VFD tuning for a Marathon motor

@Bob, I just got done installing Angular Contact Bearings in the spindle that should be good for 7k rpm. At this point, due to the gear ratio, I think if I used a higher frequency I'd lose too much torque and don't really need more rpm. If I need that sort of rpm, I'll probably get a 20k rpm high speed spindle to attach to the side of the head of my mill. In fact, that is something I thought to do someday.
My concern was not about the spindle bearings or the motor, which I assume your researched to be adequate for the speeds you intend. Beyond that, there may be other components of the drive system that are not up to the speed increase. For instance, a Bridgeport variable speed pulley system. Or something else... We don't know what mill you have...
 
My concern was not about the spindle bearings or the motor, which I assume your researched to be adequate for the speeds you intend. Beyond that, there may be other components of the drive system that are not up to the speed increase. For instance, a Bridgeport variable speed pulley system. Or something else... We don't know what mill you have...

Sorry Bob, after you asked I put my mill info in my signature and forgot to mention it. It's a Precision Mathews 1100+ pound "bench top" 3 axis metal CNC
Mill. Model# : PM -940 CNC . I've removed the gearbox and replaced it with a pulley and belt at at 2:1 ratio.

Jake
 
Sorry Bob, after you asked I put my mill info in my signature and forgot to mention it. It's a Precision Mathews 1100+ pound "bench top" 3 axis metal CNC
Mill. Model# : PM -940 CNC . I've removed the gearbox and replaced it with a pulley and belt at at 2:1 ratio.

Jake
Sorry I missed your signature change. It sounds like you are only changing speeds with the VFD and now have no additional drive parts besides the two pulleys, the motor, and the spindle. If so, you should be fine, at least at the high speed end. At really low speeds you may not have enough torque and cooling for heavy work, or have you considered that?
 
Sorry I missed your signature change. It sounds like you are only changing speeds with the VFD and now have no additional drive parts besides the two pulleys, the motor, and the spindle. If so, you should be fine, at least at the high speed end. At really low speeds you may not have enough torque and cooling for heavy work, or have you considered that?

Yes, at least initially I intend to adjust the VFD frequency when I need more torque, and down the road I intend to create a two pulley gear reduction setup for the ultra low rpm stuff. Right now I am basically just getting the mill functional and optimize it as I go. I do think about the possibility that I'll lack enough torque but have yet to mill enough to know if it's ok for my needs. It's been an "experience" just getting linuxcnc working and getting accustomed to the interface and new hardware. Baby steps :)

Cheers,

Jake
 
Please see the attached basic parameter changes. The upper frequency is set by parameter 01.00. The Fbase is the base frequency of the motor or 60Hz, the mid-point I would leave at the factory default, this is not the half way point in the frequency range. Often two parameters will be tied together, so something like the minimum output 01.05 needs to match the motor minimum output 01.28. The motor type and load need to be entered into the MOTOR 1 parameters, the default poles is 4 for a 1750 RPM motor. The default PWM frequency 02.03 is 8kHz, if you have a lot of motor whine this can be set to 12kHz. There are a number of other parameters that may need adjustment depending on the control inputs and to do some tweaking.
View attachment 231054

I just tried those settings. It worked a charm ! I can't say for sure, but I think torque may have increased, while also doubling the rpm ! Can't thank you enough.

( I put some drag on the spindle at 500 rpm and it didn't seem to slow much at all. I won't tell you how I did it, as my mother would not approve :) ).
It may have to do with some of the settings getting bumped from 50 to 60hz that you pointed out.

I also changed the PWM from 8k to 12k. This proved to reduce the motor noise. Getting closer to my goal of a silent mill ... lol :) I believe sometimes increasing the PWM can increase motor efficiency and possibly even torque ( although I previously equated lower PWM frequency with an increase in torque. A friend explained it has to do with matching the correct PWM with the inductance / windings.

I think I'll use this Delta VFD for a while before switching to the other VFD. Its working and its always nice to be able to compare stuff.

Cheers,

Jake
 
The limiting factors on the maximum speed assuming the rotor is balanced and the bearings are capable of higher speeds. Is the internal fan in the motor are how much torque you need at these higher speeds and the surface speed limits of the belt pulleys/ gears.

the motor is a constant torque device up to its rated base speed (4pole /1800rpm) and a constant HP machine past its rated base speed. What this saying is that from minimum RPM to 1800 RPM a 1.5 Hp motor produces 54 inch pounds torque but at 2600 RPM it produces 27 inLbs Torque and at 5400 RPM 18 InLbs. The second issue is that the HP required to turn the internal fan is 8 times higher at 3600 RPM and 27 times higher at 5400 RPM. Somewhere between 3600 and 5400 the motor may stall out simply because the HP required the spin the fan has exceed the motors capability. This is based on the affinity laws which states that the work (HP) required to turn a fan increases by the cube of the speed change.

As for the Pulleys/gears they have Feet Per Minute (FPM) rating that if exceeded they will fly apart.

The main difference between the various drive architectures (Volts/Hz, Sensor less Vector, Flux Vector) is how well they can produce torque at very low speeds, and how well they hold speed accuracy. Also with Flux Vector you will the ability to control Torque.

So set the drive up as if your max speed is 1800 RPM/60Hz. If the drive has an auto-tuning feature auto tune the drive. This is usually found in the SVC and FV drives. Then set the max Hz to say 120 Hz and use the machine. if it appears you have enough torque then up the speed until the machine just starts to slow down and you will be at the drive/motor maximum capability.

The Delta drive is a very good drive. several of what you would think of as the major drive manufacturers are rebranding the Delta drive. The Marathon MAX Plus motor is a top notch motor and is only exceeded by the Black Max and the Blue Max motors . you have some good stuff there.

For what it's worth I have designed, applied and sold drives for over 45 years and I do not have an inverter on my lathe I prefer using the belt pulleys because they are torque multipliers and what you need to hog out metal is torque, high speed is for polishing.
 
The limiting factors on the maximum speed assuming the rotor is balanced and the bearings are capable of higher speeds. Is the internal fan in the motor are how much torque you need at these higher speeds and the surface speed limits of the belt pulleys/ gears.

the motor is a constant torque device up to its rated base speed (4pole /1800rpm) and a constant HP machine past its rated base speed. What this saying is that from minimum RPM to 1800 RPM a 1.5 Hp motor produces 54 inch pounds torque but at 2600 RPM it produces 27 inLbs Torque and at 5400 RPM 18 InLbs. The second issue is that the HP required to turn the internal fan is 8 times higher at 3600 RPM and 27 times higher at 5400 RPM. Somewhere between 3600 and 5400 the motor may stall out simply because the HP required the spin the fan has exceed the motors capability. This is based on the affinity laws which states that the work (HP) required to turn a fan increases by the cube of the speed change.

As for the Pulleys/gears they have Feet Per Minute (FPM) rating that if exceeded they will fly apart.

The main difference between the various drive architectures (Volts/Hz, Sensor less Vector, Flux Vector) is how well they can produce torque at very low speeds, and how well they hold speed accuracy. Also with Flux Vector you will the ability to control Torque.

So set the drive up as if your max speed is 1800 RPM/60Hz. If the drive has an auto-tuning feature auto tune the drive. This is usually found in the SVC and FV drives. Then set the max Hz to say 120 Hz and use the machine. if it appears you have enough torque then up the speed until the machine just starts to slow down and you will be at the drive/motor maximum capability.

The Delta drive is a very good drive. several of what you would think of as the major drive manufacturers are rebranding the Delta drive. The Marathon MAX Plus motor is a top notch motor and is only exceeded by the Black Max and the Blue Max motors . you have some good stuff there.

For what it's worth I have designed, applied and sold drives for over 45 years and I do not have an inverter on my lathe I prefer using the belt pulleys because they are torque multipliers and what you need to hog out metal is torque, high speed is for polishing.

Hi Jim, somehow I missed your post way back when. Thank you for the info / knowledge !

Jake


Sent from my iPhone using Tapatalk
 
Please see the attached basic parameter changes. The upper frequency is set by parameter 01.00. The Fbase is the base frequency of the motor or 60Hz, the mid-point I would leave at the factory default, this is not the half way point in the frequency range. Often two parameters will be tied together, so something like the minimum output 01.05 needs to match the motor minimum output 01.28. The motor type and load need to be entered into the MOTOR 1 parameters, the default poles is 4 for a 1750 RPM motor. The default PWM frequency 02.03 is 8kHz, if you have a lot of motor whine this can be set to 12kHz. There are a number of other parameters that may need adjustment depending on the control inputs and to do some tweaking.
View attachment 231054

MKSJ helped me quite a bit with these settings for my Delta VFD. So I'm greatful, its served me very well!

And Jim, thanks for the thorough explanation! It has helped greatly too.

Now, I'm just getting around to rigid tapping ( adding a spindle encoder tonight and have a brake resistor to install in this Delta VFD.) Can you suggest what kind of Decelleration parameters I should be using with the brake resistor ? I know there are a fair number of variables but I thought I'd just ask to get some guidance before I trial and error it too much :)

Also, I'm wondering how slow I can safely use this motor at low rpm, specifically for tapping small taps. Maybe because its an inverter motor its fine at ultra low rpm too ? Perhaps I'm worrying about something that I ultimately will only do once and bump up the RPM soon after the first tries at rigid tapping ?

Thanks,

Jake
 
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I don't have rigid tapping capabilities but I have power tapped using a tension/compression tap holder. I tapped about 45 1/4-20 holes at 450 rpm. My decel was set at .5 seconds with a .5 second dwell. The speed range I was in has a low of 380 rpm and a high of 1375. As long as the motor doesn't get too hot to the touch you should be OK. If it gets hot set up a temporary fan.
 
I don't have rigid tapping capabilities but I have power tapped using a tension/compression tap holder. I tapped about 45 1/4-20 holes at 450 rpm. My decel was set at .5 seconds with a .5 second dwell. The speed range I was in has a low of 380 rpm and a high of 1375. As long as the motor doesn't get too hot to the touch you should be OK. If it gets hot set up a temporary fan.

Great, I'll give that a try. I am also using a tension/compression tap holder ( Tormach ) but figure its best to treat it like a rigid tapping operation.

Thanks !
 
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