Rockwell 6" bench grinder - anti-rotation pins

I recently acquired a somewhat rusty used Rockwell 6" bench grinder (model No 23-612 F573 G6-202-17 1/3 HM 115vac single phase, 3250 rpm). It is in the process of getting new bearings (the old ones tick when running, probably due to bits of metal in the grease).
This unit is old-time US, made of cast iron, and weighs a ton. And runs smoothly, except for the ticks.
The mystery is the wheel flanges. The arbor is 0.500" diameter, and the wheel flanges (that hold the grinding wheel) are die-cast aluminum alloy and are about 0.425" thick along the arbor shaft, and are equipped with two keyslots spaced 180 degrees apart. In the arbor shaft there was a 0.095" diameter by 5/16" deep radial hole with a spiral pin pressed in, with the tip sticking out, and engaging one of the two keyway slots (which are 0.117" wide) of the inner flanges. The spiral pins had largely sheared off, and had chewed a groove and raised a divot on the inside of the flange, where the radial pin rested. Both sides were equally affected.
I was able to drill the pin stubs out without damaging the arbor shaft, using a 0.088" diameter HSS drill in a hand drill, using black sulfur oil.
My first thought was that this should have been a woodruff key, but the keyslot is halfway between the standard sizes. But I could mill a woodruff key slot in the shaft and widen the keyslot in the flange washer.
My second though was that the original design probably had a single close-fitting but loose pin that went all the way through the arbor, and engaged both keyslots.
My third thought was to wonder why the scroll pins both sheared off. They don't lead that hard a life, so what happened? Maybe I don't want to make this too strong.
My fourth thought was to observe that few modern bench grinders have such pins or keys. What problem did they solve?
Comments?
Joe Gwinn

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The only 6" grinders I've worked with haven't been that elaborate. Usually had pressed steel washers on each side just large enough to stay on the cardboard washers on the wheel, the inner sides abutted a shoulder on the arbor, friction was the only thing that kept things from spinning on the arbor. Never had a problem with that. So I think your arbor is overengineered unless it was intended for driving some other gizzy as well as doing grinding duty. Might be the pin engaged with a flex shaft attachment or something similar. You could probably put the thing back together sans pins and it'd work fine as a grinder.
Stan

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I'll agree, and go further with that thought.
Spiral pins are easy to remove (as opposed to roll pins).
There is no apparent reason for that pin to be easily removable, unless it's intended to be removed.
Lloyd

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:
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Yes. These were roll pins (look like a fat letter C, not a two-turn spiral). There wasn't enough left to grab and pull the pin stub out.
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I agree with both of you, but still Rockwell went to some trouble and expense to put those pins and key slots in, so they must have thought it necessary or at least quite desirable. The question is why. What problems were they solving?
Joe Gwinn

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Pretty simple. The fact that they were roll pins somewhat suggests they were NOT designed to be removed.
So, they were simply enforcing that the face of the friction washer would be the ultimate yield point if something slipped, rather than having the washer slip on the shoulder of the shaft.
Although my grinders have a mere shoulder, _I_ would rather have them slip on the paper washer than to slip on the shaft -- if they ever slipped; which they have not.
LLoyd

Lloyd E. Sponenburgh wrote: ...
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How do you know that they haven't slipped? <G>
In fact, Joe posted that his flange is scored from it slipping on the shaft and the pin's stub cutting it.
BTW - the talk has been "flanges" and I say "flange", cause only the inner flange is/was pinned, right? Varying thickness of wheels would prohibit pinning the outer flange. Oh, wait ... "flanges" could mean the 2 inner ones (both sides).
Bob

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:
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Certainly. But my theory was that the original design had a pin through the shaft so the pin could engage both slots in the washer. Although my guess is that the pin was loose, trapped by the washer, it could have been a roll pin pushed all the way through as well.
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That makes sense. Prevents damage to the shoulder and washer.
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Given that both pins were partly sheared, it was certainly trying to slip.
Joe Gwinn

On Mon, 05 Mar 2012 08:21:09 -0500, Joseph Gwinn
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Greetings Joe, I think they were just avoiding a shoulder on the shaft. And since they were using a pin and cast washers why not cast in slots for the pin? Eric

snipped-for-privacy@whidbey.com wrote:
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The shaft has a substantial shoulder, upon which the big flange washer rests. The pin is in a machined keyslot, and does not prevent motion along the shaft. Only rotation is prevented, and only for the two inner flange washers (nearest to the motor).
I suppose they could have cast the slot in, but they didn't, and they use only one of the two keyslots, so my guess is that they simplified the attachment but left the washers alone because they already had the molds and tooling.
Joe Gwinn

On Mon, 05 Mar 2012 20:59:53 -0500, Joseph Gwinn
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Well then I'm stumped. If the pins only prevent rotation then maybe some engineer though it was a good idea. I have never seen a grinder like this and have never needed a pin to prevent wheel rotation Eric

snipped-for-privacy@whidbey.com wrote:
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But that engineer had to convince his penny-pinching boss to spend the money. Not to mention the boss's boss. They had to have had a reason.
Joe Gwinn

There doesn't seem to be a good reason for the pins. Maybe the only way to find out what problem (real or imagined) Rockwell designers thought they were addressing, would be to find some advertising literature from the time when this type of "feature" was introduced.
Putting a thru hole that size in a 1/2" shaft doesn't seem reasonable to me, but I assume someone thought it would be a good idea.
If there were wrench flats (or pin spanner holes) on the inner wheel flanges to fit a wrench when removing and replacing the shaft nuts, I could see some perceived practical use for the pins, but then only really useful if the nuts were nylock types (any type of locking nut is not actually required for mounting grinding wheels), because grinding wheel nuts don't require significant torque to make the mounting secure.
I've seen used bench grinder arbor threads that have been chewed up by someone using a plier on them, apparently by someone not smart enough to figure out the right direction to turn the nuts, or not confident in having the nuts just snug enough to firmly secure the grinding wheel.
I've also seen wheels with significant gouges in them, so if an accidental jam on one side caused the motor's rotor to stop, it's possible the other wheel could continue to rotate, but that's still not likely to unscrew the nut from the arbor threads.

Wild_Bill Inscribed thus:
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Isn't it possible that the idea is to hold the stone at one end whilst tightening the nut at the other. A cross pin would achieve that aim.

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On that sort of grinder, you don't really need to hold the stone at all when screwing on the nut. It ends up wherever it ends up and you true it after everything is tightened up.
I still say that cross pin is for driving something other than a grinding wheel.
Stan

wrote:
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Perhaps, but no easy way to grab the flange washer. I usually use a vice grips to keep the stone from rotating.
Joe Gwinn

In article
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Hmm. Maybe. The motor unit et al are the same. The buffer's roll pins are 1" long and go all the way through, with 1/4" sticking out on either side. By contrast, on the grinder, the hole is blind, and the pin sticks out a bit less than 1/8". But maybe.
Joe Gwinn

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Yes, but it seems like a lot of work to find that one ad. Maybe someone will know where to look.
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Why is a 0.096" diameter hole in a 0.500" shaft a problem? This does not seem large compared to the shaft.
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There are no such holes. Just RH and LH 1/2-20 hex nuts.
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Yes, but no such damage seen.
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This could be - Bubba at work. But I don't see any other evidence. The wheels are quite worn, one 6" stone being worn to maybe 4", but no big gouges in stone or metal.
Joe Gwinn
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I agree.. searching for the actual purpose/intent of a short-lived decades old design feature could result in a huge waste of time.
We'll await the day when someone poses the question: Who was asking about pins in the bench grinder shaft arbors, because..
All we might do at this point is speculate.. and someone probably nailed it, as there are always good ideas found here, IMO.
-- WB .........
wrote:
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Actually, speaking of speculation, it occurs to me that the worn-down stones may be the clue: Maybe a user was leaning into the wheels to grind faster, and what was carrying the resulting torque was the inner flanges and roll pins. As I recall, the arbor nuts were snug but not overly tight. If the wheel was able to rotate on the shaft under such heavy use, the nuts would have become very tight, perhaps too tight.
Joe Gwinn
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[snip]

A+, good conclusion Joe.. why all the mystery? heheh
I think you meant to state 1/3 HP rating in the OP.. so it's likely to stall before crushing the grinding wheels, me thinks. (however, 1/3 HP is much more powerful than today's 3/4+ HP "ratings")