RT, the speeds mentioned above (60-2000 and 50-1680 rpm) are not the speeds shown on the motors but on the gear boxes.
The ratio of the two lowest speeds 60:50 is 1.2 (same the speed increase as going from 50 to 60Hz) as is the ratio of the two highest speeds (well 1.1905)
Yes I get that BobL, but I was referring to the photos of the two motor plates, both indicating a motor frequency requirement of 60Hz, but one motor shows the RPM as 1360, and the other as 1405.
I can't see how on a line frequency of 60Hz, an ordinary induction motor will produce those RPMs. That is an awful lot of slip in the magnetic fields I would have thought for motors with a 60 Hz supply.
Good discussion boys, really appreciate the thoughts. I put the AT back together today and powered it up to check out the spindle bearings and such after my head stock rebuild. My Baldor VFD indicates RPM, voltage, freq. and current. I know it measures all the parameters but I don't think it measures RPM, rather it is a calculated value, as it indicated 1800RPM at 60Hz.
I think I will get out my optical tach tomorrow and paint a little liquid paper on the motor pulley and measure the actual RPM. I too was confused by the bizarre figures on the motor name plates, made no sense to me. Every motor I have encountered is either 1750 or 3500 RPM, which accounts for the slip mentioned.
I'll report my results tomorrow. I wish there were still people at Hercus who could tell us about these old motors.
Cheers all
PS the lathe spins up nicely and the headstock sounds good, although I think I still need to change out the Timkens at some point, not rumbley, just a little "roar" at 2000 RPM. I lubed them with ISO 46 hydraulic fluid, as that was the heaviest I had in stock. I think 68 is the correct weight based on my research.
I think that your Timken bearings are probably quite OK Kilohertz, the roar at 2000RPM most likely due to the straight cut spur gears, not bad bearings. Not many small lathes along the lines of your Hercus, would be too quiet at 2000 RPM. Then again I could be wrong, after all I'm a retired rigger and scaffolder, not a machinist, fitter or electrician!:UQuote:
Originally Posted by Kilohertz
As to the RPMs of the motor, I think that you'll find that 1800RPM might not be too far out if you were just running the lathe up with no load. Under those conditions I would expect that there would be minimal slip, so the actual speed should be close to the theoretical speed of 1800 RPM. The speeds of 1750 and 3500 RPM are the nominal speeds of 4 and 2 pole motors respectively when operating on a 60 hertz supply. The corresponding speeds when on a 50 Hertz supply are 1425 and 2850 RPM, plus or minus in both cases. Good to hear that you have your machines close to operational.
My guess is that whoever marked those info plates on the motors must have had a big night out the day before, you may have already mentioned it, but could they have been made at the same time as part of a large order? Most likely the motors would have been made at different times to the lathes, but it is strange how they seem to have messed up on them both:doh:
Thanks for the thoughts. When I powered up the lathe, the only thing turning was the spindle and the intermediate shaft (one with the 4 pulley cones at the back). I haven't connected all the spur gears for the gear box yet. And the noise is in sync with the spindle, not the back shaft. It's cool testing these things with the VFD, you can slow it right down to about 10 RPM and hear the noises in slo-mo. I put a screw driver to the bearings and listened, didn't sound bad, and when I had it all apart they sure felt good. I'm just going to to use it as is for now. I still have the other one to get to work on, the ATLH which I am looking forward to as well.
Agreed to the goofy motor data plate, must of been a bad day for that bloke. The lathes are 200 apart in s/n so probably not the same day. One is 19996 which is 1991 as I have the certificate for this one, the 18709, probably late 80's.
We have a 3 day weekend, snow on the ground now so the shop build has come to a halt, more time to work on the Hercuses.
Cheers
I went to the big city today about 2 hour drive and bought an optical tach so I can measure the actual RPM. Well cool info...with the VFD driving 240VAC at 60Hz, the motor RPM is 1775 and with the lathe set for max spindle speed, the spindle measured 2140 RPM. Mmmm, so much for the motor name plate accuracy.
I changed the spindle speeds to 740 as indicated on the plate, which actually produced 812 RPM, and set for 325 produced 374 RPM. This is on the AT machine which has the .55KW motor rated at 1405 RPM. Also the nameplate indicates 2.4A, the VFD indicates it's drawing 1.6A.
Just thought I would share that info.
I continued cleaning the saddle and cross slide, ran out of energy around 5 and will finish it tomorrow. So far very happy with the lathe, the ways although scarred, seem to have very little wear, and the saddle looks darn near perfect where it rides on the ways. I put all the end gears back on as well and tried it various speeds. I'll try to get the video off my phone and into something I can post here.
Cheers for now
I'm having a buggar of a time getting the video converted from my phone to something veiwable here, but I did manage to get a couple of audio recordings of the lathe at 2000 RPM and 325 RPM. Let me know what you think of the bearing noise. This is just the spindle, the end gears are not engaged.
Cheers
Ohhh I just remembered I have a drop box space, these are original phone video, some of your players may be able to play it.
https://www.dropbox.com/s/0bze2idfi5..._6034.MOV?dl=0
https://www.dropbox.com/s/tfn0w9smuf..._6036.MOV?dl=0
https://www.dropbox.com/s/s7owiuv6a6...%2052.mp3?dl=0
https://www.dropbox.com/s/f9tod52u0a...%2053.mp3?dl=0
Good to see it making sense at last.Quote:
Originally Posted by Kilohertz
The motor name plate current is usually for a single motor coil and for the motor delivering full power.Quote:
I changed the spindle speeds to 740 as indicated on the plate, which actually produced 812 RPM, and set for 325 produced 374 RPM. This is on the AT machine which has the .55KW motor rated at 1405 RPM. Also the nameplate indicates 2.4A, the VFD indicates it's drawing 1.6A.
240V x 2.4A x 1.73 (convert single coil current to full 3P) x Power factor (0.8) x Efficiency (0.7) = 558W
1.6A seems a bit high for a 0.55kW motor just turning a spindle but VFD currents are not always what they seem.
For example my Hercus VFD with a 750W motor just running the spindle shows 1.4A on the VFD, but a single phase ammeter on my breaker box shows it's only drawing 0.9A
The noise seems quite okay,I only heard it in both occasions with the change gears in use,with the train disengaged it may be different.
You may need to make a formal complaint to Steve Durdin about the inaccuracy of your spindle speed plate,never know your luck they might look into it for you, machine tool makers just can't be trusted.