HGR55 Linear Guide Rail

The HGR55 is the 55 mm rail for the HG standard. The profile is 53 mm wide and 44 mm high, with a hole pitch of 120 mm and an end distance of 30 mm. Rails are cut and drilled to length from 100 mm, and every block of this size — square, flange or low profile — runs on the same profile.

Like every rail in the range, the HGR55 is supplied as a part number in its own right: a replacement rail can be ordered without blocks, and a block can be ordered without a rail. That is what makes a maintenance swap possible without changing the carriage.

Dimensions

Length and hole count

A rail with n holes is L = (n − 1) × P + 2 × E. With P = 120 mm and E = 30 mm, the shortest usable rail is 180 mm: two end distances plus one pitch. Below that there is no room for a second hole and the block cannot be supported at both ends of its travel.

Cutting, drilling and joints

Rails are cut square, deburred and drilled in one set-up so the pitch holds along the whole length. If the stroke is longer than the maximum single piece, two lengths are joined; the joint is marked on the drawing and the ends are matched before shipping, because a step at the joint is felt once per stroke and wears the wiper at the same point. A rail cut on site loses its end distance, so if the length may change, order it long and cut to final length with the pattern marked afterwards.

Matching blocks and sets

Blocks up to accuracy P and preload ZA are interchangeable and can be fitted to an existing HGR55 rail. SP/UP accuracy and ZB preload are lapped as a block-and-rail pair, so the rail length is ordered with the blocks in that case. The same rule applies to a replacement: a single block is only a drop-in at P / ZA.

Blocks that run on this rail

Every block of this size uses the same rail profile and hole pattern, so the choice is by mounting and load, not by rail.

Mounting surface and alignment

The rail copies the surface it is bolted to. Before it goes on, the mounting face is checked flat and clean, with no burr at the hole edges, and the shoulder or reference edge is checked straight if the design uses one. On a long rail the face is checked along its full length, not at the ends: a bow in the middle shows as a tight spot at mid-stroke, and tightening the bolts harder makes it worse rather than better.

Two rails on one axis are set to the same height within the tolerance of the block grade, and they are drilled to the same hole count and pitch. Ordering the pair from one drawing is how that stays true; two separate drawings is how a gantry ends up with the holes a few millimetres apart and a carriage that will not sit square.

What a rail order contains

A rail line on a quotation states the model, the length, the hole count, the end distance and whether the ends are cut square or drilled to a joint. Where the rail is part of a matched set, the block accuracy and preload are on the same line, because the pair is lapped together. Bolts are quoted separately unless the order says otherwise. This is deliberately more detail than a catalogue part number: a rail that arrives 20 mm short, or with the end holes 5 mm out, is scrap for that machine even though the profile is correct.

Ordering a replacement rail

A replacement rail is ordered by model and length, not by the block that runs on it. Measure the centre distance between the outermost existing holes, count the holes, and check that (n − 1) × P matches what you measured; if it does not, the machine was drilled to a different standard and the rail has to be made to drawing. Send the photograph of the old rail's end as well — it shows whether the end is cut square or drilled to a joint, which is the one detail that is hard to describe in words.

FAQ

Send the length and the block model and the quotation states both. All rail sizes · All blocks · Rail length guide.