Getting stuck aluminium collar off a steel shaft

[Chris Green]

I have a small fan motor that I need to replace, the fan is mounted on an aluminium (I think) collar which is siezed on the shaft.

So, what's a good approach to getting it unstuck? I've drilled out most of the grub screw that should be holding it, I doubt that's the issue now. It's just that the collar is very firmly stuck on the shaft.

There's lots of "how to get steel studs out of aluminium cylinder blocks" advice I can find on the web but my problem is the other way around. Is there anything in particular that might help apart from all the usual things like soaking in penetrating oil, bashing it, etc.?

It's quite small, the shaft is about 7mm (possibly 1/4") diameter. The end protrudes only 1cm or so beyond the fan, I can hold it in a vice quite firmly but the fan is quite flimsy so brute force rotation of that is rather difficult.

[nothanks]

Heat will do it. Also, try knocking the collar down the shaft a short way (perhaps with a suitable "socket" or box spanner)

[Clive Arthur]

<snip>

The coefficient of thermal expansion of Aluminium is about twice that of steel, so I'd try heating it. Aluminium conducts much better too.

Hot oil might do it.

Cheers

[The Natural Philosopher]

+1 and a puller is handy.

[Chris Green]

Sounds a good approach, I'll get my (relatively) new gas blow torch onto the job.

[Chris Green]

There's really nothing to get hold of with a puller, the fan is in the way.

[Brian Gaff (Sofa 2)]

Unless the fan itself is plastic, in which case it will be a mess.

A bit of oil down the grub hole and either end, then gentle tapping of the spindle to see if it moves after a few hours. However if you have drilled the grub screw hole, how are you going to re attach the fan to a new motor? Brian

[Chris Green]

By drilling and tapping a new grub screw hole. :-)

Or by cleaning out the existing one, I haven't drilled it out so far that the thread has gone, however I'm not sure I'll be able to clean out the remains of old grub screw.

[Jeff Layman]

If the other methods don't work, and the collar really is aluminium and the shaft steel, then immersing it in concentrated caustic soda will dissolve the aluminium and leave the steel untouched. It is unlikely that the plastic will be affected (unless it's polycarbonate or PETE, although these would be unlikely to be used as fan blades), but it might melt if the reaction gets too hot.

A note of caution, however; it isn't called "caustic soda" for nothing. Eye protection is essential, and so are decent length gloves.

[Thomas Prufer]

Alternatively, use cold.

There's a variety of "rust shock" sprays that combine oil and some gas that cools on contact. Even if the ally gets tighter on steel with cold, it may help as it may stretch, and then be looser as it warms up again, IYSWIM.

And less chance of melting the nearby plastic...

Thomas Prufer

[Dave Plowman (News)]

You could try putting the whole thing in boiling water first. That won't melt anything. ;-)

[newshound]

Steel on aluminium can be a bugger. If the motor is dead, I'd be inclined to destroy the motor in an attempt to save the fan. Angle grinder, dremel, etc. depending on the size. Once you have the fan with just an inch of motor spindle it becomes comparatively easy, I'd start by removing the grub screw, soaking the lot in penetrating fluid of your preference, and then finding suitable spacers to let you push the spindle out in a press, or a pillar drill, or a vice. Once it has moved a bit it should be easier to remove e.g. with a mole wrench.

[Terry Casey]

You obviously never learned how they fit the (steel) tyres on the wheels of railway vehicles!

(I must have been about 10 when I came across it in Arthur Mee's Childrens' Encyclopedia!)