taper pin size vs. shaft size chart?
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  1. #1
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    Default taper pin size vs. shaft size chart?

    We have an engineer here trying to write a proceedure to cover taper pin sizes that can be used in relationship to the size of the shaft that it is used in. Looked in mhb and didn't find what he wanted. Is there a chart or is it just a ratio?
    have fun
    i_r_machinist

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    I would think it's inch pounds of torque at the shaft diameter divided by the shear strength of the pin. Really what you're asking is what size taper pin to use for a given torque transmission. Should be a straight forward calculation. You have to factor the shaft torque first, then the strength of the cross sectional area of the taper pin, but factor the shear forces, not tension.

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    Dont forget the stress state if there is also a thrust load supported and use a liberal "k" value ( generic fuge factor etc.) to account for any shock loadings/vibrations. Do the calcs for a straight pin diamater and use that valve as the average taper pin diameter (d1+d2)/2.

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    If you look in your copy of the the American Machinists' Handbook Seventh Edition (January, 1940) page 803 there is a chart showing the number size recommened for shaft sizes. In lieu of you having the manual I post the following:

    Pin- shaft

    0- .5-.75"

    2- .75-1"

    4- 1-1.5"

    6- 1.5-2"

    8- 2-3"

    10- 3-4.5"

    12- 4.5-6.5

    There is more info for collars if needed.

    Aren't the old books great. The machinists of old had it all and we have CNC high speed crap.
    Last edited by Carl Darnell; 06-24-2008 at 12:22 AM.

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    Thanks for the replys. The reason they are looking for a chart is because they don't want to do the math every time we have an issue.
    7th Edition? I would love to look through that book!
    Thanks
    i_r_machinist

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    I've alway used a rule of thumb where the pin was 1/4 the shaft size on the big end. You can't use taper pins to transmit teal torque. They're soft and beat out too easily. If there is real torque or power needs to be transmitted use a taper pin for axial location only at assembly and a straight or Woodruff key for transmitting torque. While we are on the subject, it's not uncommon for a taper pin to fall out. In those instances where a taper pin absolutely positively has to stay put (like in a shifter inside a transmission) make sure it's positively retained.

    Mostly taper pins are used for precision repeat location of assembled components not positively located by features and components subject to hand torque only.

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    We deal with them mostly on valve components. Butterfly valves in particular. Other than that for motor locations.
    have fun
    i_r_

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    Many lathes use tapered pins as a shear pin on the lead screw and/or feed screw to protect the gears.

    I wish American Machinist had continued to publish their handbook. I like the older books because they have much info that has been discontinued now days.

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    I've found most of the older books work on tables. I suspect this is because the tables are generated via empirical testing, rather than mathematical models. Today we have the ability to analyze materials and components, quantify their properties, and make mathematical models which we can input these values to generate a "right" answer.

    For the true propeller heads with a math or pile it higher 'n deeper degree, this is ideal. For the majority we just want a table derived from inputting these values, and that's how it's been for a long time. Unfortunately I think there are a couple of reasons for not publshing tables anymore, pedantics and liability.

    The pedants who publish the books say "gee, but that's not precise, they should know how to calculate this..." and the lawyers say "well, if we publish tables based on assumptions made about materials, we could be liable if some nitwit hurts himself or others".

    They can't be certain of the intelligence of who is using their data, so they just default to "here's the facts" mode and ignore the useful information.

    Fact is, if someone uses an inappropriately small "something" where a bigger "something" really should be used, they screwed up. Chances are they'd still mess it up even with the properties data. At least with a table, they can learn "gee, maybe this ain't right".

    MHB clearly states their tables, where not absolute, are [conservative] starting points for the reader. That sounds like a perfectly useful CYA for me.

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    All the more reason for the USA going to a lawsuit system that is based on intent to cause injury before a suit can proceed.

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    i r machinist - Machinist's handbooks for the time period 1940 thru 1944 are commonly available on Ebay at very reasonable prices, although when I just looked there were not many listed. I enjoy looking at the earlier ones, but the really old ones in good condition draw quite a bit of interest.

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    Dave A
    Last month I bought a (1943) 12th edition Machinery's Handbook on ebay, in perfect condition, with the exception of page yellowish color, as expected. I thoroughly enjoy and use it on a regular basis. Cost $19.00 + ship.


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