Lead Screw or Ball Screw: What to Settle Before You Ask for a Price

Two versions of the same mistake reach us more often than any other. One is an axis specified with a ball screw because the previous machine had one — on a slide that travels 150 mm twice a week. The other is a trapezoidal screw on an axis that runs all shift, where the nut wears faster than budgeted and the motor was sized against the wrong torque.

In both, the type was settled by habit and then defended with a unit price. Any ball screw and lead screw supplier will quote what the drawing asks for; the type is an engineering answer, and the price follows from it.

The engineering difference, in three sentences

A trapezoidal screw carries its load on sliding flanks, a ball screw on recirculating hardened balls, and that one difference sets everything downstream. Published figures put a sliding pair at between a third and a half of the input torque doing useful work, against about nine tenths for a rolling pair — which decides motor size, heat and duty cycle. And where a fine single-start trapezoidal screw will commonly stay put with the power off, a ball screw backdrives, so a vertical axis needs a holding device designed in.

Three ways the type gets settled by accident

1. It was copied from the last drawing. A size and a part number move to the next machine, and whether that axis needed rolling contact is never reopened. The cost is not the screw; it is the brake, the larger frame and the machining that came with it.

2. It was chosen on unit price. A trapezoidal screw is the cheaper line item, and on a light intermittent axis that is the right reason to pick it. On an axis that travels continuously it is the wrong reason, and the money returns as nut replacement, backlash and a hotter motor.

3. Nobody said the axis was vertical. Orientation is the item most often missing from an enquiry, and the one that changes the parts list.

What to settle before the enquiry goes out

These apply to any supplier, including us.

• Stroke — and whether the load is guided separately.

• Speed and duty cycle — metres per minute matters less than how many minutes per hour the axis moves.

• Thrust, and how it is applied — steady, shock, or side load.

• Mounting orientation — horizontal, vertical or inclined; this is the line that decides whether a brake is in scope.

• Whether the axis must hold position unpowered — and whether friction alone is acceptable, or the safety rules for your market require a holding device.

• Accuracy and backlash expectations, plus the budget band — one number each, not "as accurate as possible".

Where the answer changes by industry

• CNC machining. Continuous duty and high traverse rates push the main axes to rolling contact; the adjustment slides and fixture movements on the same machine usually belong on the cheaper screw.

• Semiconductor and inspection. Short travels, tight repeatability, and vertical stages that bring the brake question with them.

• Medical and laboratory automation. Short, slow, intermittent lift axes, and washdown or dry environments that can rule out a lubricated nut outright.

• General automation and material handling. Long travels and loose positioning often move the answer off screws entirely — onto a belt-driven module or a rack — while short transfer slides stay on trapezoidal screws.

None of these is a rule; the duty cycle decides.

What we can work with you on

Send us the stroke, the speed, the thrust and the orientation, and we will state in writing what we can hold for that axis. On the commercial side:

• The screw type confirmed against your numbers — including when the honest answer is that the cheaper screw is the correct one.

• Lengths and end machining to your drawing — with support units and nuts matched to the same axis.

• Inspection records on request — dimensional and accuracy data.

• Factory verification — we welcome customer factory visits and customer audits.

If one of the six answers above is missing, we ask for it before anything is priced.

We are happy to answer company-verification questions directly; our registered address and contact details are on our contact page.

Three questions we get asked before the price goes out

Can you tell us which type suits our axis? Send the stroke, speed, thrust and orientation and we will answer in writing against those four numbers rather than against the machine type. If the duty cycle is light, we will say so.

If we order for a vertical axis, is a brake included? A brake sits on the motor or in the gearbox, not inside the screw. We confirm in writing what we supply for the axis; the holding device is specified with your drive supplier, and is worth settling before the frame is designed.

Can we compare the two options side by side before we decide? Send the same six answers for each option you are considering, and we will state in writing what we can supply for each — and say plainly where we cannot — with what follows (motor torque, holding device, end machining) written into the comparison rather than found out at assembly.

Send the six answers, or come and check

If the type is still open, send the stroke, speed, thrust, orientation and duty cycle, and whether it must hold position unpowered. If it is decided, send the drawing.