Limb Thickness - Rules of Thumb

[Burnsie]

Let's assume a 66" - 68" Osage stave intended to be a 45-50# longbow.
As you rough out your stave and then work towards floor tiller, what thickness do you work your limbs down to, to get you in the ballpark, before you start tillering in earnest.  I've been using 7/16"?  Or do you even have rule of thumb thicknesses in mind when you are working toward any particular weight bow?

[willie]

Hi Burnsie

If you want to learn floor tillering by feel, then my advice would be to find a heavier bow to get the feel on.

perhaps you might try bringing a stave to thickness with a long string (and spend some time floor tillering it as you go in order to get the "feel"

maybe even find a oak board to start with and try to tiller it to your weight at about brace height or slightly more.   floor tilliering is an aquired skill and "seeing the bend" is part of it

[bentstick54]

On Osage I bandsaw off excess thickness to about 5/8” then started using a belt sander to smooth out to a 1/2”. After that I switch to rasp, draw knife and card scraper. Only got burnt once and the bow finished out a 35#. All others came in well over 50# but I started dropping to 44-45# due to shoulder issue.

[Eric Krewson]

Yuo didn't say how wide your bow is going to be. 

I make my osage bows 1 1/4" or 1 3/8" wide. I use the same method on hickory bow blanks that are wider.

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.

I tiller the rounded belly and reduce the oval shape to almost flat on my finished bow as I reduce poundage, the last 6" of the limb will remain somewhat rounded on the belly.

Others may make a wider, flatter limb bow profile, in which case the starting measurement will be less.

[Eric Krewson]

If I have too much poundage after starting at 1/2" side thickness at the fades I drop my starting measurement to 7/16" but still stop dropping the side measurement at 1/4".

My belly at the fades looks like this after tillering and transitions to almost round close to the tips. The second picture shows my transition from an almost flat belly to rounded. I can use very tiny tips this way. The extra groove is a stringing groove, I can use a simple stringer made out of parachute cord to string my bows, very safe, the stringer won't slip off the tiny tip.

[Burnsie]

Thanks guys - I'm right in that 1/2" - 7/16" range as well. 

[Selfbowman]

What was said above.

[Eric Krewson]

Because osage can be a little wavy on the back you can't normally use a ruler to mark the limb from mark to mark. I put the pencil in my right hand and my thumbnail on the back of the bow. This way my thumbnail will follow the contour of the back of the bow and mark accordingly. As I mark toward the tip, I rotate my hand slightly so my line converges with the next mark on the limb. It takes a little practice and a good eraser sometimes but you can make a neat line with practice.


The key to using these sidelines is never, never, never remove wood below them on the side of the bow limb and get lost in the process with uneven wood thickness on part of your bow limb. With this method you will seldom if ever have a bow limb that doglegs to the side because the limb thickness is so well matched.

Here is an example of what your line will look like if you have a little roller coaster in the limb.

[Jim Davis]

Here's how I do it. Call it a giz2

[Jim Davis]

This only works for pyramid bows that are uniform thickness from fade to tip.

[Eric Krewson]

OOPS! I said I used my thumbnail as a guide, I went out to the shop to take a picture to illustrate what I was suggesting and found I that use the fingernail on my middle finger as a guide for my pencil.

 

[Pappy]

I Do like Eric but that little jig Jim showed is cool, may get or make me one of them.  learn something or see something new every day.
 Pappy

[Zugul]

I use a compass to do the same thing by putting the pointy end on the very edge of the back of the stave and using the other end to scribe a line on the side, it works well and you don't have to make a jig for it

[Jim Davis]

Better to gauge from the center of a crowned back.

[Burnsie]

Yuo didn't say how wide your bow is going to be. 

I make my osage bows 1 1/4" or 1 3/8" wide. I use the same method on hickory bow blanks that are wider.

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.

I tiller the rounded belly and reduce the oval shape to almost flat on my finished bow as I reduce poundage, the last 6" of the limb will remain somewhat rounded on the belly.

Others may make a wider, flatter limb bow profile, in which case the starting measurement will be less.

Thanks Eric - this information helps a lot.
Below is the layout of my handle and fade section - I assume when you refer to the 1/2" measurement starting at the end of the fades, you are referring to the  lines on the outside ends of my layout - both are 4' from the center line of the handle.