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Thread: Centering aid for polygonal stock

  1. #1
    mklotz mklotz's Avatar
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    Centering aid for polygonal stock

    Centering polygonal stock in the 4jaw can be a trial. The centering should be done on the flat sides of the stock and not the corners. However, with the DI point bearing on the sides, one must be very careful to withdraw the DI plunger as the stock is rotated from side to side lest the plunger be 'caught' by a corner of the stock and bent, damaging the DI.

    I use a dedicated DI mounted on a QCTP for aligning in the 4jaw. I simply slap it into position on the compound and the DI is automatically at center height.

    To deal with the polygonal stock problem, I made a simple gizmo.


    An aluminum rod clamps to the DI housing with a single setscrew. Attached to the bottom of this rod is an L-shaped piece of thin sheet steel that projects up in front of the DI plunger.

    Now, as the polygonal stock is rotated, the stock corner contacts the sheet metal first and depresses the plunger as it passes, thus avoiding damage to the DI. A further advantage is that the motion of the sheet metal makes it obvious when the DI is perpendicular to the side of the stock - the position at which one wants to make the centering indication.
    Last edited by mklotz; 07-11-2017 at 04:14 PM.
    ---
    Regards, Marv


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    Thanks Marv! I've added your Centering Aid to our Measuring and Marking and Lathe Accessories categories, as well as to your builder page: mklotz's Homemade Tools. Your receipt:


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    abbreviated;
    Quote Originally Posted by mklotz View Post
    Centering square stock in the 4jaw can be a trial...To deal with the square stock problem, I made a simple gizmo.
    When not physically at a machine, I typically invest time in study of what work is coming up. Surfing the vast HMT content is more than entertainment.
    Personally, tooling is a favored keystone to streamlining work. The 'cost' is high for the first article, diminishing with each produced. Upon re-use the cost is effectively zero.
    Once again, [with equal thanks to HMT & mklotz] I have a solution for a run of link pins. Naturally, stocks larger than square collets available...Up to now, a square split bushing + 3 jaw was the only reasonable solution, and limited to one size!
    Best part; they'll be concentric enough to drill for cotter pins clamped and located by the original material.
    So, this accounts perfectly in my recurring "...this is not just a hobby" admonishment.
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

  5. #4
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    Thanks Marv, just starting to use a four jaw chuck, I need things like this.

    Ralph

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    mklotz mklotz's Avatar
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    Quote Originally Posted by Ralphxyz View Post
    Thanks Marv, just starting to use a four jaw chuck, I need things like this.
    If you're new to the 4jaw, I strongly recommend you read my suggestions on centering...

    Centering work in the four jaw chuck

    and this additional tip...

    4jaw centering tip

    The 4jaw can be frustrating for newcomers to it but following those tips will ease the process considerably and make you as comfortable with it as you probably are already with the 3jaw.
    ---
    Regards, Marv


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    Thanks, Marv. I try to keep your tips handy.

    Ralph

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    Hi mklotz
    Please forgive me if I am missing something here, but why clock a piece of hexagon bar in a 4-jaw chuck? Normally hexagon is used for making nuts and bolts and alike, so why use a four jaw when a 3-jaw self-centring chuck will hold on the flats of the bar and run true. I can understand, if a four jaw is the only chuck you have. Just interested as I have never seen this before and it seems a lot of effort to get a piece of hexagon to run true/concentric.
    Thank you again for the posts you upload they are always interesting.
    The Home Engineer

  10. #8
    mklotz mklotz's Avatar
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    Quote Originally Posted by thehomeengineer View Post
    Hi mklotz
    Please forgive me if I am missing something here, but why clock a piece of hexagon bar in a 4-jaw chuck? Normally hexagon is used for making nuts and bolts and alike, so why use a four jaw when a 3-jaw self-centring chuck will hold on the flats of the bar and run true. I can understand, if a four jaw is the only chuck you have. Just interested as I have never seen this before and it seems a lot of effort to get a piece of hexagon to run true/concentric.
    Thank you again for the posts you upload they are always interesting.
    The explanation is much simpler than one might expect.

    The original picture showed a piece of square stock held in a V-block. During the recent PhotoSuckIt screw-up, that picture disappeared and I was forced to take a new photo to replace it. The original square chunk of metal had been used for a project and I was deeply immersed in the bookkeeping of restoring all my photos so I simply grabbed the first piece of polygonal stock that would present an edge to demonstrate the action of the flapper.

    Yes, I would normally put hex stock in the 3jaw although one of my 4jaws is massive and a real beast to get on and off the lathe so I have used it for what would have been 3jaw jobs simply because I was too lazy to remove it.
    ---
    Regards, Marv


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    Now that is what I call a real explanation!!

    Thanks Marv

  12. #10
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    Hi mklotz
    Thank you for the explanation all makes sense now.
    I often put a 3-Jaw chuck into the massive 4-Jaw. As I cannot be bothered to get the crane to change the chuck. This is a common practice in the UK. This is also why the chuck keys are normally square on a 3-jaw and hexagon on a 4-jaw. Just put the hex one out of reach (in a cupboard) and then you can’t operate the wrong chuck and have the 3 jaw, job, etc. all crashing out of the 4-j. It is amazing how often you naturally go to the chuck that is, attached to the nose of the lathe spindle and not the one being held.
    Thank you again
    The Home Engineer
    .

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