Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on November 02, 2020, 12:56:00 pm
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Let's say I make a recurved bow and tiller it "perfectly". Then I cut it in half and splice it back together with some deflex and then heat in some reflex. Will the tiller still be "perfect" or does tiller requirement depend on side profile?
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I think just using tiller logic would answer your question. The thickness determines how far something can bend before it takes set. The width determines how much it will bend with X amount of force applied to it. Another bit of tiller logic, the entire limb corresponds to it's particular angle with the string at any given moment. So if you have a limb with curves in it the parts of the limb that have the highest string angle will feel the effects of force more than parts of the limb with lower string angles. You can apply that any way you choose.
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so many variables, it will need some adjustment,,
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I was thinking about thickness taper when I wondered about this. Shouldn't the thickness taper stay constant even though the limb is starting out at a different spot?
the entire limb corresponds to it's particular angle with the string at any given moment. So if you have a limb with curves in it the parts of the limb that have the highest string angle will feel the effects of force more than parts of the limb with lower string angles.
Didn't we decide in the "parts of the limb bending first or last" threads that the whole limb bends at once. I can't see how one portion of the limb would feel the force more than another.
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DC, how much reflex (to what point) and in what place of the limb?
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It's theoretical but I usually reflex the whole limb, increasing the curve as I go out so it kind of blends into the recurve.
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I wasn't talking about the timing of the bend. Think of it this way, your braced profile shows reflex in the mid to out limb, it is point upward at that point and has a lower angle to the string. You weaken that area a little to get it bending and suddenly it is bending too much because the string angle increased and it is feeling more leverage on itself.
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I wasn't talking about the timing of the bend. Think of it this way, your braced profile shows reflex in the mid to out limb, it is point upward at that point and has a lower angle to the string. You weaken that area a little to get it bending and suddenly it is bending too much because the string angle increased and it is feeling more leverage on itself.
OK gotcha but back to the original question, if it bent nicely when it was straight shouldn't it still bend nicely? I'm talking about deflexing and reflexing the limb with out any scraping or tillering of any kind. Just taking a well tillered bow and changing the side profile. The draw weight will change probably, depending on how much deflex and/or reflex.
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I think I understand DC what you want. It’s easier to perfect tiller a straight bow vs recurve. It’s a pain for me to understand where to watch and when to watch for limb bending during tiler. I haven’t done many recurves though. I also think there are to many variables to take a perfect tiller straight bow and change it to a recurve with out re tillering. If I am understanding your thoughts. Arvin
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if it was fiberglass maybe
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I think I understand DC what you want. It’s easier to perfect tiller a straight bow vs recurve. It’s a pain for me to understand where to watch and when to watch for limb bending during tiler. I haven’t done many recurves though. I also think there are to many variables to take a perfect tiller straight bow and change it to a recurve with out re tillering. If I am understanding your thoughts. Arvin
Yeah, that's it, almost. Take a straight bow and turn it into a R/D.
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Maybe if the top 1/3 didn't work on the straight bow at all then the non working part would be the recurve and everything else would work fine?
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Yes it will change drastically. As you deflex, you decrease your leverage at the tips, reducing strain in the outer limbs, forcing the inner limbs to take more strain than the outer. Deflex limbs require thicker limbs to counter this. Actually, ANY and ALL deflexed portions of a limb will REQUIRE the deflex to be thicker or it will hinge due to increase leverage over that area. This is why deflex bows, in my experience, are more efficient than reflexed bows, even if slower. They store less energy due to lower string tension, but that energy is more efficiently used because the thicker inner limbs are less likely to take set, combined with the reduced radius they bend to store a set amount of energy.
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No.
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Maybe if the top 1/3 didn't work on the straight bow at all then the non working part would be the recurve and everything else would work fine?
In a lot of cases people leave the outer 8-9" stiff which is just about how much it takes to bend a recurve so it seems like it would be OK
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I guess I'll have to try it. I have a Black Locust pyramid with fairly circular tiller. I don't really like the bow so it's a good subject. I'm I little concerned that I won't be able to get it to hold any amount of reflex but we'll see. I'll have to check that there is enough to cut and resplice. I'll take before and after pictures and measurements. Probably won't get much done today, there's something interesting to watch on CNN ;D
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OK it took a while. I had string alignment issues(still do a bit).
I cut it in half and steamed reflex into both limbs. Then I heat treated them. It had already been heat treated but this one was to help hold the reflex. Then I spliced it back together. Lost about 1/2"-1" in length from the resplice. I haven't pulled it to FD yet because of the string alignment but I wanted to get it back on here. I aslo wanted to get a picture before the reflex pulls out(if it does). I'll put the different views together so the difference is easier to see. Unbraced first.
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Braced. Top(right) limb took a little more reflex I think.
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Full draw. This is quite interesting. The before picture looks almost whip tillered. I think I like the after. I'll have to look at it for a while. I never touched the limbs except for the heat treat and cutting in string grooves to help keep the string on. The tips were quite narrow and convex. The DL on the before is 27" and the after is about 24" I'll get a better one after I sort the alignment.
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That looks good.
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It's interesting in how much it changed. You can see why and it was expected but I was surprised by the amount of change.
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That is very interesting DC
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I like that experiment too DC! thank you! Sure you will also provide further data (# - fps), before and after changing design ;D
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I like that experiment too DC! thank you! Sure you will also provide further data (# - fps), before and after changing design ;D
Unfortunately I forgot to take a before speed. Shoot me, I'm old ;D I do remember it wasn't very impressive. High 170's maybe, I dunno. I think I will be bending future bows a little more in the middle though. If you look at the before it's not bending much in the middle but it looks like it's bending a lot in the after. I really don't think it's changed all that much. I'm going to have to figure out how to manipulate photos a little better so I can overlay the images.
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mistakes happen - I do plenty even as a younger fart - always so many little thigs to consider (in advance :)) with these bows. I was expecting it to hinge even more close to the fade after deflexing and also that you need scraping the mid and outers, loosing a lot of drawweight. fades look a little critical to me already, especially right side (but could also be a natural deflex in the wood), so i think a whip tillered bow wouldn't be too bad for this experiments. keep 'em coming ;D
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Looks good, like I said, as you deflex, tips take less strain and inner limbs take more. How much reflex have you got on that bow right now?
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Cool experiment DC. If you see set starting to appear, could you note it's location for us?
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There was about 2" of reflex when it came off the caul. There is 1" now. Like I said earlier I don't have a lot of luck keeping heated in reflex. I got the string alignment sorted unless it moved overnight so I can speed test it today. The DW is about 38#, down 2# I believe.
I was mostly interested in the shape of the tiller so wasn't thinking about performance. I really dropped the ball on recording this. I should have traced the outline and forgot. I should have taken DW and speed readings and forgot. I seem to be getting cabin fever early this year. Normally happens in late winter but this year it's early fall. Age I guess.
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The only solution is to do it all again (SH)
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There was about 2" of reflex when it came off the caul. There is 1" now. Like I said earlier I don't have a lot of luck keeping heated in reflex.
loosing heated in reflex could be the wood or the reflexing job I suppose.
Do you see any set taking on the inners? Anything that might support Sleeks theory?
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The only solution is to do it all again (SH)
I may but I don't have many straight selfbows.
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There was about 2" of reflex when it came off the caul. There is 1" now. Like I said earlier I don't have a lot of luck keeping heated in reflex.
loosing heated in reflex could be the wood or the reflexing job I suppose.
Do you see any set taking on the inners? Anything that might support Sleeks theory?
Not yet but I haven't shot it much. It looks like the tips are straightening a bit and that may be where the reflex is going. I'll play with it a bit today but it's my grandsons birthday so not much will happen :D
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It shoots 180 fps so not much improvement.
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Speed stayed the same or went slightly up and you lost 2 pounds of draw weight. Thats pretty telling.