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  1. #1
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    Default metric thread cutting on old imperial (new visby) lathe??

    After obtaining a 127 tooth gear as a result of an earlier post on this forum I now seem to have come up with another problem.

    It would appear as if the thread chaser dial does not work for metric threads. Even when engaged at the same one mark each time, the tool path is misaligned. I am guessing that the way to do it is to reverse the motor and leave the drive train engaged all the time.
    Is this correct?
    It is a single phase motor so reversing is more of a task than a 3ph one.

    Has anyone else got one of these old "New Visby's? This is not a geared head model! My guess is about 1940's vintage. I ask because the metric thread cutting table attached to the lather appears to be wrong.

    Cheers.
    Bill W.

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    Default

    Hi Bill,

    In metric threading it is customary to leave the halfnuts closed.
    However there is a way around.
    In the book Texbook of turning by Hercus there is discribed the way to use a special dial that works for metric threads.

    Checking the table is quit simple.
    Providing the 127 gear is on the leadscrew: 25.4 divided by 127 divided by tpi of the leadscrew will give the movement in mm per tooth of the 127 gear.
    From there calculate the geartrain.

    cheers
    jan

  3. #3
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    Default VISBY

    Quote Originally Posted by gpigeon View Post
    After obtaining a 127 tooth gear as a result of an earlier post on this forum I now seem to have come up with another problem.

    It would appear as if the thread chaser dial does not work for metric threads. Even when engaged at the same one mark each time, the tool path is misaligned. I am guessing that the way to do it is to reverse the motor and leave the drive train engaged all the time.
    Is this correct?
    It is a single phase motor so reversing is more of a task than a 3ph one.

    Has anyone else got one of these old "New Visby's? This is not a geared head model! My guess is about 1940's vintage. I ask because the metric thread cutting table attached to the lather appears to be wrong.

    Cheers.
    Bill W.
    Hi Bill

    I have a New Visby........... well its not new but from the 40's . I will havea look at mine to see about the metric problem . Mike

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    You cannot use a standard thread dial when cutting metric threads with an imperial leadscrew, and vice versa...
    Gold, the colour of choice for the discerning person.

  5. #5
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    Quote Originally Posted by gpigeon View Post
    After obtaining a 127 tooth gear as a result of an earlier post on this forum I now seem to have come up with another problem.

    It would appear as if the thread chaser dial does not work for metric threads. Even when engaged at the same one mark each time, the tool path is misaligned. I am guessing that the way to do it is to reverse the motor and leave the drive train engaged all the time.
    Is this correct?
    It is a single phase motor so reversing is more of a task than a 3ph one.

    Has anyone else got one of these old "New Visby's? This is not a geared head model! My guess is about 1940's vintage. I ask because the metric thread cutting table attached to the lather appears to be wrong.

    Cheers.
    Bill W.
    A) If no metric thread dial is available:

    - If cutting metric threads on a lathe with metric leadscrew, you can open and close the halfnuts whenever you like, IF the pitch you are cutting is contained as a whole number in the leadscrew pitch. Otherwise you must leave the half nuts closed until finished.

    - If cutting metric threads on a lathe with imperial leadscrew, you must leave the half nuts closed until finished. No exceptions.


    B) If a metric thred dial is available:

    - If cutting metric threads on a lathe with metric leadscrew, you can open and close the halfnuts whenever you like, IF the pitch you are cutting is contained as a whole number in the leadscrew pitch. For all other pitches, you can either use the thread dial, or leave the half nuts closed until finished.

    - If cutting metric threads on a lathe with imperial leadscrew you can either use the thread dial, or leave the half nuts closed until finished.

    Note: a metric thread dial is not as easy to use as an imperial thread dial. A metric thread dial will have either changegears, or different gears on the shaft that can be selected to mesh with the leadscrew depending on pitch being cut. Not all lathe makers sell their lathe with a metric thread dial. Indeed, I believe for the majority of lathes metric thread dials are not even available as optional extra.


    As for the correct method of leaving the halfnuts closed until the thread is finished: yes, you slightly retract the cutting tool, and reverse the spindle rotation until back at the start of the thread. That is what most people do, as using a metric thread dial even if available is a bit of a time wasting PitA. There are also special "flip-up" toolholders and "quick retract" toolholders for this purpose, but I guess you would have to do quite a lot of threading to justify.

  6. #6
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    Default

    Another idea is the swing threading tool

    Swing threading tool
    Gold, the colour of choice for the discerning person.

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    Default art

    Quote Originally Posted by gpigeon View Post
    After obtaining a 127 tooth gear as a result of an earlier post on this forum I now seem to have come up with another problem.

    It would appear as if the thread chaser dial does not work for metric threads. Even when engaged at the same one mark each time, the tool path is misaligned. I am guessing that the way to do it is to reverse the motor and leave the drive train engaged all the time.
    Is this correct?
    It is a single phase motor so reversing is more of a task than a 3ph one.

    Has anyone else got one of these old "New Visby's? This is not a geared head model! My guess is about 1940's vintage. I ask because the metric thread cutting table attached to the lather appears to be wrong.

    Cheers.
    Bill W.
    I had a look, cannot find any charts relating to metric threads . The New Visby came in many different models , the factory seems to have changed the details around at any time.There doesn't appear to be any standard model , they just put the lathes together with what was on the shelf . Mike

  8. #8
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    Quote Originally Posted by cba_melbourne View Post
    - If cutting metric threads on a lathe with imperial leadscrew, you must leave the half nuts closed until finished. No exceptions.
    Come on Chris, you would have seen the testing Stuart and I did on this. You can indeed disengage the half nuts, you just need to be sure to move the saddle back an exact amount before engaging it again. Not really worth it unless you are threading a long part.

    I'll find if i can.

    Ew

    Here we go http://www.woodworkforums.com/178280...ngage+half+nut

    I see the same claim as above again several times, it just isn't true.
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

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    Quote Originally Posted by Ueee View Post
    Come on Chris, you would have seen the testing Stuart and I did on this. You can indeed disengage the half nuts, you just need to be sure to move the saddle back an exact amount before engaging it again. Not really worth it unless you are threading a long part.

    I'll find if i can.

    Ew
    Ew, that method is not practical in everyday use, that is why I never mention it.

    There is another method (or better trick) that I do personally use, but choose not to mention to the beginner. The rule for lathes with metric LS says that you can open the half-nuts whenever you like, if the thread being cut is contained as a whole number in the LS pitch. Else you must either leave the half-nuts closed, or use a thread dial. Now, with a little care you can also open the half nuts when cutting threads that are a multiple of the LS pitch, but you need be aware that you can only close the half nuts at alternating positions. Fortunately, distinguishing the correct from the wrong position is very obvious - there is never a doubt. A few examples:

    LS pitch is 1.5mm (like on my EMCO), thread being cut is 3mm. Obviously, the half nut can be closed at every revolution of the LS, but only every second revolution will be correct, every other will be completely off.
    LS pitch is 1mm (like on a Hobbymat), thread being cut is 2mm, again every second LS rotation will be the correct position to close the half-nuts
    LS pitch is 1mm, thread being cut is 1.5mm. That is a bit harder, now only every third LS revolution is a correct match to close the half-nuts. But it will be clear to the blind that the other two positions are completely off the pitch being cut.

    one can go further:
    LS pitch is 1mm, thread being cut is 1.25mm. It gets harderr, now only every 5th leadscrew revolution is a match. The correct position is not anymore obvious, one has to count the 5 revolutions to be sure. It still is feasible but maybe not all that practical anymore. I may rather leave the half-nuts closed, unless its a long thread.

    As you can see, cutting metric threads on a metric leadscrew lathe is not as bad as it may seem at first look. That is the reason many metric lathes have no thread dial indicator. I only rarely cut imperial threads, so I cannot contribute with tricks there.


    EDIT: I like to have a small handwheel at the right end of the leadscrew. Not only is it a must have for milling in the lathe. It is also very helpful to count revolutions when threading, and to advance or retard the LS by a revolution when searching the engaging point.

  10. #10
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    Thanks gents your replies. I see now that there was an earlier thread in 2013 by Vernon that fairly exhaustively (65 replies!!) covered this issue.

    I was trying to make a flywheel puller for a Stihl MS460 chain saw. I req'd. an M22 x 1.5 thread. Because I couldn't cut the thread myself, I finally got the Stihl agent to pull the flywheel off for me.

    I now see that there was in fact a simple method I could have used.....if I had made the blank a bit longer than necessary and used the first 10 or 15 mm to align the tool by using the compound slide with the motor stopped. Once aligned, start the motor again and move the tool into the new depth of cut. After the final cut, part/cut off the non required piece that was used for alignment. Should have worked ok?????

    I now just have to wait for another 10 yrs for another metric thread to cut!!!!!!!!

    Thanks again.
    Rgds.Bill.

  11. #11
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    Quote Originally Posted by gpigeon View Post

    I ask because the metric thread cutting table attached to the lather appears to be wrong.

    Cheers.
    Bill W.
    Ok I see what the problem was....me not opening my eyes!!!!

    The metric pitch ref late att to the lathe clearly states..."the sliding lever must always be in the extreme left position". See photo below.

    Did I do this ? No! As my wife always says...."my fault again"!
    Attached Images Attached Images

  12. #12
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    Default Metric screw cutting

    Hello
    you can cut it by leaving the lead screw engaged and selecting neutral on the spindle and then winding the chuck back by hand you are only looking at 10 to 15 turns Set depth of cut Engage spindle drive and do next cut
    You can also cut it by leaving the lead screw engage and retracting the compound slide a multiple of the pitch 10 mm thread length retract 15mm or 0.590 (0.059 per rev) The limit of cuts is the travel of the compound slide
    Peter

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    G'day Fellas,
    I know this might not be 100% applicable to the topic of this thread but with regards to disengaging the half nuts when turning metric threads on a lathe with an imperial lead screw, there is a technique demonstrated on youtube by oxtoolco which is handy when threading up to a shoulder.

    https://www.youtube.com/watch?v=HXt4TWa382Q

    I needed to do the opposite (cut an imperial thread to a shoulder with a metric lead screw) and as I don't have a quick flick back threading tool or any other fancy gizmos figured I would try this trick. I wasn't sure how it would go with the metric thread dial so I tried it on a test piece and it seemed to work like a charm.

    It's a bit of fiddling around to get the rhythm right but it made the job a lot less hairy and allowed me to get the thread right up to the shoulder.

    Apologies if this has already been mentioned in the thread referenced in an earlier post.

    Cheers,
    Greg.

  14. #14
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    There is a trick to make cutting to a shoulder nearly foolproof. You install the tool upside down, and run the lathe in reverse. Now the tool cuts from left to right, away from the shoulder and away from a possible collision.

    Most people at first think that this must create a left thread. This is not so. The end result is still a right hand thread.

    Caution: if the lathe is fitted with a threaded chuck (and without a locking collar) the chuck may come off unless the cutting forces are kept small.


    Edit: I even found a video to show this method in action, from a Mr Tubal Cain (no, not the Tubal Cain aka Tom Walshaw from the UK that did write for Model Engineer - this is a new and younger American Tubal Cain):

    https://www.youtube.com/watch?v=w2eWqeyO7-4

    (the demo starts at about 2:30 minutes into the video)

  15. #15
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    Quote Originally Posted by cba_melbourne View Post
    There is a trick to make cutting to a shoulder nearly foolproof. You install the tool upside down, and run the lathe in reverse. Now the tool cuts from left to right, away from the shoulder and away from a possible collision.
    It does not work so well when you need to thread a non native pitch, ie metric on an imp screw. You still need to position the start of the cut accurately, not easy whist running the lathe forwards. And you still need a run out groove to start in.

    Works a charm with a native pitch though....
    https://www.youtube.com/watch?v=rjl8...5p4rkKjPAwVO8Q

    Ew
    1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.

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