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  1. What do the experts think?
    Why is centring a piece causing you so much trouble? (A picture would help)

    If you're using an independently jawed chuck for accuracy you'll need to dial it. One can usually do it by eye to about +/- 20 thou", just using the concentric rings. It should only take a few minutes to get the TIR down to 1 thou or so.

    If you only need a rough centre ~0.003" then a self-centring chuck with 3,4 or 6 jaws would make your life a whole lot simpler.

    I'd guess your plate Idea would work to say 0.01" (if you're lucky ;)) tightening one jaw can throw the reading off by that much.

  2. #12
    Tom's Avatar
    Location unknown. Last Activity: 30-11-2016 Has been a member for 7-8 years. Has a total post count of 172. Referred 1 members to the community.
    Quote Originally Posted by GeorgeD View Post
    popped intothe spindle,tighten the jaws up and thats it.
    I'm lost, what does it do? Got a picture? If it's not a lathe what is it? :-~

    I'm with Irving - a DTI allows you to centre objects to a precision better than you can see. And they start at a tenner.
    Last edited by Tom; 28-07-2010 at 07:05 PM.

  3. #13
    Tom's Avatar
    Location unknown. Last Activity: 30-11-2016 Has been a member for 7-8 years. Has a total post count of 172. Referred 1 members to the community.
    Quote Originally Posted by Tom View Post
    I'm with Irving .....
    Edit

    I'm with Irving AND Bill

  4. #14
    I'm with Irving, Bill and Tom :-)

  5. #15
    I'm with the missus.

  6. Quote Originally Posted by GeorgeD View Post
    Might of hit the jackpot here?

    Ok this idea might work but only one way ie those who have a lathe or worked on one will know what I'mon about,the chuck jaws are twofold position one way for holding small diameter rod,the other way for holding larger diameter rod or wokpiece.

    Using the jaws in the larger format,lets supposing I aquire a lentgh of ally bar the diameter of the lathe spindle bore,cut a 3" piece of the bar,dilled a hole in the center of the bar and then tapped a thread in the drilled hole.


    Now then this is the nagging part but can be done as and when one is needed of these disc are needed.

    Take a piece of alluminium square 2"x2" plate,scribe a line from one coner to the othe diagonally and the same on the other two corners,in otherwords X marks the spot in this case dead center of the 2b2 square.
    Using this center point I use a compass to draw a circle so that it coincides with the edge of the square,cut out the cicle with tin snips? drill a hole the same size as the hole previously drilled in the aluminium bar,screw this disc to the aluminium bar with a countersunk screw,feed bar into chuck spindle and make sure its snug fit.

    Take a piece of Aluminium rod thats 2" in diameter that I want to ream/down size?
    position it level with the disc we just made up and popped intothe spindle,tighten the jaws up and thats it.

    Like I said a disc can be cut and drilled as and when we need it and the same spindle rod can be used all the time.

    What do the experts think?
    Firstly I think you need to get your terminology right... reaming is a process for accurately opening out a hole to a known size using a reamer... reducing the diameter of a bar is a process of turning...

    Secondly how are you going to drill a hole in the centre of the 3" long bar without centering it? Also how are you going to make it fit the spindle bore without turning it down accurately - each spindle is slightly different and that would have to be made for your specific spindle.

    Thirdly, the accuracy of what you have described using compass and tinsnips is pretty useless in engineering terms, and I think would be incredibly dangerous as the workpiece could easily be 0.5mm offcentre.. i wouldnt want to go near that rotating at any speed with a cutter approaching it....

    I'm all for innovation, but sometimes theres a right way of doing something devised over generations of trying alternatives... mainly due to the Darwin effect...

  7. #17
    I'm all for innovation, but sometimes theres a right way of doing something devised over generations of trying alternatives... mainly due to the Darwin effect...
    Nicley put, much more conservative than what I was going to say..:whistling:

    George
    Why dont you just say what it is you are trying to bulid and what you want it to do, it seems people are having to try and guess what the question is...

  8. #18
    I'm really having a badday here,so I'm not going to answer that.

    Really cheesed off I am.

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