Motor shaft machining

Can you give me some advices as I have to shorten and reduce the shaft diameter of a motor.

It seems that the material used is extremely hard.

Of course I’ve seen videos that shows to use a plastic bag with tape to prevent iron fillings to be attracted by the magnets.

But what tool to use and how to have a very clean and well done work?!

The shaft is 10mm dia and i have to reduce it to 8mm as precisely as possible.

Original shaft is 10mm +0 -0.007mm!!!

Concentricity is also a concern and the shaft cannot be removed, it’s pressfitted.

Have a Nice Day.


Forget the bag. Take the shaft out of the motor to machine it. To machine hardened steel, you need a precision grinder.

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Remove the shaft from the motor, mount it on a lathe and turn it down slowly until you get the desired results. I would not turn down the shaft with it attached to the motor if you want it to be any good as you do not have any good holding surfaces and holding it from the armature might damage the magnets.

Wouldnt it be easier to machine the pulley. Or just order a 10mm pulley. Its going to be hard to get it 100%


Unfortunately the shaft is pressfitted and bonded.


It goes to a planetary reducer 8mm input.

@barajabali Gave the best solution Buy a pulley for 10mm shaft

I wanna a “direct drive” into the planetary gearbox which has an 8mm input.

Perhaps it woud be possible to secure the motor and make it turn as it was a lathe and grind the shaft, good idea?

But what grinding tools to use?!

You will need a pretty decent lathe with cutting tips made for hardened steel

Precision grinding is done with special grinding wheels and coolant. You’d be better off selling that motor and buying one with an 8mm shaft


I didn’t know you could get inserts for hardened steel. I’ll bet they’re expensive and require some coolant.

At my work, the department that sharpens tools uses precision grinders.

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Thanks for your answer guys.


bit late to the party but I have removed and changed the shafts in my press-fit scorpion motors several times, you just need a arbor press or a drill press to press them out… :confused:

you need to remove the shafts or you will screw your bearings when you apply lateral pressure…

I think I need an drill press, because it seems to be a very interesting tool.

Many times I regret to have none.

Thanks, but how do you put it back on the bell to ensure it’s really well at a right angle?!

Have a Nice Day.


give me a couple minutes, i’ll find a link to a video, the guy will use a arbor pres but using a drill press is the same…

not every motor is identical, but they have the same parts in different configurations

Very instructive, and cleanly done.