Linear Motion , CHEAP!!

[M250cnc]

As Mark points out I am running bearing races directly onto Ali profile, but I always knew it was a short term solution and a small witness mark is appearing on the profile where the bearing runs over it. Not the best long term solution, although a hardened running strip might give better service.

Stray dust and chippings do get engrained on the top ali surface,

Would you say it's the dust build up that's is causing the witness mark ?

Phil

[routercnc]

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.