How to Measure Gear Box Shaft Axial Float?

You get paid to do this?

If the gear box is going to be used it will be under load; therefore measure under load. If it isn't going to be under load, it isn't being used; therefore why have it?

The manufacturer should know what the total built-in float is. There will always be some due to snap ring grooves and internal bearing clearances.

Ask the people who built the box, they can tell you what is in tolerance and what is worn out.

They have a standard way to measure this regardless of what advice you get here.

Normally axial float is limited by thrust bearings and hence total shift under load from one side to another is what matters (in yr case it is .2 mm) increase in float from a value during commissioning indicate wear amount of wear.

Getting a lesser value when load is release is ok as the shaft repositions under changes set of acting forces; as long as the value is not zero.

Zero float on a horizontal shaft indicates a pull or push probably due to flexible member in a coupling or clutch plates or wrong clearances on input / output devices attached. This a sure a sign of quick catastrophic failure.

Thanks to all

Mr.Sanjayvt thank you very much

After overhauling coupling or any other device is not attached. I placed a dial gauge directly on the shaft axis.

if suppose now I am getting 0.1mm under load. After releasing the load it become Zero is it ok ? or its better after releasing the load dial reading must be 0.05 or near some reading

which one is good?

Total float is free float + float due to flexing / flattening / riding of various parts which should be minimum need to use your judgment on tolerances loads dimensions etc.

"0" float means there is no free float and probably and in a forced lubricating system no clearance for lub oil to flow freely (dump back) means over heating and a failure.

No offense intended. But you neglected to remember that whenever there are shafts and bearings be they thrust bearings or tapered roller bearings or deep groove ball bearings they always incorporate snap rings and snap ring grooves which have an edge margin and a seating clearance which has a built in float. Everything has to float a little bit one way or another. The manufacturer can tell you whether it will float or sink.