Limb thickness on Pyramid bow ?

[legend]

Hello All ,
Can someone please tell me with a Pyramid bow  the width of the limbs obviously taper from the fades up to the tips , but how about limb thickness , does it remain constant or does that also taper towards the tips ? and if so , I know most experts on here reduce the thickness in relation to the tillering but what is an average thickness the limbs should be ?
Thanks .

[Hrothgar]

In theory the thickness is the same, but a lot of guys will still taper just a little, mid limb needs to be bending. Depending on bow length, width and type of wood the thickness will vary. Say for a 62" hickory pyramid bow that's 2 1/2 " wide tapering to 1/2" tips, 1/2 " thickness would yield around 45-50# at 28" draw. These are the figures I remember and are general. Someone else probably has a more accurate chart.

[willie]

I just posted a similar calc in the thread above, so I might be able to look up the same for you.

can you post your design nock to knock length and wood of choice?

[Pat B]

If you're working with a board bow you can predetermine somewhat the thickness but with a stave with it's irregular surface, I treat a pyramid just like any other bow... taper your limb until they bend evenly and together.

[legend]

Sorry guys , should have put wood and dimensions down .These are only ideas at present time , but ....
Elm Stave , to have static recurve
Overall length = 64" but could be made longer
27" limbs
4" handle
2 x 3" fades

So will I have to taper thickness to accommodate recurves , and what length should recurves be ? But I understand what Pat B says about taper limbs until they bend evenly

[PatM]

I wouldn't make a static pyramid bow.

[willie]

well a simple pyramid bow doesn't have much taper in thickness, and I have seen where some guys like to actually increase thickness at the tips to keep them on the stiff side. Of course your second description is a bit more complicated, but it could be estimated. Static tips will need to be thicker than the adjacent limb to keep from bending.
Don't most recurves have somewhat parallel limbs, at least for a good ways?

[legend]

Sorry Pat , I was getting a little confused , I was thinking about your 60" Elm static recurve .

[Pat B]

Just off the top of my head that recurve has limb width that slightly tapers from the fades to about 8" from the tips then drastically narrow towards the tips, Molly style. Generally 1/2" has been plenty of thickness to hold it's shape and is fairly easy to bend with heat. I leave the tips wide while bending so alignment corrections can be made later.
 I used dry heat and olive oil on that bow but I think my next will use steam or boiling.

[Wooden Spring]

Legend,
You didn't specify your desired draw weight or I could have calculated that too, but since the thickness of the bow is determined by the Modulus of Rupture, the Modulus of Elasticity, and the radius of the fully bent limb as a result of its length and your draw length (28 inches?), I calculate that for American Elm of MOE = 1,340,000 and MOR = 11,800, the thickness should be 0.428 inches thick.

Now, bear in mind, this calculation is based upon published numbers (wooddatabase.com), so the numbers of the specific tree that your stave came from could vary somewhat. If you don't conduct a standard bend test on the sample that you wish to make a bow from, it's always wise to start a bit thicker than the calculated number and then work down to that during the tillering process, making sure to keep an eye on set as you go.

Keep in mind too, this calculation is good for a straight limb, pyramid design with no reflexed tips, but I cannot imagine how that would affect the thickness calculation assuming your bending radius did not change.

Cheers!

[Hamish]

Pyramid bows with a constant limb thickness were originally developed for 1st grade bow woods like lemonwood, yew and osage. All these timbers allow for a narrower design than most whitewoods. The constant limb thickness works fairly well in the above circumstance. Historically when the constant limb theories were developed in the 1930's and 40's,they were made around 1&1/4" - 1.5" wide.
 If you start using 2-3" wide limbs pyramid limbs, and a constant limb thickness, you will quickly find the majority of the bend occuring from mid limb to the tips. It won't have the circular tiller that a pyramid bow needs. It will develop a hinge if you aren't quick about getting the inner limbs to do their share of bending.  Kind of defeats the purpose of a constant thickness, as a quick foolproof way of getting tiller. Just keep this in mind if you make a wider bow, it will need to be tillered out by eye like any other bow design

[legend]

Thanks Guys

[mikekeswick]

Follow the width taper I drew out on the paper. It is not a pyramid taper. A pyramid width taper on a recurve will lead to a limb that isn't laterally stiff enough. Elliptical tiller.

[FilipT]

I tried once pyramid bow from black locust and constant thickness thing didn't work at all. Outer 2/3 of both limbs didn't move at all. So I made taper like with flatbows and tiller become good.