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How to Measure Bore While Line Boring

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  • #16
    I thought some of you might like to see the results. I actually used two methods to check the diameter of the bore while working. As Ian suggested, I machined an accurate diameter on the end of the boring bar and used several drills as a Go/NoGo gauge. I selected a diameter to allow several dirlls with only slight differences in their diameter to be used so the method was quite accurate. It also allowed me to use several smaller sized drills to check progress as I approached the final size. I also used Forrest's suggestion of bending up an inside spring caliper. I only had one so I ordered several cheapies from Enco and one of them worked just fine after several minutes at the vise and some sand paper.

    Here's my set up:

    In use, the two methods did correspond within one or two thousanths. I attribute the differences to my relative lack of experience using inside calipers in this manner and to my haste in using them when I saw that the drills were also working well. With more experience and a bit more time, the calipers would be just as accurate, I am sure.

    The flats on each side of the tool allowed me to position two 1-2-3 blocks on it and use a depth mike to set precise tool depths. This worked fairly well.

    And here is a shot illustrating the use of the drills to check the bore diameter. I checked on two opposite sides (top and bottom) to insure no errors crept in. I acutally did this with the tailstock center in place, so this shot is just for illustration.

    And a final check with the mating part. Perfect fit!

    Thanks to all for the help, it really helps. You guys are great.
    Last edited by Paul Alciatore; 03-04-2008, 09:47 AM.
    Paul A.
    SE Texas

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


    • #17
      Boring head use

      In the past I have set a boring head up in the spindle.
      Most boring heads have a tapered shank avalible as an option.

      Set a center in the boring head. You may have to make a special center up.

      Use a dog as a driver, and set the cutting tool in line with the boring head slide.

      You can now dial the head to offset the tool for the final cuts.

      Assuming the tool hole is in the center of the bars length, the heads adjustment will be halved.

      Still have to take the bar out to check your hole.


      you must be really good to hold .0005 with a cheapo caliper!

      Good luck.



      • #18
        Nice idea kap! I assume you could make a similar arrangement by holding the boring bar in a 4-jaw with a center and dog instead of the 3-jaw and fine adjust using the 4-jaw.

        Paul, do give us final closure with pics of what it is you've built?

        Thanks for an interesting thread.


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