavy and has very high compression strength.  I had been wanting to try this wood and I got enough from Steve Quinton a couple years ago to make a bow.  I backed it with Bamboo in a R/D style and have been working on it a bit now and then.  The bow was 60" long and 1" wide and in the last couple weeks I tillered the bow out.  I had it tillered out to 27" where it was pulling 65#, I should have quit there.  When I pulled the bow to 28" the core let go in a very odd manner. The failure was not violent, in fact it was almost in slow motion.   You can see what happened in this picture



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[Badger]

       Mark, this seems to be a common problem with a growing list of tropical hardwoods. They are very strong then suddenly chrysal. I have gotten gun shy about experimenting due to my wallet not having an endless supply of money in it LOL. Steve

[Hillbilly]

Bummer, looked like it was shaping up to be a real nice one. Shame that tonka wood isn't as tough as those Tonka trucks I had back in the day.

[Marc St Louis]

Steve
I was amazed at how strong the wood is.  The failure was not your typical chrysal

Well that being the case maybe we should look into making bows with those Tonka trucks 

[Badger]

Mark, hard to see what happened, I thought it was a chrysal. I have two common problems with tropicals, one is chrsaling and the other is where it just blows out, the grain just seperates in sheer tension and rides up over the grain it was attached to. Bummer either way. What happened on that bow? Steve

[Marc St Louis]

Steve
More like the second failure you mention there.  The limb just buckled in on itself.

[sumpitan]

For what it's worth, tonka is also known as cumaru.

Tuukka

[markinengland]

Marc,
Do you think the wood would work better if the bow was narrower and thicker?
I had had a similar experience with Ipe when it was very thin?
Maybe a skinny deep bow wood?
Is there enough wood left to try making a skinny bow out of the bits?
Mark in England

[Marc St Louis]

I don't think so Mark.  It was already only 1" wide.  Perhaps a flat belly might have worked, it was a shallow D section

[Kegan]

Maybe if it were wider/longer? Would that have helped ?

[D. Tiller]

Higher humidity? Seems like bows made from these woods where originally in jungals.

[Marc St Louis]

That would have helped Kegan.

The humidity up here right now is quite high

[mullet]

  What's high up there Marc? It's 88 percent here right now.

[Rich Saffold]

Most tropicals are too convoluted grain wise to mess with on high performance belly sections. I have access to most where I  live and years ago tried many of them, and until Ipe showed up at the lumber yard I had pretty much given up..Satinwood being one of the few exceptions.

Rich

[Marc St Louis]

You got me beat Eddie. Here's it's in the 70's.

There's a few more that work quite well besides Ipe Rich.