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  1. #1
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    Default So the diameter is larger than my measuring tools

    Turning up the register on a chuck backing plate for a chuck tonight - approx 190mm diameter - I realised that my 200mm digital calipers were at work and I had nothing big enough to measure it with.

    Got me thinking that there's always going to be the case of the job that's bigger than your proper measuring tools. There must be reasonably standard tools/techniques that machinists use to get around the problem.

    With the backing plate I didn't even need an actual dimension, just way of comparing the 2 parts and getting an appropriate fit.

    So, what are the secrets ????

    Steve

  2. #2
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    Default

    Inside outside calipers.

  3. #3
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    Default

    As Pipeclay said, they can even be homemade
    Using Tapatalk

  4. #4
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    Default

    Could You use 2 squares placed like this? LL and slide one square over the other and clamp lightly.

  5. #5
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    Default

    Thanks. I've got smaller inside/outside calipers but will grab some larger ones. They are dirt cheap on eBay etc.

    Good thought on creating a pseudo caliper from squares too.

    Think I'll also knock up a simple trammel arrangement out of some 12mm rod with a flat on the back. Easy to make different jaws and pointers (or a longer rod) and would help with another challenge I've had previously - accurately locating hole centers.

    Steve

  6. #6
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    Default

    Can you use the chuck itself?

  7. #7
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    Default

    Quote Originally Posted by nadroj View Post
    Can you use the chuck itself?
    Pretty much what I did at the time. Just measured with a steel rule then took off .5mm at a time until it went in. It's a camlock backing plate so I took the plate to the chuck rather than manhandling a 20+ kg chuck for multiple trial fits.

    Not ideal though, hence the question for a better solution.

    Steve

  8. #8
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    Oct 2004
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    Default

    Half a millimeter is a huge amount to take off when approaching finished size for a chuck spigot.
    Final cut in cast iron should produce something like fine dust.

    I thought you might mention the weight of the chuck.
    An answer is to make a timber cradle that hold it at centre height, and can be slid along bed ways to match up with the backing plate.
    Camlock taper gets around the problem neatly though.

  9. #9
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    Default

    Thankfully I was aiming for a slight clearance with the intention of being able to loosen the mounting bolts and tap it slightly to true it up.
    Think I'd still have been sneaking up on it now if I wanted a close fit!!

    I'm getting older/weaker/smarter so the plan is to build some form of simple gantry to hang one of the cheap 240v electric cable hoists from. I think the dust is really heavy around here as every time I go to pick up a chuck or rotary table etc it seems to be heavier....

    Steve

  10. #10
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    Jul 2012
    Location
    Griffith NSW
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    Set your compound slide to a shallowish taper and lock the saddle to the bed. Use the compound to cut the shoulder required, but on a slight taper, and keep test fitting the chuck body to the backing plate, while taking note of the cross slide depth. Eventually, youll get the chuck to go partially onto the taper. Take note of how deep up the taper the chuck went and move the compound so that the tool is in that same position, likewise your cross slide. Now the tool is on the correct depth for creating the shoulder, the saddle can be unlocked and you can use it to cut the shouder. face a little deeper to get a better seat if required, face off the remains of the tapered part if it bothers you and bob's yer cousins pet monkey.

  11. #11
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    Default

    You could buy some cheap vernier calipers, they would get you a lot closer than guessing.
    Using Tapatalk

  12. #12
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    Default

    Thanks Scottyd - that's a good technique.

    Steve

  13. #13
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    Default

    Quote Originally Posted by OxxAndBert View Post
    Thanks. I've got smaller inside/outside calipers but will grab some larger ones. They are dirt cheap on eBay etc.

    Good thought on creating a pseudo caliper from squares too.

    Think I'll also knock up a simple trammel arrangement out of some 12mm rod with a flat on the back. Easy to make different jaws and pointers (or a longer rod) and would help with another challenge I've had previously - accurately locating hole centers.

    Steve
    Hi Steve,

    This is something that I made that is similar to a "Trammel" although I have used it a few times as one.

    //metalworkforums.com/f65/t2013...=Marking+gauge
    Best Regards:
    Baron J.

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