Bench Grinder frustrated

[mmsafd]

I have a Craftsman 6" bench grinder that I have had for approx 35 years. It has been great and is still in great shape. It is a model 319.190400, 3.5 amp. The bearings started sounding horrible. I bought new bearings for it and replaced them. Should be an easy enough task. When I put it back together I was unsure how exactly the centrifugal brake operates or how to set it up properly. I do not think the brake has been working properly for a few years. The wheels take a long time to stop lately.
When I got it all reassembled and started it, the grinder smelled horrible and started smoking within about 10 seconds of start up. It is also vibrating a lot. I even removed the wheels and guards and only had the shafts spinning. It still vibrates and starts smoking within seconds. It seems the vibrating has to do with the motor fighting itself, not a bad bearing. Almost like it is in forward and reverse or stop and the same time. I feel it is something to do with the brake system. I do not know how it operates. It seems that once the motor speed slows down enough the mechanical centrifugal brake engages and touches a contact to electrically stop the motor somehow. Does anyone have insight on this set up? I am not able to find any kind of repair info online. I thought I was making some headway on it. Smoking seemed to have stopped with only shafts assembled. When I got it totally reassembled it was running backwards. Ugh!

I really do not want to replace the grinder but I may be at that point. You know the term "they don't make them like that any more". This definitely applies here. I am reading all the new ones don't last. I know most are going to say just get a new one. I might have to do that but if I can fix this one I would prefer that.

Any ideas on that brake assembly and how it works and how to adjust it?
Thanks for the help.

 

[Walkers]

I would take the brake out of the loop. Who cares if it takes some time to spin down?

 

[seber]

Grinders don't have brakes. What you are looking at is the speed switch the cuts the start capacitor out when the arbor reaches sufficient rpm. If any part of that switch is contacting any part moving against it, you need to correct that.

 

[Davefr]

It sounds like the centrifical switch isn't disengaging. If it doesn't disengage the start windings with a few seconds after start up they'll overheat and eventually burn out. Either your wiring isn't correct or your motor isn't coming up to the full speed necessary to throw out the starting circuit. (the later could be caused by binding bearings or misaligned rotor.)

 

[tool_scrounge]

Grinders don't have brakes.

Most grinders do not have brakes, but Craftsman did make one 1/3 hp block grinder with brakes. I sold it a while back.

https://www.garagejournal.com/forum...an-397-19410-block-grinder-with-brake.402703/

 

[mmsafd]

Grinders don't have brakes. What you are looking at is the speed switch the cuts the start capacitor out when the arbor reaches sufficient rpm. If any part of that switch is contacting any part moving against it, you need to correct that.

Ok sounds like some good info there. Thank you. I assumed it was some kind of brake to slow it down. Sounds like I was barking up the totally wrong tree.
So that speed switch mechanism is a mechanical only centrifugal device. It has a contact spring that it works with. I assume that contact should be touching when it is stopped? Then open once the grinder is up to speed? That set up was kinda iffy when I took it apart. And I was not sure exactly how to put it back together. If I have “let the smoke” out of somewhere in there have I damaged it beyond repair? Any idea why it would be running backwards now?
Thanks for the help.

 

[mmsafd]

It sounds like the centrifical switch isn't disengaging. If it doesn't disengage the start windings with a few seconds after start up they'll overheat and eventually burn out. Either your wiring isn't correct or your motor isn't coming up to the full speed necessary to throw out the starting circuit. (the later could be caused by binding bearings or misaligned rotor.)

Ok great info too. I have been assuming something was up with that centrifugal switch ( what I thought was a brake) all along. I will mess with it some more tomorrow. I will try and grab a couple of pics to post. I hope I have not damaged anything permanently.

 

[nadogail]

You may need to take it to an Electric Motor Shop.

 

[torqueman2002]

Pictures will help us a great deal to make appropriate suggestions.

In the mean time, take a look at this thread. It shows the centrifugal switch.
https://www.garagejournal.com/forum/threads/cm-pre-block-grinder-115-19500-restore-ver-2.447537/

 

[mmsafd]

Ok finally got time to look at it again. Here are some pics.
This is that centrifugal switch assembly, that I incorrectly thought was a brake. It appears that in its relaxed position when the grinder is off it defaults closer to the middle of the motor. When it speeds up it pulls away from the center.

 

[mmsafd]

The switch pushes on a ring when it slows down. That ring has a contact on one end. I assume this is that assist for the start capacitor.

 

[mmsafd]

How does all that need to be set up? When off should the contact be closed? Then when it speeds up the centrifugal switch opens the contact?

 

[mmsafd]

Any input on the vibration? The bearings are some made in China bearings from the zon. The originals at NTN from Taiwan. Is there a difference? Maybe I should get a couple of better quality bearings?

 

[gba2331]

FWIW, this is exactly the problem I had with a boat lift motor. Mud wasps built a nest that prevented the centrifugal switch from disengaging and the motor kept drawing start-up amps (40) vs run amps (7). You can use a current meter to confirm (if you have space to get it in there)

 

[Davefr]

How does all that need to be set up? When off should the contact be closed? Then when it speeds up the centrifugal switch opens the contact?

Yes, the switch is normally closed which allows the capacitor/start winding to be in circuit until the motor comes up to speed. Then it needs to disengage or the start windings will start to fry. Maybe this will help. When the motor is off does the shaft spin easily? Is there any lateral play.

I always restore OEM bearings whenever possible unless they are rough, pitted or worn.

 

[mmsafd]

So if I had smoke come out of it already by doing it wrong, are the windings toast?
I have the original bearings. I did clean them with brake clean and re grease them. They feel pretty good. Would it better to re use those maybe?

 

[Davefr]

So if I had smoke come out of it already by doing it wrong, are the windings toast?
I have the original bearings. I did clean them with brake clean and re grease them. They feel pretty good. Would it better to re use those maybe?

Put an ohmeter across just the start windings and see if you get continuity. Even if you get continuity the insulation could be damaged/burnt. Burnt wire is usually pretty easy to ID. IME these windings are pretty robust and if power was killed at the first sign of smoke/overheating they usually survive but YMMV.

I always prefer OEM bearings that have been ultrasonically cleaned and repacked with Mobil Polyrex EM. But discard them if pitted, worn or rough. IME they usually clean up just fine. But I probably wouldn't bother if the new bearings you already installed are OK.

 

[mmsafd]

What exactly would the start winding be and where would they be located? Thanks

 

[mmsafd]

Update: Well thank you mucho for the advise on here. I bought some new, I assume better, bearings. I bought Timkens. I am not sure if they were made in china or elsewhere. I at least recognized the name brand. Tremendously better where the vibration is concerned. I also was able to get the start switch assembly adjusted properly on the contacts, thanks to info from here. The grinder is back up and running. it sounds like it did when it was new. Oh, and no smoke lol. Thanks again for all the info. Hopefully I can get another 35 years of use out of it.

 

[exmaxima1]

A pic of the actual grinder would have been nice. It appears to be a low-cost import. I think I would have dumped it when it needed bearings and upgraded to a better grinder. Or even further, to a belt grinder.

 

[mmsafd]

I can definitely get a pic. But I do not think it is a "low-cost import". Like I said I bought it new over 30 years ago. I would think maybe made in Mexico back then but that was probably better than the china stuff today. Seems like all the grinders I looked at are made there. That is why I am so dead set on keeping this one in play and not getting a new one. My grinder is the same as the one pictured one post above.

It had been working great but still made a noise at shut down. The noise is related to that centrifugal switch I am sure. I tried to use the grinder the other day. It would not start. It only made a humming noise. I assume that means that the centrifugal switch is still not right? Still want to try and get this thing squared away. I hope I have not damaged it in the process.

Any suggestions on setting up that centrifugal switch correctly?

 

[mmsafd]

Well I gave up.
I took it apart again and found some burned looking areas on the windings. There were small wires or strings that were holding it all together. That was all burned too. Also a burned looking spot on the centrifugal switch.

I bought the Dewalt 6" grinder. The only thing I did not like about that one is that it did not have a light. I scavenged the light from my 35 year old Craftsman cleaned it up and installed it on the Dewalt. It looks like it came that way IMO. So far the Dewalt has been good. Nice and quiet. I installed a new 1/2" wide wire wheel also on the right side.

Thanks for the help

 

[jayemm]

A pic of the actual grinder would have been nice. It appears to be a low-cost import. I think I would have dumped it when it needed bearings and upgraded to a better grinder. Or even further, to a belt grinder.

Back in around 1995 I bought a Sears Craftsman 6" grinder that looked identical except it was metallic green and without light. I got it at a traveling tool show for $20 and it appeared to be NOS because the cord was really stiff. It had good power and spun up quickly. IIRC it was made by the Hebei Grinder Company (or similar) in China.

 

[NoUserName]

Grinders don't have brakes. What you are looking at is the speed switch the cuts the start capacitor out when the arbor reaches sufficient rpm. If any part of that switch is contacting any part moving against it, you need to correct that.

They most certainly do, in fact, I have a 1960 Craftsman 1/4hp (115.19500) that has a brake that brings it to a final slow down and halt several seconds after powering it off. Brake wasn't working when I got it, I got it working again and it's worked correctly ever since. This is my second Craftsman bench grinder with a working brake, the other was a 1/3hp from a few years back that I sold.

 

[NoUserName]

Most grinders do not have brakes, but Craftsman did make one 1/3 hp block grinder with brakes. I sold it a while back.

https://www.garagejournal.com/forum...an-397-19410-block-grinder-with-brake.402703/

Yes, I had a 1/3 hp with a brake and I currently have a 1960 1/4hp with a brake that I disassembled and got working again.

 

[no704]

Can’t imagine what benefits you get from a brake on a bench grinder?? I’ll often use one and after turning it off find a little burr and hit it on the still coasting wheel.

 

[NoUserName]

Can’t imagine what benefits you get from a brake on a bench grinder?? I’ll often use one and after turning it off find a little burr and hit it on the still coasting wheel.

It still coasts, it's not a sudden brake, but it kicks in after powering down the unit when at probably 20% of operating RPM.