Is there a point in recurving tips on a 70 " bow?

[arachnid]

I have not seen anyone refering the the increase in early draw weight. A recurve/reflex bow will have higher early draw weight, improving energy storage. 2 bows with the same final draw weight, one recurved and the other straight, the recurve will be faster (assuming both are properly tillered).

[Springbuck]

  A slight rise in early draw weight would be , to my mind, the biggest change.  I have R/D bows that long (lamiantes) and loved them.  But on a self bow that long, I would look to tiller/bend distribution, and tip-weight control first to nudge performance up.  Especially if it is reflexed nicely already.

  If you do it, slightly flipped tips would be better than big or high angle recurves.  A 70" bow and a 64" bow have different enemies to defeat.  Longer bows store more energy already, and should have less set unless you screw up, so tip weight and tiller (like badly whip tillered) become your performance-robbers if badly executed.   The more extreme you make your curves, the more likely you are to end up with tips too heavy.

[PEARL DRUMS]

Ive never noticed a recurve to be faster than any other well built bow. Not the style I build. My fastest bow to date is a yew RD, hands down.

[joachimM]

  A slight rise in early draw weight would be , to my mind, the biggest change.  I have R/D bows that long (lamiantes) and loved them.  But on a self bow that long, I would look to tiller/bend distribution, and tip-weight control first to nudge performance up.  Especially if it is reflexed nicely already.

  If you do it, slightly flipped tips would be better than big or high angle recurves.  A 70" bow and a 64" bow have different enemies to defeat.  Longer bows store more energy already, and should have less set unless you screw up, so tip weight and tiller (like badly whip tillered) become your performance-robbers if badly executed.   The more extreme you make your curves, the more likely you are to end up with tips too heavy.

+1 for springbuck's answer

[PatM]

I have a longish Elm recurve that disputes all that. 

 It looks like the above stave has no reflex at all actually.

[PEARL DRUMS]

Ive never understood how 8" of straight stiff tip can weigh any less than 8" of recurved tip does. The whole static tip weight thing is jibberish.

[Badger]

  Pearl, what i run into especially on long recurves is that I have trouble keeping the limbs from twisting and end up with extra mass just to keep the string from comming off the sides.

   I recently completed what I call a hinge bow recurve. I made the last 12" as skinny and stiff as I would on a straight limbed bow and it worked out well once I got the tips alligned. About 70% of the limb is rigid so not much room for twisting. I don't think it s practical for a wood bow as I had trouble not making weight.

[Buckeye Guy]

Steve
try one pearly"s way make weight strait then re-curve
 you may see his view differently

[Badger]

Steve
try one pearly"s way make weight strait then re-curve
 you may see his view differently

  I do that all the time if I havent allready thinned the tips to the max.  I just don't get too crazy with the curves.

[dratera]

Lots of good comments, thanks. Just wanted to let you know how it played out, the stave in the picture exploded on me but I started a new one later on, wych elm, 72" ntn , aprox 50# at 28. Came out way lighter than i wanted, shoots pretty fast though i dont have the equipment to measure it. Faster than my shorter ash bows in the same # range. Working tips, and heat treated belly. Since it came out so light i tried to up the # with what is called "mælming" in norwegian,  wich is hardening the wood with heat and a resin/turpentine mix(messy!). Got a few pounds out of it, and think it made it more "springy". And also a nice color, evened out the heat treating color

Wish i could give you a more scientific answer, making an exact copy of it without the recurves and measuring the fps but im out of wood and time. Only definitive answer i have is that IMO flipped tips are prettier!

[LittleBen]

Ive never understood how 8" of straight stiff tip can weigh any less than 8" of recurved tip does. The whole static tip weight thing is jibberish.

I agree PD, we'll sort of. The idea is that a very narrow but slightly thickened tip is lighter than a wide bending tip. Theoretically, this is true, but in practice it is extremely difficult to do. You're tips have to be so narrow and light it's ridiculous, and there no way to know how narrow is too narrow until it explodes. A bending tip tells you where you're at by, well, bending: that way you can judge the strength of the tip, and more easily and comfortably reduce the mass. Needless to say, I don't bother with the static tip thing often.

[joachimM]

Sure there could be a point in doing so. The short anwser with examples: see TBB4 chapter on heat treatment by Marc St-Louis.

The principle is very simple: a certain amount of wood can only take a certain amount of strain (and store a fixed amount of energy) before failure (breakage or bow breakdown due to set). Setback, reflex or recurves will increase total tip travel from unstrung to full draw and therefore strain the wood more, all else being equal. In a straight bow fully drawn, the tips travel 2” less than in the same bow with recurves 2” in front of the handle. Tip travel length is typically around half of the full draw. So 2” of reflex will mean a tip travel of 16” instead of 14”, hence the wood is strained about 12% more. If the wood can safely take that extra strain, it makes sense to flip the tips.

Flipping tips raises draw weight. Not only early draw weight, but draw weight throughout the entire draw. It may be that you end up with flipped tips, and the same final draw weight. This means you damaged belly wood and caused (a lot of) extra set, and the net effect is close to zero.

The fyl in the ointment: If the wood can take that extra strain, it means that your original bow design was suboptimal: you have a bow taking 28” draws, but which can actually easily take 10% more, up to 31”. Remember, the total amount of energy that can be stored remains the same for the same amount of wood.
How to know if the wood can take that extra strain? There are mathematical ways of guesstimating it but few like to do that. Draw it to 30", and see if it explodes, or takes extra set. If it does, you screwed up your bow. Too bad. 
A safer way is to use Badger’s no set tillering method. Go slowly up the tillering tree from 25” with increments of 1” and monitor how draw weight changes as you go up and down with 1" increments. If you go from 27" to 28" and back to 27", and draw weight going down at 27" is lower than going up from 26", it means your wood is taking (reversible) set. If it stays the same, increase draw length and repeat process. If you want a 28" draw with 2" flipped tips, you should be able to go to 30".

On a straight bow already strained maximally at full draw, flipping tips is possible, but at the cost of having to thin the belly so as to avoid overstraining the wood at that same draw length. Cast wouldn’t be better, as you aren’t changing max energy storage. As mentioned by others, at that bow length the string angle at the tips changes too little to affect stack (and bow efficiency).

I did cut a few corners, but I think this boils down to the essence.

And for those focusing on string angle: there are two string angles to take into account: at the tip and at the arrow. see http://paleoplanet69529.yuku.com/topic/21787#.VXfv0vntlBc

[Fred Arnold]

Ben Pearson sure sold a lot of 66" wood bows with recurve tips back in the 40's.50's and 60's. I'm going to try to duplicate this old Pearson hickory bow that I refinished using osage.

I'd say from the number of these things sold it's pretty much a proven design.

[Aaron H]

Sweet bow Fred

[dratera]

Thanks for an exeptional good answer joachim, that gave me the answers i was looking for, boiled down to something easy to understand for someone like me who dont have the patience to dig deep into the science. Bookmarked and will read good before making next recurve, going to try that tillering method to see if i really should flip the tips or not