Ok my boxford which i acquired recently started playing up big time. It had a Vfd fitted . I always questioned it. How ever the motor gave way . So i ve replaced the motor and drive bearings etc . The Vfd was very complicated and with out the programming info i changed that out too. The question I have is ,, if the Vfd drives the lathe ok now, do i use the Vfd at full and control the lathe with the speed settings via the belt system or .. leave it in one belt position and control the speed via the Vfd . I only have the Hz to measure the motor output accurately with out fitting a rpm to it . If i ran it at full motor speed i could change the belt positions to get various speeds . I can vary the motor speed via the Vfd but guess the rpm. Does any one have any ideas
- Thread starter Vexis
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Guineafowl
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My milling machine has a similar setup. Belt changes are a minor pain, so I leave the belt on a medium setting and change speed with the VFD. Depending on your motor/VFD, you can typically vary speed by 20-200% using the Hz control. I only move the belt for large thread tapping or very small milling cutters.
You can work out the speed using 50 Hz = indicated speed, then calculate pro rata. Consider fitting a cheap ebay rpm meter. About £20.
You can work out the speed using 50 Hz = indicated speed, then calculate pro rata. Consider fitting a cheap ebay rpm meter. About £20.
Just my view....I have a lathe with VFD and traditional gearbox. Mostly I have the VFD set to give 50Hz and use the gearbox. The indicated speeds are then correct and there's plenty of torque at low revs
On occasions I do adjust the VFD: perhaps extra slow for threading up to a shoulder, or when facing a large diameter object, increasing the speed as the diameter gets smaller.
Having said that the gearbox is probably an easier change than the belt on a Boxford.
As @Guineafowl says you can get a rev counter on ebay cheaply enough.
On occasions I do adjust the VFD: perhaps extra slow for threading up to a shoulder, or when facing a large diameter object, increasing the speed as the diameter gets smaller.
Having said that the gearbox is probably an easier change than the belt on a Boxford.
As @Guineafowl says you can get a rev counter on ebay cheaply enough.
hunter27
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My Boxford runs through a VFD and I do use its variable speed but if I feel it's bogging down on heavier cuts I alter the belt position one pully along to it's second fastest speed. I do have a rev counter fitted using a cheap Chinese counter but hand held rev counters also work well.
Before it all went Pop . I used it on the one belt setting ,i noticed ,( although i suspect the Vfd wasn't set up right as i had no programming info ) the motor was sluggish, got very hot and started blowing the trip switch too. Once i looked at the prob it has an old Turkish Gamaz 3 phase motor shoe horned in . The belts were goosed too as well as rough bearings . That got me thinking of the best way it should be run with out causing over heating probs again .should now run like a dream
Kram
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Swapping belts takes time. Choose the most suitable belt for what your doing and use the vfd for the speed control.
If you work out the ratios, you can put that on the vfd to get the real speed instead of hertz.
On my fastest belt mine is 1:1, while slowest speed is 3:1, so its quite easy for me to work the speeds in my head from the 1:1 speed displayed.
Sounds like the old motor was done. Motors dont generally have a problem with overheating even if ran very slow.
If you work out the ratios, you can put that on the vfd to get the real speed instead of hertz.
On my fastest belt mine is 1:1, while slowest speed is 3:1, so its quite easy for me to work the speeds in my head from the 1:1 speed displayed.
Sounds like the old motor was done. Motors dont generally have a problem with overheating even if ran very slow.
Changing speeds by swapping belts on Boxfords only takes seconds and fan cooled motors do overheat if run too slow for protracted periods. Depending on your VFD, you may also lose torque at low motor speed. If you have sufficient torque and don't run it for too long at very low revs, then use the VFD frequency control, otherwise use the belts.
I run my lathe with the vfd set at 50hz and use the gearbox for speed changes. This keeps the torque up for slower speed turning.
The mill I still change the belt settings occasionally but run the vfd as a speed control as well with increased max for smaller cutters.
The mill I still change the belt settings occasionally but run the vfd as a speed control as well with increased max for smaller cutters.
Pete.
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I set the speed control so that middle of the speed pot is 50hz, giving the correct pulley speed. Then I set the Min and Max speeds on the pot for the same percentage above and below then I get a decent spread of rpm adjustment above and below the standard belt speed without straying too far. Having the ability to tweak the rpm up and down a little can do wonders for your finish and chip breaking.
All going back together now bearing a lot quieter although I think I have a headstock problem with a gear or two noise, but the motor and VFD working good decided to set to 50HZ and change belts as its easy enough when needed and use VFD for quick change of speed, the motor runs cool ok and a RPM display lets me see what is happening as well .thanks for the help Lads all very useful, Looking forward to doing the head stock when I get a few hours to play with it again .Who knows what's in there ,Ill keep you informed. Thanks again
