- Joined
- Jun 17, 2024
- Messages
- 10
I've got an old 1943 Clausing Model 100mk3 lathe. I bought it at auction in February (so had it ~8 months, https://www.hobby-machinist.com/thr...ng-model-100mk3-108-in-seattle-wa-usa.112870/). It's my first lathe, and I've generally been loving it and impressed with its capabilities, at least for the stuff I'm trying to do. It came with a Craftsman 115.6962 1/2 HP capacitor-start, 114V 60Hz 1750 RPM motor (http://www.vintagemachinery.org/pubs/222/3331.pdf, too large to attach) mounted to it. Initially I had no issues with it.
I've never crashed the carriage, but I have taken cuts that were too aggressive (very much in the learning phase here!), and the belts slip before the motor stalls. For as long as I've had it, I've noticed that sometimes after one of these events the motor would fail to come back up to full speed. I don't have a tachometer on it, but it felt like ~80% of "full" speed, with reduced power. Shutting it off and on again would bring it back up at full speed.
Recently, however, often when I start it up it never gets up to full speed, and in that condition appears to have very low torque. Cuts that shouldn't be an issue for it actually _will_ stall the motor before the belts slip. Then other times it's back to normal, which makes it feel supercharged after struggling with its low power
. Voltage looks normal during these events, never lower than 118V at the receptacle. The data plate on the motor reads 6.7 amps, but I see it pulling ~8 amps at the receptacle during these events, more like 6-7 when running "normally".
I've been trying to diagnose the issue. I know a bit about electrical stuff, but very little about motors. Michael Parrish has a post with some tear-down info (https://michael-parrish.com/2017/07/12/craftsman-115-6962-motor-restoration-part-2/) that was helpful getting a sense of what's going on inside. My understanding is that this is an induction motor, with a start capacitor, but not a run capacitor. My current thinking is that the most likely culprit here is an intermittently faulty centrifugal switch (part 21, "governor" in the manual?). I _think_ that could explain all the behavior? If the motor were slowed down enough to have a substantial drop in RPM, enough to close the centrifugal switch, but not slow enough to actually take advantage of the start capacitor being in-circuit, then it might get stuck down there? And if it got stuck on for a while, then I'd see the behavior of it never coming up to full speed? I've investigated the drive train, and I don't think this is an issue with mechanical resistance in the lathe itself.
I'd like to get some input before I go and pull the motor and start taking it apart. Given the age of this, I've also weighed just replacing the motor, and/or exploring a VFD. I've seen some lathe conversions using sewing machine motors, mostly on smaller lathes, but those motors are rated at 3/4HP, so it seems like it could work on the Clausing?
Anyway, thanks in advance for any input any of you might have,
Jack
I've never crashed the carriage, but I have taken cuts that were too aggressive (very much in the learning phase here!), and the belts slip before the motor stalls. For as long as I've had it, I've noticed that sometimes after one of these events the motor would fail to come back up to full speed. I don't have a tachometer on it, but it felt like ~80% of "full" speed, with reduced power. Shutting it off and on again would bring it back up at full speed.
Recently, however, often when I start it up it never gets up to full speed, and in that condition appears to have very low torque. Cuts that shouldn't be an issue for it actually _will_ stall the motor before the belts slip. Then other times it's back to normal, which makes it feel supercharged after struggling with its low power
. Voltage looks normal during these events, never lower than 118V at the receptacle. The data plate on the motor reads 6.7 amps, but I see it pulling ~8 amps at the receptacle during these events, more like 6-7 when running "normally".I've been trying to diagnose the issue. I know a bit about electrical stuff, but very little about motors. Michael Parrish has a post with some tear-down info (https://michael-parrish.com/2017/07/12/craftsman-115-6962-motor-restoration-part-2/) that was helpful getting a sense of what's going on inside. My understanding is that this is an induction motor, with a start capacitor, but not a run capacitor. My current thinking is that the most likely culprit here is an intermittently faulty centrifugal switch (part 21, "governor" in the manual?). I _think_ that could explain all the behavior? If the motor were slowed down enough to have a substantial drop in RPM, enough to close the centrifugal switch, but not slow enough to actually take advantage of the start capacitor being in-circuit, then it might get stuck down there? And if it got stuck on for a while, then I'd see the behavior of it never coming up to full speed? I've investigated the drive train, and I don't think this is an issue with mechanical resistance in the lathe itself.
I'd like to get some input before I go and pull the motor and start taking it apart. Given the age of this, I've also weighed just replacing the motor, and/or exploring a VFD. I've seen some lathe conversions using sewing machine motors, mostly on smaller lathes, but those motors are rated at 3/4HP, so it seems like it could work on the Clausing?
Anyway, thanks in advance for any input any of you might have,
Jack
