calculating lam stack

[Kyle Patterson]

Im am pretty new to this and have been jumping around in various aspects of bow building, but recently making a laminated bow has really caught hold of my attention. So im just curious, how do you go about calculating your parallels and tapers and whatever else in a given bow? What all needs to change in the stack when your making different kinds of bows(recurve, R/d, Hill style), does the type of wood make a difference in the size of the stack? Im sorry if this has been covered before.. I guess i just want to know how much of a science it all is? If the stack is one thickness and taper can it only be used on a certain form? Sorry for all the questions, i hope someone can sort through that mess!

[jsweka]

Kyle - The real science of it is called "trial and error".  Your stack thickness will change with bow design, how much taper you put into it, finished bow length, and limb width.  The type of core wood has less influence compared to these other factors.  In general, for a given draw weight, a Hill style will require the most stack, a recurve the least, and the r/d somewhere in between.  When you start building you need to take a lot of notes on each one of your laminations.  After a few bows you'll have the recipe for the draw weight you want to hit.  If/when you do decide to build one and have decided on a design, folks on here can give you some advice to get you close, but again it might take you a couple tries on your particular form to really nail the draw weight you want.

Hope this helps,

John

[Kyle Patterson]

Thanks John, That is pretty much what i wanted to know, Whether there was some science to it or mainly trial and error. Sounds like i have to make some bows!

[jsweka]

Kyle - It's not completely trial and error after you've made your first one.  Check out this link.  There's a spreadsheet application you can download to help you get close to a desired draw weight once you've made one that ended up at some weight for a given stack.

 http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=125;t=007699#000007

Another option is to start with plans from KennyM or Binghams and follow their designs and recommendations for stack.  This would help you get a shootable bow right from the start.

[Swissbow]

Kyle if you want to build a d/r-longbow with a mild profile I have a table that i got from Jason some time ago. I have used it for many bows and it works pretty good. Although I prefer to make the stack about 10lbs heavier than in the table, so I can make the tips nice and thin.

You can download it here...

 http://swissbow.com/swissbow_eng/download_eng.html

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Andy

[Kyle Patterson]

Thanks guys, looks like lots of good info in those links. One more thing, how do you go about determining what taper(s) to use?

[Glunt]

If you are using a proven shape, go with whatever the source suggests.  On new shapes its a bit of a crap shoot.  With a typical forward taper (thinner at tips) the higher the taper rate, the more bend as you go away from the riser.  Too much and early stacking and stability issues can pop up.  Too little and you bend hard at the fades.  In most R/D one piece bows, .002" - .004" total taper per inch is the common range I usually see.  A little different limb shape or the use of a powerlam or tip wedge is another variable.

Say you decide on a .003" per inch total taper, that can be 3 lams with .001" ea or 1 lam @ .002" and one at .001", etc.  Sometimes combined with some parallels to complete the stack.

[Kyle Patterson]

Thats just the explanation i needed. Thanks Glunt. Im picking up my new bandsaw and thickness sander tomorrow (Gift from and older gentleman i know who's eyesight is failing and cant use them anymore), so im hoping that in the next week or so i can put together a hot box and a form them maybe give this whole thing a go! Thanks again for all the advice, its great being able to ask simple questions without being insulted for not knowing already.

[7 Lakes]

No one is going to insult you over this question.  There isn't a person here that hits their exact weight every single time.  

Give me a call when you figure out what type bow you are planning on, be glad to help.