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  1. #1
    Join Date
    Mar 2010
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    Brisbane
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    Default AL320G/L141 threading question

    Hi all,

    I'm new to this forum and also new to metal work. I recently purchased a Hafco AL320G and I'm slowly working out how to use it.

    Although I'm happy with the machine, I'm pretty disapointed with the instructions that come with it - especially from an operational perspective. I chose the 320G because I'd like to be able to cut metric threads. This machine is advertised as being capable of cutting metric and imperial threads this and has a thread chasing dial however the instruction manual really doesn't cover this functionality very well. In particular there is no details regarding the use of the thread chasing dial. I've read the Hercus Textbook of Turning and expected to find similar details for this machine

    Is there anyone on the forum that has this machine that can help get me started?

    Thanks in advance...

    Peter

  2. #2
    Dave J Guest

    Default

    Hi Peter and welcome,
    Here is a bit of info for you on screw cutting
    http://www.woodworkforums.com/f65/sc...ginners-86435/

    http://www.woodworkforums.com/f65/ha...hreads-101621/
    Dave

  3. #3
    Dave J Guest

  4. #4
    Join Date
    Mar 2010
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    Brisbane
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    Default

    Dave,

    Thanks for the response and the links. I've checked my lead screw and it advances 72 mm for one complete turn of the thread chasing dial. The dial has six positions marked 1 to 6. The specs for the lathe list the lead screw as metric however they don't specify the pitch - it looks like 3mm to me.

    It looks like the instructions in the linked thread suggest keeping the half nuts locked and stopping/reversing the machine as the best strategy. As this machine doesn't have a clutch or brake I was hoping for a solution where the half nuts could be disengaged at the end of the thread run.

    It will take a bit of time to digest all the information in the threads you have linked but any suggestions would be gratefully received.

    Peter

  5. #5
    Join Date
    Jun 2007
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    sydney ( st marys )
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    Default

    You best option would be to get the chasing dial and throw it to the s it house.

    If you havent machined before or dont have much experience the chasing dial will more than likely stuff you up.

    Unless you are going to be cutting multi start threads suit to the chasing dial you have you would be much better advised to just reverse the lathe rather than trying to drop in on the correct number or letter on your chasing dial.

    If you have an Imperial machine the chasing dial is no use to you if cutting metric threads,and if a metric machine no use for cutting imperial threads.

  6. #6
    Dave J Guest

    Default

    I am not sure, as all my lathes have been imperial, but from what I have read you get a few different thead dial gears for metric lead screws that need to be changed for cutting different metric threads.
    I know one fellow made his up so all the gears were a modified shaft and he moved it up or down to suit the threads he was cutting.
    Dave
    After a bit of looking I found it for you
    Screwcutting drop in dial

    Screwcutting drop in dial revisited

  7. #7
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    Default

    Quote Originally Posted by pipeclay View Post
    You best option would be to get the chasing dial and throw it to the s it house.

    If you havent machined before or dont have much experience the chasing dial will more than likely stuff you up.

    Unless you are going to be cutting multi start threads suit to the chasing dial you have you would be much better advised to just reverse the lathe rather than trying to drop in on the correct number or letter on your chasing dial.

    If you have an Imperial machine the chasing dial is no use to you if cutting metric threads,and if a metric machine no use for cutting imperial threads.
    It's supposed to be a metric (lead screw) machine and most of the threads I'm interested in are metric, however I'm sensing the thread chasing dial is more trouble than it is worth!

  8. #8
    Join Date
    Aug 2008
    Location
    near Rockhampton
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    6,216

    Default

    Quote Originally Posted by pipeclay View Post
    You best option would be to get the chasing dial and throw it to the s it house.
    I dunno, I always used them from the very start when I taught myself to thread on the lathe.. reversing the lathe is a real PITA to do...

  9. #9
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    Default

    Choice is yours seeing self taught,
    .
    Not sure what the hard part about either throwing a switch into reverse or lifting a lever is.
    But then again havent come across a CNC or NC or Peg Board that dosent do reverse.

  10. #10
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    Default

    Quote Originally Posted by .RC. View Post
    I dunno, I always used them from the very start when I taught myself to thread on the lathe.. reversing the lathe is a real PITA to do...
    The problem I've got is there is no instructions regarding the use of the thread chasing dial - I was expecting to find a description of the position to start on for different threads as per the Hercus Textbook of Turning. Is this something that is available for this lathe or can it be calculated some how?

  11. #11
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    Is there a plate giving you the Pitches that the Lathe will cut,if so on some lathes the Plate will also indicate the appropriate engaugement point on the Chasing Dial.

    If possable take a photo of the plate and put it up.

  12. #12
    Join Date
    Mar 2010
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    Brisbane
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    Default

    OK I've been taking some measurements:
    With the standard gear set installed (M=24, N=60, A=24, B=50, C=25, D=48) I should get a longitudinal feed rate of 0.1mm/rev according to the manual.
    One turn of the longitudinal feed wheel gives 26.5 mm of longitudinal travel.
    One complete rotation of the thread chasing dial is 72mm of longitudinal feed and the dial has six positions.
    The lead screw pitch is 3 mm metric.
    10 rotations of the spindle gives one rotation of the lead screw.
    40 rotations of the spindle gives one position change on the thread chasing dial.

    How can I use this to work out the starting positions for threading?

  13. #13
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    Default

    I have no idea on that machine at all and if you dont have a plate showing the change gear set up and position for engaugement just engauge at the same mark all the time.
    Simply put the markings on your dial allow you to engauge at different spots for different pitches ,or a numerous spots around the dial for the same pitch.
    Just engauge on one number or mark and re engauge at the same mark each time.
    Only problem you will have is if you dont engauge at the EXACT same mark each time,you will start to cut another lead on our thread.

  14. #14
    Join Date
    Dec 2005
    Location
    Aus
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    156

    Default

    Quote Originally Posted by pipeclay View Post
    You best option would be to get the chasing dial and throw it to the s it house.
    Either that or learn to count and remember simple things.

    Sure it can get confusing sometimes, but if you have that much trouble, just write on a piece of paper which numbers/marks you can engage on and sticky tape it to the dial for that job.

    Here's a scenario:
    • You're cutting a thread into a shoulder and you have put a 2mm runout groove.
    • You have put the thread chasing dial, as you suggest, into the bin.
    • Your lathe has no brake, no clutch.
    Do you attempt to time it, so that when you hit the stop button, the lathe will cut the last bit and coast to a stop before the threading tool plows into the shoulder and breaks? Or do you hit the stop button and attempt to brake the lathe by hand?

    Peter, providing your calculations are correct, and you are using a thread-chasing dial gear that divides by a whole amount with the leadscrew, you can choose any one mark on the dial and stick to it, and you can't go wrong. You can only fall into place where the teeth mesh, so if you start trying to close the half nut a couple of degrees before the dial lines up, you should land perfectly every time (unless you are a whole tooth too early).

    Some threads will allow you to engage anywhere, and some can be engaged every 1/4, 1/2 or full turn of the dial. I'd have to recheck on how to do the calculations before I could give an answer with confidence though.

  15. #15
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    Default

    The following I have typed from Martin Cleeve's Screwcutting in the Lathe, p81-82:
    INDICATOR FOR METRIC LEADSCREW
    An example of a metric leadscrew indicator is given in the diagram, Fig. 13 which shows the design fitted to a Harrison lathe with a metric leadscrew of 6.0mm pitch. One revolution of the indicator dial registers a carriage travel of 120 mm, or 20 leadscrew revolutions.
    The four numbered graduations indicate actual travel in millimetres, and each of the 20 subdivisions one leadscrew thread, or 6.0 mm of carriage travel.
    The Instruction Plate reads:
    A. 0.5, 0.75, 1.0, 1.5, 2, 3, 6 mm. pitch
    Any line on indicator.
    (ie. engage half-nuts at random on leadscrew)
    B. 1.25, 2.5, 5, 10 mm pitch
    Any numbered line.
    (ie. groups of 5 leadscrew threads)
    C. 4 mm pitch
    Lines 60 or 120
    (ie. any group of 10 leadscrew threads)

    The pitches in set A are all exact sub-multiples of the leadscrew pitch, for which the half-nuts can be engaged at any convenient moment. The 6.0 mm leadscrew pitch holds exactly 12 0.5 mm threads, 8 0.75 mm threads, 6 1.0 mm threads and so on.
    Of set B, each pitch to be cut contains a whole number of threads in five lead-screw threads, one quarter turn of the indicator dial, 5 LST = 30 mm, holding 24 1.25 mm pitches, 12 2.5 mm pitches, 6 5.0 mm and 3 10.0 mm pitches
    Lastly, set C, the 4.0 mm pitch, shows 15 whole threads in 10 leadscrew threads. Note: although minimum pick-up of a pitch of 4.0 mm with a 6.0 mm pitch leadscrew is 2 LST to 3 component thread turns, it would be impracticable to read the unnumbered basic indicator graduations in pairs.
    We may also note that 0.4 mm and 0.6 mm pitches will pick-up at any line on the indicator because 6.0 mm holds 15 whole 0.4 mm pitches and 10 whole 0.6 mm pitches. For thread pitches showing a whole number of thread turns only in groups of 3 or 7 leadscrew threads such as 0.45 mm pitch, holding 40 whole turns in 3 leadscrew threads, 1.75 mm pitch, holding 24 whole turns in 7 leadscrew threads, or 3.5 mm pitch, holding 12 whole turns in 7 leadscrew threads, the lathe must be reversed with the half-nuts remaining in engagement with the leadscrew until completion of the thread, or any of the other means previously outlined may be adopted to hold pick-up. This applies also to the cutting of threads/inch, DP or module worms and other pitches outside the scope of the leadscrew indicator.
    It seems therefore that while an English leadscrew indicator will cover all ordinary English pitches in common use, similar facilities cannot be offered by a single indicator and a metric leadscrew for all common metric threads.
    Note that the thread chasing dial that he mentions is pictured in the book with 30, 60, 90 & 120 marked 90 degrees apart on the dial, and 4 lines in between each numbered line.

    Hopefully that will help you understand how you can work out how to use the thread chasing dial - shame on HAFCO for not including a table.

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