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  1. #21
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    Quote Originally Posted by Cory View Post

    Please share the model number of that calculator.

    Cory
    Please re-read post number 2.
    Please re-read post number 4.

    At this point you are becoming a troll with that request.

  2. #22
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    Quote Originally Posted by 3t3d View Post
    Please re-read post number 2.
    Please re-read post number 4.

    At this point you are becoming a troll with that request.
    3t3d,
    Are you saying that if you input a decimal into this calculator, that it will spit out the nearest 4 numbers (round value), 2 in the numerator and 2 in the denominator, chosen from a fixed set of integers?

    Mind boggling if it can do that, and, if so, sounds like the magic we'd need.

  3. #23
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    Cory,
    Be careful with the equasions, there are changes if the hob and gear are not the same hand. My machine constant is 12/n I think the equasion you have is for a 18/n machine. You must be sure of your index and feed (that's the .075) constants before calculating anything. If you are working with a multi start hob, the equasions change. It's been over 10 years since I looked at the equasions. Also if you are working with left hand hobs you will need an idler gear in the index and feed trains. I gave up working with hand calculating and wrote my own programs to figure the gears needed. unless you have a hobber that takes splined change gears, you need a 20DP 14.5degree hob to make any gear you need. With the ratio book you can pick a ratio close to what is needed when making a prime number gear. They seem to be used alot on my helical setups, I have made many gears over the years so my set runs from 20 to 100 tooth with dups on most sizes. When you have everything setup and start cutting, it is like watching a barber pole being formed as things progress across the blank. Common errors I have made are swapping gears so the ratio is wrong, setting the hob swivel wrong (usually when cutting gears with the hob of the other hand) or changing the hob and forgetting to change the hob swivel.

    If you still have the setup data for the job you have cut, see if you can use it as a check for your calculations.
    Points to remember.
    1. You can swap 2 drivers, or 2 driven or both, but not 1 driver with 1 driven.
    2. You can double 1 driver and 1 driven or multiply by the same multiplier. The # of teeth changes but the ratio is the same.
    3.ALWAYS check the setup after you figure the swaps and multipliers, by figuring the ratio of driver/drivenXdriver/driven= is the ratio you need.

    My first setup took 8+hours without the book of ratios.

    The people at Ash Gear can be quite helpful if they aren't real busy.
    The equasions in their catalog for measuring helical gears are wrong, there was a typo when it was typeset.

    12L14 or Leadloy makes a great steel for proofing out a setup, it is free machining and if there is something wrong you will still cut it instead of trashing a hob.

    Hope this helps,

  4. #24
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    Default Help for folks starting with gear cutting

    I would also suggest visiting
    Meshing with Gears - Gear Manufacturing Information and Software Resources
    and the FAQ page there. It has many ways to setup hobbers, and your B-C hobber is definitely easy to setup once you have the change gears. The formulas that make use of "C" value to cut helicals are described there, and there is a forum specifically for gear cutting questions.

    I see that your thread is years old, but other visitors might find the website useful.

    Also,
    Ash Gear & Supply TEL:248.374.6155 FAX:248.374.6255 - Gear Cutting tools the same day!
    is a strong supplier for tooling, software, etc. Scott Atkinson is very knowledgeable and helpful.

    Just some thoughts...

  5. #25
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    It's a 3 year old post!
    JR

  6. #26
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    Default 95000 For Gear Ratio Book

    Quote Originally Posted by Cory View Post
    I am trying to locate and borrow the Barber Colman book of 95,000 4 gear ratios. This book is over 500 pages of gear ratios to set up there gear hobbers. Let me know if you have one to borrow or even sell. I would like to buy it or make a duplication of it. I will make sure you get it back undamaged. I am learning gear hobbing using the BC #3 and this info would help me out. I know there are computer programs out there but I would like to learn the long hand calculation. I have talked to Terry at RPI and he only has one.

    Thanks,Cory
    HI Cory: were you able to find this book. I am also looking for it. We were at the same place you were. At the faction and not able to change it. If you do could you please let me know. Thanks Sue

  7. #27
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    Reading this old thread made me chuckle. If you have the BC manual, it has a perfectly good explination of how to calculate change gears for a given ratio. Index gears need to be exact, feed gears can have a small error- in the 5th or 6th decimal place. Learn how to factor a number with a calculator and a pencil- if you can't do that, then you will never succeed in setting up your change gears. I've found that a table of prime factors is much more usefull that a ratio book. On a non-differential machine, if you find a number that wont factor, then slightly change your feed constant and try again.
    With regard to the BC ratio book, I've found it kind of klunky to use, but it does work. A much better book in my opinion is the Pfauter change gear ratio book. It is out of print, but...……..Pfauter change gear tables: Friedrich Werner Becher, A. Koerner: Amazon.com: Books
    Last edited by Dan from Oakland; 11-25-2021 at 12:38 AM.

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  9. #28
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    Quote Originally Posted by Dan from Oakland View Post
    Reading this old thread made me chuckle. If you have the BC manual, it has a perfectly good explination of how to calculate change gears for a given ratio. Index gears need to be exact, feed gears can have a small error- in the 5th or 6th decimal place. Learn how to factor a number with a calculator and a pencil- if you can't do that, then you will never succeed in setting up your change gears. I've found that a table of prime factors is much more usefull that a ratio book. On a non-differential machine, if you find a number that wont factor, then slightly change your feed constant and try again.
    With regard to the BC ratio book, I've found it kind of klunky to use, but it does work. A much better book in my opinion is the Pfauter change gear ratio book. It is out of print, but...……..Pfauter change gear tables: Friedrich Werner Becher, A. Koerner: Amazon.com: Books
    I don't cut gears and have never had the inclination to do so, even before I became too old.

    But, for some reason the math is very interesting. I am always looking to improve my understanding of it. It is very hard to do so, because the reservoir of knowledge is disappearing and CNC has negated its need in most instances.

    My introduction to the math began when I started at a company having two G&E hobbers. I was asked/assigned to write a program to find the change gears. They gave me all of their reference materials to learn the process.

    The first two things I learned was how to calculate the Index change gears using whole C values and how to calculate the feed change gears manually with just a pencil and paper (not using any lookup charts or book of ratios -- I did cheat with a calculator and drill chart).
    Last edited by David_M; 11-25-2021 at 09:18 AM.

  10. #29
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    Quote Originally Posted by Dan from Oakland View Post
    Reading this old thread made me chuckle. If you have the BC manual, it has a perfectly good explination of how to calculate change gears for a given ratio.
    Hey ! If you don't behave, I'll give you a Cleveland

    Of course you can calculate but it's so nice to look under .963758214 and pull out a four-gear ratio, no muss no fuss.

    I'm lazy ...

  11. #30
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    Quote Originally Posted by EmanuelGoldstein View Post
    Hey ! If you don't behave, I'll give you a Cleveland

    Of course you can calculate but it's so nice to look under .963758214 and pull out a four-gear ratio, no muss no fuss.

    I'm lazy ...
    target: .963758214


    80/83 = 0.963856 - just above the target
    99/103 = 0.9611650 - below the target


    Numerators added to numerators and denominators added to denominators. Until the numerator sum divided by the denominator sum most closely matches the target number. The sums need to be composite numbers that have factors that work as change gears.


    99 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 + 80 = 2739


    103 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 + 83 = 2842


    2739/2842 = 0.96375791

    target - 0.96375791 = 0.000000297

    error: 0.000000297

    2739 factors (33, 83) drivers
    2842 factors (58, 49) driven

    It normally isn't this ugly, but this is what it took to equal a computer program using 1 each of 30 to 90 gears.
    Last edited by David_M; 11-25-2021 at 10:35 AM.

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    These are just some that are more accurate than the above, but have bad factors:

    718/745 = 0.963758389 error: 0.000000175

    7047/7312 = 0.963758205689 error: 0.00000000831

    745493/773527 error: 0.000000000001




  13. #32
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    Quote Originally Posted by David_M View Post
    These are just some that are more accurate ....
    Wish you'd been around in the early eighties ... but you'd have to write in basic, for a 286.

    See, there's a space on the PAM waiting for your program


  14. #33
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    If you remember your lights dimming in the mid 90s, it was probably me using my Packard Bell 486dx2 50 with Windows 3.1, my first (toy) computer (with a toy visual interface on top of DOS) .


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