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Hi All
I am thinking of building a 3Axis CNC mill.
I have been looking online at what others have done and I see a lot of people using rollers on the axis motion. However, all "real" machine tools that I have worked with have used sliding steel-on-oil-on-steel surfaces. No wheels or rollers just flat surface on flat surface or v on v. Do I have the wrong impression of the professional stuff or is there a reason that home brewers do it differently?
Thanks
Hubert
Many reasons, some for expediency, some related to usage.
You say 'mill' so I'm assuming a small (relatively) moving table in X & Y. At those sizes, and if you have the means to create, classic dovetail/gib arrangements work, but need far more torque from motors to overcome stiction.
For home build, and for larger machines, linear bearings, particularly profiled rails, are far easier to use and their low friction allows for much higher feed rates with smaller motors. Often these machines will be designed to cut wood as well as alloy. Sawdust and oiled steel/steel dovetails don't play together well.
I think you'll find many very large commercial HSM machines use rails as well these days.
One advantage of a linear guide system with sliding contact (e.g. dovetails) is that you get large areas in contact with an oil layer in between, which is much better for damping than bearings with point contact. But as irving said, most modern machines seem to use rails now as there's other ways to alleviate problems with resonance.
It all depends on how much money you spend. Lots of top end machines still use box ways combined with turcite, as they give a sturdier setup with the natural damping of cast iron and the turcite reduces stiction compared with conventional metal on metal. The issue with linear ways is you effectively introduce a bit springy steel into the machine, however linear rails implemented correctly it's not that big an issue.
Off course linear rails have the advantages of having less stiction, require pretty much no maintenance over their life, and are far easier to replace if they do happen to wear out.