Difference between thicker Taper, vs thicker parallel

[GWild]

My wife and I are beginning to work out our first laminated bow build. We are very excited, but have a few questions. We are very new at this so please any advice is great.
We are building a 1 pc recurve using a custom form (our own design.)
We sat down to calculate our thickness using the Bingham weight chart. (We are hoping our form is close to theirs. We will adjust accordingly after the build.) while planning out the lams to buy we ran into the following question.
When building a bow, assuming you can get the target thickness either way, what does having a thicker or thinner taper accomplish for your bow? And also, what would having a thicker or thinner veneer do for the bow as far as performance?Is higher or lower thicknesses more or less forgiving? Would the performance be about the same?

Thanks in advance.
-Grant

[Mad Max]

A .250 stack would make a heaver lb. bow than a .230 stack.
The .020 difference could be as much as 20lb.
with or without veneers
can you post a picture of the form?

[kennym]

This is my opinion only, I don't think it will matter much, once glued up it is a composite structure so to speak. So the taper and parallel are just spacing the glass apart. The veneers are also just spacers to make a thicker limb, so unless you use a pretty weak wood it won't matter a lot.

I've found that Eastern Red Cedar , walnut , and spalted hackberry veneers .030 turn out a bow a few lbs light.

I think hard maple is about as good a performer as there is, but actionboo is more repeatable. Different boards vary in hardness and stiffness but aboo is laminated so it averages out pretty close.

All just my opinion...

[Kirkll]

We are all just shooting in the dark offering advise regarding taper rates and stack height until we know what your design looks like, the riser length, and bow length.

For example a straight lay up long bow  may have a .420 stack height with two .002 forward tapers in the stack. Giving you a .004 taper rate.

a RD long bow of the same draw weight, or a hybrid long bow with more reflex in the limb shape would be lower stack height. Say .380 or .370. And run a .003 forward taper. One taper at .001 and one at .002, or two .0015. 

On a recurve bow of the same draw weight, the stack height drops again considerably, as well as the taper rate. Your width profile is wider too. Most recurves that have excellent stability run an .001 taper rate. A heavier draw weight can take a faster taper rate and still maintain stability, and lower draw weights you do better going with .001 or parallel lams, or even a reverse taper.

All the stack heights are just hypothetical here my post.   Where you measure the thickness to determine the stack varies from one bowyer to the next too. I have no idea where Bingham’s measures their thickness on a one piece bow. I measure mine where my fade tips are going to be.

To answer your question. Where the tapers and parallels are in the lay up makes no difference at all. It’s over all taper rate, and location of your fade tips, and width profile shape that determines how that limb bends, and where it bends.

After you get your feet wet , You can look into using tip wedges and power wedges to manipulate your limbs further if you are so inclined, but I wouldn’t dive into that yet. Get the basics down first.   Hope this helps….   Kirk

Ps.
Most beginners start with a long bow to get the feel of the whole process. Building recurve bows are a bit tougher to do.    Good luck

[mmattockx]

When building a bow, assuming you can get the target thickness either way, what does having a thicker or thinner taper accomplish for your bow?

As noted, it really doesn't matter much what you do with the individual core pieces. It is the overall stack thickness and taper rate that affects the draw weight and bow performance.

One thing not mentioned is that you don't want any individual core lam piece too thick or it gets hard to bend it to conform to your form shape. This especially matters for a recurve where the tighter bend near the tip needs thin core pieces to bend easily to shape.


Mark

[GWild]

Thank you everyone for your responses.

Kirk, I appreciate your information, I think you helped answer some of our concerns for sure.

Max, I think you misunderstood what I was meaning. Let me try to be more clear. If we are making a .240” thick bow, we can use a (butt thickness) .06 taper with .05 parallels and .04 glass to get to .240, or we could use a .10 taper with .03 parallels and .04 glass. Both would get us to .240, and both would have .16 of lamination.

We just want to know if one way is better than the other, or if there is a rule as to how much thicker your taper should be to your parallels. We haven’t finished cutting our forms or I would post them. Hopefully this is a little clearer.

Mark,  do you have a general rule as to how thick is too thick for a single Lam?

[Mad Max]

Like mmaattockx said the lam can be to thick to bend on the belly ramps of the riser

[mmattockx]

Mark,  do you have a general rule as to how thick is too thick for a single Lam?

It depends on the core wood and the radius you are bending it around. For hard maple or actionboo I would say you want the radius to be 75+ times the thickness of the lam. This equates to a maximum bending strain of .667% (this is an engineering term and you don't need to understand the fine details of it), which is about where hard maple will start to take a little set. Set is permanent deformation that the wood doesn't spring back from and you want to avoid putting your core wood into that condition for best performance.

This works out as:

R = bend radius
t = lam thickness

R/t = 75+

To be really sure I would say make it more like 90-100.

For instance:

With a 6" bend radius, what lam thickness do you want to stay below?

R = 6

R/t = 75

Rearranging we get:

t = R/75 = 6/75 = 0.080" thick

You want the lam to be no thicker than 0.080" where you are bending it around the 6" radius. For a ratio of 100 the lam needs to be 0.060" thick. This may sound thin to you, but the lams typically only are bent that tight at the tip of a pretty sharp recurve. The riser ramps are usually more gentle and generally the core lams don't ride up the riser fades, they go under the riser block and the fibreglass lams run up the ramps.


HTH,
Mark

[Shredd]

  If I was making a hill style or slightly reflexed bow I would use at least two core lams and more than two lams if I have a tighter radius in the riser ramps... Anything with more reflex I would use 3 or more core lams... And as a rule of thumb I try to keep the thickness at the thin end of my lams close to the same thickness...   So for instance, If I have a .075 parallel I might have tapers with .050 and a .060 thickness at the tips...  As opposed to a .075 par and a .030 and .080 thick tapers...

[GWild]

Mark,

Thank you again, This is super helpful. Can you explain what you mean by bend radius? Sorry for the NEWbie questions.

[mmattockx]

Can you explain what you mean by bend radius?

The radius of the bend (on the form) you are forcing the core to bend around.

I made these static tips from maple laminations. The form surface they are bending around has a radius of 5".








You don't have to know the exact radius on your form, you can ballpark it by using a coffee can or bucket that is close to the same size as the bend and then measure the bucket or can.


Mark

[Mad Max]

The belly ramps on the bottom of the riser, .150 butt wont bend on these but a .080 or .100 will

[GWild]

Okay here is what we’ve got so far.

Our radius bend is about 8”. using Mark’s formula we found that no lam should be thicker than.106. This is correct right?
We planned on using the following thickness’
Back glass - .04”
Back Parallel- .04”
Taper core (action boo) - .09”
Belly parallel - .04”
Belly glass - .04

That totals out to a .250” butt, which we are hoping to be in the 35# range. Does this look good to y’all? We want to get your opinions before we order the materials.

[Mad Max]

You never know what pound bow will come off a new custom form.

 

[Appalachian Hillbilly]

I would order a range of lams. You will be extremely  lucky if you hit target weight first time. Order enough for another, maybe two more tries and save the shipping. 

No one can stop at just one bow...
My one year bowbuilding anniversary is coming up and I am on like #7

[GWild]

Yes, we know hitting weight is very unlikely, but we’ve got to start somewhere right? We plan on buying more than one try, but the thickness all looks acceptable right?

[mmattockx]

Our radius bend is about 8”. using Mark’s formula we found that no lam should be thicker than.106. This is correct right?

That is correct, but I would consider that the limit and going thinner is a better idea.

Taper core (action boo) - .09”

Is this the tip thickness?


Mark

[GWild]

Taper core (action boo) - .09”

Is this the tip thickness?


Mark

No, that would be the butt thickness, we were planning to use a .001 per inch taper. So the taper  tip should be .86 if I did the math correctly.

[kennym]

If you have a .090" at butt taper at .001" per inch , you should have a .054" thin end on a 36" lam...

[Stagmitis]

So you would have approx  something less than .250  thousands at the fade depending on how long your riser is and .214 thousands at the tip-

if you can post a pic of your form profile  and riser length I think it can help everyone visualize what taper rated might be appropriate to start with.