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  • inches to degrees help

    Help oldtiffe

    I need to turn 3/4" per foot taper.

    What would that be in degrees?


    thanks
    Ken

  • #2
    3.58 degrees. atan of (.75/12). Unless you mean half of that (3/8) on the cone (3/4 total), in which case it would be half of that.
    Last edited by arcs_n_sparks; 10-05-2010, 09:37 PM.

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    • #3
      That's the Tan-1 of .750/12

      .750/12 = .0625 which can be looked up in the Sine Tables but my little calculator thinks that is 3.5763 degrees or 3 degrees, 34 minutes 35 seconds.
      .
      "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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      • #4
        In case oldtiffie's retired for the night, that would be 3.576334375 decimal degrees or 3 degrees, 34 minutes, 34.8 seconds.

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        • #5
          Assuming your dimensions are like this:

          |
          | 0.75"
          ---------------------
          12.0"

          Tan (alpha) = 0.75/12.0
          Tan (alpha) = 0.0625
          arcTan(0.0625) = 3.576334 degrees


          http://wright.nasa.gov/airplane/trig.html

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          • #6
            Thanks,
            I suspected it would come out to something not easily set, should be able to come close to get started though.

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            • #7
              If it's not +-*/ all that math is a waste of time on me

              Although it may be of help to others.

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              • #8
                Cribbing from "the Starrett book for student machinists" 3/4" per foot is listed as 3 deg 34 min 44 sec. If you are turning this taper by off-setting the tail stock, your offset is equal to the taper per inch times the total length of your workpiece divided by two. Hope this helps. Jim

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                • #9
                  Angle setting

                  Ken.

                  I agree with all of the above.

                  As you are setting it on your lathe, I'd just set the compound to 3.6 degrees and "fine-tune" it in from there.

                  The "half angle" as advised by arcs_n_sparks is also correct at 1.79 degrees - buy just set the compound to 1.8 degrees and fine tune from there as well.

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                  • #10
                    Inside/outside nothing changes correct?

                    I was going to get it close and check the fit with Prussian blue and sneak up on the final fit as need be.

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                    • #11
                      Just so

                      You got it Ken.

                      For "creeping up to it " angular adjustment of your top/compound slide, I'd suggest putting a good (say 0.001") dial indicator on the handle end of the slide at right-angles to it. You will see instantly what has been applied. You can get very fine adjustments that way - as well as seing if you have "over-shot the mark".

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                      • #12
                        Originally posted by oldtiffie
                        You got it Ken.

                        For "creeping up to it " angular adjustment of your top/compound slide, I'd suggest putting a good (say 0.001") dial indicator on the handle end of the slide at right-angles to it. You will see instantly what has been applied. You can get very fine adjustments that way - as well as seing if you have "over-shot the mark".
                        That's a good idea!

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                        • #13
                          All that math is easier than it looks when you are dealing with trig. You reduce the problem to fractions first.

                          The long dimension becomes 1 unit. The short one becomes a fraction of that unit.

                          So, 12/.75 = 16

                          The 12 becomes the unit we are dealing with so the fraction is 1/16 = .0625

                          That fraction is the sine of the angle so sine =.0625. If the taper includes both sides then divide that by 2 to get the actual sine of one side. That equals 0.03125 which is the sine of the angle of one side.

                          The hard part is converting that number to degrees which is why they used to publish trig tables for that purpose. These days you can just ask Google's computer.

                          So we just put into Google this question:

                          How many degrees in sine .03125



                          Now you know how to use a sine bar too.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #14
                            That's simple enough for even me

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                            • #15
                              The zen answer is 3/4" per foot. Or 1/4" per 4", or 1/8" per 2", or 62.5 mils per inch. This is actually probably more useful than an answer in degrees. Why convert to a unit of measure that you probably can't measure very accurately when you can accurately measure in the original units?

                              Mount a dial indicator in a tool holder on the quick change post, or equivalent, and make it perpendicular to the axis of spindle rotation. With a round, non-tapered rod installed on axis (i.e. dial it in at two positions along its length), measure the deflection of the indicator for a known travel on the compound.

                              The catch is that the compound is the hypotenuse of the rise/run triangle. Using the Pythagorean theorem:
                              hypotenuse = sqrt(rise^2+run^2)
                              = sqrt(0.0625^2+1^2)
                              = 1.0019512
                              Thus you want to move the compound 1.0019512" inches (1.0020") and see an indicator reading of 62.5 mils.

                              Or you can move the compound 1.000" and, using pythagorean theorem and similar triangles, sqrt(1.0019512^2-1^2)=0.062499658", or basically the same as the original measurement in this case because the taper is so shallow.

                              I have used 1" because some compounds on small machines have very limited travel. Use a longer distance if you can.

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