Variable frequency drive on K&T 2HL?

Hello everyone!

I've been recently considering swapping to a VFD on my -47 K&T 2HL.
Doing this I've been considering ramping the frequency up a bit to get more speed out of top gear, maybe up to 2000rpm if that's feasible, would be roughly 70hz instead of 50.
The entire vertical head has conical roller bearings so I'm sure that could handle more than current max of 1410rpm if I use less preload.
The knee itself is completely disconnected mechanically due to my CNC conversion so nothing can get damaged there from the speed increase.
What remains is the main spindle gearbox and whatever else might be connected inside the back/pillar.

As far as I can tell from the spare parts manual, everything in the back seem to be on bearings which I just assume should be able to do a bit higher speeds?

Any input on this would be greatly appreciated, don't want to do something stupid here.





Here's my thread about the machine itself.
https://www.practicalmachinist.com/vb/cincinnati-milacron-kearney-trecker-vn-usa-heavy-iron/k-t-2hl-universal-353668/

The gearing driving the head and the spiral bevels in the head are merely grease lubricated - as are the tapered roller bearings on the vertical spindle

Maybe if you attend to such things you will be okay

Might want to invest in some hearing protection

O the other hand, the 1940 Bulletin 720C lists 2400 as optional top end available at extra cost - but maybe they knew a WW was just around the corner and these things were going to be used up in no time at all

Another thought, if your still using the original electric motor it may very well not be happy at 70HZ.
I have seen more then one open/closed frame motor fail with a VFD.

dana gear said:

Another thought, if your still using the original electric motor it may very well not be happy at 70HZ.
I have seen more then one open/closed frame motor fail with a VFD.

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Do you mean the bearings don't handle well the extra speed? From the electrical point of view, I think the lower frequencies (especially in "vectorless mode") are the more demanding for the motor: higher currents and less cooling.

Paolo

johnoder said:

Might want to invest in some hearing protection

Click to expand...

And a full blast shield just in case?

johnoder said:

O the other hand, the 1940 Bulletin 720C lists 2400 as optional top end available at extra cost - but maybe they knew a WW was just around the corner and these things were going to be used up in no time at all

Click to expand...

Is this bulletin available online somewhere? I looked at vintagemachinery but couldn't find anything like that.

I was also under the impression that the motor "should" only take damage if run at too low frequency but I have no source on it.
Worst case scenario I have another 2.2kw motor I could swap in that's more modern.

Is this bulletin available online somewhere? I looked at vintagemachinery but couldn't find anything like that.

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Probably not - its an entry in their full line catalog from late thirties / early forties - one of two in my collection

I see 720B (1939) says the same - its more accessible as to catalog disassembly - I'll see if I can scan its 8 pages - such a pdf is easily emailed

Sent you an email via the forum

Paolo_MD said:

Do you mean the bearings don't handle well the extra speed? From the electrical point of view, I think the lower frequencies (especially in "vectorless mode") are the more demanding for the motor: higher currents and less cooling.

Paolo

Click to expand...

Here is some great information on older motors when used in conjunction with a VFD, not always a problem but certainly worth reading if your installing a VFD on a 50 year old open frame motor. I could type some of the problems encountered but these guys got it covered and I type slow. check out Electrical Construction & Maintenance (EC&M) Magazine, heading "mating new VFD drives to existing motors.

Figured I'd report back on the subject!

Been running it upwards of 1700rpm with no noticeable issues even for extended runs(2+h).
Just the regular VFD and old motor seems to work well, haven't noticed any downsides so far and the smooth startup is great!