Advice needed - replacing variator on lathe

I have an Harrison Model AA-10 lathe with a 2HP motor with a dodgy
Kopp varitor.
I need to replace the variator.
I am uneducated in these devices, but it has been suggested that a VFD
setup would do the trick. (I need to be able to reverse, if that is a
factor that need extra consideration.)
I have three phase power available at the lathe and a budget of about
$1000 with some wiggle room.
Any advice would be appreciated.
Paul Stine
Texas A&M University
Geochemical and Environmental Research Group
College Station, TX
Reply to
Paul Stine
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I assume this "variator" is some form of variable speed drive. Depending on what the output speed of the variator is, you may be able to use a standard 3-phase motor directly, or you may need a separate reduction gearbox between the motor and the rest of the lathe.
But, the variable speed part is straightforward. Without forced-air cooling, you can get about 30 - 150% speed from a standard motor. With heavy external cooling applied, you can get from 5% up to wherever your danger threshold is. I don't feel too comfortable spinning large motors much more than 50% above rated speed.
With a VFD, you get rated torque from 0 - 100% of the motor's rated speed. Above 100% speed, you get constant HP, so up there is works just like a variable speed drive. But, below rated speed, the power drops off linearly, UNLIKE the VSD. If the variator accomplishes a great deal of speed reduction, then just bypassing it may lead to a loss of low speed torque. If you get your low speed ranges from other gear reductions, like in the headstock, then it shouldn't be a problem.
All VFDs can handle reverse. Pretty much all of them can also brake the motor, which is a nice feature.
I have a Sheldon R15-6, which was made with 8 fixed speeds. (4 speed gearbox on the motor, and backgear in the headstock.) It is wonderful with a VFD. I get smooth starts, braking, plus a jog function for certain gears that don't want to click right in.
If you have a dual voltage (230/460 V) motor, and you set it up for the lower voltage and run it with a 230 V VFD, you get an extra level of insulation protection. VFDs can be hard on motors, but by using a motor with 460 V insulation with a 230 V VFD, you should have no problems with insulation breakdown.
Reply to
Jon Elson
I assume this variator is the same one as used in the Colchester Chipmaster. Parts (as you have discovered) are unobtainable - I got the last spider bit in existence 10 years ago. A VFD works well on them - I know of a couple of Chipmasters using electronic drives. Mine is making a horrible noise today, so I suspect the end is nigh, and a VFD and new motor will be a late Xmas pressie soon. You get the advantage of exact speed control, RPM readout, ramp up and down for speed, etc Geoff
Reply to
geoff m
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These guys were at the Cabin Fever expo and had some very nice VFDs that were reasonably priced. They could run in both directions, you could program start and stop acceleration, brake, rpm or freq. Very nice. It would be for a 3phase motor of course. The 2hp ones were running around $150-$200 and up. If I have to replace the motor on my lathe this is definitely the way I will go. 3 phase motors are cheap and this way you have infinitely variable rpm with an LED readout which can also be controlled by a CNC controller if you choose.
Reply to
Scott Black
Hey! With all the "smarts" at Texas A&M why don't you check with the Electrical Engineering Dept?
Bob Swinney
PS: Be careful about asking anyone at A&M how to stack wood, though!
Reply to
Robert Swinney
I too am an owner of a 10AA with the Koop variator. When I got this machine the variator was making a lot of noise, and I thought the unit was going bad. What I found was that there is an adjustment on the output side of the unit, that was loose. I took out the play in this bearing (?) adjustment and it quieted right down. No more banging on start up.
Also the use of the wrong lube will cause the banging noise and soon destroy the unit. This per one of the "old timers" at Harrison service.
I also found that the input pulley was loose on the shaft, and this also contributed to the noise. Take out the tool storage compartment to check this.
Hope this helps
John Normile
Reply to
John Normile

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