[Noteworthy] VFD & BP Series 1 speed adjustment

[AxeMaker]

Hello,

Not sure if this goes into this forum or the BP forum but here goes...

Okay my BP Series 1 has a 3PH motor which was wired for 460v 3PH. I installed a VFD to drop it down to 1PH and I re-wired the motor to 220v. It runs, no problems there...

I am trying to figure out the best way to word this so if it doesn't make sense I will try again... but here goes.

If the BP is physically set to 300 RPM do you run into any physical problems in the gearing/belts if the VFD runs the motor at, let's say... 3000RPM even though the BP is set to 300RPM?

Seems like in some speed change instances you could run into a overspeed problem. Does that make sense or am I not totally understanding the BP operation?

I am thinking that if the speed is set using the BP speed adjustments there are gears/belts that turn within certain RPM specs and if you introduce an external device to make the motor run faster even though the gearing/belts are set to not go fast you run into some kind of RPM overspeed.

Am I just overthinking this?

 

[cathead]

The main thing is not to over speed your motor by setting the VFD frequency maximum too high.
Stay within the motor speed ratings and you will do just fine. The gearing and or belts will take
care of themselves. What I did was set my belts (step pulley machine)to run at about 800 rpm
and that way you can control the spindle speed from slow to fast with the VFD frequency. If I
ever need more or less speed, I can use a different pulley. I set it up over a year ago and so
far I have not had the need to change the pulleys. Also, when drilling large holes or using large cutters, the back gear gives me a whole new range of abilities. At 60 Hz, the back gear
is at 98 RPM so one can go as slow as needed for power tapping or up to about 500 RPM for another
whole range of speeds...

 

[Bob Korves]

I assume you have a multi step pulley speed change system on your lathe? If you think you can set the belt in one set of grooves on the step pulley, and then control the speed from zero to multiple thousand RPM's, you will be disappointed, and may break something. You can lower the spindle speed with the VFD, and the motor will turn nicely at low speeds, until you put a real load on it, then it will stall. You can increase the power output to the motor with many VFD's but then the motor can also burn out because of insufficient cooling. You can over speed the motor by setting the frequency higher than 60 HZ, which is not recommended for ordinary motors, and can also make them fail. Also, the bearings in the head may be destroyed by running them over speed. You really have to use it as a fine adjust. With ordinary motors, you might run it from, say 40-65 HZ and get some additional speed control without over stressing anything or losing much torque or cooling. Over speeding is not a real good idea, but it is tempting. A machine with a head made to handle the RPM and a vector motor can do it, but all the components are designed for the job. Hope this makes sense, perhaps someone smarter on this than I can chime in.

 

[AxeMaker]

I assume you have a multi step pulley speed change system on your lathe? If you think you can set the belt in one set of grooves on the step pulley, and then control the speed from zero to multiple thousand RPM's, you will be disappointed, and may break something. You can lower the spindle speed with the VFD, and the motor will turn nicely at low speeds, until you put a real load on it, then it will stall. You can increase the power output to the motor with many VFD's but then the motor can also burn out because of insufficient cooling. You can over speed the motor by setting the frequency higher than 60 HZ, which is not recommended for ordinary motors, and can also make them fail. Also, the bearings in the head may be destroyed by running them over speed. You really have to use it as a fine adjust. With ordinary motors, you might run it from, say 40-65 HZ and get some additional speed control without over stressing anything or losing much torque or cooling. Over speeding is not a real good idea, but it is tempting. A machine with a head made to handle the RPM and a vector motor can do it, but all the components are designed for the job. Hope this makes sense, perhaps someone smarter on this than I can chime in.

No I have a Bridgeport Series 1 Mill that has the speed adjustments on the front of the head. The VFD also has the ability to adjust speed.

 

[AxeMaker]

A 6" vise is overkill for a RF45 style mill. A 4" is more appropiate for that size mill & IMO 5" max. I have a 5" GMT vise on my PM45 & it's slightly too big. Not enough Y axis travel to make use of the 5" full capacity. Better to save your money rather than getting something too big & most importantly the weight. I take my vise of the table quite often, a 6" is still light enough for me to be carried by hand but I'm glad I have a 5". I also have a 4" vise as well. I prefer the 5" though.

But those GMT 6" Premium vises are pretty nice. I'd love to have one but don't need one on my current mill. But if you plan on upgrading to a full size knee mill in the future than the 6" will be perfect.


Here's what the 5" looks like on my mill.



I couldn't even complete this cut without my bellows & DRO scale getting in the way. Not enough Y travel & the 5" vise is not even maxed out.



Here's what a 6" vise looks like on another PM45 (gt40's)
View attachment 253544

 

[JimDawson]

I had a V/Hz VFD on my variable speed head, I ran it between 30 and 65 Hz. So no danger of over speeding the motor or pulleys. Had a speed range of about 30 to 4500 RPM depending on low or high range. The motor runs at a nominal 1800 RPM at 60Hz, if you are in low range at maximum RPM on the variable speed, the motor is still turning at 1800 rpm, so the spindle pulley is spinning at about 4200 RPM, but the spindle is geared down to about 525 RPM or so. The variable pulleys have a total range of about 7:1

A normal 1800 RPM motor should be safe at 3600 RPM, but with a variable speed head you don't need to run it that fast. 4200 rpm is fast enough for most work. And I wouldn't want to turn those big VS pulleys much faster than that.

If you need a high speed spindle, then your next project will be to hang a router motor off of the quill.

I hope this makes sense.

 

[AxeMaker]

I had a V/Hz VFD on my variable speed head, I ran it between 30 and 65 Hz. So no danger of over speeding the motor or pulleys. Had a speed range of about 30 to 4500 RPM depending on low or high range. The motor runs at a nominal 1800 RPM at 60Hz, if you are in low range at maximum RPM on the variable speed, the motor is still turning at 1800 rpm, so the spindle pulley is spinning at about 4200 RPM, but the spindle is geared down to about 525 RPM or so. The variable pulleys have a total range of about 7:1

A normal 1800 RPM motor should be safe at 3600 RPM, but with a variable speed head you don't need to run it that fast. 4200 rpm is fast enough for most work. And I wouldn't want to turn those big VS pulleys much faster than that.

If you need a high speed spindle, then your next project will be to hang a router motor off of the quill.

I hope this makes sense.

Yes it make perfect sense! May be not this particular thread, but this subject should be made into a sticky or added to an existing document as it relates to VFD/Bridgeport operation. It, for new owner/operators, would be very good information. Especially given the safety implications.

 

[Keith Foor]

Short story on a VFD.
you can NOT expect to park the variable belt drive on a machine in one setting and have full speed range control via the VFD.

Remember that a mechanical lowering of the spindle RPM via gearing will increase torque tremendously, decreasing RPM via a VFD does NOT increase torque on the spindle so parking a 3 inch shell mill in the spindle, setting the mill drive to 2000 RPM then turning the VFD down to 200 RPM is not going to work. The spindle will stall.

 

[AxeMaker]

Short story on a VFD.
you can NOT expect to park the variable belt drive on a machine in one setting and have full speed range control via the VFD.

Remember that a mechanical lowering of the spindle RPM via gearing will increase torque tremendously, decreasing RPM via a VFD does NOT increase torque on the spindle so parking a 3 inch shell mill in the spindle, setting the mill drive to 2000 RPM then turning the VFD down to 200 RPM is not going to work. The spindle will stall.

This is a perfect example of why I suggested this be a sticky. I have not seen most of the info people have posted here before.

Wouldn't it be best to just set the VFD at whatever hz and other parameters the motor is and plainly use it as a power supply, then just use the speed adjustment controls on the mill?

 

[Bob Korves]

(snip)Wouldn't it be best to just set the VFD at whatever hz and other parameters the motor is and plainly use it as a power supply, then just use the speed adjustment controls on the mill?

That would be safest for the machine and for the motor (and for the operator), and honors the manufacturer's intentions and instructions. Once you move outside those parameters, your become the test pilot...

Edit: And on your variable speed machine there is not much real reason to use the VFD for more than simply supplying three phase power.