VFD Pulley Setup?

epanzella

epanzella

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The next item on my to do list is to install a VFD on my RF30 knock off mill. In the You tube videos I've watched on the subject the stepped pulleys were replaced with single pulleys. I don't really get this. I can understand that the idea of the VFD is to make belt changes unnecessary but the step pulley arrangement does increase the speed range available even with the VFD and as far as I can tell, doesn't do any harm. My mill currently has a speed range of 120 to 2500 rpm. Leaving the stock pulleys along with the VFD I could easily get 30 to 5000 rpm on my machine without stressing the motor. Why would I spend money to lose that capability? Why not just pick a middle of the road belt and leave it there while keeping other speed options open? Is there a down side?
 
Can your spindle bearings handle 5k rpm ?
 
Motor torque falls with RPM, as does fan speed and cooling. This is due to the way the VFD has to lower voltage as the frequency falls.
I run VFD in my Bridgeport, but there's no way I'd do away with the step pulley. Most of the time, I run on the third largest motor size. This covers a range suitable for most 6-12mm end mills you'd commonly use. Smaller, particularly carbide, want the fastest pulley, with larger tools like a fly cutter, slitting saw wanting the lower ranges or even back gear. Think of the pulley options as ranges with a broad overlap.
 
epanzella said:
The next item on my to do list is to install a VFD on my RF30 knock off mill. In the You tube videos I've watched on the subject the stepped pulleys were replaced with single pulleys. I don't really get this. I can understand that the idea of the VFD is to make belt changes unnecessary but the step pulley arrangement does increase the speed range available even with the VFD and as far as I can tell, doesn't do any harm. My mill currently has a speed range of 120 to 2500 rpm. Leaving the stock pulleys along with the VFD I could easily get 30 to 5000 rpm on my machine without stressing the motor. Why would I spend money to lose that capability? Why not just pick a middle of the road belt and leave it there while keeping other speed options open? Is there a down side?
Click to expand...

I don't have an RF30 so I can't comment on that machine, but on my lathe, I find that I still change belts to some degree, depending
on the work and then fine tune my speeds with the VFD. Why not just stay with the stock pulleys for a while and see how it goes?
As you gain experience with the VFD, you'll figure out what you want. As Lo-Fi pointed out, fan cooling and torque drops off at low
speeds, so some belt changes are still in your future.
 
Jim F said:
Can your spindle bearings handle 5k rpm ?
Click to expand...
THAT'S a good question but I can't seem to get an answer to it. I suppose I'll find out. If they can't I'll replace them with better bearings which some owners have said is a good idea on these machines anyway. My BALDOR 3ph motor is available wired for 1700 or 3400 rpm so I'm betting that that my motor (1700rpm) will be good to at least 3400 rpm on 120htz. I don't know how slow I can go without an external motor fan. I'll be happy with 30htz which will give me 60 rpm, plenty slow for tapping.
 
I kept the step pulleys when I converted my RF30 clone.
I haven't noticed any heat from my 1700 rpm motor in the 30'ish hz range with the caveat that I haven't powertapped 100's of holes in a session.
 
One more vote for the step pulley here. I like the idea of being able to choose my pulley speed if I want to.
I leave my pulley on the 850 RPM speed most of the time and picked the slower speed on my two speed
motor when hooking up my VFD. Mostly I look at the cycles to compute the tool's RPM, 60 Hertz being 850 RPM.
 
JimDawson said:
Keep the step pulley. Your motor should run fine between 30 and 90 Hz. Make sure you get a Sensorless Vector VFD to keep the low end torque,
Click to expand...
Jim, I don't know what a sensorless vector is. The VFD was a christmas gift from my son. 'bout a hundred bux.
 
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