Ball Screw Play: What to Confirm Before You Order a Replacement

An axis that used to repeat now repeats to something looser, and the part that gets ordered is a nut. Often the nut is the wrong part: the play is sitting in the fixed end, or in a coupling, or in a preload class that never matched what the axis actually does. The new nut arrives, gets fitted, and the number does not move.

That is the expensive version of a cheap diagnosis. The checks that separate the causes take an indicator and an hour, and most of them can be done before a supplier is asked for anything at all.

Two of those causes — the fixed end and the coupling — are why a replacement so often fails to cure anything. Both sit outside the nut, and both show up under the same indicator.

Where the play comes from: the short version

Play in a ball screw axis shows up as rotation that does not produce movement: command a reversal, and the carriage waits before it responds. It has more than one possible source — wear in the rolling contact is the common one, but a support bearing that has lost its preload, or a coupling that no longer grips, produces the same symptom at the tool. Which of them it is decides whether a nut is the right thing to buy.

Four things to send before the replacement is ordered

These apply to any supplier, including us.

• The play you measured, and how you measured it — a figure with the method beside it says more than a figure alone: one reading tells you where the axis is, two taken a known interval apart tell you where it is going. A reading taken at one place in the stroke is not the same finding as one taken at another.

• The duty it has been running — stroke, cycle rate, load, and whether that load is steady, shock, or carried off to one side. Shock and offset loading do not wear an assembly the way a steady axial load does.

• The nut on the machine now — one body or two, and whether its preload can be re-set. It decides what the replacement has to match, and whether adjustability is available next time.

• Whether the fixed end has been checked — the bearings, the housing and the locknut, and what the indicator showed at the shaft end. This is the check most often skipped, and the one that most often explains a nut that cured nothing.

The expectation worth setting first

The order most people want to place is the one for a nut, and when the cause is wear that is usually the right order. It is not universally the right one. Where the play is in the fixed end, a new nut changes nothing; where the axis is misaligned, a new nut follows the same path as the one it replaced, and no part survives that for long.

So the useful thing to send a supplier is not "do you have this nut" but "here is what I measured — what does that point to". If the reading points at the fixed end, we will say so, because the alternative is a part that arrives, gets fitted and does not move the number.

Where it does turn out to be the nut, the next question is commercial rather than technical: what the replacement has to match, and whether the configuration on the machine is the one worth buying again. That is a decision about the next service interval, not about this week.

How we handle a replacement enquiry

Send us the measured play, the duty and the configuration on the machine, and we will state in writing what we can hold for that axis. On the commercial side:

• The replacement confirmed against your measurement — including when the honest answer is that the nut is not the part to change.

• End machining and screw length to your drawing — so the part arrives ready to fit the first time.

• Inspection records on request — dimensional and accuracy data.

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

We ask for the missing item before we quote.

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

What buyers ask before the order goes in

The drawing gives a part number. Is that enough? It is enough to order a part; it is not enough to know that part is what the axis needs. Send the measured play with the number and the answer comes back against both.

We already fitted one nut and nothing changed. What now? That is information rather than a wasted purchase — it points away from the nut. Send what the indicator reads at the shaft end, and the support end becomes either confirmed or ruled out.

Can you tell us whether we need a replacement at all? Send the play you measured, the duty, and whether the fixed end has been checked, and we will state in writing what we can supply for that axis — and say plainly where we cannot.

Send the measurement, or come and see the plant

If the play is measured, send the figure and the method. If it is not, send the stroke and the duty, and we will tell you what to measure first.