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  • Compound Feed for Threading

    Here's the best explanation I've found of how far to feed in the compound for threading (and why).



    Assuming the compound is set at 30 degrees, the compound travels along one leg of a triangle. The length of the side is the same as the crest to crest distance of one thread. Next, reduce that travel by 1/8th to allow for the root clearance and again by 1/8 for the crest. That's a total of 1/4 or 25%. The remainder comprises the 75% thread form.

    Divide .750 by the TPI, and that's how far to advance the compound.

    -Mike

  • #2
    How many times does it take to get it through you guys heads....

    TWENTY-FRICKIN-NINE-AND A GOD DAMN HALF DEGREES.

    Or you get lines.

    Comment


    • #3
      I dont use the compound at all till I get to 5 TPI or less.
      Last edited by tattoomike68; 01-26-2008, 09:54 PM.

      Comment


      • #4
        Threading.

        Originally posted by panchula
        Here's the best explanation I've found of how far to feed in the compound for threading (and why).

        http://www-personal.umich.edu/~panchula/ToolTravel2.jpg
        ..........................................
        .........................................
        ........................................

        Assuming the compound is set at 30 degrees, the compound travels along one leg of a triangle.
        -Mike
        Hi Mike.

        Never mind the "flak".

        I will cover that subject and a lot of others on screw-threading shortly on another HSM thread at:
        http://bbs.homeshopmachinist.net/showthread.php?t=27274

        Comment


        • #5
          Originally posted by tattoomike68
          I dont use the compund at all till I get to 5 TPI or less.

          Whats a compund? I guess you like chatttttter and rub.


          Wolfie I always use 29.5 degrees is that ok with you?
          Last edited by J.Ramsey; 01-26-2008, 10:00 PM.

          Comment


          • #6
            Originally posted by J.Ramsey
            I guess you like chatttttter and rub.
            Its never been a problem on shallow threads. Also the indexable insert tool I use has the right geometry for plunging strait in.

            Comment


            • #7
              Originally posted by tattoomike68
              Its never been a problem on shallow threads. Also the indexable insert tool I use has the right geometry for plunging strait in.
              I guess you need to share your secret tool with all of us out of date thread chasers.

              Comment


              • #8


                The price is a bit spendy but they hold up for a long time. You need to go faster but the threads end up with a mirror finnish in 4140.

                http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=36659257

                Comment


                • #9
                  Wolfie's Right

                  29.5 does give a nicer finish. For illustrating the basic geometry, I thought the excerpt would be helpful for those who have anxiety about single pointing a thread. We're all at different points on the learning (not to mention tooling) curve.

                  Comment


                  • #10
                    I'm with tattoomike on this one

                    Comment


                    • #11
                      Originally posted by panchula
                      Here's the best explanation I've found of how far to feed in the compound for threading (and why).

                      http://www-personal.umich.edu/~panchula/ToolTravel2.jpg
                      ..........................................
                      .........................................
                      ........................................

                      Assuming the compound is set at 30 degrees, the compound travels along one leg of a triangle.
                      -Mike


                      Originally posted by oldtiffie
                      Hi Mike.

                      Never mind the "flak".

                      I will cover that subject and a lot of others on screw-threading shortly on another HSM thread at:
                      http://bbs.homeshopmachinist.net/showthread.php?t=27274
                      Hi Mike (panchula).

                      I have completed my task on screw-threadind on the lathe at:

                      http://bbs.homeshopmachinist.net/sho...9&postcount=14

                      Comment


                      • #12
                        Different texts and instructors assign various values for the compound setover. 29, 29-1/2 and 30 degrees are all presented as proper. With the crude graduations on most compounds, setting to 1/2 degree is only an approximation.

                        29-1/2 degrees can only be described as more than 29 degrees and less than 30 degrees, and keeps you somewhere in the middle of the range, thus it is somewhat "safer", but there is little reason to go to extremes to achieve the setting. A spring pass or two at the final compound setting is appropriate and will clean up most threads.

                        I have not seen the 0.75 method previously, and it is a handy tip. It will work well enough with either of the three setover values to get you close enough.

                        Thanks Mike, it is a keeper.
                        Jim H.

                        Comment


                        • #13
                          Originally posted by tattoomike68


                          The price is a bit spendy but they hold up for a long time. You need to go faster but the threads end up with a mirror finnish in 4140.

                          http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=36659257
                          Whats the finish like on softer materials say 1010-1045 cold rolled?
                          I've been using TNMC inserts for years with excellent results and I will always set the compound at 29.5 and use it.

                          Comment


                          • #14
                            Most of my threading is done with inserts out of Coventry die heads.
                            You only need one insert to do any threads of that pitch.

                            The holder is on the left.




                            The lathe I do most of my threading on has no top slide fitted so I can't feed in at an angle. It does have a top slide but it's in the lathe cupboard and has been replaced by a large block of steel machined to hold the toolpost and miss the tailstock when close.

                            The idea of this is you need rigidity 100% of the time and a top slide 10% of the time.

                            Given that a Coventry die head can't feed in at 29 degrees but still works I just plunge in and cut as if I was using a normal single point tool and it works for me with no problems.

                            The only time I do set over at an angle is on large pitch Acme thread when I have to rely on a single point tool with large cutting areas.
                            .

                            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                            Comment


                            • #15
                              All that I know is that it has been this way for longer than all of us have been doing this,This is how I was taught and this is what I teach to My students or anyone who will listen.

                              I also use Mikes and Sir Johns methods, They to are good , But I still set the Compound slide to 29.5*,Just Habit I guess.

                              As a side note, on some lathes the compass is 90* off so you must set up accordingly.

                              Comment

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