fiberglass tiller befuddlement

[elk ninja]

Allright....
fiberglass bows.  I have made several.  Recently though, it seems I have been spending more time tillering than before.  One limb wants to be straighter (I know I am from Idaho where Larry Craig is from, but keep the jokes to a minimum here....  
Can't figure it out for the life of me.  First several bows came out symetrical.  There is only about a 1/32" difference in the unstrung bow, but string it up and it's plain to see.... limbs are pulling straight as well.  

Here is a picture:
You can see on the right side bow a straighter limb...
 


Form is straight, no warping there.  It is a clamp pressure form, using cork on both the form itself and the aluminum pressure strip.  Glue lines look good and even all the way out.  

Running out of ideas on how to fix this.

Might just make a new form.

Anybody have any ideas?

[elk ninja]

I am analyzing the left bow as well, the top limb of the left bow looks a little straight, but it's not.  I just measured it with a straight edge, the limbs have the same curve.

[Orion]

Did you change the taper in your limb laminations?  Their thickness?  Shortening the laminations from one end or the other before glue up will change the thickness.  Did you change where you position the butts of your laminations?  Moving them up or down on the riser changes the limb thickness slightly.  Did you go to different thickness glass on either the back or belly?  Individually, or in combination, these things can change how the limbs look and flex after they come off the form.

[bvalentine002]

I've seen the same thing...

What I struggle with is getting both limbs to be the same width at any given point in the limb. I usually get them close then use a micrometer to measure and sand. I usually pick the wider limb to be the bottom limb. This provides a positive tiller. The wider (stiffer) limb usually keeps more of the curve.

-Brett

[elk ninja]

Orion,
good guesses, but none of those.  But splices are in the middle, I didn't mess with the lambs or glass at all other than to clean up the edge slightly to avoid splinters.  Even measured them along the length to check for parallel-ness.  

I think its a limb width problem.  

At least that's what has resolved the tiller before.  I worked on it a little last night and it's coming along.

Mainly just wanted some reassurance that it's not the form or something I'm messing up.

Mike

Mike

[beaver#1]

hey mike, is this the tiller problem you were talking about?

[Orion]

Yep, overall limb width changes would also change the way the limbs look.  Forgot about that one.  So would changing the overall limb length.  Because eigher of these bring additional forces/stresses into play.

[Longbow Tom]

Is the taper on the bottom limb installed backwards.  Butt or thick end at the tip??

[ONE SHOT]

After looking at your photos looks to Me like you have the two bows turned 180 Deg. from each other.

The bow on the left has a slight recurve on the lower limb in the photo and the right hand bow has the recurve on the upper limb in the photo.

You may have inadvertenly switched end for end when cutting out for the window and shelf, palm grip.

Take a long piece of Butchers paper and trace the outline of the Bow according to Dean Torges suggestions. Use a straight edge and draw a line  place the bow string on this line and then mark the outline of the upper limb to the C/L of the Riser, then turn the bow 180 Deg. and mark the Lower limb. If Both bows show the exact same contour then you end for ended the Bow when forming out the Riser.

The width or thickness of the laminations has nothing to do with the shape of the Bow coming out of the same form, it is either the same contour for each limb or it isn't, the form dose not change it is a given...ONE SHOT...              :D    :D

[Longbow Tom]

My other guess would be two parallel laminations on the bottom limb.

[ONE SHOT]

The "F" Glass on the Back and Belly are stronger than the wood laminations it makes no difference in what order they are Glued up thick or thin. The "F" Glass is what holds the shape together once the Epoxy has cured. Otherwise there would be no sense, no advantage at all in using the "F" Glass in making BOWS.

The Bow form and the "F" Glass determines the end results as far as the shape or contour outcome.

Now if you were just laminating wood to wood, then you have a whole different set of circumstances involved wood density, grain structure, moisture content, width, thickness,ETC;...ONE SHOT...              :D    :D

[wingnut]

He solved the problem some time ago.  He narrowed one limb more then the other.

One Shot,

You can alter the shape and the bending characteristics of a limb by changing the amount of taper in the wood lams.  The Fiberglass is the tension and compression but the wood is what determines the bend.

I can take a single form and build three different sets of limbs that you wouldn't reconize as from the same form.

Mike

[ONE SHOT]

Mike:

I stand corrected, Thanks for the info. was not aware, see You never get to OLD (70) that You can't learn something from other people. You should know best cause You been at this Bow building a lot longer than I....ONE SHOT...  :D    :D    :D