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  1. #1
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    Default Facing 120mm round bar resulted in convex surface

    I have just taken delivery of a AL320G Hafco lathe. So I am not sure that it is set up properly yet. I have though used the dial indicator to check the cross slide movement relative to the face of the 3 jaw chuck. The travel seems square to the chuck. I am facing the round bar and the result is a convex surface with probably 0.5mm higher at the centre. Do I need to lock up the x axis for facing to increase the rigidity. Even I did that the result is still not good enough.

    Another problem is the horizontal movement is very rough and hard to move smoothly. I have loosen up all the bolt and gib screws but it is still not travelling smoothly. What is the suggestion to fix this problem. Do I have to disassemble and front apron and see if it needs cleaning up.

    xsx

  2. #2
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    Default

    Quote Originally Posted by davekwok View Post
    I am facing the round bar and the result is a convex surface with probably 0.5mm higher at the centre.
    That’s not good. It should be very slightly concave.
    Chris

  3. #3
    Join Date
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    Default

    What tool were you using, what material and at what speed?

    Incorrect tool geometry, or speed for the type of material being cut can result in poor finish or even the tool not actually cutting but just rubbing. Or a combination of cutting and rubbing. This could result in a poor finish and a convex cut.

    Simon

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  4. #4
    Join Date
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    Default

    When facing, it's suggested always to lock the carriage, that is the X movement.
    Is the headstock position adjustable or fixed?
    If adjustable, maybe it needs that.
    Place a bar in the 3 jaw chuck, say 120mm sticking out, and leaving about 10mm on the right end and 15mm near the chuck end, roughly reduce the middle section diameter about 2mm.
    Then turn both the end sections that were untouched, any diameter but at the same setting on the cross slide, locked. Get a nice smooth finish.
    Compare the diameters of those areas with a micrometer, which will tell you which way to adjust the headstock, if needed.
    Normally lathes are made so there's a slight concavity when facing, not convex. It's to ensure the face will not rock when placed on a flat surface. I think that is done by not having the cross slide at quite 90 degrees to the bed ways.
    It's not inconceivable that a machine could be made with the cross slide biased in the wrong direction.
    Half a millimeter over 60mm is hugely wrong.

  5. #5
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    Revesby - Sydney Australia
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    Default

    I'm with Simon; suspect that the speed or tool geometry was OK near the outside, but wrong in the middle; thus it was rubbing instead of cutting cleanly. (and maybe pushing the carriage away from the work)


    A simple test would be to use your dial indicator to check the cross slide relative to the cut you have just made.

    a) If your carriage or slide were somehow loose or twisted, the dial indicator would follow the twisted path and be roughly zero from outside to middle.

    b) If it is a problem with the actual cut, dial indicator should show nearly +500 microns extra near the centre

  6. #6
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    Default

    What speed and tool type (carbide/ HSS) were you using?

    Michael

  7. #7
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    Default

    I am using a LH tools with TCMT110204 insert. I set the compound at a 10 degree so that only the tip is doing the facing. The speed is 300 rpm. The point of rubbing may be valid. I have to check that.

  8. #8
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    Also,

    Check that your lathe is level, ie bed not twisted.

    Adjusting the headstock is a last resort.

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  9. #9
    Join Date
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    Default

    Address the elephant in the room first.

    If by horizontal axis you mean cross slide travel is tight, you need to deal with that first. No amount of tool geometry or messing about with feed and speed rates will fix a bent screw or poorly made nut or mis cast compound body.

  10. #10
    Join Date
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    Do you know what the material was?

    Did you retract the tool without winding it clear of the job ?

    If you did was the spindle turning or stopped?

    If turning did it cut on the way out?

    If it wasn't turning was there clearance between the tool tip and the outer edge of the material?

    Your left hand tool should of been able to be used without having to offset your compound.

    Were you power feeding or hand feeding?

    Did you try feeding out as well as in?

  11. #11
    Join Date
    May 2020
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    Default

    I am actually more cutting from inside out. It is mild steel. I am just cranking the cross slide manually and not have much confidence to use the autofeed yet. What should I do to address the tight horizontal movement? Do I need to disassemble the front apron in order to check out the gear mechanism for horizontal movement.

  12. #12
    BobL is offline Member: Blue and white apron brigade
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    Default

    Photo of the workpiece and tool being used mid cut (stop lathe) would be useful.
    Photo of swarf might also be instructive..

  13. #13
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    One thing to get your head around if possible is your terminology of things.

    All operations on a conventional lathe are horizontal, so it makes it a little confusing to know what you are referring to.

    If you can call cutting across the front of a workpiece facing or surfacing and cutting along a workpiece turning or sliding it will make it easier to understand what you are referring to.

    Is the lathe new, reasonably new, used or well used.

    Do you have a basic knowledge of how a lathe works and what everything does or are you starting with a blank slate?

  14. #14
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    Default

    Quote Originally Posted by pipeclay View Post
    One thing to get your head around if possible is your terminology of things.

    All operations on a conventional lathe are horizontal, so it makes it a little confusing to know what you are referring to.

    If you can call cutting across the front of a workpiece facing or surfacing and cutting along a workpiece turning or sliding it will make it easier to understand what you are referring to.

    Is the lathe new, reasonably new, used or well used.

    Do you have a basic knowledge of how a lathe works and what everything does or are you starting with a blank slate?

    It is a new lathe bought from hare and Forbes I have 1 year experience on milling but only now get onto lathe.

    Ok. sorry about the terminology. So I have a problem on cutting across the workpiece to do facing. It turns out to be convex and not flat. I also have problem when travelling along the leadscrew. It is too tight although I have loosen all the gibs and stops. I suspect that it may be the track and gear being too tight in the front apron.

  15. #15
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    Default

    Has the carriage always been tight to wind back and forth.

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