Limb tips: How thin is too thin?

[Moose]

I'm currently working on a paper birch flat bow. Its 66" ntn, 68"ttt right now, 2 1/8" wide full limb until the last 6" where it tapers to 1/2" limbs tips. This is my first full on attempt at a hunting weight bow, and i've got it tillered to where the limbs are bending evenly. However, i'm at the point where i'd like to cut the string nocks to get a long tillering string on it, but my tips are down to about an 1/8-3/16" thick, which seems awfully thin to me. Is this enough wood, or should I add an overlay? Any help would be appreciated. Thanks.

[Newindian]

hard to tell with out seeing it but you should probably and a overlay

[steve b.]

So you thinned your limbs right down to the ends?  That's not good.   On a bow like that you want the last 5-ish inches to be rigid so as you are tapering the thickness toward the ends you want to taper it back up thick again on those last 6 inches so that, in your case, the tip would be 1/2" wide and, say, 3/4" thick.  Initially that is.  You can always reduce some wood off both width and thickness later on those last 6 inches but for the long string you can leave them overbuilt during the initial tillering. 

I've never measured the thickness of the tips on my bows as I generally go by looks and feel, depending on what type of wood.  Birch I think is weak so you defly want to reinforce those tips and maybe back down the limbs a ways, as opposed to just a tip overlay of only an inch or so.
Pictures are a must if you want this thing to go well.  If you can't post them I will do it for you.