1HP Bridgeport, low power using VFD for RPM

Janderso

Jeff Anderson
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Maybe this is a dumb question but here it is.
Using the BP over the weekend, had a 3/4 end mill, it had low power where I could have easily stopped the motor. Took light cuts and got the job done.
Should I be changing the belt ratio for more torque, slower speed vs. using the VFD in a case like this?
Thank you for your advice.
 
I don't know a lot about vfd's so someone who does is sure to correct me .
I think slow speed torque depends a lot on how your vfd is set up and the motor it's self .
But if it's set up right and your running the motor slow enough to stall yes you should be changing the belt to a lower ratio

I have a 1hp inverter rated motor on my lathe with a Hitachi wj vid
If I set the belt for 750 rpm spindle speed @ 60 hertz I can slow the motor down to 5 hertz and make the belt slip before the motor even thinks about stalling
 
The motor will not have much torque at low RPM's as you experienced.

MrPete222 has videos on refurbishing a Pull Gear to achieve lower speed with good torque. He removed his VFD from this drill press due to not having sufficient torque as low Hz/RPM.

You will get better torque is you change belts so that the VFD is running the motor as higher RPM's.

FYI, an Australian fellow was inspired by MrPete to make his own Pull Gear. Several videos. I found these very interesting. Part 1.

Mark Presling Pull Gear part 1 video
 
A standard Volts/Hertz VFD will provide constant torque down to roughly 1/2 of the nameplate speed. As you use fancier VFDs with Field Oriented Control (FOC) or Flux Vector Control (FVC) you can get constant torque down to 1/100 or even 1/1000th of the nameplate speed.

If you didn't pay top dollar for your VFD it probably will not have these control strategies. I would change pulleys for increased torque at low speed.
 
My VFD is a Teco, Fluxmaster FM50.
I have no idea if it is a good VFD.
I will try the pulley method and see what difference it makes.
To be honest, I looked at the programming of that thing and I just don't know enough about it to make any changes with confidence.
I am concerned I will screw it up.
 
For my lathe I tend towards using the step pulleys for spindle speed changes and use the vfd to fine tune the actual speed .
Biggest benefit is being able to take a much better guess to actual speed and material removal rates without having a tachometer.

And I thinks it's also a good idea to keep the motor speed fast enough for the cooling fan to be effective.
 
Unless you are using a sensorless vector VFD, the torque will drop off as the rpm is reduced. In this case changing the belts is the way to go. Using low speed (back gear) would be the best way to run a 3/4 endmill.
 
Is the motor wired correctly to the VFD, I had the exact same problem.

I did verify the wiring is correct.
The motor speed regarding cooling benefits makes sense.
I have never moved the belt.
Determining speeds using the belt is a bit of a challenge as I do not know the step RPM rates.
I imagine there is a diagram in the manual?
1971- J Head, step pulley 1 HP.
 
Here are the speeds. The low speeds are in back gear.
1534358679766.png
 
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