How important are tapered laminations?

[tsriberio]

Groundhog Day!

"Here is another option, if you have lots of time and patience. It's a shooting board/sled I made for truing up lams. If you mic homemade or store bought lams, you will probably find they are slightly inconsistent in taper rate. Not a big deal unless you are OCD like me.
It's a simple MDF box with angled runners along the side that correspond to the taper rate. I use it with a sanding block or low angle plane that rides on the runners. The bed is 3/4 MDF with sandpaper glued on. The thickness gets adjusted by shimming under the bed. I use it after I have ground my tapered lams, but you could use it with parallel strips to get your taper. It's not fast, but it's dead on accurate."

"

How do you get your runners to the appropriate taper?

[tsriberio]

NVM, I figured it out in my brain. 

[Holm-Made]

Another advantage to using tapered cores In your bows is it takes stress off your riser fade outs.  I also like the looks of a longbow limb that bends more in the outer portion of the limb, rather then just being “straight”.  I typically use .002 total in recurves and .003-.004 total in longbows.

[Crooked Stic]

Another advantage to using tapered cores In your bows is it takes stress off your riser fade outs.  I also like the looks of a longbow limb that bends more in the outer portion of the limb, rather then just being “straight”.  I typically use .002 total in recurves and .003-.004 total in longbows.

How does more taper have less stress on your fades??

[Flem]

You put them in upside down

[Crooked Stic]

You put them in upside down

put the tapered side down ?? 

[Flem]

I was just guessing.  Maybe Chad does a double taper

[monterey]

To understand why it puts less pressure on the fades, take a piece off a parallel lam about 15" long and clamp it to the edge of a bench with 13 or 14 inches sticking out.  Press down on the tip and watch how it bends.  Go slow until it  breaks.  It's going to break about at the edge of the bench (the fade).

Then do the same thing with a lam with 003 taper.  It might break at the bench as well but it's going to bend a whole lot further.

If you're not tired of this experiment, take another piece of parallel and side taper it in straight lines to the tip with the tip being a sharp point and do the same bend.  That would represent a pyramid bow.

[kennym]

Mike is correct. That's where I was going with the hinging thing.  Ever seen a full draw where the limb is bending most at the riser end?  That I don't like …

That's, not all taper or parallel  completely either, also how you do fades and the bow design. 

[tsriberio]

Does that mean that a super lam would be effective in an all parallel design? To push the bend further out the limb?

[kennym]

I would say it would help , or at least the power lam . The tip wedge might not be needed. Only one way to find out ... 

[Forwardhandle]

I think a lot would depend on the design and working limb length , I think designs that like circular type tiller would be perfect for all paralells and designs that like elliptical type tiller are going to be more shocky with parallel lams , all speculation on my part , but like so many things with bow making it takes building it to find out , I made this short working limb & riser bow a while back with only .001 total taper & its a great shooter but have been wanted to go back & change the tiller more circular by parallels & lighten the tips more to see if there is any difference in performance , the power lam part of the super lam did seem to diverse the bend in the lowers , this is a great topic gets my brain working don't know if thats good 

[Crooked Stic]

So then the original reason for the power lam was to take the load off the fade making it thicker in that area and moving bend out farther. Your taper and parallel test to me just proves the the taper bends farther to me is loading the fade sooner and more. But I have been wrong before 

[Forwardhandle]

Mike not sure if your talking to me or Monty but with mine I shortened the butt end of the power lam by 1" and the riser by 4" to get more working limb over the longer bow ,it worked for me !,I think the fades could be lengthened with a longer riser to avoid the hingy looking tiller to of course all this requires making some samples to find out ! I think short working limb bows with long Ibeamed , Eiffel towerd tips would be a great design for parallel lams !

[Flem]

It's true, a cantilevered rectangular beam with a constant load along it's length will fail at it's fulcrum point. And a reflexed beam, by design will have it's fulcrum moved away from the point of attachment.
So if you plan on building a reflex/deflex, recurve, or other prestressed limb type bow, a tapered lamination becomes more critical. Does not necessarily matter how you taper it, you just need to reduce the bending stress at the distal end of the beam. But it does make sense to taper for thickness rather than width. Given two limbs with the same physical mass, the one with a deeper profile relative to the bending axis will be stronger, but less elastic than the wider, but thinner limb.

[Shredd]

Good way of saying it Flem...   Lets not think of it as taking the load or stress off of the fade area...  Adding thickness to the limb is not taking  the load off that area... If anything, by adding a power lam or super lam could actually increase the load in the fade area... By adding thickness anywhere in the first 2/3rds of the limb will increase bow poundage and if you increase the poundage you have more load on the limb especially the fade area...   Think in terms of strategic placement of thickness to get a consistent bend and good geometry for max performance and longevity of the bow...  Hence the use of tapers and radius's in your limb shape...

    You may be able to cheat the general rule of adding tapers by adding about 3" to the fades on your riser and making them very lean and then being strategic with your radius's in the limbs to take up the work of what a taper would do...  It could work or be a total flop...  Just would have to experiment with it...

   Most of my opinion here is based on my experience with R/D style bows....

[monterey]

Rich, i think I get what you are saying.

My way of looking at it is that the thicker portion of the lam at the fade is not to strengthen the fade.  It's that the gradual reduction in thickness (strength) proceeding out the limb decreases the ability of the limb to over stress the fade.  Of course the nature of the width taper plays a big part too.

The glass in our bows can hide and protect against many design shortcomings.  Maybe our experienced selfbow and trilam builders can comment on our discussion?

[Shredd]

It can be said in many ways...   We all kinda view things and word things differently but are on the similar path or goal...  Sometimes I like to look at things in reverse to get a different view on things...  Like, instead of thickening up the fade area, thin the mid limb area...  Same thing but makes you view things differently which could open doors to a new method or design...  That's why I shared my view...  Most talk about taking stress off the fade...  The fade has nothing to do with any of it... It's just a tapered filler for the transition area...   In most cases it is in the center of the core and least stressed...  It is the fade area in which we are talking about...  Which is the end of the riser and the beginning of the limb...  It is a a critical area and correct me if I am wrong, but most bows fail in that area...  So you need a smooth transition from the riser to the limb...  Too stiff and the bow stacks and loses speed...  Too weak and the bow draws smooth but loses speed and may break in that area...

   I think it is a good point to get the Self Bow Guys involved...  They are the masters...  Their bend has to be right or it's history...

[Crooked Stic]

The original question was how important are tapers in a bow. We have determined they stress the fades less. Selfbows have no laminations but do need to be carved right for good even bending on both ends---tiller. All bows have tiller not all bows have lams 

[Forwardhandle]

I think any body that has made a few self bows or natural bows quickly learns where limb stresses are in any given design & different taper or no taper rates via set or breaking , then when backing is applied sinew, bamboo ,horn etc you can capitalize on using backing to compensate for the weaknesses in the design, I think the same applys for glass or carbon bows , some glass bowyers use weaknesses in a bow design to enhance shooting qualitys (HH set bows) I wonder how many glass or carbon bows would show weaknesses in the design threw out its duty life ? , so I guess what Im trying to say for what ever its worth all designs have strengths and weaknesses ,its up to your design to use them !