Primitive Archer
Main Discussion Area => Bows => Topic started by: Badger on February 17, 2018, 04:07:12 pm
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I have a small program I would like to write. A computer generated radius that represented a specific strain based on limb thickness only.
Input- limb thickness
Input- Desired strain expressed in a percent (EXP .5%)
Output- Radius needed
Could anyone here do this?
tool to go with it, You could take a coil and wind it up with sliding bands and then simply adjust it to the radius you are looking for and just hold it up to the bow,
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If you can get it sorted you could calibrate a Gizmo with it
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I'm not all that on excel, but I could spin you up a quick free webapp that'll do it if you're interested in sharing it with everyone else ;)
I'm sure we could put our heads together for the algorithm.
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After reading y'alls thoughts on the other thread, I wonder if setting up a database would be handy where people could enter their figures and keep running averages for each species. It would be cool to see what the community comes up with.
If you are interested in setting this up as a web app, i would enjoy getting something up, maybe with simple log-in, maybe without. Maybe we could put a sticky with a link to a secure-ish automatic login that would keep it away from the general public. Lemme know if you want to do this!
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The formula is simple, multiply the thickness by the strain example. .375X99.5 = 37.3 radius. You would be close enough just moving the decimal point over 2 places and using that as a radius. You could easily make a set of gages going from .300 to 1.0 in increments of 1/2". It would not be a precision gauge but a nice visual aid.
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After reading y'alls thoughts on the other thread, I wonder if setting up a database would be handy where people could enter their figures and keep running averages for each species. It would be cool to see what the community comes up with.
For me personally I have no interest in trying to determine thicknesses. I prefer to do that while building the bow. My interest is in making sure whatever thickness I have does not get bent into too tight of a radius. I hope you can follow that. Your radius gauges would only need to be about 5" long. I just thought of a way to use the gizmo as a precision measure device. Get back in a few minutes
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Ah, gotcha. So would you prefer this as an excel sheet or online page?
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I just checked out an online calculator for radius of an arch. We use this quite a bit in the construction and drapery business i was in. The arch in the case would be the gizmo, the program would simply give you a setting for the gizmo as far as how far the pencil would stick out on a 4" gizmo to give a specific arch or radius.
So the 4" gizmo would be a constant, the input would be the thickness which creates a radius by moving the decimal point 2 places. The output would be the height of the pencil lead, anyplace it did no mark you would have to not scrape. Now the one problem I see is that we seldom mark our bows at full draw usually about 2/3 draw in my case. Si it would have to be calibrated for a 2/3 draw and this is what the bowyer would have to pull his bow to for marking.
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Ah, that sounds like a cool idea. So would that be a linear relationship to adjust for the 2/3 draw? ie: strain percent would be 2/3 * 99.5 or essentially 66.3?
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so essentially we want an algorithm/formula where the user can plug in the thickness of the limb and get the setting for the gizmo, yes? I can put that together. My wife can help me set up a spreadsheet, or I can put a calculator online as mentioned.
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I found a calculator on line that will give me the exact figures I need it is called radius of an arch. I need to convert it to excel so we can pass it around. For example a .55 thick limb would have a 55" radius in the bending area, this would equate to the pencil protruding from a 4" gizmo by .168 for example. Depending on the treads you are using in the gizmo you turn the pencil x amount of turns and portion of turns to get an exact setting.
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the program would simply give you a setting for the gizmo as far as how far the pencil would stick out on a 4" gizmo to give a specific arch or radius.
Sounds pretty simple, Steve, if you know what strain you need. Would there be a way to adjust strains for different species wood?
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I can send you a link for to the formula if you send me your email
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I may nerd out on this one and create a calculator with presets that are customizable (eg: draw length and max draw to figure the proportion of draw and the resulting radius, etc) and make it available online for PA folks if that's ok with you. Might can even bribe my wife to help me set up an excel sheet and make it a 2fer :P
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K Hat, I would love it.
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So this could tell you the maximum the pencil should stick out. You could set it like that to start and then scrape away the pencil marks. When the Gizmo stopped marking you are at the max bend?
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the program would simply give you a setting for the gizmo as far as how far the pencil would stick out on a 4" gizmo to give a specific arch or radius.
Sounds pretty simple, Steve, if you know what strain you need. Would there be a way to adjust strains for different species wood?
Willie, the most flexable woods are less than 1% difference in total flex that the least flexable bow woods. One number in the middle would get you close enough
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So this could tell you the maximum the pencil should stick out. You could set it like that to start and then scrape away the pencil marks. When the Gizmo stopped marking you are at the max bend?
excactly
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pm sent
Thanks for the project. good times 8)
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pm sent
Thanks for the project. good times 8)
I emailed the web site, just scroll down for the calculator
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I'm slightly befogged Steve. It sounds like you want to know how far you can bend a limb without set. But does that mean if you have a thickness that limits your draw to 20", that's where you stop?
If you mean the info would tell you the limb needs to be thinner to go farther, then you are doing backward exactly what I look for in choosing a thickness that will bend as far as needed without set. :o
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I may nerd out on this one and create a calculator with presets that are customizable (eg: draw length and max draw to figure the proportion of draw and the resulting radius, etc) and make it available online for PA folks if that's ok with you. Might can even bribe my wife to help me set up an excel sheet and make it a 2fer :P
Sounds like a good project for Python.
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I'm slightly befogged Steve. It sounds like you want to know how far you can bend a limb without set. But does that mean if you have a thickness that limits your draw to 20", that's where you stop?
If you mean the info would tell you the limb needs to be thinner to go farther, then you are doing backward exactly what I look for in choosing a thickness that will bend as far as needed without set. :o
No Jim, there is no relation to what you are talking about. Bows are designed differently. In my case I try to use as little working limb as possible. It would likely tell me I need to use some more limb. If you design a bow wrong in width no tiller tool will help the design, it might tell you you won't make weight but that's not the tools fault.
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I may nerd out on this one and create a calculator with presets that are customizable (eg: draw length and max draw to figure the proportion of draw and the resulting radius, etc) and make it available online for PA folks if that's ok with you. Might can even bribe my wife to help me set up an excel sheet and make it a 2fer :P
Sounds like a good project for Python.
Or ruby ;)
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I may nerd out on this one and create a calculator with presets that are customizable (eg: draw length and max draw to figure the proportion of draw and the resulting radius, etc) and make it available online for PA folks if that's ok with you. Might can even bribe my wife to help me set up an excel sheet and make it a 2fer :P
Sounds like a good project for Python.
Or ruby ;)
No matter who does it, it sounds like a great thing to do.
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So this could tell you the maximum the pencil should stick out. You could set it like that to start and then scrape away the pencil marks. When the Gizmo stopped marking you are at the max bend?
excactly
EDIT I am trying to under stand an order of operations for tillering with the gizmo
so you would input...
1. the gizmo base length
2. a "not to exceed" working strain
2. the thickness of limb in the area you are tillering
output would give....
a pencil stickout length to use on your gizmo that would not let you tiller beyond the chosen strain?
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Hey Steve! Got a working app up and running. It has presets that are modifiable. I think I got all the math right on it. Still need to tweak the ui a little (add some instructions/explanation), but it is functional.
Love to hear any input. Here's the url: https://radius-calculator.herokuapp.com/ (https://radius-calculator.herokuapp.com/)
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this does assume a 99.5% value for the strain at full draw, proportioned based on the actual (partial) draw (maybe I should rename that field). I can add an input for that customization as well if necessary.
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Will look it over right now, cool! That was fast!
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That is perfect!! Id the 99.5 programmable also? I don't think it makes a lot of difference as most wood is so close it might be best to use as a constant anyway. I will try this out a bit in the real world and if it seems to work I will get back to you as soon as I can. I love it. We will name it after you. Call it the "Khat"
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Oh please don't name it after me lol. Yeah I can add a field where people can customize the strain percent as well if we want it. Small easy change.
Glad ya like it!
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Maybe on this same thread we will discuss the test parameters to see how the 99.5 works out. At what point set is a no go etc. I favor a few inches of radius before set happens as a cushion.
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I think a good method for identifying set at it's earliest stages would be using a deflection method like we would use checking spine on an arrow. As soon as it drops we have reached the plastic range. I imagine creating a radius gauge to wrap it around would be the best way to stress it so I don't get an uneven bend. Suggestions welcome.
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I imagine creating a radius gauge to wrap it around would be the best way to stress it so I don't get an uneven bend. Suggestions welcome.
you mean a set of templates of various radii? like maybe cut out of thin plywood? That would be useful for checking limbs in a stiff handled bow, or a bow with short working areas? I think there would still be some math involved to pick the correct template.
I wonder if there is a way to develop a formula that could work in the background of the calculator..... such that we only need to specify a few more inputs? One might have to plug in a few more inputs like the length of the working area, its distance from the center and the overall length of the bow.
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Willie, all you need is the thickness and then know not to exceed a min radius for that thickness. You could easily adjust a gizmo to reflect any desired radius.
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Steve, I am confused about how you propose to tiller using this web tool/gizmo set-up for anything except a constant radius bendy handled bow. What are these gauges you speak of?
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Willie, I am not so sure how well it would work it might not be sensitive enough. It is basically just a tillering aid that would let you know when you are approaching the bending limits on a specific area. You take a quick thickness reading and the calculator tells you where to set your gizmo at.
An acceptable bend for wood 7/8 thick would look nothing like a bend for 3/8 thick. If you are working on a much longer bow or anything outside your norm it would just offer a caution warning and give you advance warning before you took set.
You take a reading on the bow anywhere you want or need to and react to that specific area. I see tons of bows on here that are bending too much in parts of the limb. On a tapered bow you might want 3 setting for instance.
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Man...I've been reading this thread and although I make good bows, some of you guys are light years ahead of me. I guess my approach is a whole lot more organic...or haphazard depending on your perspective. I bet some of you guys day job is Rocket Scientist or something. Not being critical, just in awe of the brain power in this room. Seriously.