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Thread: Improving import co-axial indicator?

  1. #11
    Join Date
    May 2015
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    Somerset UK
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    2,448

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    I have one with a large selection of different length arms, it is only of use for zeroing the wobble, the graduations on the dial are meaningless. The manufacturers always seem to put milimeters or thousandths of an inch scales on which can confuse newcomers.

  2. #12
    Join Date
    Jul 2002
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    4,372

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    At the risk of getting reams o crap..... I recently bought a Shars coaxial indicator to center some critical parts in the mill. Much easier than using a dial indicator.
    I can get center to within half a thou. My coax maybe an outlier but I'm pretty happy.

  3. #13
    Join Date
    Nov 2016
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    129

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    Do you have precision ground stones?

  4. #14
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    Nov 2010
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    Portland Oregon
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    Hi Guys,

    Not to steal the tread or derail it, but I've been thinking about a coax indicator to rebuild (SU British) carburetor shaft holes in the body of the carb. My question is, do these work to find the center of the hole when 1 side of the hole has become elongated or ovaled by wear (which is the reason for the rebuild) and still indicate center? I jig the body in the mill and line bore the shaft openings then ream to size. What I've done in the past is install a new shaft in the old hole and DTI it to a center then do the operations. So far the few that I have done the butterfly has not needed to be modified to make it all work, but I do worry that I might make the shaft off center enough to have to deal with a replacement carb if I screw up.

    Look forward to your suggestions. Aribert, thanks for bringing up the topic.

    TX
    Mr fixit for the family
    Chris

  5. #15
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    Mar 2010
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    Metro Detroit
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    305

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    Thank you all for your responses. I'll leave it as is and actually begin to use it to get a feel for how well it works.

  6. #16
    Join Date
    May 2002
    Location
    SE Texas
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    12,482

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    It sounds to me that your method is probably better for those worn holes.

    On the other hand, just how precise do holes in a carb need to be located? I have only worked on a couple of them, but I did not see any need for extreme precision. A worn hole would move the center of rotation by the amount of that wear but the carb was still working when removed or, at the most, just starting to show problems due to that wear. If you recenter the new (larger or bushed) hole in the center of the worn area, then it will only be half that distance off. Perhaps I missed something.



    Quote Originally Posted by Mr Fixit View Post
    Hi Guys,

    Not to steal the tread or derail it, but I've been thinking about a coax indicator to rebuild (SU British) carburetor shaft holes in the body of the carb. My question is, do these work to find the center of the hole when 1 side of the hole has become elongated or ovaled by wear (which is the reason for the rebuild) and still indicate center? I jig the body in the mill and line bore the shaft openings then ream to size. What I've done in the past is install a new shaft in the old hole and DTI it to a center then do the operations. So far the few that I have done the butterfly has not needed to be modified to make it all work, but I do worry that I might make the shaft off center enough to have to deal with a replacement carb if I screw up.

    Look forward to your suggestions. Aribert, thanks for bringing up the topic.

    TX
    Mr fixit for the family
    Chris
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  7. #17
    Join Date
    May 2002
    Location
    SE Texas
    Posts
    12,482

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    Are you suggesting that they be used for this? It does not sound like a proper use for them. They are only supposed to be used for removing small burrs as a last step in producing a precision surface. Attempting to lap with them would probably ruin them.

    If I had to use a makeshift lapping method, it would probably be a sheet of fine sandpaper adhered to a surface plate or sheet of flat glass with some oil to keep it from curling up and rounding on the edges of the object being lapped. I have a nice, thick sheet of glass for that.



    Quote Originally Posted by hammernanvil View Post
    Do you have precision ground stones?
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  8. #18
    Join Date
    Apr 2012
    Location
    Sydney
    Posts
    759

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    For me, I would flip some of this discussion on its head. That is, if I am going to need to use a DTI to set something up I will often use the coax indicator first to get it close.

    Coax indicators are beaut; just get it cycling and twiddle the machine adjustments till the wobble settles.

    When do we need the DTI. Again, just for me, it is in the setup of lathe alignments (both head and tailstock) and for the tram on the mill.

    I have my lathe head shimmed for alignment parallel to the bed. The head also has an alignment feature that allows it to be twisted around on its base to be aligned to the bed. Both need to be correct before setting the tail stock; that I also shim at the front to get it right.

    Tram in mill is often ok with just putting it back to where it was using the degree indicators fixed to the head adjustment points. However for more precise work (long vertical change with knee or quill and/or facing of larger surfaces requiring more than one pass) having the mill well trammed helps with the precision and/or finish. I use a large flat ground disk sitting on the bed for this work.

  9. #19
    Join Date
    Nov 2010
    Location
    Portland Oregon
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    770

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    HI Group,

    That is exactly the answer that I needed paul, TX. Since the hole is oval on just one side (where the linkage is in tension) Yes the carb starts running bad and it is taking in air through the shaft hole which makes the fuel to air mixture off. Rebushing the existing holes to a standard size is what I do, with a oilite bronze bushing that I final ream to size. I think I am still finding center close enough that all is good, so I'll save shop tool money for some other item. They then run like a champ when all dialed in.

    TX
    Mr fixit for the family
    Chris

  10. #20
    Join Date
    Apr 2012
    Location
    NE Thailand
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    1,232

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    Quote Originally Posted by Rustybolt View Post
    At the risk of getting reams o crap..... I recently bought a Shars coaxial indicator to center some critical parts in the mill. Much easier than using a dial indicator.
    I can get center to within half a thou. My coax maybe an outlier but I'm pretty happy.
    Ditto.
    Marvelous invention (Chinese copy of an American invention)..

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