How to measure the radius of a boring bar
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    Default How to measure the radius of a boring bar

    Hello,

    For the sake of discussion, how do we measure the radius of a boring bar to the accuracy of 0.001 mm, when we don't have a tool presetter or on-machine tool setter?

    To be clearer, I have a boring bar here, and I wanted to measure the "R" in the picture.

    11111.jpg

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    How about cut a piece of scrap material, measure the resulting diameter, and divide by 2.

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    That could work. But then I have to make a hole about the size of the boring bar first. And If the tool deflection is too much, I will have a measurement result less than the actual radius of the boring bar.

    I was thinking maybe I can place a slip gauge between the tip of the boring bar and a planar surface with a known position. But I am not sure how accurate that could be.

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    Center your spindle on the side of the vice, move the x axis the required radius and adjust the boring bar to just clear the vice with a piece of paper. bore your hole then final adjust as required. easy peasy.

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    Quote Originally Posted by Stephan Spears View Post
    Hello,

    For the sake of discussion, how do we measure the radius of a boring bar to the accuracy of 0.001 mm, when we don't have a tool presetter or on-machine tool setter?

    To be clearer, I have a boring bar here, and I wanted to measure the "R" in the picture.

    11111.jpg
    .
    with tool holder runout different with each machine spindle and with tool deflection you cannot measure to .001mm repeatability. even a tool presetter it is common to measure and then have it bore .02mm or more different. the longer the tool and the more worn and dirty the machine spindle tapers are the more it can vary
    .
    most set boring bar -.12mm or -.25mm and measure test bore then adjust and finish bore. you might need to bore
    -.12mm
    -.05mm
    then finish bore. this is cause if bore started very small the cutting forces deflect tool then next cut bores more than expected. you need 2 relatively light cuts to get more expected results

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    Quote Originally Posted by Stephan Spears View Post
    Hello,

    For the sake of discussion, how do we measure the radius of a boring bar to the accuracy of 0.001 mm, when we don't have a tool presetter or on-machine tool setter?

    To be clearer, I have a boring bar here, and I wanted to measure the "R" in the picture.

    11111.jpg
    Quite a challenge to measure ANYTHING +/-.001mm, much less a theoretical boring bar width, which is far more dependent on machine characteristics. Try this -- mount that boring bar in the machine, put a tenths indicator on the insert tip, then push on the tool with your hand and watch the indicator move . Now re-evaluate the utility of making your +/-.001mm measurement.

    Regards.

    Mike

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    If you have a tool probe measure diameter just like any end mill

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    Turn a piece of round stock to the diameter you want, centre it on your spindle and use a dial indicator
    with a button point to pick up the edge. Just make sure the centre line of the point is at the same height
    as the cutting tip of your tool. Once you've picked up the diameter you remove the round stock, mount
    the boring bar and adjust it till the cutting tip deflects the indicator the same amount as the round stock.

    That will get you close but I still think that, because of deflection, you're going to have to make the final
    adjustment of your tool "in the hole"...

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    Use an indicator set on the table or vise get a zero off known boring head body diameter,
    compensating for runout move the boring bar to the tip of your indictor.

    Do the math,this will get you close but I always sneak up to final diameter.
    Regards.

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    there is no point in measuring R, it will not translate to the bore the tool will produce, everything is "rubber" in machining world - meaning - the tool will deflect under cutting loads, hence you measure the bore the tool is producing under current conditions and adjust from there

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    As mentioned, mic the ground portion of the bar, set up a tenths indicator at 0 against that diameter in your mill. Zero your readout on the mill. Move the axis over until sweeping the insert tip results in 0 on your tenths indicator. Do the math. It still won't cut that diameter, but it'll be in the neighborhood.

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    Cut an undersize groove of R, a tooltip lightly rubbed will do.
    Use a suitable brass/tin lap and diamond paste to lap the groove to 1-2 microns oversize.
    Use a contact probe to measure.

    It will tell you the tooltip max r, but nothing about shape.
    Likely immaterial.

    Likewise, make a set of 10 with 1 micron incremental sizes.
    Due to geometric averaging, you will have a gage set very close to 1 micron max error.

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    Inside bore non-digital micrometre gages are not very expensive and you can adjust them with gage blocks

    No hope of doing it accurately without measuring in machine.

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    You want to measure .00003"...first let it normalize for 24 hours in the same temperature, then use a well calibrated cmm, normalized in the same room. Don't touch the bar or fixture with your hands as this will ruin your accuracy.

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    Any static measurement you do is not going to do anything better than get you in the city, let alone the ballpark if you truly are talking a micron. As soon as you start spinning that long, out of balance, assembly at any reasonable RPM for machining it will be at a notably different radius.

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    There is no substitute for a test cut, even if you had a presetter.

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    Quote Originally Posted by Orange Vise View Post
    There is no substitute for a test cut, even if you had a presetter.
    But, but, but the Salesman said......4k later, it won't replace practical.

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    Quote Originally Posted by Stephan Spears View Post
    Hello,

    For the sake of discussion, how do we measure the radius of a boring bar to the accuracy of 0.001 mm, when we don't have a tool presetter or on-machine tool setter?

    To be clearer, I have a boring bar here, and I wanted to measure the "R" in the picture.


    11111.jpg

    11111.jpg[/QUOTE]

    There is no way to measure that closely for predetermination of hole size. What I am saying is that even if you measure the radius of the cutting tip to some high level of accuracy ( .001 mm? ... come on) the produced hole will be material and conditions dependent.

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    If the minimum diameter is written on the bar, you only need to divide that measure in two. Who cares about insert tip radius, wear, and tool deflection?

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    Take a picture of the setup using your iPhone. Then email it yourself. Import the picture into Solidworks (or any cad cam system). Then draw a centerline down the center of the boring head, and a point at the tangency of the cutter radius. Then set your CAD measuring increments to .001 mm (actually to be ISO, you need to set the increments to .0001 mm). Then simply pull a measurement from centerline to the point. That times two will give you a measurement to the nearest .001 mm.

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