# Tag Archives: adjustable limb pockets

## Personalizing Recurve Limbs

Recurve limbs tend to confuse beginners, intermediate archers, some accomplished archers, and even some coaches!

Sources of the Confusion
This will be about three-piece takedown recurve bows as they are the most common choice of target archers. The riser has a top limb and a bottom limb attached. These limbs come in three lengths (short, medium, long) which combined with various length risers, you can make the following bows:

 Riser ► 23˝ 25˝ 27˝ w/short limbs 64˝ 66˝ 68˝ w/medium limbs 66˝ 68˝ 70˝ w/long limbs 68˝ 70˝ 72˝

Confused yet? (There are risers of other lengths!) Did you note you can make a 68˝ bow three different ways? (Generally, the shorter the limbs, the faster the bow, all other things being equal.)

The limbs then come in typically two pound (2#) increments over a fairly wide range of draw weights: e.g. 14#–48#. So, if you get “long limbs” and put them on a 25˝ riser, to make a 70˝ bow, and those limbs are listed at 32#, will you have a 32# bow?

Maybe.

Recurve limbs have their draw forces measured at 28˝ of draw. (Unless the bow is a youth bow for which it is common to measure the DW at 24˝ or a traditional bow, which are often measured at 26˝). Confused yet? But how many archers have a draw length of exactly 28˝? My guess is not too many. My guess is that most archers will have either longer or shorter draws. If their draw length is longer than 28˝, the draw force “in hand” will be higher than the weight listed on the limbs. If their draw length is less than 28˝, the draw force “in hand” will be lower than the weight listed on the limbs.

Well, if their draw length is exactly 28˝ will that be a 32# bow? Uh, maybe. Making limbs is not a perfect science. If a manufacturer makes a limb that is 31.5# do they discard it? No, they do not. It is “close enough” to 32# to warrant a 32# sticker and it goes in the pile with the rest. Now, don’t go all ballistic on the manufacturers about their sloppy manufacturing tolerances. These are quite reasonable numbers. If they do go “out of tolerance,” the limb is scrapped. And, if we insisted on perfect limb poundages, the price of limbs would skyrocket as so many would have to be rejected as not being “perfect.” (Since they can’t be recycled, so “Make another one, Bill, that one didn’t pass muster.” And if you have to make three to get one perfect one, do not expect them to be cheaper.)

FYI The manufacturers do not measure draw force like you do, they have a machine that clamps the butt of the limbs, fixing those in space. Then they place a force, in the old days this was a weight, on the limb tip and measure how much it bends. These “limb tip deflections” correspond to draw weights of assembled bows (the lower the LTD, the higher the DW).

What You Can Do to Lessen the Confusion?
As a coach, you can help get archers into a proper-sized bow. Youths need to avoid bows with too much mass as their bow shoulders aren’t very strong yet. Shorter archers need shorter bows, etc. Once an archer is fitted with one size of bow then you need to be able to address changes.

If they grow much taller, they may be ready to move up from, say, a 23˝ riser to a 25˝ riser. (Shorter risers have smaller sight windows and if the bow has a low draw weight, too, there may not be enough room in the sight window for all of the aperture positions needed. Longer risers are better for many reasons, but they are also longer and heavier than shorter ones.)

An Aside Bowhunters often use risers that are 20˝ or even 19˝ long. They can get away with such short bows, because their bows have to have a minimum draw weight of 40# (typically) and the shots they are taking are from fairly short range (20-30 yards).

Confused yet?

Changing riser lengths is a rare event (buying a new riser of the same length doesn’t pose fitting problems). Changing limbs is much more frequent. Enter the adjustable limb pocket! The first mass produced adjustable limb pocket was introduced by Hoyt archery, and which was so popular, the design was stolen worldwide; we now call it the International Limb Fitting, or ILF. This design was for a limb that pressed into the pocket, with a click stop, and a pocket that allowed the angle the limb made with the bow to be varied a little. Prior to the invention, you screwed the limb bolts in and out to attach and detach the limbs and if you wanted to make a limb angle change, you had to make (saw, carve, whatever) small wedges to slip between the limb and the riser and then screw down the limb bolts trapping them in between. This was more than a little bit of a hit or miss procedure.

An ILF Limb Pocket on a modern recurve riser.

With the new ILF design, the limb bolts were locked in place with a lock screw and the limb had a notch in it so it rode up to the bottom of the limb bolt (the butt having a “rocker” designed into it).

Note the rocker built into the limb butt. This allows an ILF limb to rock toward and away from the archer, restricted only by the position of the limb bolt.

When the limb bolt is “backed out,” the limb angles back toward the archer. This increase the brace height a little and lessens how much the limb gets bent at the archer’s full draw. Both of these lessen the amount of energy transferred to the arrows. But you can only do this so much before it becomes dangerous, so typically the draw force can be only reduced about 10% from the printed maximum on the bow. This amount of limb lean is so small that it is hard to see whether a bow’s limbs are “cranked down” or “cranked out” visually while they are being shot.

So, here is our quandary: recurve limbs (once a length is settled on) have their draw weights rated at 28˝ of draw (which your archer doesn’t have), may be slightly less or more due to manufacturer’s tolerances, and can be anywhere from the highest value of draw weight for those limbs to about 10% less than that depending on the limb pocket settings.

Got that?

Try This Here’s a system that can simplify the situation for you and your archer. To use it you need a reliable draw weight scale (all measures must be made on the same scale). Here’s how to do it:
1. With your archer’s current bow, crank the limb bolts all the way down counting how many turns are being made in the wrench. The reference point for “turns” is the limb bolts all of the way down, so when we get there that will become the new reference point. If it takes three (3) full turns to get them all of the way in, then the limbs were “at” three full turns out from bottom.
2. Measure the draw weight of the bow at your archer’s draw weight. If they use a clicker, put one of their arrows on the bow and pull until the clicker falls off. Easy peasy. Write this number on the limbs with a Sharpie/permanent marker.
3. take 10% off of that full draw weight measure and write that number down next to the first one. That is the draw weight range for your archer’s limbs at that draw length. (Set your archer’s bow back to its original state when done.)

Moving On Up
If they want to increase their draw weight once they are “bottomed out” on their current limbs, they need to buy limbs of the same length, four pounds (4#) heavier. The previous limbs were bottomed out, the new limbs will be backed out, typically maximally. So, if moving from 30# limbs, you move up to 34# limbs and back them off fully (10% of 34 is 3.4 pounds) which gives your archer a net 0.6 pound draw weight increase, which is easily doable and he/she can crank it up from there.

No matter what their “personal draw weight” is, use the ratings on the limbs to make purchases. So, if the limbs were marked 28#, you move up to limbs marked 32#. Whatever their personal draw weight max is, it also will be increased 4# (approximately).

Their personal draw weight, the “weight in hand” is what you need for fitting arrows, etc. The marked draw weight is only used to identify limbs for purchase.

But, Wait, There is More!
Here are two sets of limbs and their maxes (in hand) for that archer:
26# limbs        29.5# max
28# limbs        31.5# max
He also has a pair of 30# limbs, can you estimate what they would measure maxxed out for this archer?
I came up with 33.5#. In each case the difference was about 3.5# and since all of these numbers are fairly close together, that pattern should continue. When the limbs get up over 40# I expect slight differences.

Now, just for fun, take off 10% from each of those max DWs to give a range for each set of limbs.
I get:

 26# limbs 29.5# max 26.6# min 28# limbs 31.5# max 28.4# min 30# limbs 33.5# max 30.4# min

Can you see that the 26# and 30# limbs cover the same range (26.6#–33.5#) as these three do? There is a small gap from 29.5# to 30.4# when the swap from the 26# limbs to the 30# limbs is made but that is a reasonable “jump.” This is why it is recommended that you buy limbs in 4# increments (another blessing from the ILF system).

Note Realize that often more that 10% can be removed from a set of limbs so that gap is often much smaller.

Safety Note Never exceed the number of turns allowed in the manufacturer’s instructions!

If you try this system, let me know how it works for you or your students.

## Another Example of Archers Getting Screwed

I received an urgent email from one of my students who discovered that one of the locking screws from the rear of the limb bolt on his recurve bow was missing. He didn’t know how long it had been missing and he had been shooting a great deal so his concerns were twofold: was it safe to continue shooting with that screw missing and how was he to find a replacement?

Top Limb Bolt showing missing locking screw (top), Bottom Limb Bolt (bottom)

* * *

For those of you who do not shoot modern recurve bows, the screw being referred to is a common part on “adjustable limb pocket bows.” Compound people know that turning the limb bolts in or out creates more or less draw weight, respectively. It has only been recently that this feature has been added to recurve bows. A common mechanism designed to accomplish this involved taking the limb bolt and drilling a hole in the very end and tapping it to accept another, slightly oversized, screw. The drilled and tapped end of the limb bolt has several saw cuts made into it and then it is inserted into the bow. Through a hole in the other side of the riser, the “locking screw” is screwed into the newly tapped hole, causing the end of the limb bolt to spread out in its hole, effectively locking it into place.

Compound people don’t have locking screws of this nature (although some models have used a kind of locking mechanism). Because three-piece recurve bows are typically dismantled after every use, they need some sort of locking mechanism, otherwise the limb bolts could move around while the bow was being jostled while traveling in your car. Compound bows are not dismantled after each use and the tension on the limbs tends to keep the limb bolts in place (although it is wise to index then with marks on the bolt heads to show whether they have turned or not).

So, the residual vibration from shooting this recurve bow caused the “locking screw” to wiggle its way out and fall to Earth. (I keep a strong magnet available to find small iron-based parts in the grass. Sliding such a magnet around where one shoots frequently might turn up the missing part.)

Is it safe to shoot without the locking screw? Yes and no. Those limb bolts are often quite tight all by themselves. But if the vibration left over from shots causes the limb bolt to turn, you are changing the tiller setting of your bow which will effect the size of your groups, etc. Nobody wants their bow to give them poorer feedback on how well they are shooting, so, clearly, it is in any archer’s best interest to replace that screw.

Here is where archers have been screwed in the past. It was almost impossible to obtain replacement parts for bows. Local vendors didn’t stock them and even their manufacturers didn’t always stock them. Once a manufacturer has made a “new, improved” model that doesn’t contain that part, they don’t have an incentive to maintain an obsolete parts inventory. When you sell millions and millions of units, you can have a thriving parts industry serving it, consider auto parts stores and restoration auto parts companies as examples. But if you don’t sell millions. . . .

So, I would recommend that archers remove the back screw from the other limb (remember to hold the front screw in place while doing so) and take it down to a good hardware shop to see if they could get a replacement (or two or three if they are cheap). The store should be able to check the threads to see whether they are metric or Imperial/Standard/English/SAE. The bow companies almost never sold spare parts but you may be able to get on the phone with customer service of said manufacturer and talk them out of one. If you had a good relationship with them, you might just get what you want.

In this case it turns out that Lancaster Archery Supply carries the needed part! They also carry replacement limb bolts for Hoyt and Win&Win bows. They aren’t cheap (\$49.99 for a pair of limb bolts!) but at least they are available.

Addendum For you history buffs, before the adjustable limb bolt bows were available, people did adjust their bow’s draw weight and tiller but it was a clunkier process. Since limb bolts were just plain bolts, archers would back the limb bolt out (or nor screw it in as far) and then slip tiny wedges, also called “shims,” between the limb butt and the pocket, then tighten down the limb bolt. If you shimmed both sides of the limb butt equally, you adjusted the draw weight of the bow (downward, slightly). If you shimmed the top limb differently from the bottom limb, you were adjusting the bow’s tiller. If you had a larger shim on one side of the limb bolts than the other, you were actually rotating the limb (slightly) which could be enough to compensate for a slight twist in the limbs.

One can argue that the advent of the adjustable limb pocket systems currently available were the result of too many bows being returned to manufacturers when initially bought due to very slight limb twists and tillers being out of spec. With the adjustable limb pockets this small issues could be adjusted out as a matter of course. I suspect that the “spare parts” available in Lancaster’s catalog (Bless LAS!) are there because of so many of them either wearing, or falling, out.