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Thread: Sliding compound-miter saw questions

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    made2hack's Avatar
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    made2hack's Tools

    Sliding compound-miter saw questions

    Hi all,

    An odd question. I've got this cheapo miter saw that I bought to use and I could never get a straight cut at the 0 degrees (or 90 deg) mark.

    Over a distance of 300mm (ie 12") I would get a deviation of approximately 2.5 - 3 mm (around 1/8 "). I mean, I don't expect it to be a professional unit but I do expect it to at least cut in a straight line.

    After a bunch of adjustments to try to cut down the inaccuracy, I decided to remove the sliding head and vacuum everything. Including inside the linear bearings.

    What surprised me was that there seemed to be a linear bearing missing. I mean, one of the rails has 2 bearings installed, the other rail only one.

    Does this seem normal on these saws? Is this a case of trying to save a few cents / unit? Or is it a gross QA oversight?

    Could this be the reason that the ends of my cut are not straight?

    I've attached some pictures for reference.

    Thanks,

    Sliding compound-miter saw questions-img_1317.jpg

    Sliding compound-miter saw questions-img_1318.jpg

    Sliding compound-miter saw questions-img_1321.jpg

  2. #2
    Supporting Member Toolmaker51's Avatar
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    Toolmaker51's Tools
    Rule 1. Cheap is when it won't work at all; AND not worth fixing. Usually not a candidate for modifying either.
    Rule 2. We love to help remedy stuff a hair's breadth better than cheap!

    I'd be surprised in a normal set of twin rails that 3 bearings would be fitted; if it was in the middle, that might triangulate the parallel attempt, but sketchy. I'd recommend finding a replacement 4th set and install it, long as the bores are same in all 4 corners. If you or a friend have a bit of machining equipment, make a tiebar for the outboard end with same center to center as the slide bars.
    There is an import chinesium miter saw here, basically similar to your photos. It definitely has 4 bearings and a flimsy little tie bar. Your pic #1 shows two tapped [?] adjacent holes. Those certainly are retainers; either a spring or a spacer separates the front from rear bearing. They save a few cents not producing a counterbore four times.
    Last edited by Toolmaker51; 06-11-2019 at 03:07 PM.
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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    If you can measure one of those bearings I can 3D print you a temporary replacement to see if that helps with the wiggle. It won't last as long as a real linear bearing, but it can help you figure out if that is the problem.

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    made2hack's Avatar
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    made2hack's Tools
    Thanks everyone. I picked up a lm25uu bearing to try. However, as Toolmaker51 mentioned, they did not bore the back end to size, it is approx 1mm under size.

    And the other lm25uuu bearings installed are half-length. It would have made sense if they had used the 3 bearings triangulated, but they did not.

    Thanks Elizabeth for your offer, I'm going to try to get the LM25UU in, since I've already got a replacement.


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