moderated sticky Re: 10L motor replacement recommendations #10l


Electronic variable speed is a good upgrade for a lathe. mill. or drill press.  I have added DC variable speed and VFD speed control to several machines and have been pleased with the results.

But there is one important point to remember - both of these electronic speed control systems produce a constant torque motor output.   Use of mechanical speed reduction ( gears, step pulleys, or var speed sheaves ) is a constant horsepower situation - as the spindle speed is reduced, the torque increases.  With electronics, the speed is reduced and the torque remains constant....thus the horsepower from the motor is reduced.

For the conversion to be satisfactory, you will probably need to continue to use the mechanical speed control  to get the full range of speed you desire or increase the motor nameplate torque ( horsepower ).  A 1/2 hp AC motor on a lathe with step pulley drive will work fine.  But a 1/2 HP DC or 3 phase VS system that has its primary speed at 1800 ish rpm which is just dialed down to 200 ish rpm will stall when loaded with a cut.  You set the gross machine speed with the mechanical system and use the electronic control to fine tune the spindle speed.  ( If you are lucky. the majority of your work will require spindle speeds within the band width of one of your systems steps and thus for  most of your work you just dial the desired speed with the electronic dial.)

I once heard of a person who was going to add a 7HP 3Ph VS motor to a Clausing 5900 lathe ( factory motor HP 1 1/2 to 2HP ).  He wanted 300 - 3000 spindle RPM with no gearbox or belt changes.  I never heard the results but one thing he said was he got a deal on the 7HP motor - which was how he could afford to do it.  I hope the increased torque didn't break something.

Also, there is Monarch 10EE lathe which has always been a wonderful but most expensive lathe.  They have used a DC motor with a variable speed control circuit.  The circuit was custom designed by them and worked fine but reportedly was a nightmare to maintain.  I don't know the current situation on that machine. 

There have been many discussions on this subject posted on the internet.  I encourage interested persons to search for them before purchasing parts to retrofit a machine.



On 03/15/2020 08:08 PM, jahick4@... wrote:


Thanks for your input. Like the other John, my heart is really telling me to stay with 220v 3ph and the VFD. I do like the idea of being able to just bring the thing home and run it in the garage on 110v, but after having run it on the VFD, I feel like it would be a real step backwards to not have the infinitely variable speed and that smooth torque. Also, electricity is expensive enough that any savings I could get with a treadmill motor would end up going toward the electric bill due to the inherent inefficiency of single phase motors. The only benefit would be to such a setup would be that I wouldn’t have to run 220v service to the garage when my boss decides that my equipment is taking up too much space in the shop.

I’m leaning toward 1.5hp at the moment, but I’m still not certain.



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