Thread cutting, making your own sizes?

  1. Hood

    Hood If it walks like a duck....

    Messages:
    12,563
    Location:
    Carnoustie, Scotland
    My first lathe was a clapped out Drummond M type badged as a Myford. Dials were non existent, backlash and wear every place but the things I did on that poor wee thing make me feel sorry for it even yet :D
     
  2. graffian

    graffian Seer unto the end of his beard

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    Location:
    gatwick
    I very rarely used to power feed on my Cincinatti as it was noisy as hell. I cut a lot of threads but if I didn't have to have the gear train spinning I didn't.
    Back gear was even worse, the large gears at both ends had a few teeth missing[not next to each other] it still spun OK but sounded terrible, it made the ground rumble.

    I used to cut non standard threads fairly often, I had a thread chart[no fancy book] but often I wanted threads with not to much depth
    and just made up my own threads. I couldn't see it was an issue, if anyone was to make another they could see it wasn't standard and have to
    work it out. Learn a little trig and remember the male and female need a little space.

    Ones that spring to mind were my home made aeroquip fittings, I went to Brabhams in Ewell and bought aeroquip hose for my chop, this was the
    70's, it was as much as I could afford to buy the hose, let alone fittings so i made them. Most of the threads were fine pitch thinking 30tpi to 36 tpi on
    a 3/8" or bigger bit of fitting.
     
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  3. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    784
    Location:
    Gloucestershire, UK
    I've just added a new section to my website with some generally useful (to me at least) metalworking-related data. As part of this, I included a table of distances to feed a tool in when cutting threads on the lathe. I have a print-out of this permanently next to the lathe as I do quite a lot of thread cutting.

    Since it seemed relatively topical, I thought others on this thread might be interested in the in-feed distance data.

    I hope it's useful to others. Comments/corrections/abuse on a postcard to the usual address...

    https://www.cgtk.co.uk/metalwork/data/threadinfeed
     
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  4. eSCHEn

    eSCHEn Bit Wrangler Staff Member

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    Oooo look at you Dr 58K on Stack, well done! :thumbup:
     
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  5. earthman Member

    Messages:
    1,559
    Looks great, but I have a question,...... what's the difference between a full thread form tool and a sharp tipped tool? And which one have I been using??

    Sorry but sometimes more information poses even more questions especially for us novices.:)
     
  6. Hood

    Hood If it walks like a duck....

    Messages:
    12,563
    Location:
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    You have not really been using either although probably closer to sharp tipped.

    Sharp tipped I will assume refers to the likes of a ground piece of HSS. they can be used for different pitches but will not properly form the root or the crest.

    Full profile refers to a carbide insert (although could be fully ground HSS) which has the full thread profile and will form the root and crest profiles correctly, they are limited to a single pitch.

    The ones you have are partial profile, they will cut any pitch within the range, say 0.5mm to 3mm , they will cut the correct root profile only on the minimum pitch they are designed for and will not cut the correct crest on any.
     
  7. Pete.

    Pete. Member

    Messages:
    9,808
    Location:
    Kent, UK
    Sharp tipped is poor practice. You end up with a weak tool and a weaker thread. Try threading stainless with a sharp tip and keep the swear pot handy :D
     
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  8. earthman Member

    Messages:
    1,559
    Oh no,.....so you telling me that there's a third option now too.:laughing:
     
  9. Pete.

    Pete. Member

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    9,808
    Location:
    Kent, UK
    Nope, there's more than three :D
     
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  10. Hood

    Hood If it walks like a duck....

    Messages:
    12,563
    Location:
    Carnoustie, Scotland
    From that Sanvik PDF I linked to earlier.

    Full Profile

    ScreenHunter_3420 Dec. 16 20.37.jpg


    Partial Profile.

    ScreenHunter_3421 Dec. 16 20.38.jpg
     
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  11. earthman Member

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    1,559
  12. Hood

    Hood If it walks like a duck....

    Messages:
    12,563
    Location:
    Carnoustie, Scotland
    earthman likes this.
  13. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    784
    Location:
    Gloucestershire, UK
    As others have said, you're probably working somewhere between the two. Full profile tools give exactly the right radius at the root (and the crest, but that's irrelevant for the table on my website) of the thread. Sharp tipped tools are really only for very fine pitch thread: for example I've never had confidence in grinding the right radius on a tool for cutting 0.4 mm pitch threads, so I just use a sharp tip there.

    If you're using a partial profile insert tool or a home-ground tool with some arbitrary radius, then the in-feed distance will depend on that radius. Having said that, it'll be somewhere between the two values (full profile and sharp tip) shown in the tables on my website.

    I've added an explanatory note on the page to help future visitors.
     
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  14. R-D-R Forum Supporter

    Messages:
    1,167
    Location:
    Derbyshire - England

    That’s weird my m250 works the other way turning towards the chuck then pulling the knob to switch to facing doesnt require a direction change it travels from outer diameter inwards.
     
  15. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    784
    Location:
    Gloucestershire, UK
    Ditto mine (although it's also an M250, so that's not surprising). I guess it's another one of those things that vary from lathe-to-lathe. I must say I can see the advantage of the way @Bill Edwards' lathe works (although I think I would find the need for a direction change frustrating overall). I have on a couple of occasions set up for a turning cut but not realised that the knob was set for a facing cut. With my lathe, the tool plunges into the work-piece; with Bill's it moves safely away.

    Probably a sign I need to be more careful...
     
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  16. Bill Edwards Member

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    4,954
    Location:
    Scarborough, North Yorkshire
    Mine is an L5 so a good few years older than your M250's! Obviously at some point they changed things.

    There certainly are times when it's a good thing to have it as my lathe is, but more often than not I'd rather it was the same setting for turning to the chuck as well as facing.
     
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  17. Hood

    Hood If it walks like a duck....

    Messages:
    12,563
    Location:
    Carnoustie, Scotland
    The Colchester Triumph 2000 I have has two push/pull knobs on the saddle, one for reversing direction, whether that be feeding or surfacing, and the other for changing between feeding and surfacing. If you just change from feed to surface then it will move out the way so you have to pull one and push the other to change from feed to surfacing in the way.
     
  18. Bill Edwards Member

    Messages:
    4,954
    Location:
    Scarborough, North Yorkshire
    That sounds quite reasonable. To change direction I have to stop the lathe from spinning then turn the knob to change the direction of rotation, much less easy!
     
  19. Pete.

    Pete. Member

    Messages:
    9,808
    Location:
    Kent, UK
    My Monarch also has a push-pull knob on the saddle for changing direction, with a centre position that is the half-nut interlock so yiu can engage the leadscrew and feed together.
     
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  20. Hood

    Hood If it walks like a duck....

    Messages:
    12,563
    Location:
    Carnoustie, Scotland
    Is that meant to be can't rather than can?

    The Triumph won't let you engage the feed if the leadscrew is engaged, not sure about the other way.
     
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