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Trying to thread, what am I doing wrong?

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  • Trying to thread, what am I doing wrong?

    Im trying to thread for the first time on my Grizzly G0602 10x22 lathe. I set the compound rest to 59.5 degrees, set the tool post perpindicular to the bar, Im moving the compound with the cross slide handwheel until it just touches the bar, set it to 0. Back it up, move the carriage so the cutter is to the right of the bar, set the cross slide back to 0, move the compound rest in about .003", wait for the thread dial to come to a number (5) and engage the half nut, wait for the cutter to get to my thread relief, disengage the half nut, move the carriage so the cutter is to the right of the bar and wait for 5 to come around and start again (advancing the compound rest handwheel another .003"). The problem is that the cutter isn't cutting in the grooves made by the previous pass, so Im getting a series of peaks. Im probally forgetting something simple.

  • #2
    I don't know if you are doing this wrong or have just put it wrong in this post but you are suppose to put the top slide at 29 deg not 59.5 deg.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

    Southwestern Ontario. Canada

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    • #3
      If the threads are not coinciding it suggests that the gear train driving the lead screw is out. Even if you have a gearbox that you can select from there are sometimes gears that need to be shuffled, so I'd suggest checking your manual and making sure you have the right gears in place. Related to this is if you are cutting a metric thread with imperial gearing or the other way around.
      What size (diameter and tpi/ pitch) are you trying to cut?

      Michael

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      • #4
        The first thing I'd suggest is to check and make sure the threading dial gear is maintaining good, complete engagement with the leadscrew, i.e. that it's not skipping a tooth sometime in the process between starting the first cut and subsequent ones.
        That happened to me the first couple of threads I tried on my lathe. I didn't have the thread dial fully pivoted down against the leadscrew.

        You are starting with the cross slide set at 'zero', backing out the cross slide at the end of each cut, and then returning to zero for each subsequent cut, right?
        Lynn (Huntsville, AL)

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        • #5
          Originally posted by loose nut
          I don't know if you are doing this wrong or have just put it wrong in this post but you are suppose to put the top slide at 29 deg not 59.5 deg.
          Depends on how your compound is graduated, 59.5 degrees is 90 degrees minus 30.5. I think it should be set. in this case, to 60.5 degrees.


          But that is not the major issue here, as I see it.

          I think Michael is right and that this is a problem re-synchronising the feed screw to the spindle.

          S&S, for the thread indictor to work (that is the device on the carriage with the numbers on it) you need the feed screw pitch to have a relationship to the pitch you ar cutting and the thread indicator must have a pinion to suit. Apparently, with imperial threads on an imperial lathe this is not a problem but when cutting metric threads it is much more complicated and when cutting metric threads on an imperial lathe it is impossible. Common practice when cutting metric threads seems to be to stop the spindle and reverse the lathe between cuts leaving the half nuts engaged the whole time.

          John

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          • #6
            move the carriage so the cutter is to the right of the bar and wait for 5 to come around
            This might be a stupid question... but you are turning your lathe off after you disengage the half-nuts, right? If you are doing this with the machine running, I could see how you could get off. I'm always carefull about using the thread dial and make sure I take the slack out of the drive train when re-engaging the half-nuts.

            Tom
            Tom - Spotsylvania, VA

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            • #7
              I thought the 29 or 59 degree setting is based on how the manufacturor referances the angle. I was going off this video (same lathe) http://www.youtube.com/watch?v=Qmc4yRJEeAE

              Tring to cut 1/2" 20 tpi threads.

              The thread dial is making good contact, I've got my eye on it the whole time pretty much.

              Just saw the problem, a change gear wasn't in the right place, thanks for the help.

              Comment


              • #8
                Are you using the right number for the thread?

                ie odd, even, or fractional tpi

                Comment


                • #9
                  Threading dial

                  OK.

                  Here is the lathe in question:
                  http://www.grizzly.com/products/10-x...al-Lathe/G0602

                  I am going to presume that the lead-screw is 8tpi (lead = 1/8" = 0.125").

                  I am also presuming that your threading dial is marked off from 1, 2, 3 and 4 with a line between each number ie at the "half-points" and that the threading dial gear (that mashes with your lead-screw) has 32 teeth.

                  If all that is the case and as you are cutting a 1/2-20 tpi thread, you should be able to engage the half-nuts at any numbered or "half" mark on the threading dial.

                  You should engage the half-nuts and move the lathe say one turn (by hand) and check that the marks on the threading dial line up with the line on the threading dial body (ie casting).

                  The 30 or 60 degree off-set angle can be a bit confusing. Just set the top-slide to be parallel to the lathe bed and head-stock spindle axis (its normal or default position) and then swing the top/compound slide clock-wise 60 degrees. Your top slide will then be 30 degrees "right" of/from the cross-slide axis.

                  Comment


                  • #10
                    What TPI or Metric pitch are you cutting? I have had a similar issue when cutting 16 TPI but I think I had the B gear in the wrong spot so that I was not really cutting that exact TPI. The B gear has to be at the bottom and the spacer on the top when doing imperial which is the opposite of how it is setup for power feed.

                    There are some pitches that are easy, any even/odd number on the dial will do, but some have to be done on a specific number. And some I have not found a way to do anything but the same number each time.

                    I usually try a test bar first now and if I have ANY trouble with staying in sync I revert to leaving the half nut engaged and doing the fwd-stop-rev dance instead. Less to worry about.

                    I do think you want to go to 60.5* instead of 59.5* since you are measuring the angle from parallel with the Z axis instead of the X axis as most directions are geared for.
                    Last edited by photomankc; 12-13-2010, 04:13 PM.

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                    • #11
                      Originally posted by oldtiffie
                      OK.

                      Here is the lathe in question:
                      http://www.grizzly.com/products/10-x...al-Lathe/G0602

                      I am going to presume that the lead-screw is 8tpi (lead = 1/8" = 0.125").
                      Nope - It's 12 TPI

                      Comment


                      • #12
                        From what you described your setting the compound at the wrong angle. Put the compound at the same direction as the crossfeed is and that would be perpendicular to the shaft in the lathe. Now look at the marks on the compound mount to see what it shows. It should be exactly perpendicular to the work. What you want is to move the knob on the compound to the right 30 deg. from perpendicular.

                        Then you have to set the threading tool perpendicular and on the center line of the part your threading.

                        Now you have to check the quick change gear box to be sure you have the right settings for the thread your cutting. Then set the rpm to about 100 rpm.

                        I don't know where your getting the #5 at but I always use the #1 on the threading dial. Most threading dials are laid out with four numbers and maybe a few marks between them. Don't use the marks between them, just use the 1 thru 4 as the chart indicates according to the thread your cutting.
                        Last edited by Carld; 12-13-2010, 04:18 PM.
                        It's only ink and paper

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                        • #13
                          Originally posted by S&S_ShovelHead
                          I thought the 29 or 59 degree setting is based on how the manufacturor referances the angle. I was going off this video (same lathe) http://www.youtube.com/watch?v=Qmc4yRJEeAE

                          Tring to cut 1/2" 20 tpi threads.

                          The thread dial is making good contact, I've got my eye on it the whole time pretty much.

                          Just saw the problem, a change gear wasn't in the right place, thanks for the help.


                          On that Griz lathe you have the compound set right.. It actually should read 60.5.. 90-29.5..

                          Those pesky change gears...

                          Comment


                          • #14
                            Later

                            Originally Posted by oldtiffie
                            OK.

                            Here is the lathe in question:
                            http://www.grizzly.com/products/10-x...al-Lathe/G0602

                            I am going to presume that the lead-screw is 8tpi (lead = 1/8" = 0.125").
                            Originally posted by photomankc
                            Nope - It's 12 TPI
                            Thanks.

                            I will give you the new dial settings later in the day.

                            Comment


                            • #15
                              The thread dial for that model lathe doesn't work for every pitch - you need to check the manual to be sure your pitch is listed.

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