Spin Grinding Wheel Before Starting

[Harold_V]

Motors get replaced.

True enough, but wise folks don't switch motors in grinders. If the machine is of any substance, the motors are precision balanced, expressly for use in grinding, where the slightest bit of vibration often translates in to the finish.

The use of a single phase motor for a surface grinder is almost a guarantee of a lousy finish. It's hard to beat the smoothness of three phases.

H

[stephenc]

Admittedly I know very little about surface grinding , but I kind of fail to see how spinning the wheel by hand would help anything at all when it comes to start up .
My grinder has a 3 hp three phase motor . When you hit the power button it is up to speed about as fast as you can blink your eyes .
I just fail to see how the minor momentum you can supply with your hand would have any real effect on things .

As to it helping save a fresh wheel dressing ... I've been wrong many many times but the little I learned and everything I have read has told me that the only real way to keep a freshly dressed wheel exactly how you dressed it is to keep the darn thing spinning .

When I first got my grinder I did the same thing most everyone who gets a new tools does ... find and read tutorials on proper procedures.
I seem to remember a general consensus being that after starting the machine and letting everything come up to a stable working temperature you then dressed the wheel .. every single time .

[John Hasler]

The transient torque when starting a three-phase induction across the line from zero speed can be as high as three times the pullout torque.

https://www.researchgate.net/publicatio ... ion_Motors

[jcfx]

Don't mount wheels without blotters.

Harold,
When you say blotter do you mean a cardboard washer between the arbor washers ?
Jim

[GlennW]

As to it helping save a fresh wheel dressing ... I've been wrong many many times but the little I learned and everything I have read has told me that the only real way to keep a freshly dressed wheel exactly how you dressed it is to keep the darn thing spinning .

And that is exactly what I do when I know I have grinding to do.

On my OD grinder it will get started when I get there in the morning and it may run for an hour or two until I am ready to grind, so that the wheel head and work head can warm up and get settled in, and at that point the wheel will get dressed and it will run until it is time to go home or the job is completed.

On my surface grinder I will do the same including energizing the electromagnetic chuck so it will be up to temp as well, as it was ground when it was up to temp.

Occasionally, though, I need to grind something I hadn't planned on, such as a shim washer or the surface of a nut that gets a specific torque and needs to have a tab washer engage it at that point, or a cutting tool. That's when I'm not really interested in setting up, warming up, and dressing the wheel, all for a couple of minutes worth of grinding. So I give it a quick spin and hit the green button.

I'm also occasionally a "wheel toucher" after dressing, but that's another topic as it isn't something to play with...

[Harold_V]

Don't mount wheels without blotters.

Harold,
When you say blotter do you mean a cardboard washer between the arbor washers ?
Jim

Yes, as there should be something present to distribute clamping pressure without point loading the wheel. Modern manufacturing procedures have, for the most part, created uniformity in wheel construction, but if there happens to exist a condition whereby clamping pressure can fracture a wheel, blotters (gray cardboard, like a soap box, if they are missing) can help limit the possibility. Even tiny wheels used with internal grinders are mounted with blotters, for that reason. Blotters tend to be of a more open construction, so they conform readily to the wheel profile.

Glenn said: "I'm also occasionally a "wheel toucher" after dressing, but that's another topic as it isn't something to play with..."

Yep! How a wheel "feels" can tell the operator a great deal. When freshly dressed, a (spinning) wheel feels like glass, but it has the potential to do great harm, especially if one contacts the edge of the wheel. One of the things I look for is an embedded bit of abrasive*, which tends to destroy the finish on a finish pass. A steadied hand is recommended, with virtually NO pressure when touching. Great care should be exercised to ensure the digit (or hand) can't get trapped and drawn in to the wheel (like between the wheel and chuck, on a surface grinder).

I fully expect OSHA would have a field day if such a report hit a desk there.

*After dressing, it's a good idea to traverse the diamond across the wheel a couple more times. That tends to dislodge any bits of abrasive that may have been trapped in the wheel when being dressed. The "touch" routine readily discloses any such particles.

H

[GlennW]

I've always found that a wheel grinds like it feels.

I usually only do it when a dress is needed prior to a finish pass on something that matters.

The wheel grinds good after dress, (as far as surface finish) then gets real good, then starts to slowly go away. The trick is to time it so that the wheel will be in the "real good" mode for the finish pass, but that doesn't always work out the way it is supposed to! I've had a bad dress just prior to a finish pass before when that didn't work out like I planned, so the touch method comes into play so there are no surprises.

This usually happens on the OD grinder with fairly long, parts.

[Rich_Carlstedt]

Wheel , I served my apprenticeship as a grinder ( trainee) and we spun the wheel no matter what size the grinder ( ^ 24")
Several reasons.
1. Check the bearing "feel"
2. look for chunks or cracks
3. a light spin tells if the wheel is balanced ----"IF" someone leaves coolant running on a dead wheel, it will soak up the coolant and could be severely out of balance, which could cause the wheel to explode on startup.
4. "feel" the dressed surface ( smoothness)
5. see if the wheel has runout or wobble.

I still do this
Rich

[Harold_V]

Wheel , I served my apprenticeship as a grinder ( trainee) and we spun the wheel no matter what size the grinder ( ^ 24")

Chuckle!
I dare say you were never assigned to a centerless grinder, then. Good luck with spinning the wheel by hand on one with a Filmatic bearing.

IF" someone leaves coolant running on a dead wheel, it will soak up the coolant and could be severely out of balance, which could cause the wheel to explode on startup.

Perhaps, but that's highly unlikely. A wheel is intended to deal with water. Still, no harm in playing it safe, although a guy would face a dilemma if he inadvertently got the wheel wet (easy to do on a surface grinder) and it wasn't running. What would you do? Discard an expensive wheel? Not likely.

In my years in the grind shop, there were numerous occasions where a wheel got wet while not in motion. Due to the wheel's open structure, water is eliminated long before the wheel reaches operating speed. I do not recall even one instance where it was troublesome.

H

[Harold_V]

The wheel grinds good after dress, (as far as surface finish) then gets real good, then starts to slowly go away.

Interesting. I wonder if you grind the same way I was taught? Just like in surface grinding, where you can take a large step-over but shallow depth of cut, repeating until depth is achieved, so, too, can one cylindrical grind that way. In fact, it's the prescribed method for internal grinding with through holes, but not necessarily for external grinding.

Finish was critical for the majority of the work we did, for the parts were generally quite small, and of high precision. Primarily, the mechanical parts of the guidance system. For that work, we used 100 grit wheels, aluminum oxide (38A), which did a great job. We, typically did our grinding by plunging at the headstock end, to preserve the corner of the wheel. We would then feed towards the tailstock to remove material, generally only one pass. We'd typically leave a few tenths for a finish pass, taken the same way. The periphery of the wheel, beyond the leading edge, did nothing but spark the part, improving the finish.

When grinding by this method, the wheel remains in pretty good condition, because the vast majority of the wheel breakdown occurs at the right corner of the wheel, to the depth of the passes being taken (the same way a centerless works in through feed). As the shoulder develops, it isn't necessarily a right angle, so as the shoulder progresses, it becomes a large taper, whereby the larger area in contact with the wheel starts to create grinding issues. At that point, the wheel would be dressed, restoring performance.

If, by chance, one uses the internal method of grinding, yeah, the entire perimeter of the wheel is in constant use, and it degrades more quickly, although I suspect that the difference in work accomplished per pound of wheel is about equal. I don't know that one method is better than the other, just different.

In my experience, the best possible surface finish usually occurred with a freshly dressed wheel. That could be more related to the wheel of choice, and the process we used. That, of course, was contingent on the wheel being free of imbedded particles---thus the typical feel of the wheel before picking up for a final pass after dressing.

H

[GlennW]

External grinding hard chrome on 3 1/4" dia. x 30" long tubing.

Huge coolant flow to keep it from moving around from the small amount of localized heat created by the wheel contact.

Grinding small areas, or solid parts with hard chrome is wonderful, large areas on relatively thin wall tubing with a one inch wide wheel, not so much!

[Harold_V]

External grinding hard chrome on 3 1/4" dia. x 30" long tubing.

Ahhh! That's very different.
Aside from grinding a set of hard chromed rolls for a rolling mill (about 12" long), I have little experience in grinding chrome. Tubing makes it all the more difficult.

Huge coolant flow to keep it from moving around from the small amount of localized heat created by the wheel contact.

That's a lot like grinding stainless, which conducts heat poorly, but creates a lot of it. If, in the process of infeeding to take a roughing pass, the wheel was fed to quickly, localized heating caused the part to move towards the wheel, causing a cascading effect. Amazing how much it could suck in the part, often leading to scrapping due to undersize. And only in one spot!

Grinding small areas, or solid parts with hard chrome is wonderful, large areas on relatively thin wall tubing with a one inch wide wheel, not so much!

Indeed.
I envy you your experiences, which do not parallel mine. I based my entire machining career on small work, aside from the less than a year when I worked in two shops where large work was the order of the day. My time there was brief, as I was out of my comfort zone.

Many years ago I built a focusing device for an 8" telescope. I've posted this picture before, but it might help readers understand the issue.

The telescoping portion of the device was made from what I recall to be 3" stainless tubing. I started with thin material, 1/16" wall. It had to be dead round and straight, which I accomplished by turning and polishing. As the skin was removed, stresses, too, were released, so it had a tendency to move. Once it was round, polishing created its own problems, as any heat applied caused the tube to go out of round. I ended up turning the tube three times, reducing the wall to an average of about .045". Polishing was accomplished under a constant flood of coolant. One hell of a messy job, but with a great outcome.

Yeah, heat is your enemy, and it doesn't take much. I can only imagine the effort expended in grinding a thin wall such as you described.

H