Mounting a linear guide: alignment, tightening torques, reference edges

The mounting surface carries the accuracy. It has to be clean, burr-free and flat before the rail goes down. Chips, paint residue or a burr under the rail produce exactly the deviation you will later read on the dial gauge. Clean the seating and stop faces and remove sharp edges before the first screw bites.

Reference edges (locating or stop edges) decide the alignment. The principle is simple: one rail is the reference. It is pressed against a fixed stop edge of the structure and fixed there. The second, parallel rail is aligned to the first, not to an edge of its own. That transfers the straightness of the reference rail onto the whole axis. Rexroth allows either the left or the right stop face as the side fixing.

Which edge you use as the reference also depends on the hole pattern and edge distance of the rail. The fundamentals are in the cutting guide.

The sequence is standard and deliberately conservative: align free of play first, then tighten from the inside outward. That keeps the rail from distorting and from walking.

The tightening torque is not a rough guide, it is a safety figure. Too little torque and the rail walks under load or vibration: the bolted joint loosens and the guide loses its position. Too much torque and you pull the rail into the mounting surface and distort it. A straight rail becomes a bent one. Both errors cost accuracy and service life.

What matters is screw size and strength class, not the feel in your wrist. The values below apply to mounting from above with socket head cap screws per ISO 4762 (DIN 912) on Rexroth profiled rail guides of the BSHP, RSHP and BSCL series.

Every rail size has a maximum one-piece length. Online, PTS supplies guide rails cut to size up to 4000 mm from a single piece, cut in-house. If that is not enough, rails are butted: several segments are joined in the correct order so that pitch and hole pattern run through across the joint.

Butting is engineering work. Segment assignment, order and the joint faces, which have to be stoned before carriage mounting, decide whether the carriage later runs smoothly across the seam. Lengths beyond the online limit or multi-piece axes are engineered by the PTS team rather than left to chance.

After bolting, the screw holes are closed. Plastic cover caps are driven flush into the counterbores so that chips and dirt cannot collect in the open holes. The R1605 rails ship with matching plastic caps for mounting from above; in the configurator the caps are stored per rail size and calculated per hole.

The carriage must not run off the rail. Rexroth supplies the carriages on a plastic assembly arbor that holds the rolling elements inside the block. Only right at the moment of pushing on is the carriage transferred from the arbor onto the rail. If the carriage runs off the rail without the arbor, the balls fall out and the carriage is damaged. To remove it, put the carriage back onto an arbor of equal height.