No announcement yet.

cheap motor speed control for hobby lathe?

  • Filter
  • Time
  • Show
Clear All
new posts

  • cheap motor speed control for hobby lathe?

    hi guys

    i've got an old sears craftsman 109 series lathe (109.20630) that i've been in the process of restoring gradually. i'm close to getting it fired up again, but read somewhere online that those particular lathes, even though equipped with step pulleys and a backgear assembly in the headstock, still turn too fast for practicality.

    i've thought about trying to rig up a countershaft to further reduce the speed, but the board i mounted it on doesn't offer a lot of additional space for the shaft, and i'd hate to waste all that work by starting over with a new, deeper board.

    i've got this solid state speed control, like a rheostat of some kind, buried in a box-o-tools somewhere (i got it for my router and haven't yet used it), and am thinking about digging it out to see if it's rated for the hp of this motor. i haven't gone out to look at the motor's tag yet, but i'm fairly sure it's one of those 1/4 or 1/3 hp 1725 rpm motors you see everywhere.

    any idea if this is an advisable idea, or if there's some other cheap way to adjust the speed of this motor electrically? the countershaft route seems a lot of trouble, especially since i haven't even had this lathe running & don't know if it works decently in the first place.


    drew j.

  • #2
    If it's an induction motor, its speed is locked to the AC line frequency. The only way to change its speed is by varying the line frequency from 60 Hz.

    You can do that with a variable-frequency drive (VFD), but with a single-phase motor it's not really a practical proposition because if you drop the line frequency by more than about 15% you'll screw up the motor's starting circuit.

    The solid-state speed control will work with a universal motor (i.e. one with brushes) but not an induction motor.
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
    There are lots of people who mistake their imagination for their memory. - Josh Billings
    Law of Logical Argument - Anything is possible if you don't know what you are talking about.
    Don't own anything you have to feed or paint. - Hood River Blackie