Author Topic: vertical grain is stronger than horizontal grain  (Read 10736 times)

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Offline Morgan

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Re: vertical grain is stronger than horizontal grain
« Reply #75 on: January 27, 2019, 06:53:46 pm »
  OK,  but hopefully he gets the other detail.
No sir. If its the detail of intertwined grain, Im not sure I follow you. If its the comment of quarter sawn, I still dont follow. You  can split elm. Its not fun but you can. In my opinion, if you split the piece then plane the exposed wood flat, to get a smooth surface, It does not  differ much from  a piece that is quartersawn at all. If youre speaking of a detail that I didnt say, please let me know what I missed.

Offline PatM

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Re: vertical grain is stronger than horizontal grain
« Reply #76 on: January 28, 2019, 02:25:18 am »
He was talking about achieving it with a more primitive scenario and getting a near clean back solely by splitting the wood.  No saws, and likely no planes.  Splitting most  Elm without better than average splitting tools is a bit more complex too.  This is not about whether it can be done at all or whether Elm makes a good board bow.

  When you make a n Elm bow  primitively you already have to make one interlocked grain surface smooth, doesn't make much sense doubling that.

Offline Artus

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Re: vertical grain is stronger than horizontal grain
« Reply #77 on: January 28, 2019, 11:49:43 am »
Thats exactly the point.

I forgot to say, when I split the log in halves I wasnt happy with the surface, so I split it in quarters and the "quarter surface" was much better. I also have to admit that this ist the first time I use green wood right after cutting it down and rough the bow out with an axe. I was very surprised how fast and yet precise I got all the wood off.

Today I roughed out a second bow out of the other quarter I got from the tree (the other two are not usable). I stored it in water to keep the wood soft. This one Im going to make the common way. The outermost ring is thick enough to be used as a back.

From that point roughing out the bow was easier to me with vertical grain. I also wont make the heck off an effort to scrape the wood. I really wanna find out how much stress the splitting surface can take.

To summarize:
From what I can say now the only benefit is, the quick roughing out. But Im still the opinion that a small log can benefit from being built reverse, as long as it can be split straight through. I tried splitting a small ash tree with wedges, but failed. Has anybody a tip on how to split small trees? Maybe hammering a large knife all the way through?

Regards from Austria/Europe (no kangaroos)

Offline willie

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Re: vertical grain is stronger than horizontal grain
« Reply #78 on: January 28, 2019, 12:48:43 pm »


But for my feeling it is faster to rough out the bow that way. I have to admit here, that Im also trying to make a bow completely outside with minimal tools. Some kind of an anthropological experiment, I wanna feel how our ancestor bowyers used to do it.


there were some examples of primitive bows made from splits in the new world.  birch and osage as I recall and maybe also the quarter side as back.

my experience with splitting is that knots will make the grain runoff. to use wedges and avoid runoff, the split has to be through the center of mass, or center of strength so to speak. when the split off piece bends away from the wedge more than a the stiffer stock, grain will run off

Offline PatM

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Re: vertical grain is stronger than horizontal grain
« Reply #79 on: January 28, 2019, 01:34:19 pm »
The problem with New World bows in a primitive sense is that they likely date from a time of metal tools or even lumber attained from milled lumber in some cases.

Offline Artus

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Re: vertical grain is stronger than horizontal grain
« Reply #80 on: January 28, 2019, 07:31:19 pm »


my experience with splitting is that knots will make the grain runoff. to use wedges and avoid runoff, the split has to be through the center of mass, or center of strength so to speak. when the split off piece bends away from the wedge more than a the stiffer stock, grain will run off
[/quote]

Thanks! Just to get you right:
The halfes must not bend away from the split. So the split line must be chosen so that:
The halfes become more thick than wide an hence bend less away aka are stiffer in direction 90 to the split line.
So hammering a knife through could help that too I guess

Offline willie

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Re: vertical grain is stronger than horizontal grain
« Reply #81 on: January 29, 2019, 01:51:46 pm »
Quote
The halfes become more thick than wide an hence bend less away aka are stiffer in direction 90 to the split line.

Not sure of the question above. Please try a different wording


generally, when wood workers split green wood the object is to control a split so that the work piece comes out close to the desired dimensions.
bending either side of the work piece creates runoff. a process called riving. It can be seen in the attached pdf

of course, a bowyers objective is to avoid runoff, so knots and excessive forces are to be avoided. a split not centered will create bending force,
a wider wedge creating more force,  so yes, a knife could be a good tool for splitting evenly.

some woods follow the grain much better than others. where I am alder splits very well and birch is the worst. I am not familiar with ash, and believe ash in Europe may differ from ash in NA.

an interesting thought is....... just how much does a good split need to smoothed to work well in a primitive bow?



« Last Edit: January 29, 2019, 02:10:46 pm by willie »

Offline Artus

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Re: vertical grain is stronger than horizontal grain
« Reply #82 on: January 30, 2019, 11:05:00 am »
Thank you very much for the file! Thats some really useful information! Probably Ill build me a riving tool.

What I wanted to say is, one should aim for halfes that are more thick then wide, so that they bend less away.

Offline Artus

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Re: vertical grain is stronger than horizontal grain
« Reply #83 on: February 05, 2019, 11:15:02 am »
Alright guys, I got some results:

But first things first. I recognized pretty early that the bow is going to be far too weak. I was a bit too eager at the roughing out stage aka was the roughing out too rough. So I had to remove quite a bit material to get it fairly smooth. But hey, that was the first time I roughed out a bow from green wood with just a hatched. But I didn`t do much sraping at the back. I really liked to see how much the splitting surface can take.

Because the bow would have become far too weak anyway I decided to just tiller it quick and dirty and left some weak spots, to really stress it out and see if the back or the belly fails first. Here is a pic at full draw. Please dont mention the tillering tree. Thats not the usual way I do it.



One can really see the weak spot in the right limb (thats the upper limb) near the handle. The midsection is too stiff. The left limb is the lower one and bends ok, but its much stiffer than the other one.
As you might expect, the weak spot got overpowered and started crysaling. The bow drew 15# at 28".
So I shortened it from 70" to 66" inches and drew it again. It broke at about 20".
I inspected the broken section to find out, that the belly collapsed. Heres a picture of the broken area.




Then I also bent the intact limb by hand to see how much it can take. I bent it till I could here a cracking sound and checked the wood. The belly started to collapse, while the back was still fine! Then I caused it to break.





The fact, that the belly got chrysals before the back failed tells me, that the split surface works as a back just fine even with some imperfections and doesnt need a lot of scraping and smoothing.

Here are pictures of the back before tillering:



To me using vertical grain is not necessarily faster then using the outermost ring under the bark. For sure its less effort than chasing a ring. And I found the roughing out quicker. I still wanna try to make a bow out of a small log that is just split in half and use the splitting surface as the back. A reversed bow if you want. In that case the advantage would be the rectangular cross section instead of the high crown a small log usually gives. But I postpone this to spring when the wood is more pliable an easier to split.

greetings from Austria

Offline Bayou Ben

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Re: vertical grain is stronger than horizontal grain
« Reply #84 on: February 05, 2019, 11:49:24 am »
Nice that you followed through with the experiment. 

I'm not following you with the advantage of a rectangular cross section, besides maybe being easier to work.   

Wouldn't tension strong woods such as ash like you used benefit from a crowned back and flat belly?  It seems that increasing the surface area of the back and decreasing it on the belly would only increase the difference between the already mismatched tension/compression strengths.

Offline Jim Davis

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Re: vertical grain is stronger than horizontal grain
« Reply #85 on: February 05, 2019, 01:52:08 pm »
...Wouldn't tension strong woods such as ash like you used benefit from a crowned back and flat belly?  ...

Just for the record, almost all woods are 3 to 4 times stronger in tension than compression.
Jim Davis

Kentucky--formerly Maine

Offline Artus

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Re: vertical grain is stronger than horizontal grain
« Reply #86 on: February 06, 2019, 10:57:43 am »
Good point indeed! Im just relating to what is written on rectangular shape in the TBB.

Offline willie

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Re: vertical grain is stronger than horizontal grain
« Reply #87 on: February 06, 2019, 02:55:56 pm »
good to see someone that like to experiment. finding out whether a certain kind of wood is "tension strong" or "compression strong" is not that easy. any imperfection in the back can cause a catastrophic failure, while a belly can chrysal in a number of places before a bow limb folds.

the descriptions are somewhat of an invention of Tim Baker.

any moisture more than Ideal will usually cause premature compression failure, and give the appearance of the wood being "tension strong"

Offline Artus

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Re: vertical grain is stronger than horizontal grain
« Reply #88 on: February 09, 2019, 12:23:37 pm »
Thats a good point. But Im gonna redo the experiment in spring, to verify the results.

Im about to finish the bow from the second stave of the same tree. I did this one the common way.
Its 71 long but quiet narrow, only 35mm at the fades. It also turned out at the weak side and draws 25#. I still have to get used to using green wood and roughing out with a hatched.
 I had planed to temper the belly anyway, but at that occasion I could flip the tips a little bit and/or string it reverse while roasting. Id like to reach about 35#.
 Let me know when you think!

https://i.imgur.com/d4UenB7.jpg
https://i.imgur.com/bmBvgWj.jpg
https://i.imgur.com/1BnzkAc.jpg

Thanks!

Offline Jim Davis

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Re: vertical grain is stronger than horizontal grain
« Reply #89 on: February 09, 2019, 01:49:20 pm »
The fact, that the belly got chrysals before the back failed tells me, that the split surface works as a back just fine even with some imperfections and doesnt need a lot of scraping and smoothing.... .

What this shows is what has been known since the first engineering tests were done: wood is stronger in tension than compression.

It says NOTHING about the  relative strength of vertical grain wood compared to "horizontal" grain.
Jim Davis

Kentucky--formerly Maine