Thread cutting, making your own sizes?

  1. earthman Member

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    1,097
    Why would you not use the thread dial for metric threads then.:dontknow:
     
  2. Hood

    Hood Forum Supporter

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    9,666
    Location:
    Carnoustie, Scotland
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  3. Hood

    Hood Forum Supporter

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    9,666
    Location:
    Carnoustie, Scotland
    You can't if the leadscrew is imperial and you are cutting a metric thread. Well not 100% true as on some lathes you can but I think they have a different dial for that. I am not 100% certain as I have never had a lathe with an imperial leadscrew, but I think the iopposite applies if you have a metric screw and are doing imperial threads.
     
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  4. earthman Member

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    1,097
    Any idea how you can tell the difference in the leadscrews just by looking at them? My lathe has the cogs for metric threads but the markings on the slide hand wheels are imperial funny enough. They are useless to me to be honest, I'd like to fit DRO's at some point.
     
  5. Hood

    Hood Forum Supporter

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    9,666
    Location:
    Carnoustie, Scotland
    Easiest way would be to measure over 10 pitches and see what it comes out to you will then know if it is metric or imperial.
    For example say it was 5TPI then it would be 2" over 10 pitches, if it was 5mm pitch then it would be 50mm, so a difference of 0.8mm over the ten pitches.
     
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  6. Hood

    Hood Forum Supporter

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    9,666
    Location:
    Carnoustie, Scotland
    Oh and metric or imperial dials tell you nothing. All of the lathes I have had had metric dials but all imperial screws.
     
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  7. Pete.

    Pete. Member

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    If you are new to threading and want to choose a random thread to practice here's a great tip:

    Choose a thread that is a multiple of the leadscrew's TPI, then you can literally engage the half-nuts anywhere without having to worry about the dial or getting it wrong. So, if you have a 8tpi screw, choose 8, 16 or 32 tpi thread. Impossible to mess up.

    For metric threads choose the pitch, half-pitch or quarter pitch. So if you have a 3mm screw choose 3mm, 1.5mm or 0.75mm. Again, it's impossible to get wrong you can close the half-nuts anywhere anytime.
     
  8. eLuSiVeMiTe

    eLuSiVeMiTe Forum Supporter

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    Il remember that.
    Haven't cut a thread yet. Missing most of my changewheels.
    Next year's project is gutting this and making a case to fit it on my lathe.
    189307-453381e74602480e8e018fc509ebbbb2.jpg 189308-b5778bc2ef56e66b4da2b485f521d796.jpg
     
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  9. earthman Member

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    1,097
    I wish that my lathe had cogs like that, I have to unbolt/change mine over, looks like it's going to be a pain in the rear end.
     
  10. eLuSiVeMiTe

    eLuSiVeMiTe Forum Supporter

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    Precisely why I'm going to try and retrofit.
    Never had one from factory. Like you I'm stuck swapping out. As I'm missing wheels it's a good option
     
  11. Dr.Al

    Dr.Al Forum Supporter

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    209
    Location:
    Gloucestershire, UK
    What's your lathe? What does the change-wheel area look like?

    Sometimes some fairly simple modifications can make swapping gears a lot easier (see for example the one I made for my mini-lathe: https://www.cgtk.co.uk/metalwork/minilathe/threadingbanjo). It'll never be as nice as a gearbox of course.
     
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  12. earthman Member

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    1,097
    Interesting link, my lathe is an Amadeal one, very similar I guess.
     
  13. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    209
    Location:
    Gloucestershire, UK
    In that case, open up the change-wheel housing and take some photos and some measurements of the distances between the first change-gear shaft and the leadscrew shaft. If it looks like it's the same as my SC2, I'm happy to post you both of my home-made threading banjos (as shown in the pictures on the website). I've got the M250 with its gearbox now, so I can't imagine ever wanting to cut threads on the mini-lathe again.

    On a positive note, if your lathe is the same, it's got a flange-mount chuck. That means you can safely run it backwards with an upside-down tool and thread with the tool moving away from the headstock. That makes for a much more relaxing threading experience and is pretty much the only way I ever do it these days. No worrying about crashing the tool into the workpiece as it just runs off the end into free space.
     
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  14. earthman Member

    Messages:
    1,097
    That's very kind of you. I'll have a closer look at that area over the weekend, need to learn what I'm actually looking at first.:laughing:
     
  15. earthman Member

    Messages:
    1,097
    Spent a few hours today looking/learning a bit more about my machine, the leadscrew is certainly a metric one, a 1.5 pitch gauge fits perfectly.:)

    First time that I've actually had a go at swapping out cogs etc, these ones came already fitted to it, rather large in diameter compared to the thread pitch options in the bag, are they that big for optimum power feed use then?
    20191214_122446.jpg

    Here's the cogs/setup for a 1.25 metric pitch, notice the 'indicator table chart' on the left hand side, under the 16T column, there are some blank spaces, would I be right in saying that you can engage the lever on any number then??
    20191214_172349.jpg

    I only tried cutting this delrin (I think), not perfect by any means but it fits/works OK, main thing is that I've learnt a lot/popped my cherry on thread cutting.:laughing:

    20191214_172635.jpg
     
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  16. Pete.

    Pete. Member

    Messages:
    8,593
    Location:
    Kent, UK
    Well done on cutting your first thread :thumbup::thumbup::thumbup:

    But if you keep calling those gears cogs I'll have to send someone round - and it won't be Santa, it'll be his evil twin Satan :D
     
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  17. earthman Member

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    1,097
    :laughing:
     
  18. 123hotchef Member

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    8,426
    Location:
    Kent
    I need to.try now
     
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  19. Hopefuldave Intergalactic pot-mender

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    1,035
    Location:
    The Shed of Danger, surrey, England
    The blanks in the indicator table are where it won't work...
    There had to be a mathematical relationship between leadscrew pitch, thread pitch and indicator gear (14 / 15 / 16 teeth) for the indicator to synchronise the leadscrew with the spindle and tell you to engage the halfnut in the right place.

    Dave H. (the other one)
     
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  20. earthman Member

    Messages:
    1,097
    You are just talking about engaging/disengaging the lever aspect? Like with the 1.25 pitch that I've just cut, I left that mechanism engaged and turned the motor on/off and went from forward to reverse from start to finish. In other words, there is still a way for me to cut all those listed thread pitch sizes on this machine?
     
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