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First try at thread cutting

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  • First try at thread cutting

    I mostly use my 9" south bend lathe for simple motorcycle parts- spacers, footpeg, etc. Recently though, I've watched a few videos about threading, so I figured I'd give it a go.

    I don't have change gears which I knew I'd need for cutting different pitches, but I thought I'd get some sort of thread with what was already on the machine.

    I engaged the dial and the back gears, waited for an even number to come around and engaged the feed. All I got was a very slow cut of around 10 thou. Did I do something wrong or am I totally unable to cut threads without more gears?

  • #2
    if the carriage moved you did get some kind thread.....one with a very small pitch. You have to put the right change gears on to get the pitch you want - ie how far the tool moves for each rotation of the work
    .

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    • #3
      Sounds like you engaged power feed and not a thread-cutting feed. Should be two different levers. Power feed is more like a very fine thread pitch.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        +1 for Darryl.
        It sounds like you engaged the carriage moving gears instead of the "half nuts". On my Clausing 100 MK3 threading is done using the "halfnuts" which depends on the gear arrangement in the quick change gear box. As you know the quick change gears replaces the gears that have to be put on the "banjo" between the spindle and the lead screw. If you haven't tried the halfnuts yet [B]give it a try without trying to make threads or even cutting anything. Be sure there is plenty of space on either side of the carriage when you do.
        Have a good day
        Ray
        Last edited by rock_breaker; 01-14-2016, 11:09 PM.

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        • #5
          This site has some helpful info on it: http://www.wewilliams.net/SBLibrary.htm Jim

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          • #6
            The 9" lathes come in several flavors.

            Some have a QC gearbox, and some have change gears. Some use a feed with a worm operated from the leadscrew keyway, and the simplest type do not have any feed other than the halfnuts. you didn't say what kind you have.

            The feed may be present without a QC box (my father in law has one like that). If your version is the simple type with just halfnuts, it could be that the previous owner just used it as a feed, and you only got the gears that he had on it for a feed, not for any specific thread.

            What did you do to get it to move the carriage?
            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              Okay, so I fooled around with this some more and I had forgotten that the existing gears could moved for different carriage rates. Unfortunately, I was only able to come up with 2 configurations and they were both too fine for threading. One moved the tool around 20thou per rotation, and the other was far less.

              Guess I'm shopping for some gears.

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              • #8
                Commander,
                If you can give us the model or even better a picture there are quite a few of us that have SB9 lathes here and we can help before you buy gears if you need them.
                Mine is a SB9 A with a quick change gear box and accessories including the milling attachment so, if you can keep asking the questions someone will help you.

                TX
                Mr fixit for the family
                Chris

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                • #9
                  I was avoiding a picture because my machine is filthy. I also couldn't figure out how to resize it on my phone. Here it is, though:

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                  • #10
                    OK Commander,
                    Now if you can take a pic of the front of the lathe and the carriage so we can point to the areas you talk about we can advise you as to what might be next.

                    TX
                    Mr Fixit for the family
                    Chris

                    Comment


                    • #11






                      Last edited by Commander_Chaos; 01-16-2016, 08:17 PM.

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                      • #12
                        So here's what I was doing:

                        I put the machine in back gears using the lever on the back and the button thing under the cover

                        I waited for a whole number to come around on the thread dial (took forever)

                        I engaged the carriage with the lead screw using the half-nut lever on the front of the apron

                        Last, I watched the tool pare off all the metal where I thought I would get threads.

                        The final pic is the stock with a relief cut into it, the tool square to the work, and the compound set to 29 degrees.

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                        • #13
                          That's the half-nut threading feed, so you got threads. The tool cut may have been coarser than the feed, so you didn't get good ones... You do not have a separate turning feed, so you have the version with half nut feed, and no QC box.

                          You have a setup that would appear to give pretty fine feed, so it's no surprise.

                          What I suggest is to have a good look at the threading chart that you should have on the gear cover. See what gears you have, and figure out what thread you can find that you can cut with the gears you have. Make it a s coarse as you can.

                          THEN do again what you did, first setting to just scratch the surface of the work. Show the result then, or just go ahead and cut the thread and show that.
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #14
                            I am not real familiar with the SB9 but from what I am seeing you will need different change gears to cut threads. It looks like the half nuts on the lead screw is the same for cutting threads and turning metal. Putting it in backgear doesn't do anything other than slow everything down, you still have the same feed per rev. until you change gears.

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                            • #15
                              Download this PDF, it should give you the info you need. If you study this it will help you get to know your lathe. The section on lathe tool grinding is a must read, it applies to small lathes in general not just to South Bend.

                              http://campkahler.com/files/How_to_R...he_SB_1of2.pdf
                              Jim

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