Arbor nuts for securing grinding wheels aren't torqued like some fasteners
in other applications, but being able to attain a specific torque value is
easy with a fine thread, and mating contact areas are of benefit to holding
a position.
All bets are off when considering low-grade hardware.

A factor someone mentioned is the deeper the thread, the weaker the arbor
(or bolt/stud) for a given size.

With blotters on each side of a grinding wheel and the appropriate cupped
plates, (typical bench grinder) arbor nuts generally only need to be snug,
and a fine thread is beneficial for achieving snug.. not even close to a
grunt.

The blotters become slightly compressed, making good/excellent overall
contact between the abrasive and the plates.

--
WB
..........


wrote in message
...
On Mon, 19 Dec 2011 01:28:48 -0500, Gerald Miller
wrote:

On Fri, 16 Dec 2011 17:45:43 -0800, wrote:

I see that all the bench grinders and buffers have their spindles
threaded in UNF - either 1/2-20 or 5/8-18. Is there a reason for this?

I am asking because I just tried to cut a 1/2-20 thread on an adaptor
I made and could not do it - most likely because of the Crappy Tire
die. I do have a good 1/2-13 SKF die. OTOH it might be God's way
telling me to finally learn how to cut the threads on a lathe.

Before I do anything so heroic I thought I would ask...

Michael Koblic,
Campbell River, BC
You may also find 1/2 24, RH or LH

Right. But so far I have not been able to ascertain why a common or
garden 1/2-13 thread would not do just as well in this application (L
or RH).

Michael Koblic,
Campbell River, BC