VFD buying advice?? mill needs to spin!!

Discussion on all milling machines vertical & horizontal, including but not limited to Bridgeports, Hardinge, South Bend, Clausing, Van Norman, including imports.

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VFD buying advice?? mill needs to spin!!

Post by belterskelter » Fri Nov 01, 2019 1:32 am

hey folks still looking to get my rockwell 21-100 running

VFDs look like the jam but which one?? prices are all over the map locally, and on line better but still not sure what to get.

the motor info plate is on the link below

I have 110 household power and also 220

Ilike the availability of slowing things down and speeding things up so I am not changing belts all the time and it looks like the previous owner modded it so it was slower any way

so ya any links or advice would be sweet


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Bill Shields
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Re: VFD buying advice?? mill needs to spin!!

Post by Bill Shields » Fri Nov 01, 2019 7:02 am

do not think for a minute that the vfd is going to replace the need to change bents.

VERY FEW old motors can be run very slowly and expected to output the torque of a 'normal spinning' motor running through gears or belts.

General rule with older motors is +/- 25% of nameplate speed is generally safe...leaning more toward the +25

I have had good luck with TECO - westinghouse / Toshiba / Allen Bradley / Siemens / ABB and GE units. Yes, you $$$ a bit more but you get what you pay for. Teco sells a unit for a 1 hp motor for a bit under $200

Irrespective, I would put the original motor pulley back on the unit (even though it will cost you some $$$)
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Re: VFD buying advice?? mill needs to spin!!

Post by Les_S » Fri Nov 01, 2019 11:12 am

Totally agree with Bill's advice.
You don't need the original pulley to run it the first time but I would get a replacement as soon as possible.
You will find that you will have much less torque if you are running your motor at very slow speed with a VFD and your motor may very well run hot because the fan isn't moving fast enough to cool the motor.
Change your initial speed with the belt to get you in the ball park and the VFD speed control is then very useful in finding the "sweet spot" if you have a little chatter.
I am using a Hitachi WJ200 series VFD on my lathe and it has been bullet proof for about 6 or 7 years now.

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Re: VFD buying advice?? mill needs to spin!!

Post by SteveHGraham » Fri Nov 01, 2019 10:51 pm

When I researched this, I found a long Practical Machinist thread which basically said speeding quality motors up--I mean like 400 Hz--was not a problem. I run my 3-HP belt grinder at over 120 Hz, and it seems quite happy.

You can always put an external fan on a motor if you run it slow.

It won't do away completely with changing belts, but it will let you do it less often. You can always use a bigger motor to help make up for lost torque.

A lot of guys are happy with cheap Chinese VFD's. You might get info on CNCZone.
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Re: VFD buying advice?? mill needs to spin!!

Post by armscor 1 » Mon Nov 04, 2019 4:47 pm

Very happy with my cheap Chinese VFD's, 2 on my Lathes, 1 on my DP, 1 on my mill and 1 on my compressor, glad to get rid of the power sucking noisy single phase motors.

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