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    Excel sheet for prod sizing (Download)

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    Spyro.Magno
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    Excel sheet for prod sizing (Download)

    Post by Spyro.Magno on Tue Apr 15, 2014 11:33 am

    Edit: 

    Hello,

    After a looong time i finally finished the sheet.  Very Happy
    I created it for personal use, but then seeing that in the forum afaik there's nothing similar i though it might help some people.
    I still haven't finished my crossbow infact its a long time i don't work on it and that why it took me so long to finish this sheet. The actual sheet was done in half an hour but the legend necessary to use it was quite a work and i worked on it sparingly.
    Rewriting technical concept in a short and concise way in your non native language is not trivial. 
    I did my best to explain what every value is, and how to insert it, but im pretty sure that even then most people won't know how to use the sheet.
    I would be willing to do a video tutorial, but atm i am missing a microphone.

    So for any doubt feel free to ask and i will reply at the best of my abilities, and i will be able to create a faq.

    Download

    ODS format :  https://drive.google.com/file/d/0B6AGECjzJxM5dWV0dHNjTWVJZk0/view?usp=sharing
    XLS format :  https://drive.google.com/file/d/0B6AGECjzJxM5VWkwbm9Dbmk0NXc/view?usp=sharing

    Spyro.Magno
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    Re: Excel sheet for prod sizing (Download)

    Post by Spyro.Magno on Sun Dec 14, 2014 7:26 am

    Reserved for future edits

    Spyro.Magno
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    Re: Excel sheet for prod sizing (Download)

    Post by Spyro.Magno on Sat Dec 27, 2014 8:36 am

    Damn no one is interested? Sad 
    I thought it would be helpful to people to be able to define the prod in advance. 

    Even if you feel to insult me it would be a feedback Laughing.

    mac
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    Re: Excel sheet for prod sizing (Download)

    Post by mac on Sat Dec 27, 2014 8:48 am

    Spyro,

    I remember when you posted this.  I was hoping to see some discussion and explanation, but that did not develop.

    Can you tell us more about this thing?  What will it do?  What does it look like?  How much information do you specify?  What materials will it work for?  I am personally too much of a Luddite to just download it and try to figure it out. 

    Mac

    Rizzar
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    Re: Excel sheet for prod sizing (Download)

    Post by Rizzar on Sat Dec 27, 2014 10:03 am

    Hey there.

    Just had a quick look onto the sheet.

    I see it difficult to state that a single calculated prod half results in the doubled effective draweight. Very, very rough perhaps.

    How could anyone know about "J"?

    Sigma is not that easy to handle with, especially concerning prod speed.
    I feel strongly forced to aim for 1050+/- MPa to gain useable prod speed, but the better the tensile strength of the material the more I tend to push it forward in my calcs.


    I think you should differ in "f" between forged deflex and under pressure applied deflex.


    Doing Calculations on prods is always difficult.
    I made a sheet some time ago, I am very satisfied with it, but I know it could be wrong/not good enough.

    That is the reason why I do not share it. I will always be responsible what someone could do with it if used wrong.
    I do try to help others with calcs but everytime I warn to act responsible and the values I provide do not give any warrant.

    I would worry about someone that uses ur sheet incorrect and gets into trouble with extremely stressed steel.

    Greetings Rizzar

    Spyro.Magno
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    Re: Excel sheet for prod sizing (Download)

    Post by Spyro.Magno on Wed Dec 31, 2014 7:12 am

    Ok, i'll try my best to explain wrote:Hey there.

    Just had a quick look onto the sheet.

    I see it difficult to state that a single calculated prod half results in the doubled effective draweight. Very, very rough perhaps.

    If i understand correctly what you're saying: It doesn't result in double effective draw weight, being the prod specular you calculate just one half of the prod. So if you for example want a 30 kg TOTAL draw weight, being the prod composed of two halves you calculate only one half for half the wanted draw weight (15 kg) 

    How could anyone know about "J"?

    You don't actually need to know about J, it is used by the excel sheet itself (when you insert the thickness you leaf spring have, the sheet use it to calculate the height of the prod at the beginning of the taper in order to achieve the draw weight you want)

    Sigma is not that easy to handle with, especially concerning prod speed.
    I feel strongly forced to aim for 1050+/- MPa to gain useable prod speed, but the better the tensile strength of the material the more I tend to push it forward in my calcs.

    Could you elaborate on what you mean/the meaning is of prod speed?

    Sigma in this case represent  only the strees put on the prod. by drawing the crossbow. For example if you calculate for 15kg of draw weight and the sheet give you a Sigma of 400 Nm (made up numbers) your material must have a higher sigma or it will break or bend.
    To elaborate: to get a safe value for example you material has a ultimate tensile strenght of 800 Nm , you multiply it by 0.7  and you get 560 Nm. You should not exceed 560 Nm of stress on your prod.



    I think you should differ in "f" between forged deflex and under pressure applied deflex.

    Yeah thats a big problem, meaning i don't have the resources to incorporate the forged/relaxed state deflex with the under pressure deflex. 
    The equation i used in the sheet for that consider a straight beam. Infact in this case that value is more of a reference. 



    Doing Calculations on prods is always difficult.
    I made a sheet some time ago, I am very satisfied with it, but I know it could be wrong/not good enough.

    That is the reason why I do not share it. I will always be responsible what someone could do with it if used wrong.
    I do try to help others with calcs but everytime I warn to act responsible and the values I provide do not give any warrant.

    Thats also true, i completely forgot about that.

    I would worry about someone that uses ur sheet incorrect and gets into trouble with extremely stressed steel.

    Greetings Rizzar

    Hope this clarify a little. 
    i will put up a little tutorial plus an explaination of the steps.

    In the meantime if you have any more doubts please you are welcome.

    @MAC: I know there is no tutorial yet, but take a look at the sheet in meantime i really put A LOT of effort to for the legend included inside (Infact the calculations are really straight forward) so there's already an explaination for what every value does (of course for a total newbie its pretty hard to come by how this works) but you can see what values you absolutely need have in order to use the sheet. 


    Thank you all

    Rizzar
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    Re: Excel sheet for prod sizing (Download)

    Post by Rizzar on Wed Dec 31, 2014 8:18 am

    Hey

    Huh, I hope I can clarify the points so it is easy to follow (describing technical/physical things in a foreign language is not the easiest thing).

    1- Draw weight calculated from one prod half:
    You apply a force on one half of a flatspring and measure it with a scale.
    But the angles between the limbs and so the directions the forces work play an important role.
    Easiest way to determine the difference between adding (*2) the forces is by drawing a parallelogram of forces with the limb forces action in different directions and a resulting new force.
    The resulting force alternates by draw length. The longer the draw the more changes the angle/draw weight.

    2-J going to skip this since you stated it is not really needed

    3-Sigma
    Sigma determines the stress that is in the material, the more stress, the higher is the stored energy.
    So the better values in tensile strength are the higher stress can be put into a material the higher can be the stored energy.
    In order to move the limb at an efficient speed (which you really want) you will have to put enough energy into the material.
    Steel is, since it is quite heavy, not very grateful when it comes into moving.
    The closer you get to the elastic limit the more force will be stored, the better will be the equation of mass to force -> resulting in a higher speed.
    If you put little stress into a limb it will consume a lot of its energy by moving its own weight.
    When you build steel prods considering very large savety values (which is not the worst, don´t get me wrong) you will lower the limb/projectile speed/energy.

    4- f
    I use the value to add it to calculated draw length when thinking of it as forged deflex without or little pressure.




    Hope this helps.

    Greetings Rizz

    Spyro.Magno
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    Re: Excel sheet for prod sizing (Download)

    Post by Spyro.Magno on Thu Jan 01, 2015 9:02 am

    Rizzar wrote:Hey

    Huh, I hope I can clarify the points so it is easy to follow (describing technical/physical things in a foreign language is not the easiest thing).

    1- Draw weight calculated from one prod half:
    You apply a force on one half of a flatspring and measure it with a scale.
    But the angles between the limbs and so the directions the forces work play an important role.
    Easiest way to determine the difference between adding (*2) the forces is by drawing a parallelogram of forces with the limb forces action in different directions and a resulting new force.
    The resulting force alternates by draw length. The longer the draw the more changes the angle/draw weight.

    2-J going to skip this since you stated it is not really needed

    3-Sigma
    Sigma determines the stress that is in the material, the more stress, the higher is the stored energy.
    So the better values in tensile strength are the higher stress can be put into a material the higher can be the stored energy.
    In order to move the limb at an efficient speed (which you really want) you will have to put enough energy into the material.
    Steel is, since it is quite heavy, not very grateful when it comes into moving.
    The closer you get to the elastic limit the more force will be stored, the better will be the equation of mass to force -> resulting in a higher speed.
    If you put little stress into a limb it will consume a lot of its energy by moving its own weight.
    When you build steel prods considering very large savety values (which is not the worst, don´t get me wrong) you will lower the limb/projectile speed/energy.

    4- f
    I use the value to add it to calculated draw length when thinking of it as forged deflex without or little pressure.




    Hope this helps.

    Greetings Rizz

    Ok, you put up a really good argument with your first point. 
    What you say is absolutely right.
    I probably advertised wrongly the scope of my sheet. The point of sheet is not to calculate the exact functionality of a prod, is more of a reference. The point was i cut a prod and the result was : damn probably i can draw it only with a goat lever! I don't want it that strong! 
    So i took up my book, did some research on the internet and ended up writing this simple sheet in order to reiterate the calculations, meaning: For my crossbow i already decided (most wrongly) the draw lenght, and i needed to reiterate the calculations to get a decent balance between draw weight, lenght, sigma etc, and i didnt want to take 10 times the time to do them by calculator (because you need to redo every single equation every time) 
    My scope was to give me a technical reference because i lacked empirical experience (if it does makes sense what i just wrote)

    Then i thought, maybe somebody else that starts at square one may need something like this to get started. 

    Back to your first point: I took for implicit (damn thats why i need some feedback Smile) the fact that the sheet considers a simple straight beam, with a perpendicular force applied.
                                     
    It is not completely right, but is enough to get started, and thats what i needed and thought people would need. 

    About sigma, you're right again but the scope of that (and all the sheet) is not towards efficiency/functionality of a particular crossbow, is will it break and get the prod on my nose or can i have some assurence that it will not? 
    Again i took my technical knowledge in general mechanics and tried to port it here, in order to get something that would work and in the meantime have a safety assurence. 

    About the forth point i may have an  idea but i have to verify it. 

    Hope i cleared some doubts.

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    Re: Excel sheet for prod sizing (Download)

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