Limb Thickness - Rules of Thumb

[Eric Krewson]

Yep, just outside your outside layout line where you fade transitions in to the limb.

[Burnsie]

I make a 1/2" mark at the end of the fade and and drop the measurement 1/16" every 6" until I get to 1/4". I hold the 1/4" measurement to the tip of the bow.  I start removing wood to my line but leave the belly rounded, I never go lower than a 1/2" thickness at the tip even though I have a 1/4" mark on the side. I drop the width to as low as 3/8" at the tip but the limb tip is 1/2" thick.

Does the 1/2" thickness of the limb tips include any tip overlays you might add, or just the original bow wood?

[Eric Krewson]

Yes, but just where the overlay sits, I cut my platform for the overlay at a slant back to belly so the overlay will blend with the limb and not be a big bump on the back of the tip. The limb up to the overlay will be 1/2" thick where the overlay starts.

I make my overlays 2 1/4" long so the blend with the limb gracefully.



 

[Burnsie]

Excuse the crude sketch.
So I would be looking at a side profile something like this, transitioning from a 1/4" limb thickness back to 1/2" tips - correct"
My example shows a 68" bow - I assume with shorter bows the amount of limb having the 1/4" thickness is less and less?  If the bow is short enough, can you end up not even having a portion of the limb at 1/4", or do you change your "formula"  for tapering from fades to tips.
Sorry for all the questions - this has been quite helpful.

[Eric Krewson]

Nope, you use the 1/4" side line but don't cut straight across the limb at 1/4", the limb thickness never drops below 1/2" anywhere on the limb, the belly is rounded at the tip not flat.

Like this;

[Eric Krewson]

I went out to the shop and got the last bow I made about a year ago to show the limb profile on the bows I make starting just outside the fade. I don't know if anyone uses the same limb profile I use, I have used this design for 26 years with good success, ease of tillering and low set bows. I picked up this profile from the Dean Torgus book "Hunting the Osage Bow" his facet tillering didn't work for me so I altered my limb profile to suit my tillering process better. This is my osage bow profile, with hickory I have wider, flatter limbs with less arc until I get a foot from the tip and then make the transition to round tips.



Hopefully these will be in order; the belly profile at the fade, 7" out and mid-limb. The squared side profile lines stay the same, the arc is cut from the sidelines across the belly to the sideline the opposite side

[Eric Krewson]

A foot from the tip, getting more rounded, 6" from the tip with more of an arc and the rounded belly at the tip.

[Burnsie]

Thanks Eric - I think my little brain has all the pieces put together.
The top of the crown on the belly stays at a 1/2" thickness the entire length of the bow - round over sides down to your side profile line - got it.

[Jim Davis]

Osage will survive a lot of different designs. Even the ELB, for which is not ideal.

I always keep in mind that wood is generally 3 to 4 times as strong in tension as compression. That's why a crowned back is strong enough to balance the belly's compression strength.

Crowning the belly puts the most compression strain on the highest part of the crown. The lower parts of the belly crown don't  start to resist compression until the high part has already yielded to  some extent.

But, as I said, Osage can live with less than perfect conditions.

[Eric Krewson]

Stiil no, the limb never goes below a thickness of 1/2", it may be thicker closer to the fade because of the arc on the belly.

[Eric Krewson]

I have never complicated bow making with the mechanical aspects, I could care less, I make bows that shoot poundage plus 100fps with 10gr per pound. The third bow from the bottom is 52#@26", it shoots 170fps with a 500-gr arrow drawn to 26", that is my best. The rest shoot poundage plus 100 or perhaps 10fps more if I am lucky and I only have a draw length of 26" on a good day. My bows in other people's hands have won over a dozen national championships so I guess I have done something right.

Back in the day I was a pretty good shot and knew when a bow was acting right or needed a little more tillering work or limb balancing, a sense of feel kind of thing, worked for me. 

[Eric Krewson]

You can't build a bow by replicating my measurements exactly, too many variables, poundage, wood type, width, tillering and so forth.

One more post and I am gone.

The bow in the profile pictures thicknesses at the same points I posted belly pictures of.

Fade 5/8", 7 " out 11/16", mid limb 9/16", a foot from the tip 9/16", 6 inches for the tip 1/2" and the tip 1/2".

The limb width is 1 1/4" to mid-limb tapering to 1/2" nocks starting 1 foot from the fade. The bow poundage is 48#@25", 51#@26", flawless osage with a clean back, no knots or pins. The bow is 64" long with an asymmetrical 1" shorter lower limb because I like them that way for no particular reason except for the drawn profile makes the bow look like the limbs are equal length not lopsided.

It is not my latest bow like I thought, when i looked at the specs I found it was made 15 years ago.



Got it?

[Doug509]

With regards to limb width not thickness.  Would it be a design flaw to start tapering 1.25" limb width immediately at the fade vs starting the taper at mid limb to tip?  Visually creating a distal taper from fade to tip before tillering and reducing thickness. 
Thanks to Eric for sharing such great detail.

[Jim Davis]

Certainly not. That's the design that is often called a pyramid bow. That's the only kind I make anymore. Easiest to tiller by far--one thickness, straight taper.

[Eric Krewson]

Jim is a pyramid bow expert and knows his stuff.