Power lam

[ptberger]

Power lams is something I had not heard of prior to finding this board so I have some basic questions.
1) Does the use of a power lam improve the performance of any bow, or are they just generally used to smooth out potential hinge problems?
2) For example a one piece longbow handle that's 16", how would you figure the length of the power lam? just a couple of inches past the handle? like 20" or 22"?
3) I assume each end of the lam needs to be tapered to nothing?
4) Back or belly side? Or does it matter?
Thanks for the info. I appreciate learning from experience, but it's cheaper to learn from someone else's.

[kennym]

Hi Tony

1-  My first p lam was .050 glass on belly of an existing one-piece 64" D/R , Added it after testing,not much if any change in weight, added 2 FPS , think it was 3" past riser fades

2- Depending on what your limb is doing and amount of deflex in riser, less deflex needs more p lam IMO.  3" is a pretty good place to start I think.

3 - Yes it has to be tapered to a feathered end, I usually go full length but you could maybe just go part way.

4 - I really don't think it matters much once glued up , I can't see it making a diff.  Need an engineer to answer this one tho...

[Crooked Stic]

Thinking the original job of the Power lam was to unload the fades a bit. Then we find it moves limb bend  toward the tips shortens working limb length in some designs can be good. Whatever makes the limb recover quicker is good

[Kirkll]

It's a combination of pushing the fades out further from the riser to eliminate hinge, and push the working portion of the limb out further. This has proven to provide a number of advantages. It shortens your limb travel, forces the energy to be stored in a short section of the limb when used in concert with tip wedges.... and... it also acts as an overload spring of sorts when you reach the stacking point. Once the string reaches a certain angle, the limb tips start coming closer together and the stored energy starts traveling back towards the fades as the angle increases. These power lams help carry that extra load and extends the stacking point.

i use a 22" riser tip to tip of fades, and a 30" double ended power lam on my one piece long bows, and go 4" past the fades. Using an .004 forward taper this produces a very high performance limb on my design..... Your results may vary depending on limb shape and limb angles.   Kirk