Possible motor for mill

very simply put,
even old school motors can be run off a vfd effectively.
just realize that torque and Hp vary by changing the frequency.
even the oldest 3 phase motors i have retrofitted with VFD control have performed in the 30 to 90 Hz envelope without incident.
the problems encountered are generally from trying to work outside the envelope.
heat is the major problem, the design of the fan is for 60Hz operation
when you go too slow, the fan can't move enough air across the under-excited motor
when you go to fast, the fan can't supply enough air across the over-excited motor
don't get too caught up in all the esoterics of VFD control,
it really is not that difficult once you get a few concepts down
they are not magic boxes
 
How would the torque be at 30Hz at 1 hp on a mill drill would it be enough to mill a 4 inch face mill
Just trying to give Dave an insight to update his mill
 
that would depend on DOC
if torque was a concern, you could possibly overspeed the motor in the lower speed belt position
 
Nigel123 said:
How would the torque be at 30Hz at 1 hp on a mill drill would it be enough to mill a 4 inch face mill
Just trying to give Dave an insight to update his mill
Click to expand...
i don't have a VFD on a vertical milling machine, but i have a few lathes that are VFD enhanced, (mainly for single to 3 phase conversion)
i use the frequency control mostly for threading operations, where major torque is not really a concern.
but usually i let the lathes work at 60Hz, and change gears if the work is heavier in nature, or i'm making too drastic of a frequency change.
one lathe i have has an inverter rated motor that i could take to over 200Hz, but i don't see the point for a lathe.

if torque is a concern for larger tooling, provision could be made to increase the size of the drive motor for higher torque and Hp values
instead of 1 hp got to 2 hp and worry not about torque or hp
 
So maybe going to more Hp on the motor would be to Dave's benefit
I don't know if it would it cost more to to go to more Hp but in the long run
to not change pulley speeds might be worth the cost
 
or he could just take lighter cuts
if he plans on production or making money, i'd recommend the larger Hp motor
for hobby and fun, go 1 hp and live with the minor limitations
 
Sorry was replying as you post came in
I agree I use a 2 Hp DC motor on my lathe love the capability of variable speed when threading close quarters and need slow speed
I always use the gearing then fine tune with the variable speed
The mill drill might need a little more power
 
I’d love to have the best of both worlds; low speed with torque and the ability to have higher speeds for aluminum.
I’m not doing any kind of production but
I would like to be able to take advantage of the rigidity that the 700 lbs of cast iron seem to be able to provide.

I have taken deep cuts with it and that’s not likely to be the norm but I also don’t want to be limited to 2 thou passes.

Seems like two options are open to me: 3ph and VFD or a DC motor and speed control. Or am I totally muddled?


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I think you'll be alright. My Bridgeport came with a 1hp and I've never felt like I was lacking torque. I do move the belts when I want the highest or lowest speed. Most of the time it is in the second to highest pulley speed. The VFD and the back gear give me enough range that I don't need to move the belts much.

It's the original motor from the 50s I think. It runs well with the VFD, but I don't let it try to run below 30hz. The fan probably doesn't move enough air that low, and it gets grumpy much below that. You can set min and max frequency in the settings, so it's easy to keep it from happening accidentally.
 
Thanks @ttabbal
I’ll keep my eyes open for a suitable 3ph motor


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