Black Chrome Plated Linear Guide - HGH Series

What black chrome is

Black chrome is a chromium plating bath that deposits a dark finish instead of a bright one. On a linear guide it goes onto the rail. The block is supplied black to match, so the assembly reads as one part on the machine rather than a bright rail with a dark carriage on it.

Why a dark rail

Two reasons come up. The first is corrosion: the plating covers rail faces that would otherwise be bare steel, and those are the faces that show rust first in a humid shop or on a machine that runs coolant. The second is reflection. A bright rail throws light back, and on optical, laser and vision equipment that light lands where it is not wanted.

Where it is used

The finish is usually specified for optical stages, laser cutting and marking machines, laboratory and medical equipment, and open-frame machines where a bright rail is visually wrong. It also shows up on equipment that sits idle in humid air between jobs, where a plain rail develops rust blooms at the ends.

Model range

Plated rails are supplied in the HGH sizes from 15 to 65, with the CA and HA block styles. The mounting holes, rail width and block envelope follow the standard HGH dimensions, so a plated rail drops into a design that was drawn for an unplated one. Dimension tables for each size are on the HGR linear guide page.

Fitting and mounting

Treat it as an HGH rail. The rail bolts down through the counterbores, and the block comes assembled on the rail with its preload set. Two things to avoid: do not file or grind the plated surface to make it fit, and do not run a scraper along the rail edge to clean it. Both take the plating off and leave bare steel in the place most likely to rust.

Care through its life

Black chrome is a thin finish, not a heavy engineering plate. It handles humidity, coolant splash and cleaning; it does not survive being used as a slide face or being struck with a tool. Wipe the rail rather than scrubbing it, and keep the block on the rail when the assembly is off the machine.

What to check on arrival

Look at the rail ends and around the counterbores, where a plating is thinnest and a bare patch would show first. Then run the block the full length of the rail by hand and check there is no tight spot at either end.

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