# single phase vari speed or 2 speed



## hothead (Feb 6, 2014)

I have a lathe with a 3 hp 220v single phase motor. the lowest speed is 105 rpm max is 2000.
I would like to try to add a variable speed drive or convert to a 2 speed motor. which ever 
would be the least expensive.  
I tried doing a search , haven't had any luck for single phase vari speed. If it would be 3 phase
it would be simple.
If anyone has any ideas or a link where i can find something to convert this lathe,please let me know.
thank's , hh


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## British Steel (Feb 8, 2014)

Sadly, single-phase induction motors don't easily run at variable speeds - the best you could do is stump up the cash for either a 3-phase motor and VFD (not as much as you'd think these days) or a DC motor and controller. Both have their limitations, a 3-phase motor run at low frequency (and hence speed) makes much less power than at its nominal 50 or 60 Hz, a (inexpensive, straight-segment) DC motor at very low speed will "cog" as each winding comes around. Both need extra cooling for low-speed, high-torque applications as the integral fans won't push enough air to keep 'em cool...

The simplest and probably cheapest approach would be to add an extra pair of pulleys to get lower speeds, or a keen inventor could take the variable-ratio pulleys and belt from a twist-n-go scooter/moped and improvise a mechanical (as opposed to the original centrifugal) control of the pulley ratio - this has been done for small mills, and even a moped transmission will handle 2hp easily, the "big boys' scooters" like the Majesty 400 transmit some tens of hp through the same arrangement!

Dave H. (the other one)


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## John Hasler (Feb 8, 2014)

British Steel said:


> Sadly, single-phase induction motors don't easily run at variable speeds...
> Dave H. (the other one)



Capacitor-run motors with the capacitor removed could run on a two-phase VFD but no one makes one as far as I know.  Capacitor-start motors (the kind with no run capacitor) could also be made to work though with restricted speed range.


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## rdhem2 (Feb 8, 2014)

Mr. hothead:

Mr. BS, (British Steel) pretty much tells the story as it is.  I can not criticize his remarks at all.  

Remember, every penny you save now is a headache you will live with forever.
Translation: Do it right, or not at all.


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## hothead (Feb 9, 2014)

thanks for all the input. Me being not vary electronically inclined, will probably leave the motor alone.
I like the idea of manual vari pulley set up . Ive seen them before, nothing new, my dads old Massey Harris
combine had that set up.
I will check into that. if i do it I will mount it on a jackshaft as my lathe has plenty of room for it.
The only thing i really need is a lower speed. Now at 105 rpm when doing inside threading, it is really too fast for me
to push out at the right place. If it were 50 rpm i could handle it. 
I know there are other ways to go about it, like starting inside and threading out, But i dont want any relief inside.
thanks for the input , and any other ideas will be appreciated.
hothead


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