Return speed test (?)

[huisme]

I've done bend tests on several woods and come to the same conclusion as everyone else, but I'm wondering how many people have tried this method.

The wood database was brought up on /r/bowyer, the normal talk about numbers happened, the normal suggestion that we need not worry about it was there, but I like knowing things to know things.

I suggest a/several 1/8"x1/2"x3' pieces of several woods be clamped to a bench, a button set to contact the wood precisely two inches below the resting point of the wood, holding the wood down, ensuring that when the wood is pulled down six inches, held for three seconds, and released the wood will strike the button and the time between release and collision can be tested.

[Badger]

  That would be an interesting test. I am not sure how much the actual weight of the wood might affect the test, usually on a test like this we are trying to isolate histerias. If it effectively did that it would be good in rating wood.

[huisme]

Perhaps for a second/complimentary test a weight can be established one of the lighter woods and any heavier woods can be carefully reduced (don't give one piece a taper while the others are square) to match.

[huisme]

So has anybody done this? I only have a tonne of locust, some vine maple and Oregon ash, and not enough osage at my disposal for now.

[willie]

marc

I have tested wood from staves I find local. what are you wanting to test for specifically? send a pm if you want to swap some black locust.

willie

[huisme]

Because of the way an optimized black locust flatbow snaps back to brace compared to the same from osage I want to perform these tests, or see results is anyone has done it themselves, to see if these numbers might be what's missing from all the mathematical approaches to bowyery.

It really all started when someone brought up the article on the wood database where the author assumed a low modulus of elasticity was essential to good bow wood and therefore a wood like black locust is mediocre at best.

And I simply can not be told not to look into it because we already know enough about bowyery, ancestors knew best, good wood is good wood, etc. It's something we could know that could tell us why good wood is good wood and I will not be kept ignorant.

[end rant]

Are you looking to get locust? What for exactly?

[Badger]

  Several years ago Tim Baker and I ran some tests on 1/8" X 2" by about 18" long. We would pull it down to a certain depth that was in a locked position and then slide our finger off. We measued how far it would spring back past center. Black locust and ipe measured the best out of those we tested, I believe cherry was up there also. There was not a huge difference in any of them. Bamboo was one of the lower ones.

[Badger]

  The test you suggest would give acceleration but I am not sure if vellocity could be accurately calculated, I think it could. If you knew the amount of mass it was moving and the work you were applying downward you could come up with an efficiency figure. Usually n this type of test you are looking for hysterias. Not sure how accurately you could in it down. You would easily be able to record losses occuring as the wood became overstrained. This would be of good value I think.

[willie]

the author assumed a low modulus of elasticity was essential to good bow wood and therefore a wood like black locust is mediocre at best.

I am not sure that this statement is true. MOE (modulus of elasticity), is not really a description of elasticity as a bowyer would think of it. it is really a measure of stiffness. Yew is known for its bendability, as is Osage, but yew has a low moe and osage a high one, as one would expect, since osage is relativity dense and yew is much lighter. One the other side of the coin there are stiff woods, both light and heavy that don't bend much before they break- think of spruce- strong for its weight, but not a very good choice for something that is going to be highly stressed. It might break without warning. good bow woods must be evaluated in ways that most wood is not, as most wood is used well below its breaking point, and unfortunately, these tests are not commonly done for most woods by those that pursue such matters. As boyers we stress wood near and beyond its proportional limit. and yes black locust is a good bow wood, otherwise I would not be asking you if you had some to trade:)

[DavidV]

Marc, we were discussing this on /r/Bowyer earlier but now I realize what you're saying. It seems a test like this would produce values to test a wood's performance rather than design requirements. The problem I see is that wood varies so much from tree to tree it would be hard to get consistent results. For example, doing bend tests on thin osage splits from 2 different logs cut here, one bent into a U shape while another (thinner ringed) snapped. I can see some value though if you had the equipment.

As to getting wood for the testing, contact a custom lam grinder for FG bows (not 3rivers or binghams) get .125" lams (tapered?) Of several species. You can request quartersawn wood only at the two supplyers here in MO.

[Marc St Louis]

Perhaps using a high speed camera and counting the number of frames between letting go of the strip and its impact on a stop?

Better yet use a chronograph and use a long enough strip to activate both sensors

[PatM]

I was thinking you could just twang the piece between the chronograph sensors.

[JacksonCash]

Perhaps using a high speed camera and counting the number of frames between letting go of the strip and its impact on a stop?

Better yet use a chronograph and use a long enough strip to activate both sensors

This would be a good method, I think. You could get acceleration and velocity and just about any instance with this. To get a sensor to do a similar thing could be quite expensive.

Maybe an accelerometer mounted to the wood, but that would vary drastically depending on where you put it on the wood.

[huisme]

I like the high speed camera and chrono idea, I have friends with both

Do you think a dozen of those lams David mentioned would be a decent sample for each wood I can get, or does everyone think like I do that I need to start making trades with this in mind? I can't make the lams consistent enough with my tools so it'd be a bit to ask of anyone (five sources?) to make a dozen identical lams of what they consider average osage and another dozen of some of their best (good luck making that happen, right?).

Willie, from the article:

In terms of looking at the raw mechanical data of woods, the best bow woods tend to be those that have a low MOE and a high MOR. (Stated another way, the best bow woods tend to be those that will bend easily, and not break.) It’s of little advantage if a given wood scores well in one area, and poorly in another (i.e., a very low MOE or a very high MOR). What is most important, regardless of how low the MOE may be, or how high the MOR may be, is the ratio of the MOE to the MOR; it must be easy to bend AND hard to break.

Locust is pretty hard to break; I've had one explosion because I'd cut right through a large pin knot and just hoped it'd be okay. Locust will, in my experience, fold over before it snaps if the back is perfect; it's MOR is 5.2 MPa higher than osage (estimated based on dry osage of course, but still), but it is significantly stiffer than any of the article's listed best bow woods.

This is why bowyers should be running these tests

[PatM]

I don't think milled lams are the way to go. Unless they  are perfectly straight grained a lot of the structural integrity will be missing.