Variable Speed Spindles: Four Reasons Why They’re The Best Thing Since DROs

I’m not a tall guy. Maybe 5’ 7” or so, and that’s wearing steel-toed boots. So while it wasn’t very nice, it’s not surprising that my fellow machinists would snicker every time I had to change speeds on my knee mill. I’d pull out my trusty wooden crate, climb on top, loosen the locknut, then wrestle the belt and pulley into place.  When done, I’d reverse the process and place the crate under my bench for safekeeping. Still, they’d hide it from me at lunchtime, sticking it on the stock rack or behind the optical comparator. One morning, I came in to find the crate full of floor dry. I could always count on those second shift guys for a laugh. I know now, however, that if I’d had one of those newfangled AC-frequency variable speed spindles, I could have avoided all that shop floor angst.

Hello Variable Speed Spindles

I could have avoided a lot of wasted time as well. But hold on: what exactly is an AC-frequency variable speed spindle? Like everything else in the world, machine tools are increasingly digital, and knee mills are no exception. Machine builders typically install variable speed drives wherever a wide range of motor speeds is needed. They use a frequency-modulated AC motor rather than the traditional belts and cone pulleys found on most knee mills. This means:

• Variable speed spindles require fewer mechanical components. This reduces maintenance costs and generates less heat, improving machine accuracy.
• Variable speed spindles are more energy efficient. This might not mean much on one machine, but adds up in a large shop.
• They’re quieter, especially at higher speeds. Again, no big deal with one machine, but get five or ten old-fashioned knee mills running at once and it’s time for the ear plugs.
• They’re a heck of a lot more convenient. Simply twist the knob to the desired spindle RPM and get machining.

Those are some good reasons for variable speed spindles. There are others. And as mentioned earlier, you’ll especially appreciate having one if your height-challenged like me. Check out Kent USA’s KTM-3VSF or any of the mills with “V” in the model number for more details. Then get rid of the crate.