Threading

  1. Kram

    Kram Member

    Messages:
    1,781
    Location:
    Sussex
    My attempt at a M50 fine thread showed me I have a lot to learn. Please suggest anything useful!
    Im told that 0.866 is the magic number to divide thread depth by, to get the compound movement at 30 degrees.So m50x1.5 has 0.81mm depth = 0.935mm on compound. Good to know for a rough idea before measuring.

    Screw cutting/wires calculator - https://www.cgtk.co.uk/metalwork/calculators/screwmeasurement

    I tried to measure but there was no way I could hold wire in the right place, let alone get a micrometer to measure it. How do you do it? Ive got wire the correct size, 0.87mm.

    Thread dial. Ive got a 48 tooth gear and 12 lines. Does that mean there are engageable spaces between the lines that I need go avoid? Most lathes seem to have much less teeth on gear.
     
  2. Ali

    Ali Member

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    955
    Location:
    Cheshire
  3. Agroshield Member

    Messages:
    1,367
    You will need to give us the thread pitch of your leadscrew to help us answer.

    Blu-tak is good for thread wires, or a smear of grease.
     
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  4. Pete.

    Pete. Member

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    9,813
    Location:
    Kent, UK
    First question - what tool are you using to thread with? Touching-off and cutting to a known depth depends on the tool nose width/radius being correct. If you ground a tool to a sharp point you'll have to go deeper because you touched off too soon with the pointy end. If your nose radius was too wide you'll have to go shallower because you touched off too late. If your lathe is a bit light and you're getting tool deflection you'll have to allow for that with spring cuts as you approach depth.
     
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  5. addjunkie

    addjunkie Member

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    Northumberland. Reet oot in the sticks
    I find it far easier, not to use the threading dial, just engage the half nuts and revers the machine, so you remove on variable. And just use a thread gauge. Dont over think or complicate things.
     
  6. zx9

    zx9 Member

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    4,325
    Location:
    South East London
    This above and trial fits, @doubleboost has a video where he makes a dummy spindle nose prior to cutting a chuck back plate, again good practice threading the dummy which is tested on an other chuck or back plate.
     
  7. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    784
    Location:
    Gloucestershire, UK
    At the risk of echoing others, don't overthink it. I use thread measuring wires extremely rarely (partly because they're awkward little s*ds). If you do need to use them, a bit of grease will help hold them in place, or alternatively some elastic bands round the ends of the wires. They're useful if for some reason you're getting confused about what a particular thread actually is or if you're making a part that specifies a very specific thread tolerance class. This doesn't happen often.

    You can get an idea of an approximate in-feed distance by looking here: https://www.cgtk.co.uk/metalwork/data/threadinfeed - for M50×1.5 just use the numbers in the M10 row (as that's the same pitch). But don't get too hung up on it.

    Start with the OD slightly less than nominal (i.e. 49.9 mm rather than 50 mm) - that will make it much easier to get the fit right. Use a thread gauge (aka screw pitch gauge) to see when it looks right or just creep up on the right size, testing with the nut. When the nut goes on and feels like a comfortable fit, stop.

    Going back to what I said about the thread measurement wires not being necessary, have a look at the tap drill size calculator on my website. Slide the little slider up and down and you'll see that the tap drill size varies a lot. This is going to make a big difference to the form of the resulting tapped hole. Now consider this statement from the Machinery's Handbook:

    Tests have shown that any increase in the percentage of full thread over 60 per cent does not significantly increase the strength of the thread. Often, a 55 to 60 per cent thread is satisfactory, although 75 per cent threads are commonly used to provide an extra measure of safety. [snip]. In general, when the engagement length is more than one and one-half times the nominal diameter a 50 or 55 per cent thread is satisfactory.​

    The point I'm trying to make is that it really doesn't matter that much. If the nut fits (even if it's very loose), it'll probably provide way more holding power than you'll ever need. So:
    • Get the thread shape right (i.e. use an insert tool or grind your HSS properly). That ensures the threads are engaging across a decent proportion of the "triangle" rather than just touching at one point.
    • Get the pitch right (d'uh!).
    • Make sure you don't engage the half-nuts when the thread dial indicator is in the wrong place (it's easily done) or just leave them engaged throughout.
    • Start with the OD a little under nominal.
    • If possible, set the compound to 29.5° or thereabouts (it's not critical) and use that to feed the tool in. If you can't (or can't be bothered), don't worry, just take slightly lighter cuts.
    • Gradually reduce the amount of in-feed per pass as you get deeper and do spring passes every now and then.
    • Test with the nut when it looks like you're getting close. If you don't have a nut (usually because you're going to make that next), test with a screw pitch gauge or a random bolt that happens to have the right pitch thread.
    One other thing worth mentioning is that I've found the insert threading tools work better when you work them relatively hard. If I'm threading with insert tooling I have the lathe going like the clappers (500 rpm usually) and don't take many cuts (i.e. relatively deep in feed per cut). If I'm threading towards the chuck I'll often go back to hand-ground HSS (made with a simple jig) as it produces a better finish when you take it slowly.

    All of the above (apart from the quotes from Machinery's Handbook) is just my opinion of course, so others might be able to provide better information!
     
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  8. Morrisman

    Morrisman Forum Supporter

    Messages:
    2,699
    Location:
    Staffordshire, England
    This is why I used to use old Coventry die box inserts brazed to a piece of square bar whenever I could.

    Can’t get much better thread form. :D
     
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  9. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    784
    Location:
    Gloucestershire, UK
    Oh, a couple more thoughts...
    1. If you think you've cut deep enough but the nut won't fit, try touching a file on the OD - you might have some burrs or you might have an OD that's a bit big.
    2. If you're going to be using insert tooling and there's a particular pitch you're going to cut a lot (I default to 1.5 mm pitch for most things if I have a free choice), then consider getting some full profile inserts. For example "16 ER ISO 1.5" (sometimes without all the spaces) is the code for a 16 mm external right-hand threading insert for 1.5 mm pitch, whereas "16 ER AG60" is the generic "partial profile" one that can be used on a number of different thread types. The full profile inserts have the advantage that they have the right radius on the tip and they also cut the outer profile of the thread. If you've made the OD too big for the nut to sit properly, you can just feed in a bit deeper and the insert will sort it out.
     
  10. Kram

    Kram Member

    Messages:
    1,781
    Location:
    Sussex
    Ok great, it is a lot simpler if I can use a rough infeed and test fitting the nut.

    I got a seller to do a mixed pack which is in the post.
    www.ebay.co.uk/itm/10pcs-16IR-1-0ISO-16IR-1-25ISO-16IR-1-5ISO-16IR-1-75ISO-16IR-2-0ISO/303516548099
    This arrived yesterday for next attempt
    www.ebay.co.uk/itm/16ER-1-5-ISO-KENNAMETAL-THREADING-SCREWCUT-INSERTS-LT-16ER1-5ISO-KC5010-P208/202873930414
    I was suprised the insert cut well at 350 rpm but needed more torque en19t is tough! So I will get the big pulleys fitted next.
     
  11. Agroshield Member

    Messages:
    1,367
    Are you aware that the first eBay listing you linked to is for INTERNAL inserts? And a 16-series internal insert has quite a large minimum bore size into which it will poke?

    Forgot to say that if it is an ER nut you are cutting the thread for, on the loose side is better as you want only the nut taper and the internal taper to influence the collet.
     
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  12. Kram

    Kram Member

    Messages:
    1,781
    Location:
    Sussex
    Ah ********! I was half asleep when I requested and ordered that, however if the thread form is roughly the same? It'd be ok to flip upside down and use as a 16EL -which are uncommon? - I have a 11IL tool for internal threading away from chuck, came with one AG60 insert, not found anywhere to buy more!
     
  13. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    784
    Location:
    Gloucestershire, UK
    They are a bit of a pain to get hold of, yes. Worth looking for 11NL as well as 11IL. I think (but I've struggled to find confirmation) that they are "neutral" as opposed to internal or external and are presumably angled on both edges which makes them more versatile. Using an internal left as an external right or vise versa won't give exactly the right thread form if using a full profile insert. It's probably close enough though...

    I think I bought some of my IL/NL/EL inserts on ebay and others on shop-apt.co.uk but I could be wrong - it was a while ago.
     
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  14. Kram

    Kram Member

    Messages:
    1,781
    Location:
    Sussex
    I have been meaning to rewatch this guys videos on threading. 5:50 - no reason to use 3 wires it can be done with one, subtract radius and double result. That makes it a lot easier.
     
  15. Kram

    Kram Member

    Messages:
    1,781
    Location:
    Sussex
    Just measured my er40 thread with a peice of 0.87mm wire I am suprised how close. 49.81 Od, 24.905mm to subtract. 50.115 over wire, 25.21 x2 = 50.42mm. should be 50.337, close enough!

    The 16IR inserts arrived. Compared to the 16ER 1.5mm kenametal, the point flat and therefore width is quite a bit thinner and pointier, even with the 2.0mm, so I will keep for internal and get another ER or EL set.
     
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  16. Kram

    Kram Member

    Messages:
    1,781
    Location:
    Sussex
    Im getting a bit lost with imperial threading, if anyone could check this for me?
    For 1/2" bsp male thread, Ive got the lathe set up for 14 tpi and OD just under 21mm. I only have metric inserts. BSW radius is 0.1373P so need 0.25mm nose radius, and 1.75ISO is close enough to that 0.23mm.
    Does this look about right?
    [​IMG]

    Thanks
     
  17. Dr.Al

    Dr.Al Forum Supporter

    Messages:
    784
    Location:
    Gloucestershire, UK
    Have you thought about just grinding a 55° tool out of HSS?
     
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  18. addjunkie

    addjunkie Member

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    6,469
    Location:
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    You need the 55 degree cutting tool either tip or as said grind one, or you thread will gaul up.
     
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  19. Kram

    Kram Member

    Messages:
    1,781
    Location:
    Sussex
    I am not good at freehand grinding, I could sharpen a 60 degree insert slightly but it might well end up 40 degrees.

    I think my numbers were correct above, found that a 1/8 bsp is 28tpi, double what I need, good enough to check pitch.

    [​IMG]
     
  20. addjunkie

    addjunkie Member

    Messages:
    6,469
    Location:
    Northumberland. Reet oot in the sticks
    A hand ground tool can be just a simple point of 55 degrees, measured using a simple gauge, to check.

    https://www.machine-dro.co.uk/moore...MI07f3u67w6AIVmKztCh2mNAPrEAQYCCABEgIq0PD_BwE

    You know the major diameter, the minor diameter, the thread angle just grind a tool up, and use the dials for the minor diameter allow for back lash obviously. As its a stadard you are cutting just have a pipe fitting to try it for size.

    Dont over think it.
     
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