how do you know your grinder needs bearings?

[Duct Tape Man]

Picked up an old Kenmore bench grinder a couple weeks back. Works good but I'm giving it a refurb. The grinder goes from "ON" to fully stopped in about 5 seconds. Max rpm is 1750, a little slow for a new grinder but par for the course 70 years ago.

Question is, how do you know it needs new bearings? Do you base it solely on the time it takes for the shaft to stop turning? There is no vibration or wobble in the shaft, but it's old and I want to replace the bearings IF THEY NEED IT while it's apart.

Your opinions?

 

[rice rocket]

Worn bearings have play. If you have no play, no need to replace. Relube, maybe. Worn brushes is more likely to cause it to be slow.

 

[mrborohachi]

+1 if you can move it with 2 fingers then it has play, hit up BOCA bearing in Florida for bearings

 

[Duct Tape Man]

No, it's slowness is factory - says 1750 rpm on the data plate, I'm giving her all she's got captain!

No play in the bearings, Guess I don't need to tear it down that much. Thanks for the info, guys!

 

[Davefr]

Just because you don't feel any play doesn't mean the bearings are good. If they're ball bearings they can be pitted and lubrication can be dried out. You should clean and inspect or simply replace them. If they're standard sizes then replacement is usually the best option and they're usually pretty cheap.

I'd never use 70 year old bearings without some form of service/replacement.

 

[PT Doc]

That rpm is appropriate for 12", 10" wheels and maybe 8".

 

[DekeT]

5 seconds to stop from 1750 rpm is a ridiculously fast time to slow down all that momentum. Replace the bearings while it is open.

 

[lilredex]

If they look like these, then it is a simple test to check their condition.

https://www.google.ca/search?q=seal...KqyATJ6YKoDg&ved=0CAYQ_AUoAQ&biw=1569&bih=714

Rotate the shaft by hand to see that the bearings turn easily and smoothly and there is no roughness. Normally there is no play in that type, unless they have really had it, and that will be obvious.

If you are looking instead, at bronze bushings, then there will be side play in the shaft if they are worn, and will need to be replaced.

 

[A_Pmech]

Assuming your machine has rolling element bearings:

If you can feel play in a ball bearing mounted shaft, the bearings should have been replaced a LONG time ago! The radial clearance on a small deep groove ball bearing is measured in low double-digit microns. Half or more of the internal clearance is taken up by the press fit between the shaft and the inner race.

Most small ball bearings will howl long before play is noticeable. A rise in temperature or "sticky" operation is also a good indication. The short coast-down time suggests failed bearings, probably due to soaped up old grease as Dave mentioned.

 

[wvrailroader]

If it is like a lot of the stuff people bring me to fix, it needs new bearings only after the grinder locks up

 

[WWIIjeep]

That rpm is appropriate for 12", 10" wheels and maybe 8".

1750 RPM was also commonly used on 7" grinders intended mainly for sharpening edge tools. The slower speed made it easier for less-experienced users to avoid removing the temper through overheating.

 

[Duct Tape Man]

I disassembled the grinder. This unit is 1930s technology, pre-Craftsman era. There don't appear to be any ball-bearing type bearings in this. The shaft comes out through the housing, through a bronze bushing which appears to have races cut in it, and a felt pad which is oiled from the backside. There is a small oil reservoir on the outside of the housing, on each end, to lube this pad, I assume. This must be what they refer to as friction bearings.

I see no scoring or damage to the inside of the bronze bushing, or the outside of the shaft going through them. I assume the only reason it stops within 5 seconds of being turned off, is that there is no oil in the reservoir.

That being said, what is the proper oil type for this bearing on this grinder? Light oil, or heavier, like 85-90W?

 

[lilredex]

3 in 1 is OK for those........the one in the blue container. Says for motors, etc.