Smooth rod tolerance, material and surface options

I'm browsing the Misumi site, and just learned that there are lots of options when shopping for linear shafts: Material, surface treatment, and dimensional tolerance.

[us.misumi-ec.com]

The following page spells out which materials/treatements are available for which tolerances (from one of the 'material' buttons on the above Misumi page).

[us.misumi-ec.com]

From this site, [www.themeter.net], I gather that the tolerance codes for 8mm shaft are as follows:

h5 0 to -6 microns
g6 -5 to -10 microns
f8 -13 to -35 microns

Price varies, of course. here are a few examples for 8mm dia 200m length rod:

h5, 52100 Bearing steel, hard chrome $10.82
h5, 440C Stainless, no surface treatment $15.70
g6, 52100 Bearing steel, Hard chrome $6.70
f8, 1045 Carbon steel, Hard chrome $4.22

If I get a typical reprap kit, what tolerance/material/surface treatement am I likely to get? What's the minimum acceptable tolerance for good linear bearing performance?

-Matt

Update: according to this Misumi page, the recommended tolerance is g6:

[us.misumi-ec.com]

Interestingly their part number is LMU8. Is this the same thing as LM8UU? ..Is there a standard way to read the code?

-Matt

Greetings all,

Has anybody tried ceramic-coated rods instead of steel rods as the linear slideways for RepRaps?

At a previous job, we had good luck using ceramic-coated Al rod, running in plastic-lined bushings; however, that was a *beefy* system with 1 inch dia. rods. In the US, ceramic-coated Al rods are available from [www.mcmaster.com] among others, in inch sizes. Interestingly, there's relatively minor variation in price/foot from McMaster, among 1/4" 3/8" and 1/2" dia rods. I also suspect that this material is easier to cut to length; once through the thin ceramic coating, it's aluminum, which is pretty easy to cut with a hacksaw.

I've only found one source for metric diameters for this material:
[www.pbclinear.com]
and no pricing online :-(

From what I've read, ceramic-coated rods are not compatible with ball bearings and require using sleeve bearings/bushings. If sleeve bearings/bushings can be found at a good price in the larger diameters, large diameter may be a sensible way to get greater stiffness of the slideways.