10" B&D bench grinder end float

[GraemeVW]

I bought this old 10" grinder, set up as a polished, a while ago and have only just got round to thinking about looking at it.
It works, it's quiet, it has good torque, so just needs a strip, clean, paint etc.

However, it has quite alot of end float. Any idea how much it should have? Minimal I'd guess.

Is this just like another electric motor where the armature will settle to be central in the magnetic field?
I'm thinking if I run it, then turn it off, the armature will be where it wants to be. I can then measure the end float and shim each end accordingly.

 

[minimutly]

You'll probablynfind the bearing retainer plate has loosened off. This clamps one end, whilst a "wavy washer" tensions the oposite bearing. If you have massive endfloat and no bearing failures this is almost certainly the issue.

 

[GraemeVW]

You'll probablynfind the bearing retainer plate has loosened off. This clamps one end, whilst a "wavy washer" tensions the oposite bearing. If you have massive endfloat and no bearing failures this is almost certainly the issue.

I'll find out when I open it.

I can't remember off hand, but has 5-10mm end float. The bearings are very smooth though, silent, and have no radial play. It spins very nicely.
It has so much end float I sort of assumed it's had new bearings fitted and they were either narrower, or something has been left out.
I haven't opened it yet though so not sure how end float is controlled.

 

[Alan Reynolds]

I have a similar machine and it has no end float.
Maybe someone left something out at some point.

 

[The_Yellow_Ardvark]

Some of the older ones had a palstic type washer that held a leather one in place, they can cause the same issue.
In the end caps, were the shaft leaves the body.

 

[GraemeVW]

Some of the older ones had a palstic type washer that held a leather one in place, they can cause the same issue.
In the end caps, were the shaft leaves the body.

It probably is old enough for that kind of thing.
Would make sense if something has dissintergrated.

It will be easy to sort, just a matter of setting the rotor in the right place, and if 540 size RC motors are anything to go by, it should want to centralize in the magnetic field.

 

[GraemeVW]

I have a similar machine and it has no end float.
Maybe someone left something out at some point.

Left out, or broken up.
That was my guess.

 

[GraemeVW]

Just measured it, it's nowhere near as bad as I thought. 1mm end float.
Still feels/sounds bad though so I'll still look into sorting it.

 

[Erie Fred]

It probably is old enough for that kind of thing.
Would make sense if something has dissintergrated.

It will be easy to sort, just a matter of setting the rotor in the right place, and if 540 size RC motors are anything to go by, it should want to centralize in the magnetic field.

How to find the magnetic center ?

 

[GraemeVW]

How to find the magnetic center ?

With other motors, it finds itself. As this quite large, I guess maybe spinning it will help.
But my experience is all with small model motors.

 

[Erie Fred]

With other motors, it finds itself. As this quite large, I guess maybe spinning it will help.
But my experience is all with small model motors.

So you'll measure it while running ?
I wouldn't worry about it, if you get it wrong, the centering forces will want
to burn up the bearings.

 

[GraemeVW]

So you'll measure it while running ?
I wouldn't worry about it, if you get it wrong, the centering forces will want
to burn up the bearings.

No, it should stay there when stopped. You could then push the rotor over, but not enough magnetism to recenter it stationary.

I'm going on instinct here. The grinders rotor won't self center although the small motors I'm used to will. I'm guessing at what to do with this one and sort of asking the group if im on the right lines.

It may not matter at all woth this motor, but when trying to get highest possible rpm from a model motor you don't want the armature pushing against the end shims while it's trying to centralize in the magnetic field.

Whatbi hoping is that someone who understands motors more than me will either say, yep, I'm on the right track, or no, I'm talking cr*p and thatbis should do something different.

I'm trying to apply my limited, related, knowledge to something that may or may not be the same.

 

[Erie Fred]

No, it should stay there when stopped. You could then push the rotor over, but not enough magnetism to recenter it stationary.

I'm going on instinct here. The grinders rotor won't self center although the small motors I'm used to will. I'm guessing at what to do with this one and sort of asking the group if im on the right lines.

It may not matter at all woth this motor, but when trying to get highest possible rpm from a model motor you don't want the armature pushing against the end shims while it's trying to centralize in the magnetic field.

Whatbi hoping is that someone who understands motors more than me will either say, yep, I'm on the right track, or no, I'm talking cr*p and thatbis should do something different.

I'm trying to apply my limited, related, knowledge to something that may or may not be the same.

This is a squirrel cage a.c. motor ?
You won't get any speed gain then.

 

[GraemeVW]

This is a squirrel cage a.c. motor ?
You won't get any speed gain then.

I don't know anything about this motor yet.
I'm not looking to optimise the rpm, I just don't want to shim the rotor wrong and accidently create a situation where there is internal sideways load while running.

 

[Erie Fred]

I don't know anything about this motor yet.
I'm not looking to optimise the rpm, I just don't want to shim the rotor wrong and accidently create a situation where there is internal sideways load while running.

Exactly.
I designed a re-work machine for in place machining, to alleviate just such a problem.
As engineering got the magnetic center wrong, the forces were very high, and wiped out the thrust bearing.

 

[Turbo]

No, it should stay there when stopped. You could then push the rotor over, but not enough magnetism to recenter it stationary.

I'm going on instinct here. The grinders rotor won't self center although the small motors I'm used to will. I'm guessing at what to do with this one and sort of asking the group if im on the right lines.

It may not matter at all woth this motor, but when trying to get highest possible rpm from a model motor you don't want the armature pushing against the end shims while it's trying to centralize in the magnetic field.

Whatbi hoping is that someone who understands motors more than me will either say, yep, I'm on the right track, or no, I'm talking cr*p and thatbis should do something different.

I'm trying to apply my limited, related, knowledge to something that may or may not be the same.

The grinder motor does not contain permanent magnets so it will not centre the armature.