Thread: Cutter accuracy

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  1. #21
    I I may add these two links to the conversation:
    Not withstanding that back lash and tramming is at its best ( minimum )

  2. #22
    There is also probably an additional error .. I would expect 95% or more likely to exist.

    If You have std BK/BF mounts .. they are one source of your error.
    Std import mounts have no preload, and do not have AC bearings in them.

    This type of errors are hard to detect, because they can appear randomly, depending on lots of factors.
    Put dti on free end of screw.
    Use some kind lever to push/pull screw at either end by 10-50-100 kgf force as appropriate.

    Does it move ?
    Almost certainly yes.
    Does it return to zero in all 4 scenarios both push and pull from either end ?
    Almost certainly no.

    Evaluate, report back, how big is the error in slop and lack of repeatability.
    A pair of std size ac bearings, and a simple shim, will likely fix it.

    You can probably use very thin "silk" type craft paper, cut with scissors, on inner ring of bearings.

    A more pro solution is 2 thin metal spacers between bearings, and slightly sanding the outer one on a surface plate with 800 grit si/c sandaper and liquid.
    Use a micrometer to measure, aim for 4-5 microns difference.
    +/- 1-2 microns wont matter, and neither will slight edge rounding from the sanding (it is not lapping).
    Adjusting the shims is a 5-10 minute job.
    It is better to start with flat shims.
    You just want an offset, the nut compresses them to each other.

    If you dont have a lathe, buy shimstock, cut to size, use 2 different thicknesses or sand the outer one a bit thinner.

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