Truth vs Reality

[Ice Mike]

Ok first let me clarify that I'm still a novice. I want to get some honest opinions from the guys that have hundreds bow under their belt and either confirm or expell some common bow building discrepancies.

1. Taper rate. How critical is it in reality? I mean the lams are typically .001 or .002 per inch. Are the tolerances that tight?  In reality we're talking about wood here after all right? It will expand and contract more than that when responding to atmospheric conditions. What are your opinions on how tight those tolerances need to be to produce a safe bow at a decent shooting weight?

2. Width taper. I've read suggestions that as little as .001 in the wrong direction can make or break the limb at certain weight. Really?

3. Grain violation. I know for a fact that this is a  huge deal with a solid bow, but how much violation can you really get away with when using bqcking materials and building laminated bows?

I look forward to your responses and thank you in advance. I'm just trying to, beings I am a novice, make sure that my bow building training focuses on the proper aspects of building a good bow, and not obsessing over details that really don't make that much difference in reality anyway.

[bjansen]

I will take a stab at providing some input from a glass bow perspective

Overall, some things are critical...others are not all that precise.  Having a paper thin fade for example is critical, while having your tip width too wide or too thin, even by .100 will not be a deal breaker.  I would say if you are starting to build bows, anything that is off by .001  (whether that be lam stack thickness, taper rate, etc) is not going to make a huge deal one way or the other. As you progress over time you will see what works best for your style of bow.

Questions 1 and 2 really go together.  They are really all about proper tiller and you will learn how to deal with that as you go based on the stack thicknes you use, materials you use, your form, etc.  All will play a role in the overall tiller of your bow.  

Question 3:  You can get away with alot here for a glass bow.  Check you some of the highly figured veneer woods in some of the glass bows posted on here and you will see plenty of grain violation.  

Have fun...its addicting

[LittleBen]

Hundreds of bows? For that I certainly do not qualify .... I'm somewhere between 25 and 50, who counts? But if you care to hear my take this is it.

1. If you want to have a bow basically tiller right off the form then taper rate is extremely critical. Since you can scrape the belly of a wood bow, you can correct alot after glue up as long as you have enough material in the belly lam. Since the wood will swell with humidity proportially to it's thickness, it should not impact tiller ... but may affect draw weight. I am a believer that you can calculate the taper rate to a degree of accuracy far beyond what the eye will allow you to tiller unless you're basically legendary at wood bows, but again this is true on paper and maybe not in practice.

2. Width taper has less effect on tiller than thickness taper per thousandth of an inch. This is because removing wood from the side of the limb reduces stiffness linearly, and removing from the belly reduces stiffness in an exponentially.

3. I believe that the limits of grain violation for a given material are the same regardless of how many pieces of wood are underneath the backing. Either way, the backings very outer surface will experience the greatest tensile stress. How much exactly can you get away with? depends on the bow design, but in general, don't try to push the limits. Straight grained hickory, pecan and bamboo is readily available, so search it out and use it.

I have had some backing failures in laminated bows where the failure was stopped by the glue line, where in a one piece it might have just been a complete explosion, but I don't think this suggests that the backing can have more grain violation, but rather just that the glue line may prevent complete, irreparable disaster.

Hope this helps, and those with more expereince may very well know better and dispute some or all of what I've said.

Good luck, and try not to fall into the trap of thinking yourself into a catatonic state instead of just building and having fun.

[Ice Mike]

I used "hundreds" very loosely to mean anyone who has built any number of bows that are structurally sound and have not broken. Your advice is always appreciated Ben!

[Roy from Pa]

HUH, Ben would be the last guy I listen too...    

[LittleBen]

Originally posted by Roy from Pa:
HUH, Ben would be the last guy I listen too...      

That's probably the best advice your gonna get right there!

[bornofmud]

Definitely haven't built hundreds, but I'll answer from what experience I do have, keep in mind I build only glass bows.

1)  it is extremely critical if you plan on having any control in the way your bow limb bends. Thousandths of an inch is definitely within our realm of accuracy with the right tools, and should be a priority if you want to limit your variables and make consistently good bows.  Remember that thickness taper changes the strength of the limb at a square, rather than linearly.

2) Width taper is definitely not as critical, but must be accurate to get the string to track through the center of the bow through the whole length.  Where to start the taper and such depends on your bow design and how you want it to bend. In my opinion, an ideal limb is thick where the limb doesn't move too much, and as thin as possible while still being stable where the limb moves the most (the tips).

3)Grain violation on glass bows means very little, or seemingly does.  None the less, I use as straight grained wood as possible for the limb cores, and keep my veneers very thin (.024-.03)to be safe anyways.  Don't know as much about wood backed bows, but I'd assume it is considerably more critical than glass, but not as critical as self bows.  Having very straight grain for the backing would definitely be important.