# Bench Grinder Rotation Direction



## Rick2058 (20 May 2013)

Hi,
I have only just joined UKW so i don't know if this is how to.
I have just bought a 6" bench grinder in a job lot at auction and it rotates the opposite way to my other grinder, it does have polishing mops on, do some grinders spin anticlockwise or is it me being daft.


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## Jojo (20 May 2013)

Hi I have never seen one that does, it sounds like the start windings have been wired in reverse and is running backwards. Not difficult to remedy. 

John


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## Rick2058 (20 May 2013)

if I change the connecting wires around will that work do you think

Rick


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## CHJ (20 May 2013)

Rick2058":3sdnv4ei said:


> if I change the connecting wires around will that work do you think
> 
> Rick




Don't touch the wiring without investigating the mechanical details of the shaft fixing nuts, the fixing nuts are handed so that the mops or wheels do not undo during rotation and applied loads.

Would be surprised if the start windings are accessible anyway, normal method of achieving reverse rotation on simple units is to turn the motor body round on its mounting base. This then of course entails the relocating of the wheel debris guards to face the correct way, do not operate as a grinder without debris guards.


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## Argus (20 May 2013)

Rick2058":1hmvaqmw said:


> if I change the connecting wires around will that work do you think
> 
> Rick



No.

To reverse a single phase motor, you will need to reverse the start winding connections in internally, not the supply wires in the plug. Seek professional help.

In general, polishing mops should rotate upwards (away from you, or clockwise looking at the shaft), grinding wheels should rotate downwards (or anti-clock wise looking at the shaft).

It follows that you need separate machines for grinding and polishing. But as ever, make sure (as has been said), that everything is secure and tight. These machines are notorious for accidents if not set up and maintained properly.

Hope that this helps.


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## Rick2058 (20 May 2013)

Thanks all
It has polishing mops on so as you say they rotates upwards all ok i will leave with the mops on.
once again thanks to you all for your help.
Rick


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## katellwood (20 May 2013)

If they are the same as my two grinders you can just unscrew the base and reverse the mounting, I did this to two of mine which allows the grinders to be fixed direct to a wall and the switch still being on top. If the grinders are fixed to a bench they do appear to go in reverse but has stated this is only due to reversing the grinder mount. 

Will take a photo later to show you what I mean


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## Dicky (20 May 2013)

CHJ wrote - "Don't touch the wiring without investigating the mechanical details of the shaft fixing nuts, the fixing nuts are handed so that the mops or wheels do not undo during rotation and applied loads."

The nuts on the spindles are actually designed to comes loose in operation as opposed to tightening up. Lorry wheel nuts tighten in motion to stop them coming loose and the wheels falling off the hub, but if the Grinder Wheel nut tightened, it could cause the wheel to burst. This is why you undo the nut will in the direction of rotation and tighten up against rotation.


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## Limey Lurker (20 May 2013)

>In general, polishing mops should rotate upwards (away from you, or clockwise looking at the shaft), grinding wheels should >rotate downwards (or anti-clock wise looking at the shaft).


I've been in Engineering since 1958, including year in a metal polishing shop, and I've never seen a polishing spindle
which rotated upwards: they rotate downwards for the same reason that grinders do.


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## CHJ (20 May 2013)

Dicky":3enho0q9 said:


> The nuts on the spindles are actually designed to comes loose in operation as opposed to tightening up. ....if the Grinder Wheel nut tightened, it could cause the wheel to burst. This is why you undo the nut will in the direction of rotation and tighten up against rotation.


View on Left Hand Wheel.






 Central motor shaft rotating clockwise.
Fixing Nut Left hand Thread (Anti-clockwise to tighten)
Grinding wheel Rotating Clockwise the same as the shaft but applied (mass of wheel) forces are in anti-clockwise direction (large arrow).
These applied loads increase in use and tend to cause the wheel to slip in an ant-clockwise direction and in so doing tighten up the fixing nut.

If it did not then the first time a heavy load was applied to the wheel the wheel clamping nut would undo and the wheel would just slip on the shaft.


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## Dicky (20 May 2013)

My apologies Chas


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## custard (20 May 2013)

Limey Lurker":28t1bn2q said:


> >In general, polishing mops should rotate upwards (away from you, or clockwise looking at the shaft), grinding wheels should >rotate downwards (or anti-clock wise looking at the shaft).
> 
> 
> I've been in Engineering since 1958, including year in a metal polishing shop, and I've never seen a polishing spindle
> which rotated upwards: they rotate downwards for the same reason that grinders do.



Here's one,

http://www.axminster.co.uk/creusen-creu ... prod19443/


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## CHJ (20 May 2013)

Dicky":hmo4022e said:


> My apologies Chas



That's OK, accepted, just that grinders can be such dangerous beasts if mis-used it's best that the reason for operating in correct rotational direction is understood.

However incorrect rotational direction should not be a hazard as long as the debris guards are fitted as the wheel should just skid and fail to rotate.


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## Argus (21 May 2013)

custard":arrjzdz5 said:


> Limey Lurker":arrjzdz5 said:
> 
> 
> > >In general, polishing mops should rotate upwards (away from you, or clockwise looking at the shaft), grinding wheels should >rotate downwards (or anti-clock wise looking at the shaft).
> ...



Thanks, Custard.

In general, with the tool tip held upward (as in grinding and after the cutting edge is formed) you don't want a polishing mop rotating into the cutting edge. 

At least, I don't.

That's why carvers like me (and turners, perhaps) prefer mops rotating upwards, away from the edge. The same action as stropping an edge with a machine.


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