How to remove gear from DC drive motor?

[IanR]

Seeking engineering advice, I have a DC motor with a helical drive gear mounted on the shaft which is about 8mm dia.

I want to gracefully remove it from the shaft and transplant it to a replacement motor without damage to the gear or the new motor. I can sacrifice the old motor if needed.

I would also like to find a replacement gear wheel, just in case. I have been searching on the internet and trying to define the parameters of the gear , so far I have M1 which I think is mode 1 , Z 15 which i believe to be 15 teeth and H15 dg which I believe to be 15 degree helix. It appears to be stainless.


Shaft diameter is 8mm
Gear diameter 12mm
Gear height 10mm
Shaft height total 15mm

Could anyone suggest a source of such gears as a one off buy and advise me whether using heat is the only way to go? i am onboard and out of the country so realistically with out an engineering shop, heat is from a butane stove on board - if this is a waste of time it would be good to know. I then need to find support or a new heat source.

Is there such a thing as a miniature gear puller?

Also the gear may be glued on, assuming the removal is a success, any recommendations for this?

All advice appreciated

 

[RichardS]

If there is no sign of a grub screw and the shaft is completely round then I suspect that the gear will be pressed on. Heating it and then hammering the end of the shaft whilst supporting the opposite end of the gear in something solid might well drive it off but you'll need a decent hammer, at least.

Richard

 

[Graham_Wright]

HPC gears have supplied me in the past.

 

[IanR]

No grub screw , I suspect it is heat pressed on

 

[IanR]

HPC gears have supplied me in the past.

Very helpful I have just called them, unfortunately not a std size so given some new ideas to follow up. Thanks Graham

 

[Alex_Blackwood]

Get a bearing extractor. Loads on e-Bay

 

[Norman_E]

If there is no sign of a grub screw and the shaft is completely round then I suspect that the gear will be pressed on. Heating it and then hammering the end of the shaft whilst supporting the opposite end of the gear in something solid might well drive it off but you'll need a decent hammer, at least.

Richard

If it is press or shrink fitted, which is most likely, try not to use a hammer as hammering will probably spread the end of the shaft. If there is space behind the gear you need to make a tool to pull the gear off by pressing the shaft through it. On board it is going to be difficult. Can the job wait until you get to a port with engineering facilites? Given a reasonable workshop it will be easy enough to make a puller.

 

[anoccasionalyachtsman]

The good news is that heat releases most glues (and Loctite).

 

[madtam]

A decent 2 or better 3 legged bearing puller might get it off. It is most likely shrunk on - using heat to expand it before placing it on the shaft.
The danger with a straight mechanical puller is if the gear "picks up" on the shaft - that is a small fragment of the shaft starts to roll up inside the gear pinion. If this happens you will rapidly create a locking wedge that will make simple mechanical force an impossibility.
Using fairly rapidly applied external heat to the gear pinion to get it to expand more than the inner shaft will certainly help. But the heat will be transmitted through and so the inner shaft will then also expand at a similar rate.
If you were salvaging the shaft then simply cutting the gear pinion off would be the cleanest solution. Since you want the pinion but not the shaft then boring/reaming out the shaft is the way to go but does then require reasonable facilities to get a clean cut of the shaft without damaging the bore of the pinion.

 

[RichardS]

Using fairly rapidly applied external heat to the gear pinion to get it to expand more than the inner shaft will certainly help. But the heat will be transmitted through and so the inner shaft will then also expand at a similar rate.

That's not strictly true. The hole (the pinion in this case) will always expand slightly more than the metal filling it (the shaft in this case) if they are made of the same material, or ones with a similar coefficient of expansion. If they are made of different materials then it's more hit and miss. A temperature difference across the two will, as you say, increase the difference in the relative rates of expansion but that's often not achievable.

Richard

 

[superheat6k]

As said already likely a heat fit. To get it off cleanly you need to put a puller on and then heat it rapidly whilst under tension from the puller, but do not let it get too hot or you could destroy the case hardening. i.e. not more than 150oC, and I would use a hot air paint stripper on high heat as this would take some doing to blue the teeth. Avoid use a flame torch unless you really know what you are doing.

Once it is thoroughly warmed a sharp tap on the puller should see it release. The idea of heating rapidly is to expand the gear, but not the shaft.

 

[IanR]

Great tips thank you all. I have a hot air gun onboard, now i need to improvise a puller. Much appreciated