Del's Pyramid Taper Test!

[Badger]

  Thank you Del, I have al;ways wanted to do that. Tim Baker always told me they would bend the same but it didn't make sense to me. Cool test! I am curious as to the handshock.

[Jim Davis]

OK, I DO want to say "I told you so!" And you, and you, and you for years.  If you can find my posts on "pyramid" bows you will find I have literally been saying this for many years and having it fall on deaf ears. Not only here but on the leatherwall too.

I have made only "pyramid" bows for a dozen years because they take less time to make and shoot as well as the best other designs.

OF COURSE, the design is not mine and not new. I came across it in Archery, the Technical Side a long time ago.

Thanks Del for posting the tests. I still urge everyone to try the test. You can make a single "limb" tapered to a point and make it out of plywood if you want or thin hickory or whatever. Clamp the big end  in a vice and flex the pointy end. Doing it yourself will make a true believer out of you.

This one was about five years ago.

Jim

[SLIMBOB]

Thanks Del. Hard to argue against the results. I have been told for years that this would be the results. Didn't disbelieve it so much as question what difference it makes (pyramid vs parallel) in the final analysis. Most efficient design?  Greatest cast?  This test has got me to thinking about things for sure. Thanks for doing it.

[Billinthedesert]

This is a headscratcher for me, but I am thinking the uniform thickness and compression/tension properties of the plastic material lend a different result than would be had using yew, osage, vine maple, hazel, etc, with some crown on the back. I could be full of beans though. My late father used to tell me, "You're all wet, mister." He was always right.

[Knoll]

Thank you, Del.
My conclusion from your test is that for a  given homogenous material and thickness and constant thickness and shaped as a pyramid, the bending profile will be the same regardless of thickness. 
Also, though wood is not a homogenous material, a given species shares similar physical/strength characteristics and, therefore, a given wood species will exhibit similar results.
Have tension/compression stresses along the length of such a limb profile ( & other typical profiles) been measured?

[Jim Davis]

This is a headscratcher for me, but I am thinking the uniform thickness and compression/tension properties of the plastic material lend a different result than would be had using yew, osage, vine maple, hazel, etc, with some crown on the back. I could be full of beans though. My late father used to tell me, "You're all wet, mister." He was always right.

It is an assumption to think that the compression and tension properties are uniform/equal in the plastic used.

With wood the tension strength is something like 3 times greater than the compression strength in most cases. But the stretch and compression are about  the same--1 percent--before failure. We're flying blind for the most part, but whatever the strengths are, their ratio remains the same from end to end.

[mikekeswick]

This is a headscratcher for me, but I am thinking the uniform thickness and compression/tension properties of the plastic material lend a different result than would be had using yew, osage, vine maple, hazel, etc, with some crown on the back. I could be full of beans though. My late father used to tell me, "You're all wet, mister." He was always right.

Nope - just the same as wood, steel, pasta.....

[mikekeswick]

Thank you, Del.
My conclusion from your test is that for a  given homogenous material and thickness and constant thickness and shaped as a pyramid, the bending profile will be the same regardless of thickness. 
Also, though wood is not a homogenous material, a given species shares similar physical/strength characteristics and, therefore, a given wood species will exhibit similar results.
Have tension/compression stresses along the length of such a limb profile ( & other typical profiles) been measured?

Nope - thickness determines bend.
Bending profile will be the same IF and only when the thickness is constant.

[mikekeswick]

I recently had an order for 'holmguaard style' re-enactment bows. I had ten to make.
I first roughed out a pyramid bow from an already thicknessed piece of ash.
Roughed out a pyramid taper.
Then further narrower the outers to give them the holmguaard outer limb look.
Over to the belt sander and a few seconds on the working limb to make it thinner than the outers.
Bingo perfectly tillered bow that took an hour tops.


The real beauty of a pyramid is that tiller is SO easy to read that it allows you to stress the wood evenly. Wood that has been stressed evenly with no stiff/weak spots returns faster. So we get back to what Hickmann said in Archery - The Technical Side.
I haven't made a true pyramid in years but this thread has reawakened the urge!

[Del the cat]

Cheers guys.
I may just run up a quick 2" parallel strip of polycarbonate just for comparison to complete the test.
Whadda mean obsessive?
Del

[mikekeswick]

It will bend too much at the center. 

[Del the cat]

It will bend too much at the center. 

Ah yes, but it's the quality of the bend... 
Del

[missilemaster]

OK, I DO want to say "I told you so!" And you, and you, and you for years.  If you can find my posts on "pyramid" bows you will find I have literally been saying this for many years and having it fall on deaf ears. Not only here but on the leatherwall too.

I have made only "pyramid" bows for a dozen years because they take less time to make and shoot as well as the best other designs.

OF COURSE, the design is not mine and not new. I came across it in Archery, the Technical Side a long time ago.

Thanks Del for posting the tests. I still urge everyone to try the test. You can make a single "limb" tapered to a point and make it out of plywood if you want or thin hickory or whatever. Clamp the big end  in a vice and flex the pointy end. Doing it yourself will make a true believer out of you.

This one was about five years ago.


Jim

    I dont doubt that the design works, but for me personally, there is more to building bows than doing it quickly. I build bows that are aesthetically pleasing and for me the pyramid design is not. I like to see the thickness taper in the limbs, beauty is in the eye of the beholder!

[Jim Davis]

Misslemaster, please modify your post to show where my quote ends. I do not want to be known as making bows for esthetic reasons--though the pyramid bow is much nicer looking in front  or back view than a flat bow, in my opinion.

Thanks

Jim Davis

[George Tsoukalas]

What surprises me is how they both bend so much in the handle.
Thanks, Del. Jawge