[ddeaton]

I have a older Bridgeport, belt drive head. Excuse my terminolgy, I am more of a electrician than a machinist. I would like to replace the drive motor with a variable speed drive of maybe vfd with encoder feedback or low end servo drive to keep torque at all speeds. I havent taken the time to search this site yet as I have just found it. I am sure someone has done this. I am thinking of keeping the belt drive just to have the flexability. This is not CNC.
thanks in advance for any info, Danny

[lakeside53]

Just put a 2hp motor (from a varispeed BP) in a step belt model. I turned the old worn rotor shaft and balanced it (to ISO G6.3 stds for 4000rpm). The VFD is a Hitachi SJ200 VFD (sensorless vector). With a 35 ohm 500 watt braking resistor and DC injection, I can get 1 second stoping from 4000 rpm. In the second belt postion (1:1) I plan to use it from 800 to 4000, and use the back gear (low) for 30 to 800rpm. Torque? Not an issue that I can see...

[ddeaton]

thanks for the answer. I am going to do this, just wanted to hear from someone that has done it. I think I might adapt a black max 2 hp motor though and keep the rpm around 3300, unless I can find a motor you mentioned. Are they readily available? I just use this mill for misc general purpose stuff and gov jobs. I dont use it for production purposes. I think I have a Yaskawa V7 laying around that will work just fine.

[Mike Nash]

I'm wondering if there isn't more value in the old varispeed motors as trade-ins somewhere. A friend has been having real issues with his motor. He had the shaft (replaced/straightened/something) and has gone thru great misery replacing all kinds of things, including reworking the motor bearings and balance (again) and now the motor is back in the shop. It seems the diameter of the old varispeed motor is critical. The upper pulley was ever so barely a loose fit on the shaft and was causing enough vibration to shake the machine and screw up the motor, even with a new pulley. Hopefully they will get the shaft built up, turned back to the proper size and it will be okay. But I know you can get trade-in credit for the old motors if buying a rebuilt.

And yeah, this is sort of off topic. On topic, the V7 is a great little drive!

[ddeaton]

Mike, even if off topic, I accept any conversation about this. I want to use this mill more, as I am into gunsmithing now as a hobby. That is why I want to get it in shape to learn on. We have a full machine shop with one CNC mill, and several others, but my input to the group is machine control. I have only dabbled in CNC, with most my experience in offset printing presses. I upgrade drives and plcs all the time. This old mill is my personal, so I dont tear up the good stuff around the house! I am going to put a vfd on my drill press also.

[lakeside53]

I'm wondering if there isn't more value in the old varispeed motors as trade-ins somewhere. A friend has been having real issues with his motor. He had the shaft (replaced/straightened/something) and has gone thru great misery replacing all kinds of things, including reworking the motor bearings and balance (again) and now the motor is back in the shop. It seems the diameter of the old varispeed motor is critical. The upper pulley was ever so barely a loose fit on the shaft and was causing enough vibration to shake the machine and screw up the motor, even with a new pulley. Hopefully they will get the shaft built up, turned back to the proper size and it will be okay. But I know you can get trade-in credit for the old motors if buying a rebuilt.

And yeah, this is sort of off topic. On topic, the V7 is a great little drive!

Varispeed: You can get a new rotor/shaft for $300... A replacement shaft is about $140, but by the time you change it out and re-balance the rotor, you may as well just buy a new rotor. In my case, I had a J step belt head that needed a new motor, and a varispeed with a worn shaft (9 thou... clattered real bad..), so it was a real easy choice. And fun... (but a few hours...). I bought a used varispeed motor with a good shaft on ebay for about $200. If you do buy a used motor, have the seller mic the shaft, and stand behind it.

If you do intend to use a BP motor with a VFD at significantly higher rpm than designed, get it balanced for your highest target RPM. "Balance" at 1725 is not necessarily ok at 3600.

[ddeaton]

If you do intend to use a BP motor with a VFD at significantly higher rpm than designed, get it balanced for your highest target RPM. "Balance" at 1725 is not necessarily ok at 3600.

What is wrong with adapting a out of the box new cface motor?

[lakeside53]

What is wrong with adapting a out of the box new cface motor?

Nothing at all. I just happened to have a motor that was going to be junked... and I didn't need to adapt anything. The BP step pulley head needs a shaft a little longer than is commonly available, a 3/4 shaft, and you need to take into consideration the thickness of the adapter plate.

Even new though, a 1725 rpm motor may not be "in balance" at say 3600 or 4000 (assuming you intend to overspeed it on with a VFD).

[ddeaton]

Nothing at all. I just happened to have a motor that was going to be junked... and I didn't need to adapt anything. The BP step pulley head needs a shaft a little longer than is commonly available, a 3/4 shaft, and you need to take into consideration the thickness of the adapter plate.

Even new though, a 1725 rpm motor may not be "in balance" at say 3600 or 4000 (assuming you intend to overspeed it on with a VFD).

Thanks for the replies and tips. Always nice to think outloud. The Marathon black max is rated at 3400 from the box and I have it laying around also. With a .25" steel adaptor plate cutout for the motor cface I have about 1.125" of shaft to slide into the pulley. I think that is enough as I will be running the belt on the pulley close to the motor. Looks like plenty of support. I will post results if I live through this.

[lakeside53]

Thanks for the replies and tips. Always nice to think outloud. The Marathon black max is rated at 3400 from the box and I have it laying around also. With a .25" steel adaptor plate cutout for the motor cface I have about 1.125" of shaft to slide into the pulley. I think that is enough as I will be running the belt on the pulley close to the motor. Looks like plenty of support. I will post results if I live through this.

My pulley needed 2.5 shaft inches to get a complete fit... 3400? That sounds like 2 pole motor. If you use a VFD, it might be lacking in torque/HP low down. I like to use a 4 pole (1725) motor, over speed it for the high end, and stay above 800 (still 1 hp if my math is correct) on the low, but...
Of course, I can change the belt if I have to, but I'd actually like to get rid of of the BP pulleys and put a different single flat belt on.

With the larger inertial mass rotors (like mine), without a serious external braking resistor, the motor will turn into a generator, and vfd will trip out if you try to stop in in less then 5-10 seconds (my case).


Let us know how it all works for you.

[ddeaton]

My pulley needed 2.5 shaft inches to get a complete fit... 3400? That sounds like 2 pole motor. If you use a VFD, it might be lacking in torque/HP low down. I like to use a 4 pole (1725) motor, over speed it for the high end, and stay above 800 (still 1 hp if my math is correct) on the low, but...
Of course, I can change the belt if I have to, but I'd actually like to get rid of of the BP pulleys and put a different single flat belt on.

With the larger inertial mass rotors (like mine), without a serious external braking resistor, the motor will turn into a generator, and vfd will trip out if you try to stop in in less then 5-10 seconds (my case).


Let us know how it all works for you.

Yes, I am sorry, it is a 4 pole and I am overspeeding with the vfd. I will use a external braking resistor with the drive also. I will post a pic, we just about have the motor mounted.