Anyone ever go to Direct drive on a KM3 ?

[Rich Carlstedt]

Most all of my work is in the 1200 to 3000 RPM range.
While I like my Hurco, the noise and vibration ( at times) from the manual variable belt speed drive can be agrivating.
I use a VFD for spindle speed control most of the time .
If I removed the varispeed and went direct drive of the spindle to the motor, does it work ?
Am I asking for trouble.
Maybe I should put in a regular V bely/sheeve setup ?
I imagine my bushings are getting worn and iff I have to tear it down, maybe I can improve on it ?

Thanks for any comments
Rich

[skullworks]

If you could get the replacement pulleys with belt that would fit...

The conversions I have seen swap in a 5hp Inverter duty motor and VFD and can sometimes give you from 10% speed to 666% (6hz to 400Hz) at the motor and offer a higher top speed (not full torque) like maybe 5000rpm spindle.

A normal KM3 does not have a spindle tach so it just relies on the operator to set the proper speed when prompted.

I have the KM3P which does have a speed adjusting motor and a tach and it gets the spindle speed very close.

Ideally there would be a way to bypass the voltec card and send speed and direction directly to the VFD but that is a good ways away yet, if ever.

Were I to convert to EMC2 I would say adamantly yes there would be a direct belt drive with fully programmable spindle (rigid tap ability).

As is, I don't know far you could push the OEM motor with a VFD. You might be able to do 50%-120% just de-rate the motor power as you get away from nominal use.

[Rich Carlstedt]

Wow, I had no idea that a VFD Motor could run that high---very interesting.
I will keep an eye out for one.
When I replaced my spindle bearings at 15 K hours, I checked their rating and they have a 4 K max RPM top end, so it explains why Hurco put the 3 to 4 K numbers in red on my machine.
My VFD has a built in convertor that I can program for RPM.
Right now, It is set so that when my varispeed is at 1700 RPM(ie) the VFD reads 1700 and when I cut the VFD in Half ( to 30 CPS) it reads 850 .
So if I use a set pulley ratio , that will work too.
I would like to eliminate the pulleys entirely (more HP !) but that means
some kind of linear coupling ? and a new mounting on the head.

Thanks for the thoughts Skull
FYI I have run the Hurco Spindle Motor at 100 CPS, which means it was running about 3,000 and it seemed to handle it OK..but I prefer to do no more than 90 which is 50 % over factory speed

Rich

[skullworks]

Running fixed speed motors outside there spec'd ratings can be bad for some types.

Big issue is trying to use full torque at less than 50% rated rpm can cause rapid heat buildup in the windings. The fans on (or inside) are not turning the rated speed so airflow is below normal. Another issue is motor braking. The OEM setup would cut power to the motor and let it coast down a bit before applying the pneumatic brake. VFD's try to electrically brake the motor which is another additional source of rapid winding heat buildup. This is why the conversions which run at fixed ratio pulley sets using the VFD to control speed vrs gearing usually replace the OEM sized motors with larger 4-5Hp motors running de-rated so as to have more thermal capacity.

Inverter duty motors are built to cope with these issues. I was looking at a 1725 RPM motor for a mini lathe.

This BALDOR INVERTER DUTY MOTOR (on ebay) is plated as able to be over speed balanced to 6000rpm. - I post this just as an example.

[Rich Carlstedt]

Skull
You have provided just the information I needed
Thanks for the explaination on braking. I now understand some of the factors missing in my thoughts, and thanks for the link. I will check it out.
Wouldn't hurt to have an auxillary fan on the motor.
I would intend to keep backgears ( 6:1~) for very low speed work
Rich