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  1. #11
    Hi Phil,

    Mostly I think it is the weight of the gantry, spindle etc. pressing down onto 4 bearing races which are only about 10mm wide. The contact patch (per bearing) is probably less than 0.5mm long, so in terms of area it is pretty small. I've not weighed the gantry system but it must be 20kg or more, so the stress (force/area) is pretty high. Aluminium is fairly soft so these lines are appearing. I think the cutting forces are tiny compared to the static weight running back and forth over many cycles.

    Having said that, a few tiny chips have slightly pitted the surface where they've been run over. But I quickly stopped most of these occuring by using small screens along either side of the x axis.

    I agree with Ross and Mark and anything which either increases the contact area (width or quantity of rollers) or increases the hardness of the ali rail (e.g. steel wear strip) should help. Wide nylon rollers are worth a go.

    I have never had to do this but I suspect it is possible to calculate by using the force/area (gantry weight in newtons / area in m2) compared to some surface stress value for aluminium.
    Last edited by routercnc; 29-01-2011 at 09:34 PM. Reason: update
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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