ergo the distinction between variable speed/stepped pulleys moot (at least w/ 3 ph motors)?
One thing is for sure: VFD is lot more expensive than stepped pulleys! :( But mebbe the way to go, if there are no other disadvantages.
-- Mr. P.V.'d formerly Droll Troll
Bill
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See
Depends totally on how much power your cutter needs. I have a 1hp VFD and motor with a stepped pulley and I go for weeks without moving the pulley. I do mostly AL and small cuts.
If you do lots of steel with big cutters, then you need to 'downshift'.
I've been told by a machinist I trusted that the vari-speed heads are more trouble than they are worth. I'm sure we'll hear from everyone that has had a vari-speed for 30 years and no problems, but I'd stick with a stepped pulley and VFD.
keep in mind that the torque of the motor is pretty well fixed and at speeds below it's normal rated speed, it may overheat, and may not have enough torque to do the job it's requested to do. this is when the pulleys come into use. for light duty you CAN run in a high gear and run the motor at a low rpm but the motor speed times the torque is what determines the real horsepower. i use VFDs from automationdirect.com for relatively small stuff. they're cheap and good, and you can run small stuff from single phase mains. sammm
One of my mills has a vari-speed head on it. And I hate it. It needed a rebuild with less than 2000 hours on it. Though it is rated at over
7000 RPM, anything over 3000 sounds pretty bad.I'd stick with a stepped
He probably never read the directions. "adjust speed only while spindle is running"
John
absolutely - the reeves drive is much noiser than a pulley (I have a reeves drive on my metal lathe, don't like it given that I also have a VFD), and you have no need for a phase converter since the VFD does that for you, and it also will start/stop smoothly, saving wear and tear on machinery and also reducing loading on your electrical system
- AND, it will protect the motor from overcurrent, etc. If you are going to run the motor slow (say 100 RPM) for a long time, you will want to add a muffin fan to cool it - I do this with my wood lathe - I set the motor to turn at maybe 5 RPM to dry stuff that I've just lacquered so I don't get any runs - the motor can run this way for a long time without overheating with a 5 inch muffin fan blowing air through it, but without the fan, even with minimal load, it gets pretty hot since the motor's own fan doesn't do anything at low RPM.
hope this helps.
(oh, my mill has a 20something speed gear box so I don't use a VFD on it, just a capacitor (aka static converter) to get it started)
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The only issue you have with VFDs..is lower torque at low rpms..and possible heating issues if you are turning the motor too slow for the internal fan to move much air. Which can be solved by adding a simple muffin fan at the fan end of the motor.
Check Ebay for VFDs.
My Gorton Master Mill (step pully) is controlled by a Yuskawa PC-3 VFD. The belt is set on the middle pully and the VFD does all the work, from dynamic braking (1 second stop from 5000 rpm) to virtually instantanious reversing for tapping.
My nice big Rockwell drill press has an older Emerson VFD, which gives me universal speed control
My little Kitakura second ops lathe (4C collet) is run by a Hitachi
1/2hp vfd, with universal speeds, instant reverse etcI dont think Ive got $100 in any of the drives.
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3
As a service tech, who has to rebuild variable speed heads..yes..very much so.
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3
Does your Gorton have a 3 phase motor in the knee for table drive? If so, how do you run it? Another VFD? A RPC? A static?
I want to put a VFD on the spindle motor of my 8D. It also has a knee motor that's 220 3phase and I have a static PC that'll run it, but with the motor at 1/4 HP I don't think I can spare the HP in order to use the static. I'm wondering of I should be using 2 VFDs on the mill...
Peter
No..unfortunately I dont have a power feed for either of the Gortons. They are rare as hens teeth. Someday I may try to modify an aftermarket drive from a Bridgeport etc etc..but I have to be able to afford one
You could..though Id run the knee off a phase a matic.
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3
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