lever arm bow design advice needed

[PlanB]

.....the one in the photo  is not for Trade in any way but to build my skills to do the Trade bow properly......

Oh, okay. I think it wasn't clear to me and most folks who replied that this was not for the trade. Interested to see what you do and find out, then.

[stuckinthemud]

Yeh, the Trade thread is so huge that it is easy to miss posts - I did say it wasn't for Trading but like about 100 pages ago

[PatM]

Hi joachimM, this asymmetry is one of the things I am struggling with a little. So when I lay out a self bow, the arrow pass is just above half way along the length of the bow; the bow balances nicely on your index finger at half way, then there is a four inch handle (in a stiff handle design) so the lower limb is always 4 inches shorter than the top limb and a stiff handle self bow is always asymmetric with the tiller compensating by making one limb wider or thicker to compensate?
  the bow shown appears to be asymmetric but only because I started off with a self bow which ended up this way by accident. It was intended as a two piece but the project took me in a different direction as I mucked up the join as I specifically wanted to make a bolt together and did not want to use a sleeve, mostly to find out why bolt through take downs are so uncommon- guess I found out 

   
    Eh?

[stuckinthemud]

Hi Pat, which bit 'Eh?'
Am I correct in thinking that lower limbs are always shorter than top limbs by   the length of the handle? Also, the reason, I think, that through bolting is not as common as a sleeve is because the holes for the bolts weaken the handle in a two-piece take-down, meaning they either need to be longer or fatter, or both longer and fatter, or the bow needs to be a three-piece take down.

[bushboy]

Not sure about hazel?maybe Del will chime in.google Horsen Fjord bow to get an idea.

[stuckinthemud]

Thanks, will do

[PatM]

Hi Pat, which bit 'Eh?'
Am I correct in thinking that lower limbs are always shorter than top limbs by   the length of the handle? Also, the reason, I think, that through bolting is not as common as a sleeve is because the holes for the bolts weaken the handle in a two-piece take-down, meaning they either need to be longer or fatter, or both longer and fatter, or the bow needs to be a three-piece take down.

No. Limbs are whatever length you make them.
Bolts do require reinforcing the riser etc. but it's probably the more glass bow look that deters people from making them.

[stuckinthemud]

Oh.    That will make bow layout easier in future.  Got to agree about the appearance of a three-part, self bows are so graceful, and you can't always say that about a three part take down

[joachimM]

In any way, a 4" difference in limb length to compensate for off-center pressure point at the handle is huge and exaggerated IMO.
If you have a 4" handle, the average pressure point will be at most 2" from the center of the bow. So if you want to make the lower limb shorter, 2" is plenty.
I don't often make one limb shorter than the other and mostly the difference is limited to 1".
There are other ways than different limb lengths to compensate for this issue.

I try to hold the bow rather loosely, with a narrow pressure point on the soft pad between my index and thumb, not all the way down to the base of my thumb. That gives a sweeter release and reduces the amount the bow is held off center during shooting (with uneven strain on upper versus lower limb as a result). This works best for lighter bows (whatever you're used to).

Joachim

[stuckinthemud]

Hi Joachim, that's really useful, I've tended to mostly do bendy handles for that reason but I will definitely change the way I lay out stiff handles from now on

[Springbuck]

  Yeah, stuckinthemud, I know how hard it is to get a satisfactory answer sometimes, but I do think you are laboring under a couple different misconceptions.  In this case, about asymmetry.

So, measure the exact middle of the next bowstave you work.  You have the two options of making it symmetrical, or asymmetrical on the grip and limb length.  If symmetrical, you know the drill: mark middle, mark handle length, limbs and fades the same, and tiller it.

If you go the other route, somehow you ended up with this 4" number, and the difference shouldn't be anything like that much, unless you are doing it on purpose to learn something or just mess around.  Take that exact middle, and grab the bow so the point of deepest pressure from your hand is right on that line.  For me, that is essentially the fat part of my palm at the base of my thumb, and when I wrap my hand around the bow that exact middle line is sitting between my pointer and middle fingers.

 If I now mark where my hand is, top and bottom, I maybe have an inch plus above the middle line and three inches plus below.  BUT, the arrow has to pass somewhere, with or without a shelf, so above my hand I leave the thickness of an arrow, and a little bit more so I can see past the bow without the widening flare of the limb in the way.  so, maybe an inch and a half above my hand before I start to widen the limb.

So, see how that worked out?  From the middle of the bow, I now have a handle section, say 3.5" below the exact middle, maybe 4 so my pinkie isn't all up in the flares, and 2.5" above the exact middle, maybe a tad more, just enough room for a finger width, and a little arrow pass before the limb widens.  That puts us right on a number you always hear; 6" handle section, plus fades, etc....

The difference in limb length then is not 4", but closer to 1-1/2", MAYBE 2".  So, if you have enough length and width, that is SO much more manageable than 4" difference.

 I made an experimental elm exaggerated Mollie once with grossly asymmetrical limbs and ridiculously long levers, at least 4" length difference, maybe 5",  But that bow was quite long, I adjusted ratios of lever to bendy limb, and I made the lower limb bending section over 4" wide, more than half an inch wider than the top.  It takes compensation like that.

[stuckinthemud]

Yes, definitely been getting it wrong; have put the arrow pass at .5 inch above dead centre, then four inches and a bit for the hand grip means difference in limb length of about 3.5 inches, maybe 4.... Certainly going to change bow design for my next few projects but at least I can tiller an asymmetric bow now, Redhawk's blog has some beautiful asymmetrics in it for anyone interested in such things

[bradsmith2010]

of course bows can be made with different limb lengths,, they just have to be tillered to shoot well,, its not so much about the figures on the paper, thats just a start or rough estimate,, its about how the bow flings an arrow,, thats the bottom line,, if you can get it too shoot, then you have a success,, what ever the measurements are... sometimes there is no exact formula,, you just have to start shooting the bow and adjust accordingly,, thats where the skill and experience comes into play,, 

[mikekeswick]

I gave all the advice I am going to. You don't listen.

About the same level of detail as your normal advice!!!
Pot and the kettle......

[stuckinthemud]

I was chatting with one of my students in work about learning styles and we came to the conclusion that the worst students are teachers, and the most difficult to teach teachers are university teachers! Guess what I am!