Linear guideways for long axes: butt-jointed profile rails installed against a reference edge, with staggered joints and oil-fed blocks

01

Rails longer than one piece: section length, arrow and number marks, and staggered joints

HIWIN lists its HG series heavy-load ball guideways, for machining centres, NC lathes, grinding and heavy cutting machines, with rail lengths of 100 to 4,000 mm, and states that jointed rails must be installed following the arrow and ordinal number marked on each rail, and that on a matched pair of jointed rails the joint positions should be staggered to avoid accuracy problems between the two rails. [1] Bosch Rexroth gives its BSCL ball rail system a one-piece rail of up to 4,000 mm and multi-section rails of up to 15 parts, for a maximum length of 50 m, in sizes 15 to 45 with dynamic load capacity up to 99,800 N, speeds up to 5 m/s, accuracy classes N, H and P and preload classes C0 to C2. [2]

Editorial calculation: a 12 m axis needs three 4 m sections per rail; staggering the joints means the second rail might be built 2 + 4 + 4 + 2 m so that no joint lines up with a joint on the first rail. At 15 sections of up to 4 m, Rexroth's 50 m maximum works out at about 3.3 m per section. [1] [2]

LinRail lists ball, roller, miniature and heavy-duty guides in rail sizes of 15–65 mm, accuracy grades Normal, H, P and SP, standard and customised rail lengths and grease or oil lubrication. [3]

Give the supplier the axis stroke and total rail length, the load and moments on each carriage, the accuracy and preload class, whether rails are paired, the bed's reference edges and machining, the fixing method, and the lubrication system (central oil or grease).

02

Master and subsidiary rails, mounting-surface tolerances by preload, and parallelism by rail length

HIWIN marks the master rail of a non-interchangeable pair with 'MA'; its datum plane is more accurate and serves as the installation reference. Against vibration and impact it recommends fixing rails and blocks with push plates, push screws, taper gibs or needle rollers, and installing by cleaning the mounting surface, setting the rail gently on the bed in close contact with the datum plane and checking thread engagement before tightening. The allowed parallelism of the two reference surfaces tightens with preload: for HG35 it is 50 µm at Z0, 35 µm at ZA and 30 µm at ZB, and the allowed reference-height difference 210, 150 and 120 µm. [1]

For oil lubrication HIWIN recommends oil of about 30–150 cSt, fed through an oil piping joint in place of the grease nipple at about 0.3 cm³/h, since oil evaporates faster than grease; it lists refilling rates for HG blocks from 0.2 cm³/h (HG15, HG20) to 0.6 cm³/h (HG65). [1] Editorial calculation: eight HG45 blocks at 0.4 cm³/h each take 3.2 cm³/h, about 26 cm³ per 8-hour shift, which sizes the central lubricator's output. [1]

03

Send the axis length, loads and installation details together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Axis: [stroke; total rail length; number of rails]
Loads: [per carriage; moments; speed]
Class: [accuracy; preload]
Rails: [section lengths; joint staggering; marks]
Bed: [reference edges; surface machining; fixing method]
Lubrication: [central oil; feed per block; grease]

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