Hammond grinder bearing questions

stevewatr · Oct 9, 2018

My hammond precision grinder has an issue.

I decided to replace the bearings.

I should've left it alone! It was working okay, just a little bearing noise.

I decided to give it a little TLC. There was a small threaded plug above the bearing end cap. I removed it and could see grease inside the hole. So I threaded in a zero fitting and pumped in grease. Something didn't seem right, so I removed the retainer cap, and after cleaning out the grease, found the bearing was shielded.

I'm guessing they are replacements and some one decided to put in shielded bearings??

So, so much for getting grease in them.

They were Hoover 5204z. Funny thing is one side was fully sgeilded, one side only had a shield on the inside.

These are double row, angular ckntact.

So I ordered cheap replacements online (a big mistake) and right out of the wrapper, something wasn't kosher. One bearing felt smooth when rotated by hand, and quiet, but a little stiff. The other had an audible click of the balls, and was easier to turn.

Undaunted, I installed them anyways.

The grinder took longer to spin up to speed, and seemed noisier than ever. Within a couple minutes green grease started oozing out around the shields. Even the looser bearing was oozing, and they both began to get hot.

My questions:

Should I be using a shielded bearing, or even one with a rubber seal?

Do I just need to buy a better quality like fafnir, or skf?

Regards,
Steve Watroba

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Mebfab · Oct 9, 2018

I have not had the best luck with chinese bearings. Last batch of 1" id measured 25.2mm. Guess they split difference

jhruska · Oct 10, 2018

Steve,
Do I just need to buy a better quality like fafnir, or skf? Yes!
Fafnir is part of SKF.
Dental tools/picks are handy for removing the shield on bearings for cleaning. Why not reinstall the Hoover bearings, clean and repack with fresh grease.
Sometimes bearings do not seat during assembly and it takes a tap(s) on the shaft, axial or perpendicular to it, to put the bearings in proper alignment. Rotate the shaft by hand to feel the drag, tap with a deadblow or lead hammer and find the sweet spot. This might be a bit elusive given the mass of the armature.
John

stevewatr · Oct 10, 2018

Mebfab said:
I have not had the best luck with chinese bearings. Last batch of 1" id measured 25.2mm. Guess they split difference

Funny you should mention size. The hoovers are a light press fit into the housing, and onto the shaft, the chinesium are a slip fit in the housing, and seem too easy to slide in or out.

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stevewatr · Oct 10, 2018

jhruska said:
Steve,
Do I just need to buy a better quality like fafnir, or skf? Yes!
Fafnir is part of SKF.
Dental tools/picks are handy for removing the shield on bearings for cleaning. Why not reinstall the Hoover bearings, clean and repack with fresh grease.
Sometimes bearings do not seat during assembly and it takes a tap(s) on the shaft, axial or perpendicular to it, to put the bearings in proper alignment. Rotate the shaft by hand to feel the drag, tap with a deadblow or lead hammer and find the sweet spot. This might be a bit elusive given the mass of the armature.
John

Good advice!

Regards,
Steve.

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stevewatr · Oct 23, 2018

I ended up finding nos Hoover bearings on Ebay. 5204zz. Got the pair for under $30 shipped. Like a lot of nos bearings, they felt sticky at first, but after a few minutes run time they loosened up, and seem fine.

Thanks for the advice.

Steve.

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stevewatr · Nov 19, 2018

Well, nothing can be easy. So with the new old stock hoover-nsk bearings installed, and sounding okay, I turned my attention to re-assembly. I noticed damaged insulation on one of the wires where it goes through a ferrule in the capacitor housing. I was able to remove the metal cover, and to my surprise found the capacitor is actually a 2 segment capacitor like those used on ac condenser units. The 2 were tired together under the cover, so in fact it was 2 3.3 mfd in parallel, equating to 6.6, and actually measuring about 8 mfd. So this got me thinking, I may never know what size the original cap was.
It still starts with the old cap, but the brown oil oozing from one terminal tells me it might be time to replace it.

A few days later I decided to experiment.

I tried a 50 mfd. It increased starting torque, allowing the grinder to come up to speed quicker. I then bridged in a 22.5 mfd I had, raising total capacitance to about 70 mfd.

This didn't seem to change startup much, but the sound while running changed.

It almost seemed as if the rpms were altered.

From the outset of day 2, I noticed a new noise from the motor. That of ball bearings rattling around. Could my NOS bearings be unhappy to be awoken after several years on the shelf??

However, the most alarming thing I didn't realize at first, was the fact the windings were getting too hot!

Too much current appears to be a flowing.

I tried researching the subject of motor design of a permanent split phase motor, and didn't get any clues as to capacitor sizing.

One winding measures about 2 ohms, the other about 18. But this is AC, so I'm guessing impedance is what I really would need to know, right?

The cast iron housing held the heat so well, I decided to call it a night. My next plan is to start cold with the 8 mfd cap, and run it a while whilst monitoring the temperature.

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Larry_D · Nov 20, 2018

stevewatr said:
Well, nothing can be easy. So with the new old stock hoover-nsk bearings installed, and sounding okay, I turned my attention to re-assembly. I noticed damaged insulation on one of the wires where it goes through a ferrule in the capacitor housing. I was able to remove the metal cover, and to my surprise found the capacitor is actually a 2 segment capacitor like those used on ac condenser units. The 2 were tired together under the cover, so in fact it was 2 3.3 mfd in parallel, equating to 6.6, and actually measuring about 8 mfd. So this got me thinking, I may never know what size the original cap was.
It still starts with the old cap, but the brown oil oozing from one terminal tells me it might be time to replace it.

A few days later I decided to experiment.

I tried a 50 mfd. It increased starting torque, allowing the grinder to come up to speed quicker. I then bridged in a 22.5 mfd I had, raising total capacitance to about 70 mfd.

This didn't seem to change startup much, but the sound while running changed.

It almost seemed as if the rpms were altered.

From the outset of day 2, I noticed a new noise from the motor. That of ball bearings rattling around. Could my NOS bearings be unhappy to be awoken after several years on the shelf??

However, the most alarming thing I didn't realize at first, was the fact the windings were getting too hot!

Too much current appears to be a flowing.

I tried researching the subject of motor design of a permanent split phase motor, and didn't get any clues as to capacitor sizing.

One winding measures about 2 ohms, the other about 18. But this is AC, so I'm guessing impedance is what I really would need to know, right?

The cast iron housing held the heat so well, I decided to call it a night. My next plan is to start cold with the 8 mfd cap, and run it a while whilst monitoring the temperature.

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The capacitance is chosen specifically with the AC inductance of the windings so that the secondary winding is at the proper phase angle relative to the main winding. Just messing with the capacitance willy nilly is going to alter that. Does the capacitor have a rating on it? Then stick with that. If you want to replace it, that's fine, but unless you are able to work through the motor design, I'd leave it alone. If you get the phase angles messed up enough, it could cause the motor to fight itself (heat), and it will lose efficiency.

It sounds like a cap start/run motor. Both caps are in parallel to start with, then one is disconnected during running.

Edit:
Okay, since I'm thinking about this. Imagine it like you and a friend are standing at a merry-go-round, but it only has like 4 or 2 handles and you can only pull towards yourself. You and your friend are spaced 90 degrees apart, facing the center. As the handle comes to you, you have to time your pull so that you are speeding it up (or at least keeping the speed constant). You friend will need to do this later than you as the handle comes towards him. The exact timing is dependent on the speed you want. But you friend gets messed up, and he is late. Now when he's pulling, the handle is not coming towards him, it's going away from him. Now his pulling is actually trying to slow it down. If you get the windings too far out of phase, that's what's happening.

stevewatr · Nov 20, 2018

Larry_D said:
The capacitance is chosen specifically with the AC inductance of the windings so that the secondary winding is at the proper phase angle relative to the main winding. Just messing with the capacitance willy nilly is going to alter that. Does the capacitor have a rating on it? Then stick with that. If you want to replace it, that's fine, but unless you are able to work through the motor design, I'd leave it alone. If you get the phase angles messed up enough, it could cause the motor to fight itself (heat), and it will lose efficiency.

It sounds like a cap start/run motor. Both caps are in parallel to start with, then one is disconnected during running.

Edit:
Okay, since I'm thinking about this. Imagine it like you and a friend are standing at a merry-go-round, but it only has like 4 or 2 handles and you can only pull towards yourself. You and your friend are spaced 90 degrees apart, facing the center. As the handle comes to you, you have to time your pull so that you are speeding it up (or at least keeping the speed constant). You friend will need to do this later than you as the handle comes towards him. The exact timing is dependent on the speed you want. But you friend gets messed up, and he is late. Now when he's pulling, the handle is not coming towards him, it's going away from him. Now his pulling is actually trying to slow it down. If you get the windings too far out of phase, that's what's happening.

Hello Larry. I took electronics at a voc tech school way back when. So I have a rudimentary understanding of inductance, and capacitance. I get that were using the capacitor to create about a 90 degree phase difference between the 2 windings.

Allow me to clarify. There is no centrifugal switch in this motor.

The one can that was mounted under the base has 2 sections. It is marked 3-3 mfd 330 VAC. I measured it, and it has two 3.3 mfd caps. They were wired in paralell, so in effect there is one approximately 8 mfd cap in series with the higher resistance winding, and the other winding is directly across the line.

Now, it's clear to me this is not what was intended by the manufacturer. In fact, I suspect the 2 section cap was robbed out of an old air conditioning condenser.

So even if I just put in what was in there when I started, there's no guarantee it'll be correct. So that's why I'm advocating the trial and error approach.

If I measured the inductance of both windings, is there a way to calculate what capacitance I need?

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stevewatr · Dec 12, 2018

I settled on a 10 mfd capacitor after doing some testing. I tried a few sizes, monitored rpm, current draw, and temperature increase each time, and the grinder seems to be happy with a 10 mfd. No overheating, low current draw unloaded, and decent spin up time.

Steve.

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JST · Dec 12, 2018

You seem to have a "PSC motor".

To find the best capacitor for a PSC motor, you load the motor to near full load, and then choose the capacitor that produces the LOWEST line current in that condition..

stevewatr · Dec 13, 2018

JST said:
You seem to have a "PSC motor".

To find the best capacitor for a PSC motor, you load the motor to near full load, and then choose the capacitor that produces the LOWEST line current in that condition..

That's basically what I did, except there was no load, other than the grinding wheel. Hard to create a consistent load on the grinder.

I agree this is a permanent split phase motor.

Based on the data plate, my current no load rpms are a little high, and my current is low.

I figure this is not unusual since I measured the motor was unloaded.

Also, the motor is 110 volt, and I'm pumping about 120+ into it.

Steve.

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