Hinge, tiller, and arrow flight

[whiskyweasel]

I was gifted a Bear Montana several years ago after I had a limb crack on my old recurve. When I got the Montana, I noticed that there seemed to be an irregular sweep to the upper limb that appeared to me to be a hinge but it was slight enough that I decided I was seeing things and have shot the bow ever since. However, I've had an absolute bear of a time tuning arrows, most notably unsolvable nock high flight that is noticeable even with fletched shafts.

Well, I was looking at the bow again yesterday after I had unstrung it and noticed that it seemed to have string-follow. I placed it on the floor and while the bottom limb tip touches the floor on the same plane as the handle, the top limb sits off the floor by an inch or more. I know this is probably not a great way to test such things, but I'm fairly certain that the limb is hinged with string-follow.

So, my question is, 1) is the bow safe to shoot, 2) what does this mean for bow performance (ie., poundage, cast, etc.), and 3) more specifically, are my arrow tuning headaches a result of this?

Yours truly,
Should have figured this out a long time ago

[Orion]

The shape of the riser can cause one tip to be higher than the other when you just lay the bow on the ground.  String it and check the tiller. (I.e., measure from the end of each fade out perpendicular to the string.  Most bows will exhibit about 3/16-1/4 positive tiller --greater distance-- on the top limb.) If it's way off, then you might have a problem. 

Bows with some fairly lopsided tiller can be made to shoot an arrow well by adjusting nock point height. If that's the case you might lose a few fps of performance, but not enough to worry about. 

However, if your top limb truly is a lot weaker than the lower limb, it might indicate that the limb is coming apart.  Check it over very carefully for hairline separations on the edge of the limbs between laminations and between the laminations and the glass. check the entire length of the limb(s).   

[McDave]

I’ve had limbs delaminate on me, but when they start to delaminate, they tend to go pretty fast.  I’ve never had one start to delaminate and then stay in the same state of delamination for any length of time.  If you have successfully tuned other bows and arrows and you can’t tune this one, there is probably something wrong with it.  It could either be a manufacturing defect or some inherent weakness in one of the limbs (which I guess amounts to the same thing).  Don’t be afraid to go really high with your nock placement to find out if there is some location where you can achieve level bare shaft flight.  If you find out that level bare shaft flight can be achieved at somewhere higher than 1”, you may not like it, but at least you will have satisfied your curiosity. 

[whiskyweasel]

Thanks to you both for your insights. It looks like I'm about a 1/2 inch off between the top limb (further from the string) and bottom limb (closer to the string) when measured at the end of the fade-out. Like I said, since getting this bow I've noticed that the top limb has a "hinge" appearance - located where the fade ends and the limb begins. To McDave's point, I've had the bow for 4 years or so with no sign of delamination. But it's been 4 years of frustration because I can't get the thing to tune because of a persistent nock high. I'm going to try to run the nock point up the string and see what it gives me.

[Twostrings2]

  I have a Bear Montana, and if it started to look like you describe I would stop shooting it, cut it in half and get another.

[Orion]

Hmmm. It's a bad sign if the hinge is right at the end of the fade out.  That's where there's most stress on the limbs and where they're most likely to break, though a hinge anywhere indicates relative weakness related to the surrounding area.  If it hasn't worsened in 4 years, there's probably a fault in the layup/construction. Perhaps one lamination was too thin, etc., Regardless, I'd be wary.  A half-inch positive tiller on some older bows is an occasional occurrence.  On a Bear Montana, it's an unusual, rare occurrence.