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  1. #16
    Join Date
    Aug 2010
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    Toorloo Arm, VIC
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    39
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    1,270

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    I assume you're using the same pinion each time you tighten the chuck up... Looks like one is marked with a '0'? That should in theory be the most accurate, but check all of them to confirm. Normally one pinion will pull the stock more true than the others.

    You could change the countersinks to shallow counterbores, and cut the register on the backplate undersize a bit, make it into a poor mans set-tru... If the chuck is consistently off in the same direction this should let you improve it a fair bit for general use with just the one adjustment.

  2. #17
    Join Date
    Oct 2007
    Location
    Alexandra Vic
    Age
    69
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    654

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    One thing I noted early in the backplate machining thread and was reiterated in the later bare backplate images is that the spindle nose and thread protrude through the backplate by maybe a full turn of thread.

    In another image looking at the thread turned in the backplate with the chuck mounted, the bore in the chuck is chuck is smaller than the faceplate thread, and the back of the chuck is close to the faceplate.

    If that is the case, it would be probable that when you mount the chuck/faceplate assy, you are in fact registering the chuck back to the spindle nose because they contact before the register faces of the spindle and the faceplate contact, negating the care in accurately machining the spindle register rebate in the faceplate.

    To check this, I would mount the faceplate only and mark the spindle and faceplate alignment and measure the distance from the back of the face plate to the headstock casting, then repeat for the faceplate and chuck combination. If the marks created do not line up perfectly, and the faceplate to casting distance doesn't match, then something is preventing the backplate from registering accurately on the spindle, and in your instance, it could be the spindle nose meeting the back of the chuck.

    I may be spouting BS but it is based on what I see in the pics and if so, I apologise in advance.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  3. #18
    Join Date
    Jun 2007
    Location
    sydney ( st marys )
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    64
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    4,887

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    Based on the above comments and looking at bore sizes of TOS 125 mm chucks the bore is smaller than the spindle OD, you may need to use a spacer.

  4. #19
    Join Date
    Aug 2019
    Location
    Revesby - Sydney Australia
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    56
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    1,183

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    Quote Originally Posted by Jekyll and Hyde View Post
    I assume you're using the same pinion each time you tighten the chuck up... Looks like one is marked with a '0'? That should in theory be the most accurate
    Well spotted. I forgot about that. Some testing today (16mm and 50mm rounds) showed repeatable to about 0.001" T.I.R-o, so I might hold off on stripping the chuck.


    You could change the countersinks to shallow counterbores, and cut the register on the backplate undersize a bit, make it into a poor mans set-tru... If the chuck is consistently off in the same direction this should let you improve it a fair bit for general use with just the one adjustment.
    By now (after pulling it off and on the back plate several times), I'm sure the spigot is undersized to the chuck recess. Loosening the countersinks and hammering chuck relative to back plate might do it.

    But for now, I'm happy with the 1 thou

  5. #20
    Join Date
    Aug 2019
    Location
    Revesby - Sydney Australia
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    56
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    1,183

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    Quote Originally Posted by malb View Post
    One thing I noted early in the backplate machining thread and was reiterated in the later bare backplate images is that the spindle nose and thread protrude through the backplate by maybe a full turn of thread....
    I may be spouting BS but it is based on what I see in the pics and if so, I apologise in advance.
    No apology needed, and well observed.


    It would have been a problem, but I bored a spindle cavity in the chuck several days ago, in a bigger lathe:
    IMG_1623.jpg


    At least 1mm clearance around the spindle (in case I ever re-machine the spigot step on the front of the back plate)

  6. #21
    Join Date
    Aug 2019
    Location
    Revesby - Sydney Australia
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    56
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    1,183

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    Quote Originally Posted by pipeclay View Post
    Based on the above comments and looking at bore sizes of TOS 125 mm chucks the bore is smaller than the spindle OD, you may need to use a spacer.

    I did think about that. A longer thread through the 5lb weight might engage better on the spindle (though, a smaller register?), but having to remember/find the spacer each time I swapped chucks would frustrate.

    Relieving the back of a new chuck was a shame, but seemed easier.

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