Announcement

Collapse
No announcement yet.

screwcutting problem!

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • screwcutting problem!

    i set the harrison lathe up with the correct changewheels for a 5mm pitch cut (trapezoidal), set the top slide at 90 deg to the bed, the tdi states that if "odd threads" to engage at any "numbered" gradual, engaged at number 1 took the cut then set up for the next cut again hit number 1 again but the tool hit the right hand side of the thread wall each time, so i engaged at no 2 then three and so on and the cutting tool kept cutting the right hand side wall, i could understand this happening if i was feeding in from the top slide if set at 30 deg but i was feeding in from the cross slide at 90 deg, this led me to beleave that its something im probably doing wrong and not the machines fault, anyone give me a bit of guidance please.

    bill

  • #2
    Bill, you can't use the thread dial for a metric pitch when you have an imperial leadscrew.
    You will have to engage the 1/2 nuts and keep them in, reversing at the end of each cut, either by hand or under power.

    .
    .

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



    Comment


    • #3
      hi john, not even with the metric conversion 127 toothed gear wheel?

      Comment


      • #4
        Nope,
        It's a wind in, wind out situation.

        .
        .

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



        Comment


        • #5
          right i see, the 127 toothed wheel just gives a feed rate, ok, ill have another go tomorrow. thanks john, (see even the best of us can get it wrong!)

          thanks again

          bill

          Comment


          • #6
            Also you need to set the compound at 30deg and feed in with the compound to cut the thread. That way it will cut on the left side of the thread and chase the thread on the right side. You use the cross slide set to "0" and back it out at the end of a cut, reverse the motor to clear the thread area and reset to "0". Also, do not change speeds because on some lathes it will slip the lead screw out of sinc with the thread you just cut. If you feed straight in it will cut on both sides and not cut a clean thread.
            Last edited by Carld; 10-30-2006, 10:37 PM.
            It's only ink and paper

            Comment


            • #7
              I think if you could stand a thread dial with a multiple of 254 teeth on it, that you COULD use it for metric.....only

              But while you were waiting for your number to come around, you could have wound it back and cut another pass......

              Never mind having to lean over that big sucker.....
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                Carld, he's doing a trapezoidal (=Acme) thread. No 30 degrees there.

                Benta.

                Comment


                • #9
                  One note:

                  When cutting 'V' threads set your tool post to 29-1/2 degrees not 30. You'll get a better thread.

                  Comment


                  • #10
                    On the Harrisons I am familiar with the metric lead screw lathes also came equipped with a chasing dial that had multiple gears on the shaft. Depending on the pith you needed to use the right gear. This is a 12mm metric acme done on a Harrison with imperial leadscrew. Lots of fun NOT

                    Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

                    Comment


                    • #11
                      Spin,

                      Nice work. How long did it take you to make that piece?

                      Rob

                      Comment

                      Working...
                      X