Post by: Jon Lipovac on May 31, 2024, 11:00:30 AM
Back to Belly configuration:
- .018 Carbon (45/UNI/45)
- .012 Stablcore
- .040 PAR bamboo
- .065 .0015 Taper zebra wood
- .040 PAR bamboo
- .040 Black Glass
.215 total stack at butt end (28” laminations)
10” butt wedge .300-0
6.25” tip wedge .030-0
16* limb pads
Roughed in draw weight 49@28-62
Limbs get to 90* to string at 30” draw and start to stack significantly. I’d want this to draw to 32” before or when the limbs get to 90* to string, what would you change?
Less tip wedge?
More/less taper?
Longer butt wedge?
Longer riser?
Post by: OldRawhide42 on May 31, 2024, 11:10:21 AM
Jim
Post by: Longcruise on May 31, 2024, 12:12:21 PM
Just spitballin.
Post by: Kirkll on May 31, 2024, 02:08:21 PM
What is your limb pad angle? Length of limb from tip notch to riser on the belly side? wedge Length and taper rate?
Is that curl staying static at the end of the draw? or is it opening up a bit? Got tip wedges?
Have you done a DFC chart on this yet and measured the PPI accurately from 28-32" ?
Have you done any performance tests on it?
The reason i'm asking all this is that those limbs look to be bending beautifully to me, and the string angle at the fingers location doesn't look to bad for a 30" draw. That is typically the angle i pay attention too. Kirk
Post by: Kirkll on May 31, 2024, 02:12:13 PM
Post by: Crooked Stic on May 31, 2024, 02:45:30 PM
Post by: Crooked Stic on May 31, 2024, 04:59:43 PM
Post by: Buemaker on May 31, 2024, 05:49:31 PM
Post by: Buemaker on May 31, 2024, 07:04:01 PM
Post by: kennym on May 31, 2024, 09:40:21 PM
On my D/R TD longbow, it stacks at 29 with a tip wedge and will go to 31 without before stacking. 64" bow.
I'm not even sure you need a tip wedge, looks like you keep plenty of hook there at full draw. Unless for stability.
Thats my .02 and with the inflation, it ain't even worth that... :laughing:
Post by: Kirkll on May 31, 2024, 11:53:12 PM
Kirk. Hope you do not mind me moving this from your post on What did you do today, where you show your bow at 31 inch draw. Not so different from Jon’s.
This 64” bow is at 31.5” in this photo and does not stack up at 32”…. When The pounds per inch at the tail end of the draw takes a jump up, that is when it’s considered staking….shes drawing smooth and then it hits a wall and jumps from 3 PPI to 4 PPI . But…. A 48 pound bow should be less than 3 PPI.
If you shorten your wedge too much there is a trade off… you may get a bit softer PPI at the tail end, but it won’t help your string angle at all, you’ll loose preload tension, and increase your limb travel. And…. You’ll start getting a bit more hinge effect at the fades too. This will cost you in performance doing that. I guarantee it.
Do some testing with those limbs John. I hate to see ya shoot yourself in the foot here. She’s looking pretty darn good to me…
If you want to push the envelope, and have good torsional stability, try cutting your tip notches a half inch further out on the curl and lengthen your string. Or just shorten the limb at the butt to keep it AMO length if you like…That will help your string angle, and increase preload.
Kirk
Post by: Jon Lipovac on June 01, 2024, 11:31:58 AM
Here is the DFC
DFC showing stacking really not starting to 30-31"
I'm guessing that the 'felt' stack was more pronounced to me being it's heavier than I feel comfortable pulling and holding at 31"
Post by: Jon Lipovac on June 01, 2024, 11:47:45 AM
Jon. After my point of view I don’t think you measure string angle as should be done. Sorry about crappy drawing, but that is where the angle should be measured,most people do it that way.I think your string angle is very good.We had a post about that some time ago. A bow with no recurves will start to stack severely when that angle reach 90 or more. This is roughly speaking. I know Kirk like to measure just the string where the drawing fingers are placed.
I have a hard time measuring that angle you have drawn since its on a curved surface and I don't know how to reference the same point everytime.
Hey Jon, Where are you measuring your 90 degree point at? off the limbs?
What is your limb pad angle? Length of limb from tip notch to riser on the belly side? wedge Length and taper rate?
Is that curl staying static at the end of the draw? or is it opening up a bit? Got tip wedges?
Have you done a DFC chart on this yet and measured the PPI accurately from 28-32" ?
Have you done any performance tests on it?
The reason i'm asking all this is that those limbs look to be bending beautifully to me, and the string angle at the fingers location doesn't look to bad for a 30" draw. That is typically the angle i pay attention too. Kirk
All those specs are in the opening post.
Agreed on the angle of the string at the fingers and not wanting to create any more finger pinch than necessary
I have not built a string yet to measure string tension at brace yet. I should do that at some point.
Ordered a Garmin Xero C1 chrony that should be here this week so I can get reliable performance data. My Caldwell Ballistic Chrony, even with the light kit, would give me inconsistant numbers and when we are talking a 10fps difference between an good performing number and a great number, I want something that is as accurate as possible.
I may have to change my preferred butt wedge material as well. This bow has a good amount of preload and at brace you can see it bending the butt wedge as soon as it gets past the limb pad. Total limb thickness at the end of the risers is .404”. Almost a like a small hinge area. First time I have noticed that.
Post by: Buemaker on June 01, 2024, 03:12:52 PM
Post by: Crooked Stic on June 01, 2024, 05:40:12 PM
Post by: Kirkll on June 01, 2024, 08:00:45 PM
How does that wedge look unstrung? I have a designstolen :bigsmyl: that the wedge does not touch the end of the limb pad until strung. You may need a bit more preload.
Both my hybrid and RC limb butts have a reflex in the wedges. Crooked Stick only pirated the Hybrid design... :biglaugh: BTW... and it definitely adds to your preload.
here is my RC wedge without a string and with a string.
Jon.... That bow is not stacking at all.... And....its is very similar to my string angle. Once that string angle gets to 90 degrees at the finger location is when things start staking up BIG time.
Post by: Crooked Stic on June 01, 2024, 09:29:26 PM
Post by: Kirkll on June 02, 2024, 11:09:08 AM
My curve limb uses a STW also but it sits flat on the pad. I am thinking of putting a bit of preload in it also. But mine is a full working limb.
Those working RC designs do have a softer PPI at the tail end of the draw, but they don’t help with string angle in a long draw situation. The static tips rule in that dept, and are higher in performance by far until you start getting into the super hook design. That’s a whole different ball game, and I have no desire to go there myself.
Kirk
Post by: Jon Lipovac on June 03, 2024, 08:05:59 PM
So here are pics of the unbraced limb. Dead flat for 6” then a 5/16” reflex the next 4-4.5”
I looked closely at every other bow I still have and I do not have this hinged look in the butt wedge. Most of the previous bows have the same bloodwood wedges.
BTW. This is the first limb set off of this form
It bends enough right at the end of riser that I’m hesitant to put a limb pad overlay on the limb thinking it will fail at the fade by shearing.
Post by: Crooked Stic on June 03, 2024, 08:28:35 PM
Post by: Bryan Adolphe on June 04, 2024, 07:22:24 PM
Post by: Buemaker on June 05, 2024, 06:57:19 PM
Post by: Bryan Adolphe on June 06, 2024, 08:37:24 PM
Post by: simk on June 07, 2024, 04:38:29 PM
Post by: Jon Lipovac on June 07, 2024, 10:13:53 PM
Post by: Crooked Stic on June 07, 2024, 11:00:13 PM
Post by: simk on June 08, 2024, 04:18:58 AM
This may help me understand how guys measure this angle. Are you running a straight edge through the string groove to the throat of the riser for a reference to the string?
You measure from the imaginary line between tips and middle of grip. Having discussed that topic with a bowyer that is physician this seems to be the only way to actually measure string angle. If on the other side you would meadure from tangent where the string lifts of from a recurve the angle is always zero, and that cannot be correct. That was his explanation and I found it logic. If you measure that way the impact of recurves on the angle is a lot smaller than you might think...but there still is an effect. However, there seems to be a lot on confusion on that topic.
Post by: Kirkll on June 08, 2024, 10:39:39 AM
You measure from the imaginary line between tips and middle of grip. Having discussed that topic with a bowyer that is physician this seems to be the only way to actually measure string angle. If on the other side you would measure from tangent where the string lifts of from a recurve the angle is always zero, and that cannot be correct. That was his explanation and I found it logic. If you measure that way the impact of recurves on the angle is a lot smaller than you might think...but there still is an effect. However, there seems to be a lot on confusion on that topic.
[/quote]
I think you’ll find that running an imaginary line from the tips to the center of the grip it is going to be a mirror image of the string itself….
You guys are making this way too complicated….. It’s the “String Angle” we are talking about here. And it’s the angle of the string itself at full draw that matters.
The string angle on a long bow or a recurve increases as the limb tips slowly get closer together as the bow is drawn. The long bow limbs typically control that string angle with more length. So a longer draw length requires a longer bow. But…. Manipulation of where the limbs are bending, and how they are bending effects that string angle too. But long bow limbs start moving closer together much quicker than recurve limbs do…
With shorter length recurve tip limb designs. Especially static tip designs, as you start drawing the bow the limb tips go from reflexed to straight up and down and lets you draw the string further back before the tips start moving closer together.
As the string starts lifting off the back of the curl, that’s when the limbs start compressing. This is the point where your PPI starts increasing and the draw force curve starts curling upward on the graph.
There are a lot things that effect this stage in the draw a guy could devote a whole chapter in a book explaining them. But the location of the working portion of the limb, and the length of that working portion seems to be one of the key factors, and string length, and preload determines how far you can draw the bow before the limbs start moving. Paying close attention to the first 3” of draw and getting good early draw weight plays a huge part in how that bow performs.
What I’ve always found was getting good preload with a longer string is the ticket. Staying 2.5” shorter than AMO bow length, is much higher in performance than the same limbs using a 3” under AMO length, and your string angle is better at full draw.
A lot of guys are too quick to change their limb geometry, or limb shape to increase performance and fine tune things. Often times just changing limb pad angles, and string length can make a huge difference. And changing riser lengths can have an effect too….
The bottom line on string angle is ….once it starts pinching your fingers you start stacking….The hell with all those other angles off the limbs. Kirk
Post by: simk on June 08, 2024, 11:09:20 AM
[/quote]
I think you’ll find that running an imaginary line from the tips to the center of the grip it is going to be a mirror image of the string itself….
You guys are making this way too complicated….. It’s the “String Angle” we are talking about here. And it’s the angle of the string itself at full draw that matters.
[/quote]
Yes that imaginary line must mirror the string.
But the problem of stacking occurs because of changing the angle of attack at the tips.
But practically you probably very right also (-; just because of course there must be a direct relationship between all those angles in the square.
Dont wanna be dogmatic here - its just a topic i was interested for a while. Give you the original words of my bowyer physician - maybe someone finds it interesting too:
Concerning the string angle - I guess that you mean the angle between the string and the tangent of the limb at the nock, see fig. 1). If so, this angle really does not matter, or at least not as you think it would. You can imagine a small circle at the end of the limb in front of which the string is attached (at the back side). Then the angle is always zero, because the string is always tangent to the limb irrespective of the shape of the limbs (recurve, straight, etc.) and stage of drawing. Obviously this can not affect the shooting characteristics of a bow - a straight limbed bow will perform as a straight limbed bow.
What really matters is the angle between the string and the line segment connecting the middle of the bow and the point where the string is attached to (the nock), see fig 2). The shape of the force-draw curve, fig 3), is mostly determined by this angle, NOT the string angle (other quantities on which it depends include material properties etc.).
You can always approximate the limb of a bow by the line segment connecting the middle and the nock. If you recurve a bow, it acts as adding any kind of (non-contact) reflex into the bow. You pre-stress the material, which results in a force-draw curve, which is more concave, thus you store more energy in the bow (total energy is the area under this curve). This is the reason why it seems to you that low string angle "adds" energy to the bow.
From this consideration it also follows that reflexing the handle and tips has no effect when the limbs are deflexed and the overall reflex is zero. It has no advantage, except it looks fancy.
On the other hand, when you feel "stacking" it can be caused by several factors. 1) The bow is short - the angle phi in my drawing is low, so the cos(phi) gets high and the drawing force rises rapidly. This happens in short composite bows.
2) The bow is deflexed - the force-draw curve is more convex - see my drawing. This is the typical cause of stacking in longbows.
3) You push the material beyond the linear dependence of force on the strain (Hook's law) and it gets stiffer.
Post by: Kirkll on June 08, 2024, 12:04:12 PM
It’s quite obvious this bowyer is old school and doesn’t have a lot of time into manipulating energy storage and working limb lengths, and location of where that limb is bending in composite limb bows. Quite simply it’s the key to the whole equation.
But….. then you start looking at some of these wild horn bows, or horse bows they pull way past their ears using a thumb rings, and it just blows my mind how well they perform…. :dunno: :dunno:
Post by: Crooked Stic on June 08, 2024, 04:38:03 PM