What is considered acceptable set on a design/ material basis?

[scp]

I am simply trying to understand in ordinary language terms, what it means for viscoelastic material like wood to get the set, possibly in view of the "compaction" hypothesis. And whether such set is always detrimental and irreversible. Are we all agreeing that the set in bow limbs is bad? If so, do we really know how to prevent it? Wouldn't shooting the bow cause the set eventually? Is there any way we can actually prevent the set in wooden bows? How about all other viscoelastic materials? Do they all get the set?

"Cracking occurs when the strain is applied quickly and outside of the elastic limit."
https://en.wikipedia.org/wiki/Viscoelasticity

Is the set in bow limbs basically a kind of cracking? Can it be cured somehow?

What would be the best way to keep the stress in bow limbs within the elastaic limit of the material? No set tillering?

[willie]

It is my understanding a piece of wood can exhibit some viscoelastic properties, and to different degrees

What would be the best way to keep the stress in bow limbs within the elastaic limit of the material? No set tillering?

"No set" tillering as proposed by Badger can tell you early on when your chosen draw weight for the stave is too high. Lowering your weight goal lets you tiller for lower stresses before the damage/set/compaction becomes too apparent.  Steve (Badger) also has remarked, staves that take some permanent set without exhibiting viscoelastic properties make better flightbows.

[bradsmith2010]

I think it would vary depending on what the bow is intended to do,,
I hunt with a bow that has taken quite a bit of set over the last 25 years,, but it will  shoot a hunting arrow at acceptable fps to take game,,
I would not be happy with that much set on a new bow,, so I have a wide range of what is acceptable for a bow,, of course I always stirve for least amount of set,, but if it shoots hard and accurate,, with some set, Im ok with that too,,

[mmattockx]

Steve (Badger) also has remarked, staves that take some permanent set without exhibiting viscoelastic properties make better flightbows.

How do you arrange for that?


Mark

[willie]

From what I have read, wood exhibits varying degrees of recovery depending on microfibral angle (MFA) of the fiber in the cell wall.

How do you arrange for that?

By selecting a stave of mature wood rather than juvenile wood or compression wood. IIRC, wood from lower down in the bole has straighter MFA also.

[Don W]

Mature wood as in bigger older trees?

[PatM]

I think the evidence showed that juvenile wood was better.  That's likely why people report great results from practically sapling sized trees.

[Morgan]

I think the evidence showed that juvenile wood was better.  That's likely why people report great results from practically sapling sized trees.

Better for what Pat? I must have missed something. Something that I have come across in my relatively little experience working with saplings is that I can ask more of a sapling than I can of a large tree of the same species. I know that it isn’t a scientific statement, and scientifically I don’t know why, but I will explain what I mean. Last handful of bows I’ve made has been from elm and hackberry saplings. The diameter of the saplings demanded a limb width of 1 1/8”-1 1/4” at the widest point. Length has been 60” - 66” and draw weights were in the low 40’s to the mid 50’s. All bent through handle eastern woodland inspired bows. I haven’t had an appreciable amount of set in any except one hackberry gave me 2” and I’m certain it was my fault. I have tried to go narrow and short with staves from larger trees before and can’t achieve what I can with saplings. That may be my inexperience, or a fault in my tillering. I can say with certainty that the rule of wide and long for less set with whitewoods can be bent when using saplings, at least in some species, and I don’t know for sure why? Is the wood itself more pliable and or resilient? Or is it the inherent crown that helps? Or have I been lucky?

[Morgan]

To address the question of the post. Acceptable amount of set is a personal matter. If it’s ok with you it is acceptable. I like to be under 1 1/2” on string follow. More than that and early string tension feels soft. I have not hunted with the bows that I make, but I make every one with the idea in mind that I may, and though I haven’t chronograph proof or anything like that, I know that a light limbed 50 lb bow with a tight early string shoots harder than the same with a soft early string .

[Fox]

I think the evidence showed that juvenile wood was better.  That's likely why people report great results from practically sapling sized trees.

I would think the high crown in sapling staves has a lot to do with the better compression abilities of saplings….. Morgan, have you ever tried trapping a bow made from a large diameter tree and then using the same widths as you use on your saplings stave bows?

I have basically no experience in this matter, just what I believe from reading…. That said I did make one bow a while ago that was hickory 59” long bend thru the handle and only maybe 1 1/4” wide… although it was only drawn to 26” at 35# but it only took 1/2” of set.


Set over 1” starts to annoy me…

[willie]

I think the evidence showed that juvenile wood was better.  That's likely why people report great results from practically sapling sized trees.

For flight bows?

Mature wood as in bigger older trees?

Yes.  One thing I have found in bigger older trees however is a declining earlywood/latewood ratio as the tree becomes more aged, or otherwise less robust. I think it has a lot to do with the size/health of the crown relative to the trunk it serves. wood density can be a good indicator of this ratio in ring porous species.

Wood grown in windy conditions or otherwise subject to more severe bending, develop cells with a higher MFA. It does seem to make a tougher bow from my limited experience with a few species I have local, but the ability to bounce back from severe strains, in my opinion, comes with a higher hysteresis, which hurts efficiency when shooting very light arrows.

[Morgan]

Fox, I have not ever really trapped a bow. I have came close a couple times, but can’t ever bring myself to do it. I know it works and others are successful with it but there’s some reason I just haven’t committed to it.

[bassman211]

Black Locust for me always seems to work out best with a trapped back, and your tillering skills must be spot on to make one with a nice reflex  profile when finished. If you end up with no belly frets, or broken backs, and the bow holds it's profile after number of shots over a period of years you can give your self a little pat on the back, and that all has to start with a good stave.