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  1. #16
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,436

    Default

    G Morning Bill,

    You are going to be disappointed now ! I set the gearbox for 48 threads and ran the lathe in reverse at 65 rpm. Yes these little carbide inserts are razor sharp. The only criticism of an insert on parts this small is that you cannot get right up to the top of the workpiece. There is just about 1.5 - 1.75 mm of shoulder on the insert.

    Just for the record ! This was done with a straight plunge in, no setting the compound at 29 degrees.
    Best Regards:
    Baron J.

  2. #17
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
    Posts
    733

    Default carbide thread cutting tips

    Thanks Baron, thats great, means I can probably use those bits on my lathe too, not dissapointing at all.

    Have just started learning about carbide toolbits following succesful use of cutters recommended by Anorak Bob in a recent thread.

    Maybe these really sharp carbide cutters can still cut well at lower than recommended speeds - seems to have worked well enough for you at 65rpm on a 4mm diameter ........... thats a surface speed of approx 3fpm as opposed to 200fpm which is what I previously believed was required to get good results with carbide bits. Seems like a massive difference have I made mifstake somewher

    Bill
    Last edited by steamingbill; 19th Sep 2018 at 10:40 PM. Reason: corrected fpm calculation

  3. #18
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,436

    Default

    Hi Bill,

    Sorry I had to run off a bit quick this morning. Hospital appointment.

    Anyway what I wanted to say was that thread was on a 2.85 mm diameter spigot. So 4 mm was being generous.

    Also the carbide insert was an inside cutting one. I prefer to cut away from the chuck, and despite nay sayers, I've never had my chuck unscrew when doing this. OK I agree it could happen, but so far, NO it hasn't.
    Best Regards:
    Baron J.

  4. #19
    Join Date
    Nov 2008
    Location
    Perth WA
    Age
    71
    Posts
    6,458

    Default

    Hello John,

    When I made my indicator holder I incorporated a step to facilitate alignment of the indicator and lathe spindle centrelines. If the sawcut in your holder is centred you could simply align the cut with your tailstock centre. Another way, and probably more accurate and easier, would be to make a vertical spacer that sits on the cross slide under the holder or the indicator's stem, and is of the correct height to ensure centreline alignment if that should be a requirement.

    033 (Large).jpg

    I like your threading from the rear.


    Bill,

    I have found that carbide threading inserts tend to tear, probably the result of a combination of low speed and material choice. If your workpiece could be held in spindle mounted collet or collect chuck, you could do as John has done and cut the thread from the rear and at high speed which may result in a finish better than you might achieve at 50 rpm.

    Bob.

  5. #20
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
    Posts
    733

    Default

    Thanks Bob, yes will keep that in mind. At the moment am simply interested in finding out what I can/cannot do. When I used the carbide bit you recommended previously to cut a 60 degree point I could clearly see the finish deteriorate towards the sharp tip of the point as the speed decreased. Will investigate further am keen to try a carbide thrad cutter.

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