# Shortening a motor shaft



## Jim F (Dec 3, 2020)

What is the preferred method to shorten the shaft on a motor ?
I have a 1/2 HP Marathon dual voltage I just got. Set-up as a redneck buffer, but may put it to better use.
Has a 1" shaft that has been turned down to 1/2" at the end.
There is 11 1/2" of shaft out of the body.


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## markba633csi (Dec 3, 2020)

A hacksaw with a good blade will usually cut it with minimal effort
-Mark


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## tq60 (Dec 3, 2020)

Hack saw works...

If you have a mill you ca cut with hack saw, place on mill table andwth motor running bring In an end mill from end to true up end.

Or place on lathe bed strapped down and use lathe tools to true it up, visualise the motor as head stock and turning shaft as spindle.

No lathe or mill, angle grinder touching end of running motor shaft.

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## Dabbler (Dec 3, 2020)

-- are you just taking the 1/2" part off, or going shorter?


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## rwm (Dec 3, 2020)

After you cut it, touch it up with an angle grinder while the shaft is turning.
Robert


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## Jim F (Dec 3, 2020)

Dabbler said:


> -- are you just taking the 1/2" part off, or going shorter?


Not sure , but I don't think I need almost 12" of shaft.........


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## Jim F (Dec 3, 2020)

tq60 said:


> Hack saw works...
> 
> If you have a mill you ca cut with hack saw, place on mill table andwth motor running bring In an end mill from end to true up end.
> 
> ...


I have a lathe and a mill.


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## rwm (Dec 3, 2020)

Could you chuck up the shaft in the lathe and spin it with the motor body strapped down? That would allow you to turn the shaft to a specific size and thread it. I have always wondered about this and whether it could damage the windings? I'm sure the bearings would be fine. Can any motor experts weigh in please.
Robert


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## Jim F (Dec 3, 2020)

rwm said:


> Could you chuck up the shaft in the lathe and spin it with the motor body strapped down? That would allow you to turn the shaft to a specific size and thread it. I have always wondered about this and whether it could damage the windings? I'm sure the bearings would be fine. Can any motor experts weigh in please.
> Robert


That is what I was thinking, versus pulling the rotor out.
I do know that if you turn a large 3 phase fast enough, it turns into a generator.


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## benmychree (Dec 3, 2020)

Jim F said:


> That is what I was thinking, versus pulling the rotor out.
> I do know that if you turn a large 3 phase fast enough, it turns into a generator.


That may be true, but I think only if power is applied into the motor, then it will "push back"  One of my friends did this with relatively small hydro electric installations with Pelton type water wheels.


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## silence dogood (Dec 3, 2020)

With my luck, a week later after cutting the shaft I'll need a motor with a long shaft.


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## Jim F (Dec 3, 2020)

benmychree said:


> That may be true, but I think only if power is applied into the motor, then it will "push back"  One of my friends did this with relatively small hydro electric installations with Pelton type water wheels.


That was from what my father told me, he was going to do a water wheel generator.


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## Ulma Doctor (Dec 4, 2020)

i have shortened motor shafts while the motor is running, with an angle grinder and a cut off wheel. (PPE was used)

i don't recommend the practice for the faint of heart


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## cathead (Dec 4, 2020)

My inclination would be to keep the motor as a buffer and locate another motor.  Let's say you decided
you wanted a long shaft motor and went looking for one.  The odds are you won't find one.  I have never seen
one .  My out of the box thinking tells me that rarity increases the value exponentially.  At least think it over
before amputating the shaft... Especially one with a one inch diameter output.......rare!


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## Jim F (Dec 4, 2020)

cathead said:


> My inclination would be to keep the motor as a buffer and locate another motor.  Let's say you decided
> you wanted a long shaft motor and went looking for one.  The odds are you won't find one.  I have never seen
> one .  My out of the box thinking tells me that rarity increases the value exponentially.  At least think it over
> before amputating the shaft... Especially one with a one inch diameter output.......rare!


I do not plan on cutting it until I need to.


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## sdelivery (Dec 8, 2020)

Ulma Doctor said:


> i have shortened motor shafts while the motor is running, with an angle grinder and a cut off wheel. (PPE was used)
> 
> i don't recommend the practice for the faint of heart


This is how I have done it. Like ANY job setup is key, a practice run without actually cutting so you can make sure of stability and comfort, ability to finish the cut ect


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## lis2323 (Dec 8, 2020)

I would scribe a line with a fine permanent marker with shaft running. 

Use an abrasive cut off wheel such a Zip Cut while motor is OFF to sever. 

Use an angle grinder with flap wheel OR hand file to dress the cut with running. 


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## sdelivery (Dec 8, 2020)

Looks like a coolant pump motor


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## Jim F (Dec 8, 2020)

sdelivery said:


> Looks like a coolant pump motor


I got it with a buffing wheel on it.
Shaft has been turned down about 3-4" back, end of the shaft has what appears to be 10-24 or so thread


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## Janderso (Dec 8, 2020)

benmychree said:


> One of my friends did this with relatively small hydro electric installations with Pelton type water wheels.


Would that be Pete Sr.?
I know he did a lot with water pumps up in Almanor.


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## Illinoyance (Dec 9, 2020)

I stripped the motor.  One end in the chuck or preferably a collet.  Outer end on a center.  Setup the steady rest inboard of where you want to cut it.  Part off.  Establish a new center in the end.  For extreme accuracy single point bore the 60* surface.


I did the opposite on a T&S cutter motor shaft. I welded on an extension.  Same procedure except the center goes in the outboard end after welding.  Using that center the OD is turned and/or threaded.


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