# Connecting 1/2" shaft to 3/8" shaft



## Goatguy (Aug 23, 2007)

I am trying to figure a cheap way to connect the 1/2" drive shaft of a small electric motor to the 3/8" shaft of a small gear speed reducer.

Neither shafts are "keyed" but both are flat on an edge (so somethign with a set screw would work well.

I have tried looking for a coupling, but most i see are like $50, and that is jut too much for a tiny metal part. I've also looked at trying to find a 1/2" to 3/8" shaft reducer, but can't find one. I also can't find a shim or bushing that would work.

3rd, I've considered using two pulleys and small vbelt... but that seems like it would be hasslesome, as well as add a lot of friction drag to the already loaded motor.

I'd like to keep the price under $20 for this connection. Any ideas?


Oh! and by the way, the system is goign to run my grain mill (the wife and I are tired of grinding by hand...)

Thanks!


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## Ed Norman (Jun 8, 2002)

It would be a 5 minute project if you knew someone with a lathe. 

Or you could try this: http://www.grainger.com/Grainger/DAYTON-Rigid-Steel-Coupling-6L014?Pid=search

You would need to shove in a 1/2 bit past the first set screw.


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## Goatguy (Aug 23, 2007)

yes, i agree, a lathe woul make this a piece of cake! 

That is a good idea, the only concern I have, is that after boring the one side to 1/2", there would only be 1/8" material left around it, Do you think 1/8" would be strong enough, and give enough depth for the set screw to "bite"?


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## Bearfootfarm (Jul 13, 2006)

I'd try turning the 1/2" shaft down to 3/8ths.

Another option is use a 1/2" bore coupler, and one of these $4 adapters:

http://www.gsistore.com/3idx1odshadb.html



> 3/8" ID X 1/2" OD Shaft Adapter Bushing


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## Navgatr (Aug 3, 2011)

I would be more concerned with how you are mounting the motor.
As for the coupling:
If it were me, I would want to use some kind of flexible coupling like a Lovejoy or a helical coupling.
These may not be real cheap, but you never want to couple two shafts solid.
That would be hard on the the bearings of the motor and gear reducer, it would make it hard to keep set screws tight , and you'll have a lot of vibration.


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## fishhead (Jul 19, 2006)

Look through these and if none will work for you send them an email with your specs.


http://www.surpluscenter.com/sort.asp?catname=&byKeyword=yes&search=coupler


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## Ross (May 9, 2002)

What Navgator said. I've seen single wire hydraulic hose clamped to the shaft as a coupler too, but I don't know how much load that will take.


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## CIW (Oct 2, 2007)

Lovejoy makes a coupler that adapts from 1/2" to 3/8". It can be mounted in a direct drive setup.


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## Old Vet (Oct 15, 2006)

Ed Norman said:


> It would be a 5 minute project if you knew someone with a lathe.
> 
> Or you could try this: http://www.grainger.com/Grainger/DAYTON-Rigid-Steel-Coupling-6L014?Pid=search
> 
> You would need to shove in a 1/2 bit past the first set screw.



*This would make one shaft out of line with the other.*



Bearfootfarm said:


> I'd try turning the 1/2" shaft down to 3/8ths.
> 
> Another option is use a 1/2" bore coupler, and one of these $4 adapters:
> 
> http://www.gsistore.com/3idx1odshadb.html


*This would make the shafts the same size and use the first one to couple them if they are mounted to a smooth and level surface.*


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## DaleK (Sep 23, 2004)

Ross said:


> What Navgator said. I've seen single wire hydraulic hose clamped to the shaft as a coupler too, but I don't know how much load that will take.


My old silo unloader used hydraulic hose as a coupler/shear protection. That was on a 7.5 hp electric motor and it had to jam up pretty hard to shear.


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## Ed Norman (Jun 8, 2002)

Old Vet said:


> *This would make one shaft out of line with the other.*


Not if you know what you're doing.

But I'd still want a flex coupling.


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## Goatguy (Aug 23, 2007)

Excellent! Thanks for the help folks. I found a lovejoy or "Spider" coupler on McMaster.com for $12 (both hubs plus the middles "spider" piece). Excellent ideas and thanks for the help! I'll let you all know how it works out when it gets here.


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## Ky-Jeeper (Sep 5, 2010)

Been intsalling flexable couplings since 1987. I think of them as insurance or a fuseable link. Don't skimp at this point.


Navgatr said:


> I would be more concerned with how you are mounting the motor.
> As for the coupling:
> If it were me, I would want to use some kind of flexible coupling like a Lovejoy or a helical coupling.
> These may not be real cheap, but you never want to couple two shafts solid.
> That would be hard on the the bearings of the motor and gear reducer, it would make it hard to keep set screws tight , and you'll have a lot of vibration.


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