Model-5 rotor removal

[federalfan]

I have a large Federal siren made in the late 1930's. It was still working when the FD recently built a new firehouse and installed a Model-2. I couldn't find any model identification plate on the housing of this old siren but it looks like a Model-5. The 7.5-hp three phase motor is housed in a cast iron frame with four legs which extend down to a large iron ring made for mounting the siren on a level surface. The rotor appears to be made from aluminum alloy.
I want to remove the rotor so I can inspect the motor. I think it was rebuilt about twenty years ago. The rotor is installed on the motor shaft with a key but it doesn't have a central bolt for holding the rotor on the shaft. There is no threaded hole in the shaft for such a bolt. What keeps the rotor from coming loose? Is it a press fit?
There are two threaded holes in the rotor hub on either side of the motor shaft. I cleaned the threads with a tap and installed a steering wheel pulling tool. The rotor wouldn't come loose. I sprayed some PB Blaster on the shaft and tapped on the rotor hub with a hammer. I repeated this process every day for about a week. I tried the puller again but no luck. Should I heat the rotor hub with a torch while I use the pulling tool? If I removed the stator ring from the frame I might be able to use some pry bars under the rotor on opposite sides. Could that method work better than the pulling tool?
This rotor has twelve vanes and measures a little less than 18-inches in diameter and 5-5/8 inches high. The hole for the motor shaft seems to be about 1-1/8 inch. What Federal sirens used the same kind of rotor?

Thanks

[holler]

Your on the right track. Does it have a GiB key or standard keyway? If it's a gib key it will have to come out first. Put some heat to it and pull the GiB key with a claw hammer, then pull the rotor.

BTW, don't go mongo with the heat.

[federalfan]

Your on the right track. Does it have a GiB key or standard keyway? If it's a gib key it will have to come out first. Put some heat to it and pull the GiB key with a claw hammer, then pull the rotor.

Success!!!
I decided to go for broke with the steering wheel puller. I applied another dose of PB Blaster around the top edge of the motor shaft and tapped on the rotor hub with a hammer for several minutes. I greased the threads on the puller screw to reduce the friction. This time it seemed too easy to turn the puller. That's when I realized the rotor was starting to lift. I was able to remove the key by hand when the rotor had lifted about an inch. Now I could see that it was a Gib head key. That fact hadn't been obvious to me because the notch in the head of the key was flush with the surface of the rotor hub. That defeats the purpose of using a Gib key, if you can't get a tool under the head to pull it. The key has a taper of about .015" along a length of about two inches. That must be one of the reasons it was so hard to pull the rotor. I was trying to lift a tapered key by its head along with the rotor.
I continued to use the puller until I could lift the rotor off the shaft. There was about three inches of the motor shaft in the rotor. I could see that the PB Blaster had wetted most of the shaft. That must be why I was finally able to pull the rotor.
So the moral of the story is, don't give up. It may take many days of applying the penetrating fluid along with hammering but eventually something has got to give. Fortunately it was the rotor that gave, not the puller. I was concerned that one of the puller bolts might break off in the rotor hub. That would have been a bad day. Also, be sure to check if you have a Gib head key. My rotor would have been a lot easier to pull if I had been able to remove the key first.
Now I'm wondering how I will reinstall the rotor on the shaft. I don't think I can push it on by hand, but I also don't want to hammer it too much. That's not good for the motor bearings. I might have to lightly sand the inside of the rotor hole and/or the motor shaft to relieve the fit a little. I think it has to be a fairly tight fit to prevent it from coming loose in operation but the weight of the rotor and the tapered key should be enough to keep the rotor on the shaft. I also plan on getting a longer or thicker Gib key, so the notch in the head of the key will be above the rotor hub when the key is installed. That will make it much easier to remove the key.
Next, I get to see the inside of a 75-year old 3-phase motor. I'm assuming it's the original motor. Maybe it was designed by Nikola Tesla! lol

[holler]

Heat the rotor up and it should slide right on the shaft.

[federalfan]

Heat the rotor up and it should slide right on the shaft.

A shrink fit is probably how the rotor was installed on the motor shaft at the factory. I could heat the rotor in a kitchen oven for perhaps an hour, then quickly install it on the motor shaft. I would have a limited time to get it on the shaft and line up the keyway before it would start to tighten up. I'll worry about that after I check out the motor.
I'm thinking of doing a test run with the motor on 220-V single phase, using two of the three phase windings connected in series. The third winding would be unpowered. The motor would run at about 2/3 power, which is 5-hp for a 7.5-hp 3-phase motor. However it wouldn't be self starting. I would have to get the rotor turning and then apply the electric power. I've found that I can use a large rubber wheel or tire, like the kind made for walk-behind lawn mowers, powered by an electric drill, to apply rotation to the top surface of the rotor near the outer edge. I can get it up to a few hundred RPM before I remove the drive wheel. That should be enough to start the motor on single phase power.

Fun times ahead.

[holler]

Yes pretty much all sirens use a press fit to retain the rotors, with a secondary retention device to keep it in place in case it decides to walk off.

You can do the single phase test with the rotor off the motor, you try it with the rotor on it (loaded) and it will quickly smoke the motor, since your basically single phasing it. The amperage of the two powered phases will be double of what the motor is rated for, not good. We test them all the time unloaded with single phase power, but NEVER with a load on them.

I generally use a pull rope to start them if the bearings aren't too stiff. That's how I start my 1 horsepower phase converter.

You'll need to get that rotor up to 450* for about an hour (preheat oven to 450* before) to allow the rotor to heat up completely. I use the same method to install timing gears on engines. Put the crank gear in the toaster oven, let it run wide open for an hour, and put a bag of ice on the shaft to shrink it down some. Work fast because if it gets stuck midway it's going to be a royal PITA to get back off.

A rosebud tip or large propane torch works really good too. Even with welding gloves on it's going to be really hot.

[federalfan]

Yes pretty much all sirens use a press fit to retain the rotors, with a secondary retention device to keep it in place in case it decides to walk off.
You can do the single phase test with the rotor off the motor, you try it with the rotor on it (loaded) and it will quickly smoke the motor, since your basically single phasing it. The amperage of the two powered phases will be double of what the motor is rated for, not good. We test them all the time unloaded with single phase power, but NEVER with a load on them.
I generally use a pull rope to start them if the bearings aren't too stiff. That's how I start my 1 horsepower phase converter.
You'll need to get that rotor up to 450* for about an hour (preheat oven to 450* before) to allow the rotor to heat up completely. I use the same method to install timing gears on engines. Put the crank gear in the toaster oven, let it run wide open for an hour, and put a bag of ice on the shaft to shrink it down some. Work fast because if it gets stuck midway it's going to be a royal PITA to get back off.
A rosebud tip or large propane torch works really good too. Even with welding gloves on it's going to be really hot.

Thanks for that important advice. I hadn't considered the possibility that the motor could be damaged by the higher current from running it with a load, such as the rotor, on single phase with two legs powered in series.
You mentioned that you have a 1-hp rotary phase converter (motor) but have you tried building a phase converter circuit using capacitors to run a 3-phase siren motor on single phase? Other than replacing the 3-phase motor in this Model-5 with a single phase motor, I think I'm headed in the direction of building a phase converter circuit to run the motor on 240-V single phase. It would require a starting capacitor with a timed relay, along with a run capacitor for each of two motor windings.
I'm surprised to hear that most siren rotors are installed with a heat shrink fit on the motor shaft. It would seem more efficient for a manufacturer to use a drilled and threaded motor shaft that could accept a bolt and washer to hold the rotor on the shaft, along with a key to prevent rotational slippage. Did Federal eventually use that method?
I'm going to need some serious gloves to carry a 450-deg aluminum casting weighing about forty pounds from the oven to the motor. I suppose it might be best to do it in the winter when the motor can be outside in the cold. That would make the best temperature differential between the heated rotor and a cold motor shaft. It's amazing how much technology can be involved in a seemingly simple hobby such as this.

[holler]

It's not a heat shrink fit, it's a press fit, two totally different animals.

If you add capacitors you still wind up with a static phase converter with high current on the two powered legs.

[Wdr]

As far as running on single phase your best option would be a vfd. You would need a fifteen horse model for a 7.5 hp motor. Second to that would be a rotary converter which could be built yourself. Basically use the capacitor circuit to start a separate motor(at least 15 hp in your case) it will generate the third phase, however at a poorer quality than the utility so it could still overheat the motor. There is a forum called practical machinist that has a section devoted to phase converters and such, there is a lot of good info about the subject there on both commercial and home built units.