PM 1340GT max spindle RPM with VFD

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Carcajou

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Hello, I am considering buying one of these lathes, but do a lot of small diameter collet work in plastics and soft metals. What would be a reasonable maximum spindle speed to expect with the stock 3ph motor and the Hitachi VFD many here have used? Thank you for all the detailed information provided here on this topic, I have read most of it, but could not find an explicit top speed, most seem more interested in low end for threading. I would also be open to swapping pulleys and giving up low end if that is a practical option.
 
Probably 2,000 RPM, beyond that you are risking problems with lubrication since it is not a pressurized system. Typically the maximum speed for splash lubrication in a lathe headstock would be in the 2200-2500 RPM range. Also be sure to use an ISO32 oil in the headstock and allow it to come too temperature if the ambient temperature is cold. A synthetic oil might be an option after breaking it in if working over a wide temperature range.
 
I was curious myself what was possible. My 1340 has a VFD with max output at 100Hz. I run a 1.9" small pulley on the motor, and the stock larger 5.5" pulley on the spindle drive, and in top gear at 100 Hz VFD output I get 2060 RPM. Assuming I turned the pulley around and made the spindle pulley the 3.5" side, that speed would increase to 3800 RPM or close to it. But like Mark said, the limit here is lubrication and bearings, not what's possible with the pulley drive train.
 
Mksj, are you aware of anything about this lathe that would limit it below the 2200-2500 range you mention? The pm1440gt spins to 2200 rpm stock and I believe the maximat v13 and Harrison m300 at 2500rpm were also splash lubricated though likely with better bearings. David’s theoretical 3800 sounds fairly terrifying but I am frequently north of 2500 on the HLVH at work in similar situations so even 2200 would be nice in intermittent use If that wasn’t foolish.
 
I, too, have the 1340 with VFD that MKSJ built for me and I flipped the pulleys. I run it with the slowest speed lever and only use the VFD to adjust speed. In the other lever positions it's just way too fast for my work, even in Delrin. I can't keep the feed rate slow enough to keep smooth finish if it's running that fast.
 
There are many factors that limit the upper speed range, I would be concerned about using the norton gearbox at high speed, you also have limitations of the internal rotating gears and bearings in the headstock. My ERL-1340 in the gear head (splash lube) version goes to 2500 RPM, and the factory VFD version is rated to 3000 RPM. But the factory VFD version only has a 2 speed head, vs. 8 speeds so a lot less rotating mass. With the 1340GT I do not foresee an issue of short periods with speeds on the in the 2000-2500 RPM range but not for extended time. You would need to use a high grade oil with good anti foaming properties, there are also issues of oil drag and shear at the higher speeds. I would monitor the bearing temperatures and make sure the machine is broken in before extending the upper end speed range. In the VFD builds with the stock motor, I often suggest flipping the motor pulley so you are running from the large motor pulley to the large headstock pulley, ~1.5:1 pulley ratio. This requires a slightly longer belt, I have seen both BX26 and BX27 used but varies by belt manufacturer. With the stock motor set pushing it to 100 Hz would be in the neighbor hood of 2000 RPM, 110 Hz would be 2200 RPM. Alternative is if you are primarily doing high speed work is to just run the belt position in the stock high speed belt setting which is close to a 1:1 drive ratio with a maximum motor speed of 80 Hz would give you 2,400 RPM.
 
Parshal, David, mksj, thank you for the detail and confidence check. It sounds like that setup would be great for my uses. 2000 rpm would be fine for the vast majority and for the small but critical portion in the Itty bitty diameters I would be just fine with swapping belts/pulleys and low duty cycle. Noted about break in, temps and oil selection. Thanks!
 
Carcajou, you didn’t talk about feed rate requirements, which might also be a consideration. FYI, the slowest carriage feed rate on the 1340 at 2,000 RPM is ~4” per minute using the Norton gearbox.
 
Thanks for the heads up, I would be ok hand feeding for the smaller parts at top speeds. Can’t have it all in a $5k new lathe. It doesn’t seem like there is a great new option for smaller capacity lathes in between toolroom lathes and China hobby lathes. Grizzly heavy 10, anything else I should consider? The extra capacity of the 1340 is appealing on the bigger end.
 
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