Bench grinder/buffer motor bearing questions

[yota]

I do quite a bit of wire wheeling, mostly to remove rust as I restore or refurb things. for years I've been using a baldor buffer but it's only 1/3 hp and 3.2 amp and it stalls constantly. it also runs at 3000 rpm which in my opinion is too fast for wire wheeling although I've made it work.

yesterday I picked up a monster of a grinder from a craigslist posting. its old and making bearing noise so although it would have worked ok as is of course I had to pull it apart to replace the bearings. this machine has had the bearings replaced before (it's 38 years old) as one bearing is a japanese NTN and the other is a USA SKF. the SKF is metal shielded on one side and the NTN is unshielded. both bearings are OD 62mm, ID 30mm and 16mm thick. the SKF number shows it to have been a 2 side shielded bearing so someone apparently removed the shield on one side. the NTN numbers shows it to be a heat compensating bearing.

my questions:

should a grinder motor bearing be open type, be shielded 1 side, be shielded both sides or be sealed bearings? I've been googling and some say modern trends are to go with sealed bearings. I know sealed bearings limit rpm but I picked this machine for the 1720 rpm speed and the high hp (no bogging) so I don't think this is an issue.

if using a 1 side shielded bearing should the shield face in or out?

should I use bearings with a C3 rating since it's a motor? the SKF I removed is a 62062Z. it is also available as a 62062Z-C3.

as always, thanks for any knowledge on this subject.

 

[yota]

FYI, I realize this grinder is overkill. 1hp would have been fine. but, it was close by, inexpensive and it came with a nice stand, also, I don't believe the 2hp rating on the label. 14 amp is just under 1 1/2hp on motors of this type IMO.

 

[woodchucker]

Looks like my JET..
C3 is a good choice, it's not a precision machine. it will allow good results with heat.
if using 1 shield it should be out.
I would do the sealed keep the dust out as much as possible.

 

[Firebrick43]

Looks like my JET..
C3 is a good choice, it's not a precision machine. it will allow good results with heat.
if using 1 shield it should be out.
I would do the sealed keep the dust out as much as possible.

Almost all motors have doubleshielded bearings.(ZZ) I have used sealed in dirty environments. There is more friction from the seals and more expensive but it is of little consequence on a 1750 rpm motor. It would be hard to quantify just how much longer a sealed bearing would last that a metal sheilded one for a buffer.

 

[Cadillac]

Shielded both sides.

 

[Mitch Alsup]

should a grinder motor bearing be open type, be shielded 1 side, be shielded both sides or be sealed bearings? I've been googling and some say modern trends are to go with sealed bearings. I know sealed bearings limit rpm but I picked this machine for the 1720 rpm speed and the high hp (no bogging) so I don't think this is an issue.

if using a 1 side shielded bearing should the shield face in or out?

Think about it like this: The outside of the motor is brushing all sorts of rust from steel/iron parts.
Rust is bad for bearings.
The fan on the motor will suck up air filled with rust particles, blow it threw the motor, to keep the motor cool.
You don't want the rust entering the bearing from either side.

 

[yota]

assume sealed bearings must come pre greased. shielded 2 side also?

 

[woodchucker]

assume sealed bearings must come pre greased. shielded 2 side also?

yes they do. As I was told long ago, sealed are much better than shielded.
I was actually told the on this forum and also on PM.

 

[yota]

Looks like my JET..
C3 is a good choice, it's not a precision machine. it will allow good results with heat.
if using 1 shield it should be out.
I would do the sealed keep the dust out as much as possible.

I just picked up this Jet a couple of weeks ago on craigs for 40 bucks to replace the little baldor but decided I wanted a low speed for wire wheeling. this thing does not bog down at all. going to move this to buffing and polishing. I've been using an old Ingersol Rand (rebadged baldor) for polishing but it's as weak as the baldor buffer and bogs down even worse.

 

[woodchucker]

HP is valuable for a bench grinder, and buffer. it's nice when the wheel does not slow... you can control things much better, without getting frustrated.

Still can't figure out why my JET gets to 145degrees F