Mass and bow shape

[DC]

This is the F/D of my last two bows. The black line is an Ocean Spray selfbow and the red is a Boo backed Yew. The Yew has a little Perry reflex glued in and the OS is about 2" longer. You can see the graph lines are almost identical and yet the Yew is 10 fps faster. Around 190 compared to 180. Would the Perry reflex increase performance that much and not show on the F/D? Or is it a mass thing. The Yew weighs 363 grams and the OS weighs 521. I made the limbs on the OS narrower by an 1/8" or so but I was concerned with it twisting and tossing the string. Is this a case of the design not suiting the wood? Sorry for the blurry pic.

[tattoo dave]

Wish I could help ya on that one DC. I don't think I could pinpoint that answer, but not sure anyone would be able to. You are dealing with a piece of wood. I'd say if I were getting those numbers on a self bow, I'd be happy as can be, and shoot the snot out of both.

Tattoo Dave

[Badger]

  You gave us no idea what kind of bows these are. If the yew is about 64" long and bend through the handle the weight is about right. If the OS is 2" shorter and has a stiff handle the weight would be about right. If you are working with a dense wood and you feel it is too narrow change the design to match the mass. You could have stiffened up the handle on the OS and had good mass.

[DC]

Sorry, these bows are virtually identical except the OS is 2" longer and has narrower limbs. They are my copies of Marc's Maple backed Buckthorn. Stiff handles, deflexed grip. reflexed limbs and small recurves

[DC]

  If you are working with a dense wood and you feel it is too narrow change the design to match the mass.

Sorry, I don't quite understand. How else would I change the design other than narrowing it? Do something completely different, like a longbow?

[Springbuck]

"Would the Perry reflex increase performance that much and not show on the F/D? Or is it a mass thing."

 This will be a can of worms, but, as I read the TBB "Bows of the World" chapter, Perry reflex is in some ways all about mass.  The forced and glued reflex makes limb wood OTHER THAN the superficial surface of the belly take on some of the strain.  Because of this a bow can be narrower, or thinner, or take a more extreme profile, or all of the above.  In (almost) Baker's words, it relieves strain on the belly when the profile would appear to increase strain.

However, experience also tells me that good tiller and mass management for the design (front and side profiles corresponding properly) trumps stuff like how it came off the form. 

10 fps seems like a BIG difference to me, so I can't explain it, but for starters I would say that yew is a LOT lighter than oceanspray, and it's more elastic.  Then you Perry-ed it, etc.....thus the mass is a lot different.  I would expect the yew to be faster if EVERYTHING else is the same, but 10 fps surprises me.

[PatM]

I think it's the combination of both. The lower mass and glued  in reflex seem like they would account for the difference.

 I've never liked Baker's claim that Perry reflex relieves the belly of strain.   Bows cut apart after use show that belly was under just as much strain and it's just hidden by the back pulling it back when unstrung.

[Badger]

   Bows with a laminated back will usually shoot about 7 to 10 fps faster than same design self bows even with similar mass. Yew in particular will be lighter than most any other wood bow not because it is lighter wood but because it is more elastic. I have several elbs I built over r the past few months that are the same draw weight and same mass weight but drastically different in appearance because cherry is very light and ipe is very dense. They also shoot about the same speed.

  D/C how long are the bows?

[DC]

62" and 64" NTN following the bend. Is that how I'm supposed to measure a recurve, following the bend?

[Springbuck]

I've never liked Baker's claim that Perry reflex relieves the belly of strain.   Bows cut apart after use show that belly was under just as much strain and it's just hidden by the back pulling it back when unstrung.

That's the can of worms, right there!

[Springbuck]

  Badger: " Bows with a laminated back will usually shoot about 7 to 10 fps faster than same design self bows even with similar mass."

I believe you Steve, but this is one of those things I haven't been able to come up with a reasonable explanation for, esp. when combining similar woods like hickory-backed hickory, or similar.

 Early on, I fooled around with the idea a lot of various wood combos making better laminated bows.  I did things like tri-lams with a reverse-tapered cherry or elm middle lam with a bulletwood belly lam, so there was more cherry toward the tips and all that.   I did a lot of Perry reflex in stages, so the cherry and bulletwood wee like one lam before applying a reflexed backing.

All I learned was that my tillering skills were not good enough to make the difference I thought it should....

[Badger]

   I am not so sure the Perry reflex explanation is exactly right or not. But I am pretty sure the Perry reflex does consistently boost performance. I can make a run of the mill backed bow and hit 180 or better consistently with 10 grain arrows. It is rare a self bow of mine hits 180 unless I do recurves which I don't like to do.

[PatM]

   The whole stack might be working harder but saving the belly seems speculative.   Tim used to throw around a lot of explanations with little questioning because he was basically the only one experimenting.

[joachimM]

I think it's the combination of both. The lower mass and glued  in reflex seem like they would account for the difference.

 I've never liked Baker's claim that Perry reflex relieves the belly of strain.   Bows cut apart after use show that belly was under just as much strain and it's just hidden by the back pulling it back when unstrung.

Let me pick a worm out of that can

Depends on how you look at it.
if your bow is 10% lighter for the same draw weight, you have less wood to strain. So surely it must resist straining better, if it requires less wood for the same amount of force that's applied. In the end, it's strained the same amount (takes as much set), but since there's less of it, you have less mass, and hence there's an advantage that is, indirectly, the result of perry-reflexed bellies handling strain better.

[Springbuck]

 Badger: I admit, I doubt I have made any laminated bow at all without some forced/glued in profile improvements.  I just thought you meant simple lamination/backing, like a straight stave flatbow vs a straight laminated flatbow.