Originally Posted by
carl mesaros
Roger I must disagree with your statement regarding the brushless DC motor. My new Laguna 2436 has a 3 hp brushless DC motor that is ultra quiet, cool running and has amazing torque at low rpms. I have found little need to move the drive belt to the low side. I am comparing this lathe to my Jet 1-1/2 hp 1642, which was a great lathe but no comparison to the Laguna.. The cooling fan is far louder than the motor on my lathe. The most annoying feature is the fan never shuts off unless the machine is unplugged.
Carl, you can disagree, But you are also wrong. It's a simple fact of motor design. Firms use DC motors for "variable" speed based simply on cost. A DC motor, and controller, is cheaper then a variable speed AC motor, and controller.
Also three-phase AC motor simply provides more power, over a broader range of speeds, then a DC motor.
Even then, in-order to provide power across the entire speed range we turners use, the most lathe manufacturers ends up using two, three, etc speed ranges with pulleys.
Part of why the DVR motor (used in Teknatool lathes and ShopSmith-Mark7) can provide full power from 100 to 4000 rpms is it's unique use of 24 "phases" (it's not really 24 phases, but.... the DVR is a very interesting motor).
By way of background, I have a BS EE and worked for many years as the Lead Engineer for the US Navy in a large motor rebuild/repair shop (as in motors up to 1000 HP)
Making sawdust mostly, sometimes I get something else, but that is more by accident then design.