I found a motor at the dump. It works great and appears to even have been part of a woodshop at one point (covered with sawdust). What I'm not sure of is if it fits the requirements Gingery lays down.
The frame is a little larger than NEMA 48, but that's not a big deal. Gingery also says it should be "split phase", which from my research seems to mean that it has an extra circuit in when it spins up to give it extra torque for a fast (or just strong?) start. The plate on this one has a box labeled "Phase" and in the box is the value "1". So that's a single-phase motor then? If so, does that rule this one out, even considering it's a 1/2 HP instead of the 1/4 Gingery lists as minimum?
If that "Phase" box is unrelated to the split-phasedness, how can I tell if this is a split-phase?
Single phase just means is runs on normal household current, nothing more. A split phase motor doesn't have any capacitors on it, a cap-start has one, a cap start/run motor has two.
Split phase motors are actually the weakest and slowest of the three. Less starting torque than the other two. I have no clue why Gingery would recommend one, other than for cost reasons. Maybe the design isn't strong enough for the fast start a cap start motor would have. You can use any kind of motor you want on a lathe.
As I recall, I don't think it was "use only", it was more a matter of "split phase motors are easy to find for cheap or free", especially old appliance motors. A cost issue, basically. I think the 1/2 horse motor will do fine. More to the point, what RPM's does it run at? This will tell you if you have to change some pulley sizes to get it to work at the speeds he selected... (worth doing, especially for this motor). --Glenn Lyford
The plate says 1725, just like Gingery's. It's a 110/220, though, and has a wiring diagram on the other side that indicates maybe it could be faster or slower at a different voltage. It's out on the cold, cold back porch right now or I'd check that.
Ah, here's the exact quote from the book: "Any split phase motor of 1/4 HP or more will do the job." I took that to mean that anything that
*wasn't* a split phase motor wouldn't do the job. But your reading also makes sense. This dual-interpretation issue is the exact same problem I had with the lid. I'll be sure to document this when I actually get to the point where I need to use the motor (I'm months away from that still, at least).
No, this is done by running the windings in series or in parallel, the speed remains the same, and is a function of the number of windings and the line frequency (60 cycles per second in the US), minus some fudge factor for "slip". Given the opportunity (probably not a big issue for 1/2 hp), run motors on 220. The amperage draw is less, so they don't pop breakers as much. I remember it as P=ixV, power is current times voltage. For the same power (1/2 horse), if you double the voltage, the amperage is half.
I don't think this will be a problem with the Gingery lathe, though, you'll probably run into chatter from lack of stiffness long before you are taking a heavy enough cut to pop the breaker.
The key to interpreting Gingery is his emphasis on doing this on a budget, not necessarily for best practice. He tries to recommend his cheapest solution that will still work acceptably. If you think another method will work, or even improve it, by all means do so. Many others already have when they have built his projects. If you decide to spend a little more money on a nicer component because it will be easier to use or give a better result, do not feel guilty unless low cost is a primary motivating factor for you, as opposed to ending up with the tool. Low cost was his driving factor, and it's why his books still sell very well.
I think his emphasis here was so that, of the _cheap_ motors, you'd pick ones that would work. A shaded pole motor from a box fan wouldn't work very well, for example. Any motor taken from a larger tool, especially wood working tools that are notoriously power hungry (ripping wood fibers is hard work) would be more than suitable.
Gingery does not recommend them merely because by and large, they are not cheap, prices often start at $100 when new. If you can find them cheap, then by all means do so. Just avoid ones that need brushes, like the ones in a hand held circular saw (universal motor). They're usually too fast and too loud. Oh, and ones that say "Phases: 3" won't work on house current without additional work (phase converter or VFD) either.
Oh I see, I thought maybe it held current constant to double the power. Now that I think about it, it would have been labled 1/2-1 HP instead of just 1/2 HP if that was the case.
This is good advice on how to interpret Gingery. Of course, it only helps if I know which items are the "cheap but acceptable" ones and which are the "excellent for this purpse if you can get it" ones. Not knowing anything about motors, I couldn't do that here. I will surely have the same problem at several other stages.
But that's why I'm doing this, to learn. I don't really have a "primary" motivating factor, just 3 subfactors. Learning, low-cost and having-the-tool.
That's what made me check this motor, which has been sitting unmoved on my back porch for something like 18 months. "American Science & Surplus" has treadmill motors for around $40 and I wasn't sure if I should get one.
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