thickness for a given radius

[Jim Davis]

To not hijack Badger's thread, I started this one.

There is a particular thickness for each wood that will just barely not take set (yield) at a given radius.

To me, this information for each wood we commonly use would be very useful.

For instance, I have found that 1/2" to 9/16" is that thickness for the bows I make of Osage.  I make mostly "pyramid" bows and the thickness is close to uniform from fade to tips. Those bows are 66" ntn with a 4" stiff handle and 2" fades.

Since I know the thickness, if I want a stronger or weaker bow, I make it wider or narrower.

When I was making black locust bows, it seemed that 7/16" to 1/2" was the best thickness. The bows were much wider for a given weight than the Osage ones I've been making.

So, anybody want report what you have found to be the best thickness for a 66" ntn pyramid bow of other woods?

[Badger]

  Jim I think most woods will fall into that range of 7/16 to 9/16   some woods are good for a .4 strain and some a point 8 strain. Most white woods fall into about .6 I believe. Changing the working limb area on a limb can greatly change the radius of the arc a bowyer might use as well as the thickness. On my calculator I am trying to make a bowyer would find his approx. thickness just as he always does but before he gets to far he figures out a radius that limb should be bending on based on a known strain value. I was going to make a band with slip clamps holding it together, when I found out my desired radius I would simply adjust the band to the radius I wanted and hold it up to the bow to make sure I wasn't going to far or maybew I could go more. 

[PatM]

Won't elliptical versus circular skew that?

[Badger]

Won't elliptical versus circular skew that?

  Pat, on a tapered limb yes it would, about 3 readings would have to be taken and then average it out. I work with as little bending limb area as I can get away with. I don't mind having an area slightly understrained but I don't want any areas overstrained.

[George Tsoukalas]

Don't y'all account for the width? 

For me, the species (density) determines the width.

I actually never think too much about thickness. I start at 3/4" thick and remove  wood until the limbs are bending well and I have the weight I want.

Like Dean of eternal memory said inis all about dry wood expertly tillered.

Also helps keep set to a minimum.

But anyway ...I suppose there are different ways to arrive at the same point in time.

Jawge

[Jim Davis]

Won't elliptical versus circular skew that?

That's EXACTLY why I stipulated this: "So, anybody want report what you have found to be the best thickness for a 66" ntn pyramid bow of other woods?" A true pyramid bow has circular tiller. Of course, people modify every design...

Steve, the area only changes the best thickness if the area is increased by length. Width doesn't change what is the best thickness.

[PatM]

   I was only directing that at Steve.   But I just don't think you can   give more than a ball park figure for any wood due to variables within each species.
  You'll just end up with a similar chart to Baker's width recommendations for species.

[Badger]

   I was only directing that at Steve.   But I just don't think you can   give more than a ball park figure for any wood due to variables within each species.
  You'll just end up with a similar chart to Baker's width recommendations for species.

  Jim, I know that. That is why I am only concerned about radius. The tool won't tell you anything about how thick or thin to make it. It will only tell you if you are bending it too much nothing else.

[Selfbowman]

Guys this is where I was going witha chart for perfect deminishing mass on a given 28" limb. If you know this in one inch increments from fade to tips on say a 50 pound bow .you should be able to cut a piece of the stave to a desired size and weigh that section. I think Tim Baker did this in the Bible . Related math Arvin has not figured it out and would probably approach it backwards any way. This would be most helpful in bow design. Not the perfect answer by any means but get us close. Arvin

[Springbuck]

 Badger sadi:  Pat, on a tapered limb yes it would, about 3 readings would have to be taken and then average it out. I work with as little bending limb area as I can get away with. I don't mind having an area slightly understrained but I don't want any areas overstrained

So, elliptical tiller is a larger radius near the handle (and the limb correspondingly thicker or tapering in thickness) smaller radius midlimb, even smaller towards 2/3 of the way out, and resolves to a stiff tip in the last 6" .  Or whatever.  Right?

[Springbuck]

Jim, I do think this is a good track to get on.  I have mentioned before that understanding what a pyramid bow is, and does, and why, really nailed down bow design for me in general.  I kind of think of every bow I make as a modified pyramid.  "I wish I could make a pyramid, but since the stave dictates it has to be parallel HERE, and it's only this long, then I'll do this and this...."


Regarding thickness, I can tell you that for most white woods I have available to me, at @ 66" give or take, thinner is better.  I guess this is the concept of the "overbuilt" bow.   About 7/16- 1/2" is what I would have said, and a little thicker if I have to, or if it's very long.

I'm going to add that heat-treating whitewood bellies has been a real blessING to me.  However, while it seems to limit set and increase stiffness a bit, it doesn't seem to let me go narrower AND thicker.  Just narrower, and sometimes THINNER at the same drawweight.

Just impressions, I'm bad at writing things down.

[Badger]

Badger sadi:  Pat, on a tapered limb yes it would, about 3 readings would have to be taken and then average it out. I work with as little bending limb area as I can get away with. I don't mind having an area slightly understrained but I don't want any areas overstrained

So, elliptical tiller is a larger radius near the handle (and the limb correspondingly thicker or tapering in thickness) smaller radius midlimb, even smaller towards 2/3 of the way out, and resolves to a stiff tip in the last 6" .  Or whatever.  Right?

   The difference is pretty slight, if I can get away with a less elliptical tiller I just start narrowing down the outer limbs