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  1. #1
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    Default Centering rectangular stock in 4 jaw

    I am working on a project where I want to face off some rectangular stock and if possible drill a centre hole (although I could do that on mill later). I intended on facing one side, then flipping over to the other and have two nice parallel surfaces. I have centred round stock in the independent 4 jaw previously using a dial indicator but I am unsure of best approach with the rectangular stock. I wondered if I should pick a corner and basically find a sort of top dead centre to compare and adjust to? I am sure there is a better way so I hope someone can set me right.






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  2. #2
    elanjacobs is online now Apprentice gear maker and machine doctor
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    Default

    I picked up this trick from an Abom video, it requires 2 centres, at least one of which should be dead. This works for clocking up any arbitrary point you want, not just the centre.

    Make a punch mark in the centre of the stock, hold a dead centre between the punch mark and another centre which is in the tailstock, then indicate the "floating" dead centre. Picture...1000 words...etc:

    PXL_20201117_111121068.jpg

  3. #3
    Join Date
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    Default

    Hi Ian, Guys,

    That is basically the technique that I use ! Draw a pencil line from corner to corner and prick punch the centre. I have a 10 inch length of 5 mm silver steel rod with a point on one end which I clamp in the tailstock drill chuck, then using a dial indicator with an elephants foot resting on the rod. Adjust for no indicator movement as the chuck is rotated.
    Best Regards:
    Baron J.

  4. #4
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  5. #5
    Join Date
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    Norwood-ish, Adelaide
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    Default

    It should be no different to centring square stock, except do the opposite sides before moving around 90 degrees. I find that I usually have to wind the carriage back so I don't wipe out the indiator tip when I rotate the corner past the indicator. The centre in a punch mark technique will work, but relies on the punch mark being spot on. Using an indicator on the sides will get you closer to the true centre if it is important

    Michael

  6. #6
    Join Date
    Feb 2013
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    Laidley, SE Qld
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    Default

    I think I've seen these long skinny centring devices called a pump centre?


    Quote Originally Posted by BaronJ View Post
    Hi Ian, Guys,

    That is basically the technique that I use ! Draw a pencil line from corner to corner and prick punch the centre. I have a 10 inch length of 5 mm silver steel rod with a point on one end which I clamp in the tailstock drill chuck, then using a dial indicator with an elephants foot resting on the rod. Adjust for no indicator movement as the chuck is rotated.

  7. #7
    Join Date
    Jun 2007
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    Default

    I normally just draw 2 diagnose lines then eyeball it with the dead centre on the tailstock if accuracy is not required

  8. #8
    Join Date
    Jul 2011
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    Berowra Waters
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    Default

    I reckon I would be more concerned about how likely it will snap the tip of the tool off when you get out to the outside and there’s fresh air before the edge of the workpiece hits the tool. It wouldn’t matter if it was not exactly centred if you’re just facing it off would if?

  9. #9
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    I find it is better to use HSS for interrupted cut, the insert tends to chip/break.

  10. #10
    Join Date
    Nov 2007
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    melbourne australia
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    Quote Originally Posted by bob ward View Post
    I think I've seen these long skinny centring devices called a pump centre?
    That's what I know it as.
    Chris

  11. #11
    Join Date
    Sep 2012
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    Default Spring Centre !

    Hi Guys,

    This is my spring centre, I usually use it for keeping taps straight when threading holes.

    01-09-2018-001.jpg

    Its home brew and very simple to make. Though not a good tool for centre finding !
    Best Regards:
    Baron J.

  12. #12
    Join Date
    Sep 2012
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    Default

    Quote Originally Posted by riverbuilder View Post
    I reckon I would be more concerned about how likely it will snap the tip of the tool off when you get out to the outside and there’s fresh air before the edge of the workpiece hits the tool. It wouldn’t matter if it was not exactly centred if you’re just facing it off would if?
    With thin material it would be likely to hit the jaws !
    Best Regards:
    Baron J.

  13. #13
    Join Date
    Feb 2012
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    Quote Originally Posted by jackaroo View Post
    I find it is better to use HSS for interrupted cut, the insert tends to chip/break.
    Yep will be very light cuts using HSS so hopefully will be OK.

  14. #14
    Join Date
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    Interrupted cuts are a good situation for using up the 100° corners on CCMT inserts.

    Quote Originally Posted by jackaroo View Post
    I find it is better to use HSS for interrupted cut, the insert tends to chip/break.

  15. #15
    Join Date
    Mar 2011
    Location
    Adelaide
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    Default

    For a job like that, seeing as you mentioned using a mill, I’d use a face mill or fly cutter, then bore the centre hole. Only have to clean and oil one machine then...

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