Need help bottom limb has more set

[Walski]

I've built several bows that seem to have more set on the lower shorter limb, what causes this?
The top limb has less then a 1/4", and the bottom has 1 1/2" set.

[SLIMBOB]

The lower limb often has more strain placed on it as a matter of geometry. That is the reason some, myself included, make the lower limb a tad stiffer as measured in brace height. To compound this, your bottom limb is shorter, making it even more strained, hence the difference in set between the top and bottom limbs.

[bownarra]

Slim is right.
However you should be aiming for equal set. You can, if you want, experiment with making the lower limb a shade wider.

[Dances with squirrels]

I make bows with a longer top limb too, but rather than tiller a bow to certain measurements at brace height, I ignore that and balance the strength of the drawn limbs relative to my holds on bow and string, and then the brace height tiller is whatever it ends up as... and it can vary from bow to bow. But it doesn't matter what they measure. Balanced is balanced. They're balanced in strength when it matters, when drawn. But if I see an issue or concern and decide to leave the bottom limb just a little stronger than the top, I don't gauge it by brace height measurements. I can easily do it by adjusting limb strength to allow the hook on the string to drift toward the bottom limb a wee bit during the draw. Then I know how much stronger it actually is relative to me, dynamically, when drawn.

Usually when I do this, you wouldn't know it by looking at the braced tiller afterwards because they don't show it at brace the way most folks would expect or want them to. In fact they may still show an even tiller at brace. By making a brace height assumption, many of you would say the bottom limb on such a bow is too weak, when it's actually slightly stronger than the top limb during the draw in my hands. I don't have the problem of the bottom limbs taking more set, and that seems counterintuitive huh. And speaking of counterintuitive, I've wondered if making the bottom limb too strong can cause set in it. The stronger the bottom limb is, the more heel pressure in the bow hand, i.e. the more strain directed into the bottom limb, and less to the top. I don't know, just something I've wondered.

 

[SLIMBOB]

I would not argue against what DWS just said.  1/8 inch or so less on the bottom limb does not always balance the bow, but I would argue that it does get me close enough on most, and near perfect on some.  On the others I will just work with them in hand until they're right.

[BowEd]

I'm one to watch the line that hook on the poundage tester makes on the line I have on the background board while pulling it to full draw.Tips will go down evenly then too.
Bows generally end up close to even or slightly positive at brace.They always feel good in the hand while shooting then and shoot that way too.
Grip is bulbous with pressure on the web between index finger and thumb while drawing.
The limbs don't change much adversely compared to each other over time then with even thousands of arrows through them.They stay that way even when not shot for a few years and strung up to be shot again.
A little even set in each limb is what I go for and what usually happens then.
Example.Only close to full draw picture I've got on the tillering board,

[Eric Krewson]

I run into this all the time on my style of bows, always finish a bow over poundage so if the lower limb goes a bit weak during shoot in I have some wiggle room to even things out again and keep my target poundage, I make my bows with a shorter lower limb.

I am a big fan of heat treating, if I have a limb that continually wants to go weak I give it an extra round of heat treating, this usually makes it behave.

To me wood quality seems to be the determining factor if a limb wants to develop more string follow. I made a pile of bow blanks out of random unmatched billets after I had some surgery  that wouldn't let me do much more than band saw work. While working my way through the pile I have found that I often have a blank with one end hard osage and one a bit softer. A double heat treat on the softer wood makes it perform like the harder wood limb and turn out a nice shooting bow that keeps a little reflex on both limbs equally.

About half of the pictures posted here show an indication of a slightly weaker lower limb.

Here is my last random billet bow, the dark, aged billets looked the same when I pulled them out of the pile to splice, the bottom limb was the softer wood and drove me nuts by continually going weak, out with heat gun, now the bow is one of my best shooters. The reason the splice shows above the rest is I had a senior moment when I cut the bow to length, I had extra length on the bottom limb and too short on the top so moved my handle down a little to get the required length for my top limb.