Linear Guide Selection Guide

Selection is four questions in a fixed order: what load the carriage carries, how long the guide has to last, how stiff the axis has to be, and how much space the frame leaves. Asking them out of order is how machines end up over-specified in one place and weak in another.

Step 1 — the load

Start with the load per block, not the total machine weight. On a four-block carriage the load splits between the blocks, but not evenly once the centre of gravity moves off centre; a cantilevered head can put most of its load on one block. Work out the worst case, then compare it with the dynamic rating C of the size.

As a rule of thumb, keep the working load under about a third of C. Above that, deflection and life both suffer, and the answer is usually the next size rather than a higher preload. The table above is the square-block HG range; flange blocks of the same size carry the same load, and the miniature series starts much lower — MGN15 is around 4.6 kN against 11.38 kN for HG15.

Step 2 — life

Life is a calculation, not a promise. It depends on the load ratio, the stroke, the lubrication and the environment, and it is worked out per application. Two machines with the same block can differ by an order of magnitude in service life because one runs clean and lubricated and the other runs dry in dust. Ask for the calculation with your load case rather than accepting a catalogue number.

Step 3 — stiffness

Stiffness comes from three places: the size of the guide, the preload, and the structure it is bolted to. Increasing preload is the smallest of the three levers and the one that costs the most heat. If an axis chatters, check the frame and the rail mounting first; a P-grade guide on a frame that flexes will chatter exactly as much as a C-grade one.

Roller guides are the step up when ball guides are not enough: line contact instead of point contact gives higher rigidity at the same envelope, at the cost of more friction and a matched-set supply. Roller guides are supplied as sets in SP/UP accuracy, so the rail length is fixed with the block order.

Step 4 — space

The mounting height decides more designs than the load does. If the frame is already machined, H is fixed and the choice is between square, flange and low-profile blocks of that height. If the carriage plate is thin, the flange pattern spreads the bolts wider; if the frame cannot be raised, the low-profile block keeps the same rail and lowers the carriage. Miniature sizes exist because the space around a printer gantry will not take a 15 mm block.

Boundaries worth checking before you commit

Dust: standard wipers handle chips; for fine abrasive dust use the heavy-duty wiper codes. Lubrication: grease nipple or oil port, with the interval set by duty cycle; a self-lubricating series helps where re-greasing is impractical, it does not replace the wiper. Speed: higher preload means more heat at speed, so a fast light axis is usually Z0 or ZA, not ZB. Temperature: standard guides run in normal machine environments; for furnaces and vacuum the metal end-cap version is the one to ask about.

Three mistakes that cost the most

Over-preloading a light axis: the customer wanted accuracy and got heat. Over-grading: SP on a frame that was never measured. Over-sizing: a 35 mm block on a carriage that weighs ten kilos, which raises cost and height for stiffness the structure cannot use. All three are avoided by answering the four questions above in order.

Sizes and models to compare

Start from the size that matches your load: HGH15CA, HGH25CA, HGH35CA and HGH45CA for the square range; HGW25CC for the flange version; HGL30CA where the height is fixed; MGN12 for miniature axes. Series pages: HG, miniature, RG roller; the full index is on linear guide blocks.

FAQ