Southbend 13”-5’ with a VFD

Hello, I recently installed a VFD to my 3 phase south bend lathe… it works great, extremely quiet, etc…
My question is of such nature.
With the VFD I’m using (teco Westinghouse 1hp 115V single phase L510-101-H1-U ) I’m able to adjust speeds of lathe with the VFD from O-60 as default setting, right now I’m running speed #25… AS well I have the speeds on the lathe with 4 belt positions, back gears, etc…
This is a 1hp GE original motor and this lathe although from 1950 has/show minimum usage and well taken care of…
Question- what are the common or a decent recommendation for the VFD speed to be set at? Currently it’s on 25… is this to low? Seems like lathe in 3rd position from left seems ok in speed… Is it a matter of purchasing a rpm indicator?
The answer is prolly on this site, but wow there is a lot on this site and I didn’t see anything online about VFD set speed per lathe?
I’m really like to just leave the belt position on lathe alone and use a few speeds on the VFD by taking speeds on key pad up/down, or setting VFD at 1 speed that puts the 4 belt positions when changed in proper rpm range in which lathe was intended for.
Thanks in advance, pastor Joseph Hart.

Just my opinion, set vfd for 60hz and change belt position as needed, maybe tweak speed as needed with the vfd. Speed at the motor gives you torque thru the speed reduction of the pulleys. Changing the belts is not that hard, seems lazy to just turn a knob, doesn't the bible say something about sloth

Cone pulley selection should be the primary mode of speed control. Keeping the motor at rated speed optimizes it's performance and cooling.

TEFC/ODP motor... loaded to 100% FLA... at 20% of rated RPM... with no auxiliary blower? Not a great combination, even if it *is* thermally protected. (A lot of these old machines were wired up without any thermal overload protection to speak of.)

Use the VFD only for minor speed adjustments to fill in the gaps between step pulleys - e.g. for alleviating tool chatter/resonance, etc.

You can change pulleys very easily on the 13 - it takes about 7 seconds with practice. Don't even need to open the lower door. Just release the tension, open the headstock cover, shift the belt over, close the cover, re-tension and away you go. It's a very fluid operation, like most things on these lathes. (Except for the lantern tool post, lol.)

Yes it does. Don’t work. Don’t eat , but wisdom is the principle thing, get wisdom and get understanding, working smarter leads to more wisdom!
And I agree, simple change. And will take advice and set at 60. Thank you

I have a Heavy 10 with a VFD and as mentioned above run it at ~60hz most of the time and shift the belts when needed. I set the lower frequency limit at 30hz and upper limit at 75hz. I tweak the speed for chip formation and chatter mostly. I haven’t run in to overheating problems yet but I also don’t push it really hard either.

I have found that single point threading at the slowest belt position and 30hz without back gear is really nice without all the back gear noise.

I have read somewhere that there is a minimum rpm required to maintain the stable oil film in the spindle bearings. I can’t find the reference and it probably depends on lots of factors but I wouldn’t go much slower than the slowest back gear speed for an extended period of time.

Hope this helps.

Ben

Just a Sparky said:

Cone pulley selection should be the primary mode of speed control. Keeping the motor at rated speed optimizes it's performance and cooling.

TEFC/ODP motor... loaded to 100% FLA... at 20% of rated RPM... with no auxiliary blower? Not a great combination, even if it *is* thermally protected. (A lot of these old machines were wired up without any thermal overload protection to speak of.)

Use the VFD only for minor speed adjustments to fill in the gaps between step pulleys - e.g. for alleviating tool chatter/resonance, etc.

You can change pulleys very easily on the 13 - it takes about 7 seconds with practice. Don't even need to open the lower door. Just release the tension, open the headstock cover, shift the belt over, close the cover, re-tension and away you go. It's a very fluid operation, like most things on these lathes. (Except for the lantern tool post, lol.)

Click to expand...

Don't totally agree with that.

Your older GE motor may be different (assume its a ODP enclosure?), but modern decent TEFC or ODP motors have a typical speed rating of 4:1 (run at 25% speed) at full load and still maintain rated heat rise. Some may hit class F heat rise (105C rise by resistance @1.0 SF) while others may hit B rise (80 deg C rise by resistance @1.0 SF). But this assumes a continuous use. That just does not happen on our SB lathes.

IEEE841 is a process industry motor. I believe that in the latest version it will allow class F rise at 4:1 speed range - this version is not yet released but we had a lot of discussion about what to allow. Some users still limit to class B rise at 4:1 but that sometimes means a more robust motor and sometimes cannot be done in the same frame size.

On my 16" SB, I have a 20 year old 3hp TEFC motor with a WEG VFD with dynamic braking. I leave the belt on position 2 out of 4 (second fastest speed). I never change it. With the sensorless vector mode, the motor has great speed and torque control even at low speeds. I overspeed the motor some to make up for the lower pulley setting and full speed gives me rated lathe rpm due to the slight overspeed. I don't remember where I set my minimum speed, but even at minimum speed I get pretty much full motor torque and very good speed control.

The other day I used a die to thread 3/8 mild steel rod. It did not even blink and did not have to engage the back gear. Ran it at minimum speed.

Bottom line you have a low chance of ever damaging the motor due to heat and the VFD is made to vary speed - use it as intended and vary the speed at will and only change the belt position if the lathe tells you it is not happy. You have a much better chance of frying the windings due to VFD voltage spikes than overheating the motor in my opinion. If you ever get into low rpm long (sustained) hard cuts then I would probably change pulley position, but not for normal use.

I'm with Mark ^ - use the spindle pulley to set the speed range that you'll be working in, then use the VFD to vary speed within that range. Seems a bit silly to have the ability to vary speed by task or cut and not use it.

You can get a cheap hall effect tach for $10-15 to measure spindle rpm, which I find pretty handy, but after a while you'll get used to where you set the dial for different materials/ diameters/ types of cut. The big plus with variable speed is if you find you have the spindle running too fast (chatter) or too slow (falling asleep) you can easily tweak it while the lathe is running to find the sweet spot.

Thank you for replying and comments. I really appreciate them.
God bless.

Maybe I'm too late to jump in an comment on this. I have the 13" lathe (1975 vintage) also with a 3 phase motor, but I think mine is 2 hp. I also have the Westinghouse TECO VFD. I have used the lathe with this VFD for about 3 years now. I have the VFD set up to run up to 100 Hz, so I'm going beyond the normal max RPM for the motor at anything above 60. As the two prior posters do, I typically have the belt set on one of the two inner steps (I have 4 steps on my pulleys) and set my final speed with the VFD. I will start my cut and then I'll vary the speed using the little knob. Often times adjusting the speed will clean up some chatter, and also to adjust the color of the chips if I'm cutting steel. I'm usually cutting with an HSS cutter, so I dial in an amber color. If I'm cutting aluminum, I'll see how the cut is going and often crank up the Hz to 100. I am not a professional machinist, just somebody that is usually making a part to fix something.