Trad Gang
Main Boards => The Bowyer's Bench => Topic started by: on September 30, 2016, 07:13:00 PM
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Here's a tip for you if you are into the numbers on developing and comparing bows to reach a higher level of performance...
I have been comparing and measuring the string tension at a 7" brace height on my 62" string hybrid bows ... The number to shoot for on my bows is double the poundage at 28"... So if you have a 50# bow you would want a 100# or more string tension for good performance... 90% or 90# for a 50# bow may get you up to the 180fps mark or more... There are other variables involved also so this is not a definite but it can be used as a barometer if you stick to one design or similar design bows... Higher string tension definitely makes for a faster bow...
I am curious if anyone else has been measuring string tensions and what kinda results they are getting... Please let me know what string size, style, poundage, brace height, string tension and what FPS you are getting... Thanks... Rich
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Just curious, how do you measure it?
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The forces acting on a bow string are not static.
The deceleration forces acting on the string as an arrow is shot are much higher than a gentle pull.
A bit along the lines of 'jumping off the roof isn't the problem, it's the sudden stop.
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Originally posted by Dan Landis:
Just curious, how do you measure it?
Yeah. I'll play, but I don't know how.
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I put a digital scale and a turnbuckle on a bow string...
I am not sure I follow you Passion... Can you explain more in detail?? Or explain why or if you disagree with my findings on string tension otherwise known as preload...
If you take your fastest bows you should find that they will all have a higher string tension than your slower ones...
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In other words you have the scale mounted between the ends of the string, if I understand what you are saying. A pic would sure help me get my head around your set up.
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Yes... You have the string loop followed by about 12" of string then one end of the turnbuckle attached to the string and the other end of the turnbuckle attached to the scale followed by more string attached to the other side of the scale then the loop...
Basically just run everything in line with two lengths of string on the ends...
Sorry my friend has my camera and I won't be seeing it until mon. or tues....
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"If you take your fastest bows you should find that they will all have a higher string tension than your slower ones... "
I'll second that, but have never checked tension of string. Surprising that it is that much.
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If you have two bows with the same length string just pluck them both like a guitar string and listen to the pitch...
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So if you have two 50# bows with the same specs, how do you get a higher tension string, other than going to a shorter string?
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Start changing up things... Limb angle, lam tapers, profile taper, move your wedges around if you use them, how much reflex or deflex, length of limb, glass thickness...
Use it as a tool like a DFC chart to make comparisons or to see if your changes are going in the right direction... Remember also changes can make or break how a bow shoots...
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Always thought a lower brace height will increase arrow speed. This Is is a performance enhancer, so why increase string tension.
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By lowering brace height you are actually increasing string tension... More string tension equals a faster bow...
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And now we know why recurves are generally faster :)
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Originally posted by PEARL DRUMS:
And now we know why recurves are generally faster :)
Are you sure about that???
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Originally posted by Shredd:
By lowering brace height you are actually increasing string tension... More string tension equals a faster bow...
The arrow stays on the string longer having lower brace, the tension may be increased at full draw but not brace.
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Originally posted by Shredd:
Start changing up things... Limb angle, lam tapers, profile taper, move your wedges around if you use them, how much reflex or deflex, length of limb, glass thickness...
Use it as a tool like a DFC chart to make comparisons or to see if your changes are going in the right direction... Remember also changes can make or break how a bow shoots...
The tool IS the Draw force curve chart.
Don't reinvent the wheel
:)
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I will take that back.
I have been thinking :banghead: (be quite roy)
You band saw blade tention (up and down)is more lb's. than it takes to pull or push the blade left and right lb's
When you are making a self bow the brace profile is different from the long string and the short string.
the short string is pulling from nock to nock in a straight line.
this post could go on and on and on and on
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Don't reinvent the wheel... Lol.. Good One...
The tool is the DFC chart??? Yes if you can make an accurate one... How can you truly compare bows if the readings are inaccurate... I have not seen anyone make an accurate one yet... Maybe someone on this forum can...
Measuring string tension is a simple valuable tool that can help you to understand the inner workings of a bow and can help you to achieve higher performance...
Anyone that has an interest in this and wants to discuss it more in detail can PM me... Class is over gents...
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Originally posted by Shredd:
Don't reinvent the wheel... Lol.. Good One...
The tool is the DFC chart??? Yes if you can make an accurate one... How can you truly compare bows if the readings are inaccurate... I have not seen anyone make an accurate one yet... Maybe someone on this forum can...
Measuring string tension is a simple valuable tool that can help you to understand the inner workings of a bow and can help you to achieve higher performance...
Anyone that has an interest in this and wants to discuss it more in detail can PM me... Class is over gents...
x2
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Max I did not see your last post when I was posting my post...
Trust me, more tension = higher performance...
So measure the tension if you want to compare bows with numbers to fine tune your design...
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Recurves store more energy than straight bows hence the speed difference. String tension on a recurve is related to the reflex in the bow just the same as any other bow design.
Wolftrail string tension at brace is a factor determined by the preloading of the limbs eg. how reflexed the unstrung bow is. what the OP is talking about is nothing to do with adjusting brace height.
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BTW sting tension goes down as the bow is drawn. It has to do with string to ilmb angle and leverage. Took me a while to wrap my head around that. One would think that as draw weight went up so would string tension but that's not the case. Shredd do you have any numbers with your rig other than at brace?
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Finally... Somebody talkin' My language... No I did not record any numbers on drawing a string but only at different brace heights... But you are definitely right about tension going down as you draw... If you push in on the string towards the riser the tension goes up...
Here are a few numbers on a 43# hybrid...
Brace -- Tension
7 1/2" -- 74.54#
7 --0" -- 76.24#
6 3/8" -- 78.97#
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So, are those numbers derived from pushing the string in towards the riser?
It would seem that the way to compare tension at brace height would be with a brace height reduced with a longer string.
Not entirely clear on the theory you are talking about, but since Ben is somewhat on board, I guess there may be something to it. :)
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Those are brace heights... No pushing on the string... No theory just facts... Just as a longer draw will give you a faster arrow... More string tension will also give you a faster arrow...
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Geeze, now I gotta fugger string tension into my trilams. Heck I might invent a round thing ah ma jig and glue it on the end of the limbs. I'll call it a wheel.
LOL Rich, no harm intended.
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Pope wrote about string tension in his book. Page 79, in chapter 5, how to make a bow!
Nothing new. A good read!
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Roy, you need a wheel, yours is shot! LOL :jumper:
Shredd
How does that work on a Static recurve?
How many lb. are you looking for 86 ?
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Mike don't say things like that, you don't know how screwed up I am. And no comments from the peanut gallery Roy!
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What you are describing is ultimately a function of string angle. Consider the values given by Shredd:
Originally posted by Shredd:
Brace -- Tension
7 1/2" -- 74.54#
7 --0" -- 76.24#
6 3/8" -- 78.97#
As the brace height goes down and the string gets closer to the belly the angle between the string and limb also goes down.
String Angle refers to the actual measured angle between the limb and the string when measured at the nocks. The tighter the better. The mechanics behind this are similar to that of a hammock and the angle of the suspension lines. As that angle is reduced the tension increases radically using T=mg/2sina where "T" is tension, "a" is angle, and "mg" is load applied by the limb.
(http://i1255.photobucket.com/albums/hh633/die_dunkelheit/Archery/bowphysics_zpsx4lxfbgt.jpg)
This isn't perfect because we aren't actually considering a static load as in the equation, but it works to explain the relationship of string angle at the nocks to cast speed.
This explains the seemingly paradoxical pattern that though the limb is less loaded by a lower brace height the tension in the string goes up.
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Not gonna say nuffin, Benny Boy...
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Well said Ghost...
Max... I only mess with R/D's A recurve is a different animal... My guess is that it would be a bit higher because at brace you are actually dealing with a shorter limb which could give you a bit more tension...
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Now that's what I'm talking about Anthony!
Thank you Roy, you're becoming more of a gentleman every day but dang you're setting the bar high and I need to clean up my act. :notworthy:
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Originally posted by Shredd:
Well said Ghost...
Max... I only mess with R/D's A recurve is a different animal... My guess is that it would be a bit higher because at brace you are actually dealing with a shorter limb which could give you a bit more tension...
No string tension is determined by how much reflex the bow has unstrung. Recurve or longbow - it doesn't matter, just total reflex. It is only comparable one bow to the next at the same brace height. If you want more string tension then you should use more reflex. It is as simple as that.
It is more a byproduct of a good design rather than a specific thing to aim for on its own.
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Originally posted by mikkekeswick:
Originally posted by Shredd:
Well said Ghost...
Max... I only mess with R/D's A recurve is a different animal... My guess is that it would be a bit higher because at brace you are actually dealing with a shorter limb which could give you a bit more tension...
No string tension is determined by how much reflex the bow has unstrung. Recurve or longbow - it doesn't matter, just total reflex. It is only comparable one bow to the next at the same brace height. If you want more string tension then you should use more reflex. It is as simple as that.
It is more a byproduct of a good design rather than a specific thing to aim for on its own. [/b]
That argument implies that string tension is totally dependent on limb load. What you are saying is basically; "The further reflexed the limbs are the greater the load when braced thus the string tension must be higher." But it fails to answer why when measured from a lower brace, thus the limbs are less loaded, does the tension go up instead of down?
Does reflex (and thus limb load) play a part here? Yes, but the string angle affects how the limbs impart that load into the string.
The really cool thing is how string angle does one thing on draw, but something very different in cast. But that's a different story and a lot more math..
Shredd,
You got it buddy, recurves unlocked a couple things in archery when someone accidentally discovered them. One, you have compounded lengths at work as it gets longer as it is drawn. Two, the string angle is consistently lower throughout the draw as the string angle is never higher than the angle between the limb and the string at the point the string breaks contact with the limb.
In part, my reference here and in my initial response was TTBB vol. 1 chapter 3 wherein Tim Baker discusses the effects of various elements of bow design; my other reference is my love for physics which, like Honest Abe, never lies.
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I thought the question was on general percentages... Where recurve's draw wght to tension will be different to an R/D...
So you are saying that reflex only determines string tension.?? Not other variables like limb thickness, glass thickness and length of limb.??
I agree it is a by product just like arrow speed, DFC and draw weight... And they all can also be measured to see what direction you are headed when making and designig bows...
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My post was directed at Mike...
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Hey Ghost... I am interested in you cast/string angle theory... If you get some time pm me or post it on the forum... Would love to see it... Its been something I been thinking about recently...
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Shredd
what kind of speed's are you getting with 10gpp?
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I have been working on that a lot in the past year... I make a 62" string which I call a Hybrid... I am getting a better average lately of about 177 to 183fps... I just shot a bow Sunday and got 190fps with a 43# bow -- 410 gr -- at 29" draw...
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Max... What kind of speeds are you getting and what kind of bow do you make.???
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The last one I made was 191 with 10gpp
Static recurve, 8" of reflex
I will finish my new one this month.
hoping for more speed.
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Damn... Are you using carbon??? How many lbs. and what string length.??? How long you been building bows???
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Originally posted by Mad Max:
The last one I made was 193 with 10gpp
Static recurve, 8" of reflex
I will finish my new one this month.
hoping for more speed.
That sounds like the magic of a static recurve...
How long are the recurves and how far recurved are they?
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4" to the bridge and 7" of static
(http://i1293.photobucket.com/albums/b593/osagemark/wenge%20bow/100_0542_zps06efedb3.jpg) (http://s1293.photobucket.com/user/osagemark/media/wenge%20bow/100_0542_zps06efedb3.jpg.html)
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Originally posted by Shredd:
Hey Ghost... I am interested in you cast/string angle theory... If you get some time pm me or post it on the forum... Would love to see it... Its been something I been thinking about recently...
Sorry, I meant to reply to this in my last post..
Yeah give me a day or two to get it written up more clearly so it will make sense.
The short version is it's how string angle affects us in one way when we draw and how it affects the arrow differently in cast.
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Originally posted by Mad Max:
4" to the bridge and 7" of static
(http://i1293.photobucket.com/albums/b593/osagemark/wenge%20bow/100_0542_zps06efedb3.jpg) (http://s1293.photobucket.com/user/osagemark/media/wenge%20bow/100_0542_zps06efedb3.jpg.html)
That is a fine looking static recurve sir. I'm guessing you laminate the siyah in a jig and then smooth out the tapper before it goes into the limb? At what point in the draw does the string lift off of the bridge?
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At what point does reflex turn into recurve? :scared:
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die_dunkelheit Yes that is how I did it.
first one's were 22/23" now 18/20" off the bridge.
That is a 64" bow, number 4 T/D
number 5 I am going to a 62" one piece, back to my original tip angle and going for 30/32" draw and trying to get more bend at the levers.
Crooked stic ???????
(http://i1293.photobucket.com/albums/b593/osagemark/wenge%20bow/100_0543_zps73b738b9.jpg) (http://s1293.photobucket.com/user/osagemark/media/wenge%20bow/100_0543_zps73b738b9.jpg.html)
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Everyone is talking string tension. And has agreed that more reflex gives more tension. So at what point is reflex turn into recurve. So now lower Brace = more tension = better performance or lower brace = more power stroke =better performance or hand in hand ?
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I'd say hand in hand. I just build them my way and have never even given string tension a thought!
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yea, what Roy said
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What I was thinking to. Keep it simple!
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Originally posted by Crooked Stic:
Everyone is talking string tension. And has agreed that more reflex gives more tension. So at what point is reflex turn into recurve. So now lower Brace = more tension = better performance or lower brace = more power stroke =better performance or hand in hand ?
Originally posted by Crooked Stic:
What I was thinking to. Keep it simple!
The point about lower brace was only that it demonstrated that string angle has a greater effect than limb load. The goal should be to be more educated about what makes a bow efficient so that we can achieve above average cast speeds with a given draw weight.
A bow with so much reflex that the tips cross but is whip-ended so the string angle is 90 degrees would cast slower than you could throw the arrow and would also stack like crazy. A bow with no reflex but with a 1 degree string angle would be very fast and would not stack at all. The result? A bow with lots of reflex and tight string angle throughout the draw (recurves) would give no stack and very, very, fast cast.
Reflex affects string angle, recurve affects string angle, recurve is reflex focused at the tips, reflex is recurve spread through the rest of the bow. I don't care how you do it, an understanding of what is going on is my goal here.
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die_dunkelheit
"more educated about what makes a bow efficient so that we can achieve above average cast speeds with a given draw weight".
two bows off the same form, one 30# the other 50#
will they cast the same speed with 10gpp ?
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Maxi boy, mine does. Cause I adjust the 30 pounders string tension higher than the 50 pounders string tension. Nutten but 10 rings.
LOL.. Come on guys, this thread is getting repitious beyond reality.
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Where's our engineer canopyboy when we need him? :laughing:
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Be quite Roy
exercise your shoulder and order a dust collector.
:p
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No may Maxi Boy. After this thread, I may just quit making bows cause I've been doing it all wrong... :)
But I need to know, if this tension theory is factual, and is there a calculated fractions factor draw curve I need to implement in there, if I switch between B-50 and FF string? I just love splitting hairs ya know...
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Originally posted by Mad Max:
die_dunkelheit
"more educated about what makes a bow efficient so that we can achieve above average cast speeds with a given draw weight".
two bows off the same form, one 30# the other 50#
will they cast the same speed with 10gpp ?
How on earth did you take something that ridiculous away from my post? My interest here is what makes them efficient. As in what design elements. If you can effect a change in the design that makes your 50# bow shoot faster without sacrificing a smooth draw would you scoff at that too?
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I have been wondering about the speed for some time now so I thought this would be a good time to ask.
I'am not trying to take anything away.
I find this whole post very interesting.
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I'm sorry Max, my dyslexia kicked in pretty hard when I read your post and I fired off a half cocked response thinking I'd been insulted by some kind of mockery. I'm sorry about that.
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cool
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Wow...
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30# and 50# off the same form will not cast a 10gpp arrow at the same speed. They will be close because the design is the same BUT thicker limbs return faster. Thinner limbs return slower.
String tension isn't something to really think about - it is a byproduct of a good design.
Keep It Simple Stupid!
All things have to be equal to compare one bow to another. If two bows have different brace heights you can't make a direct comparision.
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mikkekeswick
Thank you for that Info.
when I started doing tool and die work in the 80's we always used the KISS factor.
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Originally posted by mikkekeswick:
String tension isn't something to really think about - it is a byproduct of a good design.
Keep It Simple Stupid!
All things have to be equal to compare one bow to another. If two bows have different brace heights you can't make a direct comparision.
Okay, there is some miscommunication of what I've been trying to say. All I've been trying to say is that by adding some mid-limb reflex or changing the degree of recurve you lower string angle, and string angle is key. Tight string angle reduces stack, and speeds up cast. The only difference between the hypothetical bows in comparison would be recurve, mid-limb reflex, or otherwise that effects string angle; not draw weight or brace height. So the point being when designing your next bow, as in literally the form on which you will glue it up, keep in mind the angle between the string and the limb at the tips when braced and what you can change in that design to lower the string angle.
BTW, My interest in string tension here is only that it illustrated the effect of the string angle.
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I been away with no internet and wrassling with a hurricane...
I see you boys been chatting it up...
There is something beautiful about simply making a bow a shooting it... There is also something beautiful about delving deep into the inner workings of a bow...
Some may use a rule of thumb, copy other designs and come out with a good shooting fairly fast bow that looks pretty... Some others get off on developing their own design and shoot for a high performance bow that shoots well...
If you are into pushing the limits and producing a high performance bow I would think you should arm yourself with every tool available to give you better insight into the inner workings of a bow... Yes, string tension is a by product... But it can be measured and used as info into figuring out how to get better performance... If you have two similar bows and they have the same string tension or DFC and one shoots 10fps slower than the other... Or two bows are similar but one has more string tension... Knowing certain info can help you to narrow down how to improve a bows performance... I think its kind of a shame to have a good designed bow shooting 10- 20fps less than it is capable of because of a lack of knowing its full potential...
Some of you are making this sound way more complicated than it is... Just put a scale on a string, measure the weight at desired brace and record it to compare to other bows to help you narrow things down... Pretty simple... If you choose not to do it... It is fine... If you chose not to measure arrow speed, arrow wght,string angles and draw weight, that is ok also... :)
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Good info Shredd! I see it as just another method to improve a bow design. Just like using a force draw curve, a tillering tree to observe how and where the limbs bend etc. I see no downside to finding out what string tension is, and using it for future modifications. Thank you for sharing your thoughts and findings with us. Gains in performance are often made in very small increments and this should certainly help.
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shredd
I like this post
Your info is very interesting to me.
Tip weight, or less of it will speed up your arrow.
Narrow/thicker tips.
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=125;t=012157#000000
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Thanks Jess.... Yes... If you only measure draw weight, arrow weight and arrow speed you are kinda working blind if you are looking for improvements... Like you said, Gains can come in small increments and you would never see them without them numbers...
DFC's are a good tool also but you are pissing in the wind if you are trying to compare bows and they are not accurate... I go more by the numbers than the curve... Maybe that will be a good topic to discuss...
Max... Yes I wanted to talk to you about that... I tried to message you last night but the message boss said I can only write you after you write me back... What a jip... I like your design and was gonna suggest molding some carbon fiber for your tips...
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DFC would be much more helpful if we can come up with a consistent method of getting the exact draw length. Just a quarter inch either way and the DFC is off, probably not significant in the big picture but, if we want to squeeze every bit of performance out of a design, well then it is.
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Jess it doesn't need to be a 1/4"... 2- 3/100's will start messing things up...
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Welcome back from the dark Shredd, how bad did it hit you?
I'm still working on that long explanation of string angle. Making some simple graphics to help explain it a little more clearly too.
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It was a close shave... Lots of broken branches and debris... No missing shingles...