The stroke on a slide table is not the same as the travel your process needs. Stroke is the distance the carriage can physically move between the two mechanical end stops. Usable travel is smaller, because limit switches, hard stops and deceleration distance all sit inside that stroke. Order the process travel and you will spend the first week of installation discovering that the axis cannot reach its home position.
The correct input is total required travel: from the furthest point the tool must reach to the furthest point it must retract, plus whatever the fixture and the tool changer demand. Everything else is derived from that number.
The four numbers that decide stroke
Work through these in order. Each one can force a frame change, so getting them wrong late is expensive.
- Process travel. The span the tool or workpiece must cover in normal operation, measured on the drawing rather than estimated on the machine.
- Switch and stop margin. 15–25 mm per end for a limit switch plus mechanical buffer. On a fast axis with 5 m/s² acceleration, allow 30 mm at each end.
- Fixture overhang. If the workpiece overhangs the table, the carriage must travel further to bring the edge under the tool. Measure the overhang, do not assume it is centred.
- Frame allowance. The moving element adds length at each end. The allowance changes with the bearing block, end plate and bellows stack, so take the overall length for the exact model from its drawing rather than adding a fixed figure to the stroke.
Worked example
A drilling axis must cover 380 mm of workpiece, the fixture overhangs 40 mm at the far end, and the axis runs at 2 m/s².
- Process travel
- 380 mm
- Fixture overhang
- 40 mm
- Switch margin
- 2 × 20 mm
- Ordered stroke
- 460 mm → 500 mm standard
- Frame length
- stroke + model allowance
The frame-length penalty
A slide table is always longer than its stroke, and that extra length is what usually kills a design. If your machine envelope has 700 mm for the axis, a 500 mm stroke will not fit: the frame is always longer than the stroke, and the allowance comes from the drawing. Designers routinely forget this and then discover the axis fouls the machine column or the cable chain has nowhere to run.
Two escapes exist. The first is a belt module, where the profile is the structure and the frame allowance is smaller, but repeatability drops to ±0.05 mm. The second is a custom frame with the screw bearing moved inside the base, which recovers 40–60 mm at the cost of a longer lead time. Neither is free; decide before you commit to an envelope.
Why long stroke limits speed
A ball screw is a slender shaft in compression. As it gets longer it becomes a whirling shaft, and the speed at which it starts to whip drops with the square of the unsupported length. A Ø16 mm screw at 600 mm is comfortable at 500 mm/s. The same screw at 1500 mm is limited to roughly 200 mm/s before vibration appears in the positioning signal.
If you need both length and speed, the answer is not a bigger screw — it is a different drive. A belt module has no critical speed in this range and will run 1500 mm/s at 2 m. A rack-and-pinion axis behaves similarly. The rack-and-pinion slides are a separate drive family for travel beyond 1200 mm.
Accuracy does not scale with stroke
A common expectation is that a longer slide table is proportionally less accurate. That is only half true. Repeatability is set by preload and rail quality and stays roughly constant across the stroke. Positioning accuracy accumulates with lead error, which is quoted per 300 mm and therefore grows with length.
At C5 grade, lead error is ±0.023 mm per 300 mm. Over 600 mm the accumulated error can reach roughly 0.04 mm before any other contribution. If your process needs ±0.02 mm over a 900 mm stroke, a scale is not optional — it is the only way to close the loop at the table rather than at the motor.
Vertical axes change the calculation
On a vertical axis the load is always in one direction, so backlash does not show up the same way, but gravity does. A 40 kg head on a vertical slide needs a brake or a counterbalance, and the motor must be sized for the accelerating case rather than the steady case. Stroke also has to account for the counterweight travel if you use one — it doubles the envelope.
When a custom stroke is cheaper
Between standard steps there is no cost penalty: a 460 mm stroke is priced as a 500 mm standard because the frame is cut to order either way. Above the standard maximum, a custom build is usually cheaper than forcing a bigger frame into a small envelope. Our custom slide table service quotes from a sketch with three dimensions.
Whatever you order, put the frame length and the mounting hole pattern on the drawing before you approve it. Stroke is the number everyone checks; frame length is the number that stops the machine from closing.
Common questions
Yes. Stroke is the mechanical travel between the hard stops. Usable travel is smaller by the switch margin and deceleration distance at each end.