Post by: Longcruise on June 07, 2022, 03:18:48 PM
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Post by: Crooked Stic on June 07, 2022, 03:56:24 PM
I go 1.375 on R/Ds
Post by: Jeff tech on June 07, 2022, 04:59:14 PM
Post by: Longcruise on June 07, 2022, 05:59:32 PM
Rough shaped at 1.44 it was 51.2#. At 1.375 it and with a serious trapping of the back it was 44.3#, now it will probably be 41 ish. Going trap the back jus a bit probably end at 39 ish.
Glad I didn't have a target weight. :biglaugh:
Post by: Kirkll on June 07, 2022, 07:15:24 PM
My experiments with narrow profile have mostly resulted from missing draw weight really high, and figuring I got nothing to loose. Some of These crazy adventures have produced some seriously fast bows too.
One thing I did find out was that your torsional stability requires a certain amount of depth, or limb thickness, in the outer working portion of the limb. Narrowing the limb at the fades doesn’t have a serious effect on the limbs stability. This magic stack thickness is different for each limb design.
What I found helpful on those borderline draw weights between hunting and target. Say 32-42 @ 28” …. Is that changing your forward taper from a .004 to .003 will give you better stability. Or going from .003 down to .0025 FT can give you another .020 in thickness in the working section and add stability.
This is really important on recurve limbs. Especially target weight bows under 40# @28. Same theory applies. On my static tip design, my magic # is .190 using an .001 FT. Once I get under 40#, I go to a par to keep it tracking straight, and under 35 # I use a revers taper and a longer working limb. This thickness trumps width 8:1.
My .02 worth….
Kirk
Post by: Longcruise on June 07, 2022, 08:01:11 PM
I shot this bow at 1.375" with a 520 +/- 44#. No chrono numbers but it seemed a bit pokey. Just shot it again at this new width (scaled 41.3#) and it seemed actually quite a bit faster.
So, narrowed at the fades, more side taper added (not a plan. The end result getting the twist out) with .003 taper and 4.25" tip wedge. This seems to be a pretty good formula for this design.
I think on my wider versions I'm going to go to .002 in the taper. I think Kenny might have mentioned that he uses .002. Might be wrong on that 🤔
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Post by: Kirkll on June 07, 2022, 08:39:21 PM
I'm a bit curious on the limb geometry coming out of the form.
looking at the strung bow and the shape of the limbs at brace....... it makes me want to ask about your brace height too. I'm just curious.... Kirk
Post by: Shredd on June 08, 2022, 02:03:21 AM
When I was a Greenhorn Kirk used to tell me, "Out of one form you could make 25 different kind of limbs"... I found this to be true... First it takes a decent design... After that you may have 15 bows that are slow and a few that shoot like crap... Make 5 that are moderately fast and 1 or 2 that shoot really well... About now you are zeroing in on a good recipe for that design.... 3 that are pretty fast and shoot good too... 2 that are very fast and shoot well also...
I learned a lot of tricks on slinging an arrow fast and look at me now... I'm still a Greenhorn... :laughing: So much to learn out there...
Tip... If you change one thing and the bow shoots faster... It probably wasn't that one thing that made the bow faster... It was 1 to 4 things that were out of balance and the one thing you changed brought one or more of the others in better balance for better performance...
Just a few cents I'm tossing out there...
Post by: Longcruise on June 08, 2022, 10:49:36 AM
You got a photo of that bow unstrung?
I'm a bit curious on the limb geometry coming out of the form.
looking at the strung bow and the shape of the limbs at brace....... it makes me want to ask about your brace height too. I'm just curious.... Kirk
Brace is 8" from the back and 6 1/8" AMO. Not what I'll be settling on in the end. Just a handy string that was suitable to the build process.
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Post by: Kirkll on June 09, 2022, 08:09:05 PM
You got a photo of that bow unstrung?
I'm a bit curious on the limb geometry coming out of the form.
looking at the strung bow and the shape of the limbs at brace....... it makes me want to ask about your brace height too. I'm just curious.... Kirk
Brace is 8" from the back and 6 1/8" AMO. Not what I'll be settling on in the end. Just a handy string that was suitable to the build process.
Thanks for the photo…. That explains the strung limb shape. I played with something similar in shape years ago when I was first getting started. As a matter of fact…. It was crooked stick that send me a pattern. I built a few using that form including my wife’s first long bow…. Then I moved on to a different shape that allowed a deeper core and better energy storage with much better vertical stability. You can definitely squeeze some good numbers out of that design by shifting wedges around, but the ones I built had poor vertical stability I didn’t care for. Kirk
Here are a few pictures of that design. The photo of my wife is a full 32” draw. I had to have special long arrows built to put broad-heads those shafts.
https://photos.app.goo.gl/8JyQW2uhFUpkLrh96
Post by: Longcruise on June 09, 2022, 10:29:30 PM
You got a photo of that bow unstrung?
I'm a bit curious on the limb geometry coming out of the form.
looking at the strung bow and the shape of the limbs at brace....... it makes me want to ask about your brace height too. I'm just curious.... Kirk
Brace is 8" from the back and 6 1/8" AMO. Not what I'll be settling on in the end. Just a handy string that was suitable to the build process.
Thanks for the photo…. That explains the strung limb shape. I played with something similar in shape years ago when I was first getting started. As a matter of fact…. It was crooked stick that send me a pattern. I built a few using that form including my wife’s first long bow…. Then I moved on to a different shape that allowed a deeper core and better energy storage with much better vertical stability. You can definitely squeeze some good numbers out of that design by shifting wedges around, but the ones I built had poor vertical stability I didn’t care for. Kirk
Here are a few pictures of that design. The photo of my wife is a full 32” draw. I had to have special long arrows built to put broad-heads those shafts.
https://photos.app.goo.gl/8JyQW2uhFUpkLrh96
How long was your bow?
Post by: Crooked Stic on June 10, 2022, 08:51:40 AM
Post by: Kirkll on June 10, 2022, 10:32:50 AM
I remember that design. Was not the best Mrs. Kirk made it look good tho. :bigsmyl:
Seeing this bow that Longcruise has going reminded me a lot of that old design we played with. Hell….. that was 15 years ago Mike…. Time flies…
That bow that Kat was drawing was 64” in length, and pretty light draw weight.
I think is close to 40 @ 32” . I shifted the wedges on her bow to get a longer draw and it did ok….. but that design is borderline vertically unstable. Too much reflex sweep in the outer portion of the limb. I did figure out that going down to a .002 FT helped that design a lot.
I figured out that doing a more moderate R/D shape with a little more reflex pushed out closer to the tips works much better . It allows a deeper core in the working portion and totally eliminated the vertical stability issues…..
the down side is that 62” is as short as I can go with this Flatliner design and still get it to 30” without stacking. I build a lot of 64” and 66” lengths that go to 32” draw.
Look at the shape of this limb design and keep in mind I use 8” tip wedges.
https://photos.app.goo.gl/xYs1QFHSwS6XwoBz7
https://photos.app.goo.gl/6chkz7wRRkjjq8zo9
Kirk
Post by: Longcruise on June 10, 2022, 10:42:43 PM
Post by: Kirkll on June 11, 2022, 09:31:35 AM
I’m drinking coffee in my bathrobe right now using my IPad.
But a simple explanation is…. If you grab the string and move it up and down vertically, the limbs move. In some cases a lot.
Or set the tip of the bow on the ground, and lightly bounce it…. The limbs flex too much with pressure vertically on the tips. They are floppy….. can be damaged easily, and even throw a string occasionally if the tracking isn’t perfect.
The funny thing about these borderline unstable designs is they can be in the upper end of a performance test on the chronograph.
There was a software developed years ago by an engineer called “super tiller” that calculated energy storage capabilities on different geometrical limb shapes. The limb shape with highest energy storage capability was very similar to the design in question here, and considered vertically unstable by most experienced archers and bowyers alike.
Years ago Zipper Bows built a hybrid R/D design that was pretty hot on the chronograph, but had floppy limbs at brace. But …..he sold a lot of those because they were good shooting bows. They may even still produce that design. I don’t know…. I met the owner at ETAR about 10 years ago. He was a very nice guy.
Sooooo….. It’s not the end of the world if your bow is a bit floppy at the tips. That design can be a joy to shoot. It’s just a bit too fragile for my liking. Btw…. The heavier draw weights are much better in the same design. But this is true for stability on most limb designs too….. the true test of your limb design will tell the story rather quickly building 32- 35# bows.
When I get to building target weight bows like this I change my taper rate to keep them from going sideways to easily. Kirk
Post by: Shredd on June 11, 2022, 11:08:37 AM
Kirk, how do define vertical instability? You've got me thinking about it and I need thoughts on how it manifests.
How it Manifests.?? I would like to know some others view on this also...
I believe Stic says, If you put too much reflex right off the fades it will cause instability... If my memory serves me correct too shallow of an angle coming off the fades with certain limb types can cause instability... Too long of a limb for certain designs can be too unstable... I took a 64" r/d with a decent amount of reflex out to 68" and it was highly unstable...
My theory for vertical instability is when you have two limbs and they are pulling the string at a shallow angle it is easier for one limb to over power the other because of a mechanical advantage... A tighter radius in your limb shape (agressive R/D) somewhat adds to a shallow limb angle to the string...
Brace height can be a factor also... Too little of a brace height can cause things to go floppy... But mainly because you have a floppy design to begin with and your limbs could be riding on that semi unstable/very unstable balance point...
So if you are gonna have reflex in your bows it's probably important to know how much that you want to add and the angle of the limbs... There is gonna be a balancing point... Tip the scales too much and you have got instability...
If you are concerned about Performance in relation to Stability and Limb Angle off the Fades... I have found with certain limb designs that there was no change in performance with changing the angle of your limbs...
Post by: mmattockx on June 11, 2022, 11:31:09 AM
There was a software developed years ago by an engineer called “super tiller” that calculated energy storage capabilities on different geometrical limb shapes.
Super Tiller is Alan Case's baby. I use it and a couple other pieces of software in my bow design work. It does much more than calculate energy storage for a given design and is very useful, but not very user friendly.
I believe this is the video about limb stability you mentioned:
https://www.youtube.com/watch?v=sEOF6eCD-Mc&t=100s
Mark
Post by: Kirkll on June 11, 2022, 04:46:09 PM
last year I sent him a set of seriously heavy limbs to play with, and never heard whether he actually build a bow with them or not…..He is a seriously busy guy….
Kirk
Post by: Longcruise on June 12, 2022, 09:25:23 PM
Definitely not a speed demon, but OTOH, it doesn't give me any stability sensations or problems when shooting it. Room for improvement for sure. One thing I'm satisfied with is that this design and be brought down to this 1.154 width without any problems. It does have stabilcore under the belly glass.
---------------------------------------------------
6 1/8” BH, B55 12 strand string,
445 grain arrow = 10.18 GPP
Average of five shots.
1. 163.1
2. 165.7
3. 164.7
4. 163.4
5. 162.4
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Total: 819.30 / 5 = 163.8
Dynamic efficiency = 61.82%
-------------------------------------------------
6 1/8' BH, B55 12 strand string,
538 grain arrow = 11.37 GPP
1. 151.7
2. 151.2
3. 153.1
4. 154.7
5. 148.3
----------
Total: 759.00 / 5 = 151.8
Dynamic efficiency = 66.27%
Post by: Longcruise on June 12, 2022, 09:27:28 PM
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Post by: Kirkll on June 12, 2022, 09:33:25 PM
Post by: Longcruise on June 12, 2022, 09:48:35 PM
I'm curious why your DFC graph starts at zero @ 8" when your brace is just over 6" ? just curious... Kirk
Heh heh, I knew that would come up! :) I adjust my rule (yardstick) to compensate for the "AMO" surface of the riser. I don't have a typical tillering tree so I clamp a block on top of the yardstick so the riser sits up against the block with the bow laying flat on the table and then draw the bow down the yardstick inch by inch with a scale in my hand.
It's a very stout table! :)
Post by: Longcruise on June 12, 2022, 10:00:10 PM
BH
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Addjusted
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Post by: Kirkll on June 12, 2022, 11:28:36 PM
You would be wise to build a tiller tree so your riser is about head height, and use a small boat winch with pulleys. You can see the way your limbs are bending much better stepping back and looking at them.
I think a hand pulled rope on a tiller tree works better for exercising a self bow. That hand crank holds it too long in one position me thinks…. But it’s great for glass bows.
Food for thought… Kirk
Post by: Shredd on June 13, 2022, 07:32:36 AM
Post by: Kirkll on June 13, 2022, 09:51:44 AM
Once you get the perfect combo going extending your fade tips out further, it’s a thing of beauty watching the string angle flatten out, and those wedges, or extended fades start working like over load springs. This is a huge part of a limb design that is often overlooked by the masses. Another .02 cents. Kirk
Post by: Shredd on June 13, 2022, 10:14:01 AM
I would like to see a side profile drawn to 28" without a cluttered background... By the looks of bow now and the dfc it appears that the bow is bending too much at the base of the limbs... Which will be very smooth drawing but lack performance...
Post by: Longcruise on June 13, 2022, 12:29:51 PM
Kirk, that tillering tree is something I need to put together. I have all the materials needed but have been held back by a place to put it for use and to store it. I did see one of our members photo of their tree strapped to an actual tree. That is going to be my solution.
I don't have a shop per se. Just a very small 5 X 8 alcove in the corner of the garage. All the power tool action is done on the driveway with the tools pulled out and set up for each session. I also use the covered patio in the back. Pretty much a fair weather operation. Recently I managed to set up a work table in the basement that allows me to do glue ups indoors which is a big help.
Nuff of my tribulations! :tongue:
Shredd, I've built quite a few off this form but those have been at 1.4" width. They were all good shooters and had pretty good chrono numbers but I had a drive crash and it wrecked my data during a lengthy period of time. Shoulda kept paper copies! I'm ready to glue up another of the same design which I plan to keep at 1.4" so I'll do some comparisons.
So, this morning I did some further experimenting with string length and the chrono.
Increasing the BH a mere 1/4" to 6 3/8" made a noticeable difference in vertical stability.
Shooting over the chrono with the same arrows as posted above resulted in only minor variations in speed. with a sample of five it's not enough to conclude anything.
Switching to a FF at the same 6 3/8" BH and once again the same arrows showed about a 4 fps increase for the 445 grain arrow, but the surprise was an 11 fps increase for the 538 grain arrow. Still only a sample of five.
I'll see if I can get a photo at full draw.
Post by: Kirkll on June 13, 2022, 01:14:07 PM
I built one years ago before i bought a hooter shooter. I used a stout piece of oak 4/4 X 4" X 5' long and mounted a small boat winch on one end and mounted it on a stand that was about 40" off the floor so i had good clearance. I just used 1/4" braided nylon rope and rigged up a trigger release aid to hook on the string and just clamped a yard stick on the board with spring clamps. I just used bungi cords to hold the bow in place for awhile until i fashioned a rubber strap that worked better.
Something like this can be used for DFC charts, tiller tree, and an accurate way to measure your speed. Doing DFC charts shooting by hand is not accurate enough for measuring the true performance differences in your bow while tweaking limb design. 3 different guys shooting the same bow will get different numbers, and your numbers will change from one day to the next. A shooting machine with very accurate arrow weights, draw weights, and draw length is the only way you can really see small differences of gain or loss.
another .02..... At this rate you will have a bucks worth in no time,,, :biglaugh: Kirk