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  1. #16
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    Dec 2013
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    For something like this senario that I can't get in the mill,
    I use grub screws put in reverse put in by fingers, then a few light taps with a hammer and you have centre marks.
    If you don't have grub screws machine some threads to a point.

    Other than that, I mount it in the mill and find the centre of each hole and replicate it.

    Your shoulder will keep it aligned as pipeclay said, though I usually make my shoulder for chucks a little smaller and have a tap true chuck, similar the the set tru chuck, but without the adjusting screws.



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  2. #17
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    May 2020
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    australia
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    Quote Originally Posted by BaronJ View Post
    Hi Dave,

    Clamping one chuck in another is never going to give you any accuracy ! Once you remove and refit it things will change.

    All 3 jaw chucks have a few thou of runout and that will be multiplied by the runout of the second chuck ! 4 Jaw chucks are good simply because you can adjust them for minimum runout.

    But i am surprised that it can be that bad. The back plate was faced and square, holes are drilled and then fitted on the back of 1 chuck. Because I have not turned the circumference at all due to very small thickness on this plate, about 16mm. I have decided that clamping on the installed chuck will hold the back plate and turn it to the correct diameter. Then things go downhill. I have a live centre to support the set up. So from left to right, the lathe chuck clamps onto the installed chuck, the back plate is in turn held against by live centre with the tail stock.

    But it is so out of line, the back plate was turned and squared, the mounted chuck is squared, the lathe chuck is square. I am scratching my head.

  3. #18
    Join Date
    Jun 2007
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    sydney ( st marys )
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    Not sure why an OD of 16 mm would be a concern for turning the circumference.

    You should of faced the back plate and bored and threaded if required.

    If threading was not required you should of bored faced and cut the mounting spigot for the chuck as well as marked the PCD for mounting holes.

    If this chuck was to be used on a tee slotted table or similar, after mounting the back plate to the chuck, the chuck could of been secured with jaws removed face down on your tee slotted table or similar and had the rear face machined, this would then make things square to the table and spindle.

    If the later is the use it would be beneficial if the back plate was at least 20 mm larger in diameter than the chuck body so as to allow provision for mounting.

    What is this going to be used on?

  4. #19
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    May 2020
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    16mm is the thickness of the plate, not much to turn when clamping. The chuck with the back plate will be mounted on rotary table. Therefore, the OD is 170mm and the rotary is 150mm.

  5. #20
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    Thickness is not circumference so that bit is cleared up.

    The more questions you ask the better, from what you are trying to achieve you should of asked how to go about machining the backing plate before you started.

    Is this the same plate you were milling with an end mill?

    This job apart from drilling the holes should of been completed on your lathe, you could of even left the facing cut for the mounted surface to your dividing head for last.

  6. #21
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    Possibly I’ve misinterpreted the measurements you’ve provided, but I’m wondering how you’re going to attach a 150mm chuck on a 170mm backing to a 150mm rotary table?

  7. #22
    Join Date
    Nov 2007
    Location
    melbourne australia
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    3,228

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    Imagine how useful a photograph would be.
    Chris

  8. #23
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    May 2020
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    Attachment 394319Attachment 394321Attachment 394320

    So this the setup after backplate is completed. The reason to clamp the second chuck with the plate is to turn the OD of plate to size and square up the backplate for mounting to the rotary table. Although the 2 faces have been turned before, I just want to check whether they are square.

    Yes, this is the plate which was done with milling and failed. So lathe is the right tool for this operation.
    Attached Images Attached Images

  9. #24
    Join Date
    Sep 2012
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    York, North Yorkshire UK
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    Hi Dave, Guys,

    The correct item for doing the new backplate would have been to use a faceplate that fastens directly to the lathe spindle. The faceplate would have been skimmed a couple of thou whilst mounted on the spindle, then the backplate would be bolted to it with three or four screws from the back, getting it a central as possible. Then skim the plate to get the surface true. Turn the plate over and do the other side ! You now have a plate that is the same thickness all over.

    Assuming that you got the plate well centred I would now drill a centre hole and turn to size ready to thread and fit on the lathe spindle. Once you have the backplate fitted to the spindle you can now turn a register to suit the chuck that you are going to fit onto it.

    The rest is drilling the holes for fixing the chuck and checking it !
    Best Regards:
    Baron J.

  10. #25
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    Hi Baron, thanks for the reply.
    I want clarify that mounting the backplate onto a faceplate would need to drill and tape holes onto the backplate right. So bolts can be affixed the backplate during turning for both front and back side. If then, what consideration needed to place these holes just for facing operation.

  11. #26
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    The photos you show are they finished photos or just for set up?

  12. #27
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    Werribee, Melbourne
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    First off, let me clarify that my earlier suggestions were done assuming you were making a backplate for a lathe spindle so aren't really applicable.
    When you mentioned this was intended for a rotary table in one of the later posts that changed things somewhat.

    There are many ways to tackle this problem now but what I would do is firstly remove the backplate from the chuck that is mounted backwards in the jaws of your lathe chuck and make really sure the chuck that is being held is being held squarely.

    Do you have a 4-jaw chuck for the lathe that will hold the chuck intended for the new backplate? If so, I would use that to hold the other chuck so you can set it up as close to perfect as you can.
    Measure the set-up of the second chuck using the register to measure off and adjust for as close to zero as possible for runout on both the face and the OD of the register.
    If you only have a 3-jaw chuck on the lathe then you can adjust runout on the face of the register but the OD runout will be whatever your 3-jaw holding runout is now. This shouldn't be a showstopper for the OD of a backplate.
    Once you have done that mount the backplate onto the chuck while being super careful not to disturb the previous adjustments.
    Now you can face what is the bottom of the backplate and that should then be as close to parallel to the chuck register as you can get (make sure that your mounting screws are recessed enough to avoid hitting them with what should only be a reasonably light skim).

    There won't be a really good grip on the chuck being held looking at the photos so be really careful here - your previous centre hole might well be off now so carefully recut that centre and I would consider facing most of the backplate and trimming the OD with the live centre in place and only move it out of the way to clean up the nub in the centre.
    If you aren't confident in recutting the centre then another approach would be to put a nut between the faceplate and the live centre and tighten the tailstock so the nut is held firmly against the faceplate while providing a recess for the nose of the live centre.

    There may be other ideas that I haven't thought of but I would think that should result in your backplate being pretty accurate in relation to the chuck register.

  13. #28
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    If I am going back to the beginning. I have the spigot of the backplate machined reference to the 3 jaw chuck. Would it be workable if I dismount the backplate and put it back to the 3 jaw chuck on the lathe, use test dial indicator to true up the spigot both on the circumference and the face. I assume that I will have a true reference then I need to clean up the OD of the backplate. Once the OD is turned to size, then I can flip it over, true up by reference of the OD and clean up the face again. In theory, all my faces and OD should be true, right?

  14. #29
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    If I understand your proposed order of operations correctly, you would have to hold the backplate by its current OD in order to clock off the spigot you machined to match the new chuck register?
    If that is the case you wouldn't be able to machine the OD given it would be held by the lathe 3-jaw?

  15. #30
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    You are right. May be part of that OD.

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