Installing and Maintaining Linear Guides

Most running problems are decided before the first bolt is tightened. The rail follows the surface it is bolted to, the block follows the rail, and no preload can correct an error that entered at the mounting face. This page is the order of work we recommend, and the checks that catch the common failures.

Before the rail goes on

Check the mounting face is flat and clean, with no burr at the edges of the bolt holes. A burr under the rail lifts it locally, and the block then runs with a step that looks like a preload problem. Check the shoulder or reference edge, if the design uses one, runs straight: the rail is aligned against it, so any error in the shoulder is copied into the rail.

Two rails on one axis need their mounting faces at the same height within the tolerance of the grade. If they are not, the carriage sits tilted before it moves, and the blocks wear on one side. Measure both faces with the same instrument on the same set-up; two measurements taken on different days with different setups are not a comparison.

Bolting the rail

Start from the middle and work outwards, alternating sides, so the rail is not pulled into a bow by tightening one end first. Tighten in two passes: snug the whole rail, then torque it in the same order. Grease or oil the bolt threads lightly so the torque goes into the bolt rather than into friction, and use the bolt grade the drawing specifies — a soft bolt at the specified torque stretches instead of clamping.

For rails supplied in more than one length, the joint is set before bolting: match the two ends, check the running surface is continuous, then bolt outwards from the joint. A joint that is not matched shows as a click under the block at one point of the stroke, and repeated passes make it worse.

Fitting the block

Slide the block onto the rail from the end, using the plastic keeper that ships with it until the block is on the rail — the balls can drop out of an unsupported block. Set the carriage on the blocks before tightening the block screws, then move the axis through its stroke by hand and check for tight spots. Tighten the block screws in a cross pattern and re-check the feel; if it binds after tightening, the carriage or the mounting face is not flat, not the block.

Bolt sizes by size

The block screws and rail bolts for the common HG sizes are listed below. Use the grade and torque stated on the drawing; the table gives the thread, not the torque.

Lubrication

Grease nipple or oil port, both shown on the dimension table. The first fill matters more than the interval: a dry raceway run at speed for a few hours can mark the balls before the first re-grease. After the first fill, the interval follows load, stroke and environment, and it is agreed for the application rather than fixed on the datasheet. In dusty areas the wiper is part of the lubrication system: if it passes chips, the grease is contaminated within a shift.

Wipers and end caps

Wipers are wear parts. Replace them when the lip is cut, hardened or no longer touches the rail, or when chips appear under the seal at the end of the block. End caps take the impact when a carriage over-travels; a cracked cap lets dust straight into the raceway, so replace it before running the axis again. Both are ordered against the model, not the size, because the cap profile differs between block types.

Troubleshooting

Models and parts

Installation is the same across the range; the numbers differ by size. Compare HGH15CA, HGH25CA, HGH35CA, HGW25CC, HGL30CA and MGN12; rails are on linear guide rails, the full block list on linear guide blocks, and the series pages are HG and miniature.

FAQ