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Need a Leadscrew, But from which Lathe?

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  • #31
    Originally posted by Peter. View Post
    If you change the leadscrew from 16tpi to 8tpi you'll double the load on the screwcutting gear train. 8TPI is already quite coarse for a 9x20 lathe without stressing the gear train more.
    Peter, it is so appropriate that you make this observation and post this comment.
    Mostly because I see your avitar is a picture of an HLV-H.

    Hardinge knew this in regard to their lathe design. For those that don't know,
    the HLV-H Norton box only goes down to 11 TPI. For lower pitches, you have
    to build the ratio with change gears. And these change gears will NOT compound
    through the QC box. Reason being, the gears in the box are not strong enough
    to support overdrive gear ratios to spin the leadscrew that fast. An engineering
    work around really, to protect from OD ratios. But it screws you if trying to build
    an in-between ratio like 27 TPI or whatever, because as I said, the change gears
    will not compound through the QC box.

    -Doozer
    DZER

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    • #32
      There's a out east of me called Ron Grob Precision Machine, 8466 U. S. 34, Johnstown, Co 80534, 970-667-5320 that manufacturers precision acme threaded stock. You might give them a call.

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      • #33
        The Smart& Brown model A is only a 9 x 20, but has a 1" X 6 ACME leadscrew. It runs to 8tpi as standard, with a safety link in shear, a 1/8" steel bar wasted down to 1/16" in the centre. If I want a coarser thread, I double the gear ratio, but fearing that the link will spontaneously fracture, I replace it temporarily with a plain 1/8" one. Last Thursday, I produced a twin start 10 tpi Acme by setting 10 tpi with the double speed. I hope the OP realises that unless he halves the leadscrew speed, the entire selection of threads available will be doubled in pitch.

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        • #34
          Originally posted by wierdscience View Post

          You've got plenty of time, I'll buy the parts, you build them
          If you lived nearby, I would!

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          • #35
            Originally posted by old mart View Post
            I hope the OP realises that unless he halves the leadscrew speed, the entire selection of threads available will be doubled in pitch.
            That is actually why I want to change it, the lathe as built has far too many extra fine pitches availible.

            I just need one more tool,just one!

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            • #36
              Okay does either the Atlas or SB leadscrews have the full length keyway?
              I just need one more tool,just one!

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              • #37
                Originally posted by wierdscience View Post
                Okay does either the Atlas or SB leadscrews have the full length keyway?
                The SB model A and B both have full length. Depending on the specific model, screw length will be anything from 3 feet to 4 feet.

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                • #38
                  The Atlas 12 x 24 will have a longer leadscrew than you need, so if the slot is not running right to the left hand end, it should still work for you. I will checkout and measure the leadscrew tomorrow.

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                  • #39
                    One more option, which is probably unappealing, but which I'll mention for the sake of completeness. Princess auto and no doubt other places, sell plain shafting with a keyway already cut the full length. If you're concerned about milling the keyway, but comfortable with cutting acme threads, get a length of that stuff and go to it. Much cheaper too.
                    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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                    • #40
                      X2 for that matter, Surplus Center sells Acme shafting with the keyway already in it for less than $20 IIRC but no guarantees for accuracy because it's meant for Ag applications.

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                      • #41
                        I have had a look at the Atlas 12 X 24 leadscrew. This lathe has the qc gearbox.

                        Starting at the tailstock end:
                        2 3/4" plain and threaded for nuts (probably 1/2" UNF)
                        28" of ACME thread, with slot.
                        Overall length 38" + a little out of sight.

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                        • #42
                          Originally posted by mickeyf View Post
                          One more option, which is probably unappealing, but which I'll mention for the sake of completeness. Princess auto and no doubt other places, sell plain shafting with a keyway already cut the full length. If you're concerned about milling the keyway, but comfortable with cutting acme threads, get a length of that stuff and go to it. Much cheaper too.
                          Accurate threading when there is a keyway, really sucks to do. The keyway changes the loading as it passes the cutter, and the whole setup wants to jump a bit, so the accurate lead is a bit variable, depending on the size and weight of the lathe.
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • #43
                            Originally posted by wierdscience View Post

                            Correct on all counts, more a statement about them being "precision". I wonder what the difference in precision is between the general purpose rod and the "precision"? Does the up charge hold weight?
                            "Precision" acme is rolled then finish ground, the grinding is more costly then the material and the rolling combined, it can be very accurate however.

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