Overspeed

[ozzie34231]

I bought a milling machine with a 3ph 3hp motor. I then bought a 3ph 3hp motor to build a RPC, which I built and it worked. But then I bought a 2.2kw vfd and that is just so cool.
So now I have this second motor and I'm pretty sure I'm going to fit it to my 14-40 lathe and drive it with a vfd. At this point I'm working on pulley ratio possibilities.
My question is:
How much can/should I over speed the motor. I think the nameplate RPM is 1725. What would be the effect of running it 3000 RPM. How much power would it produce; more, less? What about heat? Is that too much speed for the bearings?
I want a top spindle speed of 3000. If I can overspeed that much I can run a top gear/pulley system of 1:1. At 60 cycles, top gear would be 1725 and low gear about 100 RPM. And slower speeds would be achieved with lower cycles.
So another question is: How does the torque curve relate to reduced frequencies?
Thanks, Ozzie

[mike_Kilroy]

....
My question is:

1) How much can/should I over speed the motor. I think the nameplate RPM is 1725. What would be the effect of running it 3000 RPM.

2) How much power would it produce; more, less?

3) What about heat?

4) Is that too much speed for the bearings?

5) At 60 cycles, top gear would be 1725 and low gear about 100 RPM. And slower speeds would be achieved with lower cycles.

6) How does the torque curve relate to reduced frequencies?
Thanks, Ozzie

Ozzie, I think it is great that at 73 yrs old you are doing this stuff!'!

But your "question' is really 6... so I numbered them to address each individually.....

1) 99% of 1725rpm motors can run 3000rpm a-ok - do it!

2) no more, no less: exactly the same. 3hp motor will produce 3 hp from 1725 to 3000rpm.

3) heat will be the same from 1725 to 3000rpm.

4) nope.

5) I dont understand ur use of the word gear..... sorry. see #6 tho.

6) torque produced will be 9#-ft from some low speed like 300rpm upto 1725rpm. then torque will go down linear as speed goes up to 3000rpm for constant hp.

great questions Ozzie!

[ozzie34231]

Many thanks Mike.
The gear thing relates to it being a gear head lathe. There are nine gear ratios.
The lathe originally came with a 2HP 1ph 220V motor. I've been big on using DC motors with controllers. I have a 3 in 1 Shoptask with two 1 HP DC motors and my drill presses also use DC.
The 14-40 has a 1 1/2 HP dc now and I own a 2HP that I was thinking about using. The DC controllers give me almost instant reversing and a wide range of speed control. I can do tapping with both the lathe and drill press.

After mounting the VFD on the new, (to me), milling machine, I'm very impressed. Setup took me forever but I now have it working to my satisfaction, with one small exception, I have yet to dope out of the Chinglish instructions. If I slow the spindle too quickly the VFD faults. I can reverse it without problem, but slowing is. I need to find the deceleration setting I guess.
So with your good advice, I'll use the 3 HP 3ph on the lathe at about its present overall 1 to 1 drive ratio.

Now perhaps you might give me your thoughts on overspeeding the milling machine. You've already told me there's no problem with the motor. But, what about the rest of the mechanism?
The machine has a variable pulley belt system and originally topped out at 3800 RPM. The belt is new. The quill looks huge to me, over 4 1/4" diameter with a 6" travel, #40 taper. So I imagine the bearings in there are big.
I can't find out much about it, but I'm told it was built in Japan in the early seventies for a NY company that added electronics to make it CNC. Somewhere along the way someone stripped it and converted to manual operation. I'm converting it back to CNC. After 40 years its ballscrews still have no backlash that I can measure.
I tell you all this extra stuff just in case it might help you judge the condition and quality of the parts.
Thanks for your help,
Ozzie

[mike_Kilroy]

great ozzie. i am not qualified to comment on the machine mechanics, sorry. hopefully others who know and love this type machine will reply!

[UUU]

The motor is likely OK - the casing and bearings are probably the same as a 2-pole equivalent rated at twice the RPM of this one.

Many geared-head lathes were available in a double-speed variant - so the normal one would have 40 to 1500 speeds, but there was an 80 to 3000 version - e.g. Harrison M250. I suppose (but don't know for sure) that this was achived by fitting a 2-pole motor. See also one like the Colchester Bantam where the standard model has a two-speed motor so would offer two ranges. I'm trying to put forward a case here that the lathe bearings and gearbox are also likely to be OK at the speeds proposed.

Beware the chuck. Big lump of cast iron rotating at 3000? Interesting to know if the manufaturer rates this component for that speed. I'm expecting OK, but I wouldn't want to go any more than that.

[ozzie34231]

Thanks for your reply.
Yes the lathe will only be run at high speeds using an er40 or c5 collets, and I have run it at those speeds with its current DC motor.
My latest question was probably not framed well, but it concerns the advisability of running my milling machine at spindle speeds higher than its original 3800 RPM as described above. Concerns are spindle bearings, variable speed pulleys and belt.
Ozzie

[UUU]

Don't know how I kept thinking of lathes - sorry!

Sounds like your one-to-one is the way to go. It should give you a reliable 3000. If your motor had a 2-pole version running at 3450 then I'd go for that as your upper limit.