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Motor Shaft Removal

Tight Shafts and Stubborn Grub Screws

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Andrew Ray01/09/2012 09:31:21
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My Eflight Hurricane hit the ground pretty hard and bent the motor shaft. I pulled the motor out of the airframe and started to remove the grubscrews holding the shaft. They were very difficult to remove and secured with a thread locking compound, one grub screw came out with a bit of persuasion and heat, the other would not budge despite trying all the tricks, I even broke an allen key trying to remove it. In fairness Horion Hobby were very good, I returned the motor to their service department and received a new motor by return.

In the meantime I purchased a Turnigy motor and needed the shaft to poke out of the other end. This time the grubscrews came out easily but try as I might I could not shift the shaft, it was solid in the housing.

Has anyone had any success removing stubborn motor shafts and how have you done it?

Andrew

Mark Powell 201/09/2012 09:39:55
430 forum posts

Blood, sweat, but no tears. A little heat. Put the motor bell resting on a vice jaws with the shaft facing the gap. Tap with a hammer, A metal one, putting wood blocks as a shock absorber spoils the effect, you can file the burrs off later.

Bob Cotsford01/09/2012 10:38:03
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or find a deep socket that fits inside the bell and use the vice to press the shaft through. The socket transfers the pressure to the area around the bearing and saves risking distorting the bell.

Andrew Ray01/09/2012 10:53:37
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Posted by Mark Powell 2 on 01/09/2012 09:39:55:

Blood, sweat, but no tears. A little heat. Put the motor bell resting on a vice jaws with the shaft facing the gap. Tap with a hammer, A metal one, putting wood blocks as a shock absorber spoils the effect, you can file the burrs off later.

Done that, hit it as hard as I dare, maybe I need a bigger hammer.

Andrew Ray01/09/2012 10:55:45
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Posted by Bob Cotsford on 01/09/2012 10:38:03:

or find a deep socket that fits inside the bell and use the vice to press the shaft through. The socket transfers the pressure to the area around the bearing and saves risking distorting the bell.

Didn't think of that. I have been concerned that I could damage the end of the bell if I belt it too hard.

Martin Harris01/09/2012 11:03:54
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I'd recommend the vice method - hitting the shaft is much more likely to damage the bearings.

Martin Harris01/09/2012 11:03:54
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I'd recommend the vice method - hitting the shaft is much more likely to damage the bearings.

 

So much so that I hit the post button twice!  blush

Edited By Martin Harris on 01/09/2012 11:05:17

Mark Powell 201/09/2012 11:04:54
430 forum posts

I assume you want to turn it round so that you can attach the prop adaptor to the bell rather than the shaft. Some turnigy motors are supplied with such an adapter. But they won't fit anyway. Some of their motors have only two screwq holes on the bell and curved 'non hole' arms so the adapter wobbles about. Been on another thread.

So check that before you bother at all. If that is what you are doing.

Andrew Ray01/09/2012 11:15:52
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Posted by Martin Harris on 01/09/2012 11:03:54:

I'd recommend the vice method - hitting the shaft is much more likely to damage the bearings.

I have separated the motor so the bearings are in the armature not the bell

Andrew Ray01/09/2012 11:19:12
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Posted by Mark Powell 2 on 01/09/2012 11:04:54:

I assume you want to turn it round so that you can attach the prop adaptor to the bell rather than the shaft. Some turnigy motors are supplied with such an adapter. But they won't fit anyway. Some of their motors have only two screwq holes on the bell and curved 'non hole' arms so the adapter wobbles about. Been on another thread.

So check that before you bother at all. If that is what you are doing.

Instead of the motor mounting on the firewall/bulkhead it mounts on the front of the nose (cowl) so the shaft needs to protrude through the stationary (fixed) part of the motor, in that way a standard prop adaptor will fit. I think that makes sense.

Andrew Ray01/09/2012 17:56:37
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Shaft is out of the Turnigy using the vice method, I placed a couple of large washers inside the bell before inserting the socket to spread the load evenly. When I come to replace the shaft I will leave the shaft in the freezer overnight to shrink it and warm up the bell to expand it as the shaft was incredibly tight in the housing. I'm not sure the grub screws do much, there are no witness marks on the shaft.

Thanks for the advice guys.

Chris Bott - Moderator01/09/2012 17:59:03
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Nice one Andrew.

Just don't let the magnets get too hot if yr warming things up. There is a limit, above which the magnetism is affected. Somone here may have some idea what that temperature is?

Stephen Grigg01/09/2012 19:17:02
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Ive always found the vice method works fine and without any problems,The grub screw certainly do there job as well as a circlip if yours has one.I think the forces these motors create are higher than we appreciate,.I know a firend who started a motor and the shaft shot out with prop attached and he found it at the top of the garden in the cabbage patch.

PatMc01/09/2012 20:11:16
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Posted by Andrew Ray on 01/09/2012 17:56:37:

Shaft is out of the Turnigy using the vice method, I placed a couple of large washers inside the bell before inserting the socket to spread the load evenly. When I come to replace the shaft I will leave the shaft in the freezer overnight to shrink it and warm up the bell to expand it as the shaft was incredibly tight in the housing. I'm not sure the grub screws do much, there are no witness marks on the shaft.

Thanks for the advice guys.

Did you need to remove the shaft ? I usually just push it through from one end to the other using a pillar drill in a similar way to tha vice method.

BTW apart from damaging the bearings hammering the shaft can also loosen the magnets.

PatMc01/09/2012 20:13:11
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Posted by Chris Bott - Moderator on 01/09/2012 17:59:03:

Nice one Andrew.

Just don't let the magnets get too hot if yr warming things up. There is a limit, above which the magnetism is affected. Somone here may have some idea what that temperature is?

310 - 400 degrees C, the solder we commonly use melts at around 180 degrees C.

Chris Bott - Moderator01/09/2012 20:45:01
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Ah OK thanks PatMc, probably nothing we should worry about then.

Shaunie01/09/2012 22:24:24
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Got no figures to hand but the stronger the magnet the lower the temperature it can withstand, some of the strongest rare earth magnets can be affected by any temperatures over 50 deg C from memory.

Shaun

PatMc02/09/2012 09:57:25
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I was quoting the Curie point temps for the strongest neodymium magnets, the cheaper magnets can withstand higher temps.

The temp at which neodymium magnets start to permanently lose strength is 176 degrees C (depending on grade). More info here

Edited By PatMc on 02/09/2012 10:05:32

malcolm woodcock 102/09/2012 10:50:12
397 forum posts

I might be coming to this a bit late but I can't see it mentioned above. I always keep old, bent shafts to use as drifts and you don't have to be so scared of giving it a good old whack.

Andrew Ray02/09/2012 14:24:16
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PatMc, yes I did want to remove the shaft as there was only one circlip recess and by pushing the shaft through there was nowhere for the circlip to fit. Replacement shafts have two slots and that's what I am fitting. Having said that thrust from the prop would hold the motor together whereas in a standard bulkhead mount the circlip is needed to hold the motor together.

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