Sneak peak.

[mmattockx]

The bow is still taking set it will probably end up tips and handle against the wall. By trapping the back almost 30 percent did the bow fail in compression or tension?

If it's taking set then it is failing in compression.


Mark

[Selfbowman]

So I’ve always heard that Osage was pretty even in compression and tension. This trapping makes me wonder how true that is. Less mass on the back but it is still failing to compression??? Explain to me in the most simple terms possible please.

[bjrogg]

Happy New Year Arvin.

I agree with Bob. Looks like a nice shooter. Nice profile yet and I’m sure it has many years of good shooting ability.


I know your are after more than that though.

I guess I have always assumed the set came from compression and crushing cells.

I suppose it could be tension and stretching cells?

I think it is more than simply tension or compression. There’s so many things that effect set. And in the end we are dealing with a material that although very similar to each other as a species can still be very different individually.

Would be interesting to know though.

If the trapping actually caused more set. I might speculate that the back actually stretched more than the belly compressed?

Got me starting the year out thinking 🤔

Bjrogg

[Selfbowman]

Well not impressed with the speed 169. 497 gr arrow.

[Selfbowman]

I might try one more like this with thicker late rings and less early wood. Don’t know?

[superdav95]

With the back trapped I would lean more to tension was little compromised over the compression.  Just my way of looking at it.  If the back is trapped would that not be putting more strain on the back to beef up your belly a bit if one was worried about compression failing a little this could be a balance that is struck.  In this case it would seem to me that unless I could see some evidence of crystallization happening on the belly I would be looking more at the back as the culprit perhaps.  Could still be a bit of both tension and compression and bow has just settle in now to where it will be but if no obvious signs of compression happening I would lean to tension being the cause.  Just my thoughts on it.   Wet nice bow still regardless.  Congrats!   

[mmattockx]

So I’ve always heard that Osage was pretty even in compression and tension. This trapping makes me wonder how true that is. Less mass on the back but it is still failing to compression??? Explain to me in the most simple terms possible please.

Without having precise measurements of your trapping I can only guess, but it is hard to shift the neutral axis much more than 10-12% with trapping unless you really go nuts with it and it doesn't look like you did from the pictures. A 10% neutral axis shift adds 10% to the tension stresses and reduces the compression stresses by 10%. Very few woods are close to even on the tension limit versus the compression limit, so even if your osage compression limit was only 15% less than the tension limit it still would have failed in compression first.

Many (probably most) hardwoods have the compression limit at 50-60% of tension, so your osage would be considered really good at 85% but still not good enough to avoid taking set.


Mark

[Bob Barnes]

So I’ve always heard that Osage was pretty even in compression and tension. This trapping makes me wonder how true that is. Less mass on the back but it is still failing to compression??? Explain to me in the most simple terms possible please.

Without having precise measurements of your trapping I can only guess, but it is hard to shift the neutral axis much more than 10-12% with trapping unless you really go nuts with it and it doesn't look like you did from the pictures. A 10% neutral axis shift adds 10% to the tension stresses and reduces the compression stresses by 10%. Very few woods are close to even on the tension limit versus the compression limit, so even if your osage compression limit was only 15% less than the tension limit it still would have failed in compression first.

Many (probably most) hardwoods have the compression limit at 50-60% of tension, so your osage would be considered really good at 85% but still not good enough to avoid taking set.


Mark

"New bow design somewhat.67” ntn,9” handle, 1-1/8 at fades, 9/32 at tip, pyramid. Trapped on the back3/8 total. Pretty much the whole limb.3/16” on each side."

[Selfbowman]

Ok Mark I’ll try one trapped to the limits . Give me the the dimensions for a narrow pyramid bow similar to this one. From what I understand what you said the mass may get down to5-6 oz per limb on this bow.

[Selfbowman]

Mark I feel it’s failing in tension and here is why. I think the neutral Plane has changed with the  trapping because of less mass . If we was to bend that limb the opposite way it would fail miserably I think we could all agree. The problem may be by reducing the elastic abilities or properties in the mass it’s stretch did not return to its original state. If I shoot this bow a thousand times it might fail eventually. We just can’t see the damage. I still think that perfect diminishing mass is where we will find the best performance. By adding reflex on the ends we have a need for more mass at inner limbs. It’s been a interesting build though. If thicker is quicker can we ever reduce the mass in the limbs of a 67” bow with a 8-10” handle to closer to 6oz instead of 8 oz??

[Selfbowman]

Also I have took the force draw curve pounds of one of my best bows and wrote them every two inches on the  tillering tree. This bow went from 21  at 14” of draw in the beginning of the tiller to about 17#s after set came into the picture. Then at 20” of draw the bow starts hitting the targeted numbers of the previous bow. So at 20”where set usually starts is where the numbers start getting back on target for the rest of the draw. Interesting.

[superdav95]

Also I have took the force draw curve pounds of one of my best bows and wrote them every two inches on the  tillering tree. This bow went from 21  at 14” of draw in the beginning of the tiller to about 17#s after set came into the picture. Then at 20” of draw the bow starts hitting the targeted numbers of the previous bow. So at 20”where set usually starts is where the numbers start getting back on target for the rest of the draw. Interesting.

Arvin, I think you are on to something there with the 20” draw and starting to see set.  I’ve seen this as well with some of my bows.  For this very reason is why I stopped tillering much past brace prior to applying sinew to my bows.  I found better results with getting to just past brace height then making careful thickness measurements of each limb every 2” to get me close enough after sinew.  I found that less crushing of cells on belly as I leave what mass is needed to match the tension of added sinew if that makes sense.  On final tillering I remove what is not needed from the belly and round it a bit to match the crowning of back with sinew.   I think better performance can be had by not overstraining the fibres prior to sinew.  Anyway off topic a bit but find your observations interesting how it relates back to what I’ve found with the use of sinew.  Thanks for posting this. 

[Selfbowman]

Dave I noticed that at 20” is where set starts happening. So has Badger. The interesting part is noticing where it affects the force draw. So a whip need bow would show up loosing weight at the end of the force draw??

[mmattockx]

"New bow design somewhat.67” ntn,9” handle, 1-1/8 at fades, 9/32 at tip, pyramid. Trapped on the back3/8 total. Pretty much the whole limb.3/16” on each side."

That's not really precise enough to use for calculations. When I shape my bow limbs I measure with vernier calipers to get everything as close as I can.

Back in 2007 Badger did a red oak board bow challenge. David Dewey made the only entry, designed using his spreadsheet. This thread talks about it and post #11 shows details of how he made the bow, with pictures. That's the level of accuracy you need to maintain for this to work well.

https://www.tapatalk.com/groups/paleoplanet69529/woodbear-s-red-oak-entry-t13237.html

Ok Mark I’ll try one trapped to the limits . Give me the the dimensions for a narrow pyramid bow similar to this one. From what I understand what you said the mass may get down to5-6 oz per limb on this bow.

1-1/8" wide again? I don't know how low the mass will get, but I can get you to where the entire limb is sharing the strain as evenly as possible. That minimizes the set by not overstraining any particular area of the limb. I forgot to ask, where did the limbs take set on this current bow?

Mark I feel it’s failing in tension and here is why. I think the neutral Plane has changed with the  trapping because of less mass

The thing is, I have seen no evidence that wood can fail progressively in tension. In the various testing research I have seen the tension failures are always blow ups. It is only in compression it will progressively fail by taking set. If someone has data to show progressive failure in tension I would love to see it.


Mark

[Selfbowman]

Fade to mid limb. First part of the draw is affected after set. Also cast is lost at the end when the bow starts bottoming out.