Author Topic: massaging out set in bow after several hours of shooting your self bow  (Read 8034 times)

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Offline Jim Davis

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #30 on: January 25, 2017, 12:12:45 am »
Reply to asharrow:

...Having said this, I don't think there is anything wrong in asking a question,  having a general discussion about set, string follow and what actually happens in the wood during that process.

Having curiosity is something that has served me well and it is the only way to further knowledge, either through the wisdom and experience of others or by experimenting yourself and seeing what goes right and what goes wrong and to educate yourself and to become better at whatever you set your mind to do.

Absolutely right.
Jim Davis

Kentucky--formerly Maine

Offline Jim Davis

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #31 on: January 25, 2017, 12:15:32 am »
Jawge has it exactly right. The centuries old definitions.
Jim Davis

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Offline Pappy

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #32 on: January 25, 2017, 05:02:32 am »
Yep Jawges definition is how I view it also. As far as bending it backwards, not usually a good idea especially if you go to far, a little I guess might not hurt but not worth the chance to me. I have seen several bow broken from folks unknowingly trying to string the backwards.  :) The belly is like a badly violated back and you don't want that.  ;)
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Offline WillS

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #33 on: January 25, 2017, 06:16:44 am »
Jawge said exactly what I said, essentially word for word.  But I'm glad somebody got it right... ::)

Offline George Tsoukalas

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #34 on: January 25, 2017, 09:46:50 am »
Pretty much, Willis, except for set being temporary. I didn't say that.
I've noticed that some of it is temporary after unstringing but most remains.
Jawge
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If you ain't breakin' you ain't makin!

Offline mwosborn

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #35 on: January 25, 2017, 10:24:06 am »
Good discussion.  All I know is that after building maybe 30 all wooden bows I only have a few that haven't taken some set.  Two were osage and the other is sinew backed.  Being as careful as I can and going as slow as I can my white wood selfbows all take at least some set.
Enjoy the hunt!  Mitch

Offline Badger

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #36 on: January 25, 2017, 11:31:29 am »
Good discussion.  All I know is that after building maybe 30 all wooden bows I only have a few that haven't taken some set.  Two were osage and the other is sinew backed.  Being as careful as I can and going as slow as I can my white wood selfbows all take at least some set.

   All wood bows will take some set, I think the challenge for a bowyer is to do his best to keep it under as much control as he can. There are several tecniques you can use that can help you to monitor it as you go along. The most basic thing we can do it to not ask too much from a design, make sure the bow is wide enough and make sure we have enough bending limb and that the bow is long enough for the draw length. Keeping moisture under control is another big factor. Patience is another one. If someone gets impatient because scraping wood isn't dropping weight fast enough the tendency is to pull it further to make the change register. If I have 50# say at 20" I may have to check it 5 or 6 times scraping it inbetween each scrape just to get it to 21". Patience is the biggest most important tool we have.

    Someone asked me to elaborate on the statement that I prefer no recovery or as little as possible. Recovery of set doesn't ahppen at the same speed. It doesn't just creep forward at say 2" per hour. It starts off fast and slows down. You might recover a full inch when you unstring it before you can even put the bow against a wal to check it, less than 1 second. The second 1" might take a full hour. If the bow doesn't recover at all chances are you are not suffering as much hysterisis durring the shot. Kind of like what you see is what you get.

    Another one is when we use heat to reflex a bow. Sometimes we keep almost all of it and sometimes we might only keep 1/2 of it. It might be set and it might be that the reflex we put in just didn't hold. The difference is that belly fibers may not have ben crushed at all it mmight just be that the compression bend we put in the back of the bow pulled back out and doesn't really hurt a thing besides loosing some of the reflex we wanted.

Offline Philipp A

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #37 on: January 26, 2017, 08:13:25 am »
Thank you all very much for the responses, it is much appreciated. It has been definitely educational and I am looking forward to learning more about the mechanical properties of wood from all of you. I have also found several interesting scientific articles in this regard and hope to be able to get a better understanding of the compression failure mechanism in wood of which string follow and set seems to be a mild form of it. One of the articles I have read is called "Compression failure mechanism in small scale timber specimens".

It describes it as follows:

Under a compression load parallel to the grain, small clear-wood specimens undergo four main deformation steps: linear elastic (a), incipient kinking (b), transient kinking (c) and steady-state kinking (d). The incipient kinking is the plastic shearing and buckling of the fibres, localised close to the resin canal region where the fibres are misaligned [I am assuming this is where string follow / set happens]. The transient kinking phase is defined as the unification of all the incipient kinking areas in a unique kinkband that goes through the entire width of the specimen and starts when the peak stress is reached. This step is also characterised by a decrease in the stress, which eventually reaches a plateau when the fibres inside the kinkband can no longer rotate (lock-up angle). The process that takes place during this step is a broadening of the kinkband at a constant stress level (steady-state kinking).

The Swedish article has many illustrations and was primarily written to further the understanding of failure modes in glulam beams.

Cheers,

Phil

Offline willie

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #38 on: January 26, 2017, 02:32:54 pm »
thanks for posting that quote, and good luck with your search for better understanding.

in the article you cited earlier     https://www.doitpoms.ac.uk/tlplib/wood/printall.php     

Quote
The structure of wood (I)   

Cell wall schematic

Further cells are aligned parallel to the cell shown. The middle layer is the thickest and most important, and the orientation of the cellulose microfibrils is significant. The orientation of the microfibrils has only been shown for this layer. The cell wall is approximately 50% cellulose fibrils. To toughen the structure, the fibrils are aligned at 10 to 30° to the tree trunk axis in the middle layer of the cell wall.

Microfibril angle might be a factor worth noting, and if you uncover pertinent info related to set, would you be kind enough to pass it along with a follow up post?

 

Offline PatM

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #39 on: January 26, 2017, 03:37:54 pm »
That may explain why chrysals typically run at angles rather than straight across.

Offline Marc St Louis

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #40 on: January 26, 2017, 05:23:45 pm »
Phil, I don't think bending it backwards  is a good idea either.

Regarding set and string follow...they are cousins.

This is how I see it.

String follow is when the bow appears to be strung when it is not.

Set is when the bow moves from its starting point when it was a stave.

Here's an example.

A stave starts with 3 in. of reflex. After tillering it retains 1 inch of reflex so it does not follow the string but it does have 2 in. of set.

Jawge

Essentially what I was saying.

My definition of string follow is what Steve describes as the limbs recovering after you unstring the bow.  All bows have that, some more than others
Home of heat-treating, Corbeil, On.  Canada

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Offline Philipp A

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #41 on: January 26, 2017, 06:09:59 pm »
To Willie: I found this article on the impact of MFA (microfibril angle) on compressive strength in wood and it is negatively correlated. Please see article link below:

https://www.researchgate.net/profile/Paulo_Ricardo_Gherardi_Hein/publication/262745273_Relationships_between_microfibril_angle_modulus_of_elasticity_and_compressive_strength_in_Eucalyptus_wood/links/00b7d539af9b26a7ac000000/Relationships-between-microfibril-angle-modulus-of-elasticity-and-compressive-strength-in-Eucalyptus-wood.pdf

Next step for me is to find an article on the applicable MFA for the different types of bow wood  :)

Cheers,

Phil


Offline Philipp A

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #43 on: January 26, 2017, 06:55:44 pm »
PS to my last post: you can also download that article on MFA as a pdf file. It is much more readable that way.

Offline willie

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Re: massaging out set in bow after several hours of shooting your self bow
« Reply #44 on: January 27, 2017, 02:42:45 am »
thanks for the links, looks like good reading after work tonite.

there was a discussion a while back about MFA a while back.

http://www.primitivearcher.com/smf/index.php/topic,55682.0.html


sure would be nice for a bowyer to be able to inspect his materiel, and see the actual microfibrill angle of any given piece.


a paper that might interest Yew guys      http://e-collection.library.ethz.ch/eserv/eth:30567/eth-30567-02.pdf
« Last Edit: January 27, 2017, 03:23:51 am by willie »