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Thread: Determining if a Shaft is Parallel to a Machined Surface

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    Supporting Member rgsparber's Avatar
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    rgsparber's Tools

    Determining if a Shaft is Parallel to a Machined Surface

    Given a shaft and a machined surface some distance away, how would you determine if they were on the same plane? Applied geometry to the rescue!

    If you are interested, please see

    https://rick.sparber.org/TestWithA_Plane.pdf


    Your comments are welcome. All of us are smarter than any one of us.


    Thanks,

    Rick
    Rick

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    Thanks rgsparber! We've added your Parallel Plane Measuring Method to our Measuring and Marking category,
    as well as to your builder page: rgsparber's Homemade Tools. Your receipt:




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    Supporting Member Paul Alciatore's Avatar
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    Paul Alciatore's Tools
    Interesting application of measurement techniques.

    Your check of that aluminum channel on the surface plate only checked four points of the channel. Perhaps you slid it around and extended that to four lines. But such shapes are extruded and can have a number of defects, including a cross section that is not a straight line. A straight edge laid across the bottom of that channel may show contact at only two points and have daylight come through in other areas.

    Another source of error would be the angle of the fixed vise jaw. Since the aluminum channel is not horizontal, that vise jaw must be dead square to the shaft if your measurement is going to be accurate. Any angular error there will transfer to the 1-2-3 blocks and then to the fit between them and the aluminum channel.

    Finally, there is the use of just an edge of the 1-2-3 block. Those edges are usually chamfered but there is no spec on just how wide this chamfer is from one side of the edge to the other. If the chamfer is a bit deeper on one side then that error will also translate to an error in your measure.

    Overall, a 0.002" difference would, IMHO, be well within the expected error in the technique which could easily be double that amount.

    At the very least, I would take the vise jaws off and make the check with the aluminum channel parallel to the flat surface. Use your adjustable parallel under it to make it so and be sure that the adjustable parallel runs from one side of the channel to the other because the surface plate you checked it on did that. So you should catch the same high points and not miss one that may be near the edge of the channel. You may need to use the 1-2-3s on the flat surface end and the adjustable parallel on the shaft. If you do it this way, I would not be surprised if you get another result.

    Another improvement would be to add four feet to the channel and adjust them to be coplanar on the surface plate. Then do the check as I described above, using those four feet and keeping the channel parallel to the flat surface. This would eliminate any irregularities in the channel's surface.

    That leaves two more questions in my mind. Just how flat is the flat surface of the saw? And, just what can be done about it if the shaft is not parallel to that surface?
    Last edited by Paul Alciatore; 05-16-2020 at 04:00 PM.
    Paul A.

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    Supporting Member rgsparber's Avatar
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    rgsparber's Tools
    Quote Originally Posted by Paul Alciatore View Post
    Interesting application of measurement techniques.

    Your check of that aluminum channel on the surface plate only checked four points of the channel. Perhaps you slid it around and extended that to four lines. But such shapes are extruded and can have a number of defects, including a cross section that is not a straight line. A straight edge laid across the bottom of that channel may show contact at only two points and have daylight come through in other areas.

    Another source of error would be the angle of the fixed vise jaw. Since the aluminum channel is not horizontal, that vise jaw must be dead square to the shaft if your measurement is going to be accurate. Any angular error there will transfer to the 1-2-3 blocks and then to the fit between them and the aluminum channel.

    Finally, there is the use of just an edge of the 1-2-3 block. Those edges are usually chamfered but there is no spec on just how wide this chamfer is from one side of the edge to the other. If the chamfer is a bit deeper on one side then that error will also translate to an error in your measure.

    Overall, a 0.002" difference would, IMHO, be well within the expected error in the technique which could easily be double that amount.

    At the very least, I would take the vise jaws off and make the check with the aluminum channel parallel to the flat surface. Use your adjustable parallel under it to make it so and be sure that the adjustable parallel runs from one side of the channel to the other because the surface plate you checked it on did that. So you should catch the same high points and not miss one that may be near the edge of the channel. You may need to use the 1-2-3s on the flat surface end and the adjustable parallel on the shaft. If you do it this way, I would not be surprised if you get another result.

    Another improvement would be to add four feet to the channel and adjust them to be coplanar on the surface plate. Then do the check as I described above, using those four feet and keeping the channel parallel to the flat surface. This would eliminate any irregularities in the channel's surface.

    That leaves two more questions in my mind. Just how flat is the flat surface of the saw? And, just what can be done about it if the shaft is not parallel to that surface?
    Paul,

    Thanks for your insights. If I needed better accuracy, I would certainly use your 4 feet method and stay away from the edge of the block. I think the adjustable parallel placed parallel to the fixed jaw would be better.

    You are right about the flatness of the extrusion. I didn't explain what precision I needed.

    There is a footnote that explains that the fixed jaw was first set parallel to the pivot shaft but it is easy to miss.

    For the complete context, I recommend reading https://rick.sparber.org/HorizontalBandsawAlignment.pdf pages 9 through 12.

    Thanks,

    Rick


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