The mass principle question

[freke]

Have read about the mass principle and find it interesting, I calculate my bows according to it and they come all out really close except for sinew backed that was way heavier than excepted.
Dose mass principle work for sinew backed, and if how should I think?

Thanks in advance,
Jonas

[bownarra]

the cured sinew and glue matrix is around 1.3s.g. so to start with the sinew is much denser than most wood. Add to that sinew has very low stretch resistance compared to most woods....
Probably the mass principle won't work too well. You could build hundreds of sinew backed wooden bows in loads of different designs and come up with a new mass principle for sinew backed bows!!

[freke]

the cured sinew and glue matrix is around 1.3s.g. so to start with the sinew is much denser than most wood. Add to that sinew has very low stretch resistance compared to most woods....
Probably the mass principle won't work too well. You could build hundreds of sinew backed wooden bows in loads of different designs and come up with a new mass principle for sinew backed bows!!

Thanks, thought in those term's but felt unsure and better ask. The actual weight was relative much different on sinew so I was curious, next step would be to use it on a bow build but will skip it on sinews for now.

[Badger]

   When I worked out the mass principle I made no allowances for sinew. I haven't done much work with sinew so most of my experience was handling others sinew backed bows. I have seen some good performing sinew backed bows that were actually quite a bit lighter than I would have made if all wood. Not speaking factually here but just an opinion, I think sinew can mask set by pulling the wood back into it's original position. If I were to build another sinew backed bow I would expect it to come out about the same as an all wood selfbow. Another design that seems to come in quite a bit lighter and they are very often sinew backed are recurved deflex/reflex bows similar to the Mark St Louis style. That deflex seems to make a big difference on the stress in the wood.

[bradsmith2010]

my sinew bows were in the ball park,,

[bownarra]

My best sinew backed osage does 185fps @ 10gpp.  I haven't ever weighed it. Might do and see what it should come out weight-wise with regards to the mass principle.

[Marc St Louis]

Yes I've had a few sinew backed bows shoot in the 180's with 10 gpp arrows and using dacron strings, all reflexed recurves

[BowEd]

Yes same here on the arrow speeds on some of my sinewed bows even with narrowed straight tips.
When denser material is applied properly onto a bow made from elastic/dense enough wood or compression strong enough wood & tillered properly a certain amount of side tillering can be done which reduces mass weight.Some of my sinewed bows actually come in lighter mass than projected as a self bow.
To put it into context comparing sinewed bows to self bows mass weight wise.A well design sinewed bow with 6" of reflex is called for with the self bow mass formula to have 3 extra mass ounces added for durability reasons.When the sinewed bow comes in at the same weight mass wise as a flat profile self bow,the advantage goes to the sinewed bow with the sinew helping it's durability being reflexed that much.

[Selfbowman]

Makes sense to me Ed!

[BowEd]

It's always held true for me Arvin.A well designed self bow like the ones you make and occasionally I make,make the need to sinew not needed.

[bownarra]

I'd love to see a straight limbed sinewed wood bow or selfbow do 185fps with 10gpp. Never seen it yet

[BowEd]

I have occasionally into the lower 180's.Long bows.Some with slightly flipped tips also and not really a recurve in the technical sense.I use them to hunt so over time they don't stay that way but still shoot into the middle and upper 170's with a 10 grain arrow.
I'm deer hunting right now but am going to tiller a sinewed bow afterwards that I sinewed back in august/september that's cured by now.I'll see once if I remember while shooting it in to show it with some pictures or even a video.

[Selfbowman]

Interesting . I’d have to think on that a while. Maybe 180 on straight limbs but I don’t know about 185. Don’t make me try I do t have the time right now or the shop. 😬

[Marc St Louis]

I'd love to see a straight limbed sinewed wood bow or selfbow do 185fps with 10gpp. Never seen it yet

Same here.  High 170's maybe

[bradsmith2010]

I thought I had one,, looked at notes,, it shot 180 fps with 500 grain arrow,, but the bow was 55#,, so in 170's like mark said,, this bow was pulled to 26 inches,,,and was about 52 inches long,,
the sinew came off,, so I bent the tips to recurve and was gonna sinew back it again,, havent got to it yet,,