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A Threading Adventure :)

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  • A Threading Adventure :)

    Hey guys! Thought Id share a moment...or so from the new shop Im (trying) to get going.
    My supposed partner needed a couple of long bolts.. 3/4 NC x8" for a none critical application.
    Hmmm...gee...once again...he has no money....
    Yep...I could go buy him a couple...but Im tired of that already...so...

    He has a very ancient Pratt and Whitney conehead lathe. It runs through a 3 spd car tranny and an old electric motor of some sort...
    He has a rack of salvaged farm machine parts....I find some 5' long spreader bolts from an old combine.
    Hmmm...but they are 7/8"NC....wont worky.

    Hack two pieces off...pop one in the lathe....grind up proper HSS tooling...turn them down to .750.
    Nice old lathe....once I get it all sorted out. The owner doesnt have a clue how to run it.
    Oh oh...now...threading...hmmm.....

    I look around the lathe...no info there but a small change gear plate.
    Tells me the spindle gear and screw gear I need....but nothing about the idler gear.
    I look thru the gears...hmm...here's a well used one...try that...
    Ooops...nope...50 or so tpi isnt good...
    Ok...need a bigger one....dont feel like doing all the math so I grab..this one...
    Bingo....10 tpi...lucked out

    Oh dear...now...the hodge podge bastardized tool holder...thats a big problem.
    Grind up a thread cutter....shim it all up on center...get the compound swivelled around..
    Ooops....no threading dial....
    Never cut threads without one before...but no biggie...Im well armed..
    My buddies from HSM told me...years ago...how to do this...
    I cut a shoulder where I want the threads to end...take the tool back...spin the tool in to make a light cut..
    And let her rip....hit the switch just before the tool gets to the shoulder....stop....a few times had to spin it by hand to finish the cut...put the ol tranny in reverse....back tool out...spin tool in a few thou...put tranny in forward....cut thread....repeat...repeat...bolts are made....it worked perfect!

    Now...the guy thinks I walk on water....lol.
    But I know...and you guys know...its just....HSM saved my ass again!
    Thanks Guys!
    Russ
    I have tools I don't even know I own...

  • #2
    No pictures?
    Andy

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    • #3
      No Andy...I have no computer anymore...just my smart phone.
      I have no idea how to post pics thru it (yet)
      Id love to show his early 1900's P&W lathe.
      I cant find any info on it anywhere. Tony's UK site has nothing.
      I have tools I don't even know I own...

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      • #4
        I assume the flat belt is gone since it is transmission driven now? Sounds like a very interesting lathe!
        Andy

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        • #5
          Andy...it is a VERY interesting lathe. I think...its 11" x 40 ish.
          It doesnt have the usual levers for feed engagement. It has knobs that you loosen/tighten to engage.
          It has power cross feed...and two different speeds for long feed.
          The feed knob on the tailstock side is rapid feed...its the one I needed to use for threading.
          It had a pretty wide bed...and fairly deep. It has nice cast iron legs.
          I showed the guy how the back gear works also.
          With the transmission drive...the low gearing on this is insane...lol
          I have tools I don't even know I own...

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          • #6
            Sounds like an interesting lathe and kudos to you for figuring it out...but...if, as it sounds like, you're trying to get a shop--as in business--up and running I think you need to toss that old piece of junk outside and use it as a planter or something. Find a real lathe that can actually make you some money...
            Keith
            __________________________
            Just one project too many--that's what finally got him...

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            • #7
              Lol...I know Keith...I ran a 18" Mazak for the last two years.
              Have owned a few myself.
              I know one thing...for now...this ol thing...is waaaay better than no lathe
              I have tools I don't even know I own...

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              • #8
                Originally posted by torker View Post
                ...I know one thing...for now...this ol thing...is waaaay better than no lathe
                True enough...point taken.
                Keith
                __________________________
                Just one project too many--that's what finally got him...

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                • #9
                  Russ, your PM inbox is full. Can you send pics via email ? If so I will post them for you,

                  jim216 at frontiernet.net

                  Jim

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                  • #10
                    fun story

                    The idler tooth count? It doesn't matter!
                    All the teeth of that one gear hits both change gears equally!

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                    • #11
                      Hey Russ. Haven't talked in a bit. Good to see you Mr JR
                      My old yahoo group. Bridgeport Mill Group

                      https://groups.yahoo.com/neo/groups/...port_mill/info

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                      • #12
                        Hi JR!!!! Yer alive
                        Cal...hmmm...how you figure that?
                        With my first setup...I had 1.18 final drive ratio....the second...gave me 1.46 final drive. Id say it matters...
                        Thanks Jim...ill get some pics of the ol girl.
                        Russ
                        I have tools I don't even know I own...

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                        • #13
                          Ok...here it is...
                          First try... 112/36/76
                          The one that worked...
                          112/86/76
                          The math says idler size matters...no?
                          I have tools I don't even know I own...

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                          • #14
                            Idler gear doesn't matter unless its a compound gear.
                            your maths must be wrong.
                            MBB

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                            • #15
                              Originally posted by torker View Post
                              Ok...here it is...
                              First try... 112/36/76
                              The one that worked...
                              112/86/76
                              The math says idler size matters...no?


                              In a 3 gear train, the idler makes no difference to the ratio, its only there to fill the gap between in the input and output gears. That's why the screwcutting chart on your lathe didn't specify the idler, built in the days when the machinist was supposed to have some common sense and work some things out for himself.
                              Now a compound train, with 2 gears on the idler pin, input meshing with one gear, output gear meshing with the other, that's different

                              112 input gear, 76 output gear gives 1.474 whatever the idler, in a 3 gear train.

                              Richard
                              'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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