Operating bench grinder using CBN wheels without guards?

[Steve Mathews]

I'm all for safety but the question about whether to use a guard on a bench grinder running CBN wheels has me stumped. Using guards with aggregate wheels is an obvious no-brainer but it seems to defy logic in using them with CBN wheels. Hopefully a discussion about this may shed some additional light on the question.

The primary argument for not using a guard with CBN wheels seems to be that they are not capable of disintegrating like aggregate wheels, which apparently is the primary reason the guards were developed. I don't know for sure if a CBN wheel can in fact break apart but it seems highly unlikely. By comparison, when do you ever see a similar guard used on a metal lathe where rotating metals take place? The other argument for a guard is for dust collection. Again, it's apparent that aggregate wheels generate some particles taken from the grinding wheel and whatever is being ground but it seems to me that the later is virtually the only byproduct of a CBN wheel. Is it really necessary to use a guard for collecting ground particles or is there a better way? Another factor to consider in our application is that most of the grinders used are slow speed thereby minimizing the dynamics that come into play. A plus for not using a guard seems to be that better visibility is afforded without them. Although not directly related to safety, better visibility of the working area can enhance it.

Well, that's my thoughts on the matter. What say you?

[Tom M King]

No guard on mine. I don't use it much, but when I do, I lay a couple of wet paper towels under it to catch the chips. The paper towels have to be wet enough so they stay in place without getting blown out of position. The junk thrown off seems to not go all the way around the wheel, but comes off pretty soon past the point of grinding. You can even see the most dense area on the wet paper towel that catches it. Mine is full speed, so it might get thrown off faster than a slow speed grinder.

[Dwight Rutherford]

No guards for me. Do have rare earth magnets under the wheels to collect metal fillings.

[John K Jordan]

I don't use the guards and do not yet collect the dust, but need to. I have some magnets stuck to the back side of my bandsaw about 10' away from the CBN wheels. After some use I noticed the magnets coated with extremely fine steel dust. In bright light at the grinder I can see the steel dust floating in the the air. Can't be good for the lungs - I wear a mask but what about that out in the shop? Run the air cleaner on the ceiling?

JKJ

[John King]

Ditto Dwight above. - John

[Curtis Myers]

I use a magnet shroud to collect the grinding dust. Works well. See below thread on the subject.
http://www.sawmillcreek.org/showthre...-grinding-dust

All the Best
Curt

[Reed Gray]

I still don't have a hood for my CBN wheels, but will keep the wheel covers on as much as possible, which means the part up against the grinder. I saw where some one, no idea who, put a spacer on it so they could put the outside on. I would have far more confidence of that working than magnets, or if the magnets are there as well, that might get most of the dust.

robo hippy

[Jamie Straw]

All this talk of magnets (a shop aid I love, BTW), I must raise a flag of caution: If you use a magnet to collect the metal dust from your CBN grinding wheel, be sure it is fastened securely such that it can't get grabbed by the wheel and thrown. I know one person this happened to, and he felt extremely lucky he didn't get nailed by the magnet as it flew across the shop. He'd been using it for months, no problem, and then wham!

[Larry Frank]

I would have some concerns about hot sparks starting a fire.

[John K Jordan]

I assume the magnets were pulled into a steel wheel by the magnetism? If so, not an issue for the aluminum wheels. Around the shop I usually use the magnets with countersunk holes and fasten them up with screws. A removable holder could be devised.

Has anyone using the magnets experimented with placing magnets around the back, top, and sides of the wheel? I wonder if a magnet placed in a single position would catch enough of the fine steel dust.

As for the fire hazard, unlike the conventional grinding wheels I've never seen heavy sparks from my CBN wheels, only an occasional weak spark that was extinguished far before it even reached the table. Are others seeing lots or long persistent sparks?

JKJ

[Reed Gray]

The brand new wheels do put off more spark than my old broken in ones. I have a bench top air scrubber that might pull in the dust, but the grinder needs to be hooded. I have heard of wood shavings in the wheel cover and CBN wheels starting to get a red glow, but not sure if there was a fire. So, still more experimenting to do...

robo hippy

[Terry Vaughan]

There's another reason for enclosing the wheel, which is to reduce the risk of entanglement. Long hair or loose clothing might get dragged in, particularly with a coarse grit wheel that would be more grabby.

I can't say how serious the danger is, but it is something else to consider.

As for the metal dust, it's possible to detect that right across the workshop. Magnets collect dust wherever they are, and sparkles can be seen in a flame after grinding. Some of the dust is very fine.

[Geoff Whaling]

A couple of responses have already touched upon some good reasons to keep guards on grinders, to reduce the hazards & risk from,

1. inadvertant contact with wheels,
2. fire from hot work - sparks
3. entanglement
4. falling objects - vibration causing objects to fall from shelves, or an item leaning against the grinder bench contacting an exposed wheel in our nice tidy workshops
5. metalic dusts
6. flying particles - sparks & eye injury; or objects
7. damage to the CBN wheel from 4 above
8. wheel or coating disintegration

Admittedly the risk from some hazards is significantly reduced due to the inherent design of CBN wheels, that we may consider that they are remote but they are not completely eliminated. The probability may be so low that we may be lulled into thinking that they are "impossible." Other risks are also significantly reduced from our other safety and hazard management actions - like restraining long hair & loose objects, maintaining a clean & tidy workshop with good ergonomic design etc.

One hazard we always have to manage is the "us or people hazard" - mostly we are an older bunch so medical issues, slips, trips and falls are becoming more probable. A grinder running with exposed wheels, CBN or friable, makes such an event even more likely to inflict severe injuries.

[Geoff Whaling]

By comparison, when do you ever see a similar guard used on a metal lathe where rotating metals take place?

The hazard profiles of a grinder and a metal lathe have some common factors but they have a different risk / probability profile. Grinders tend to run at a higher and typically fixed RPM with no ability to change speed. A grinding wheel also has a much higher peripheral wheel speed than typical recommended cutting speeds on metal lathes plus the work piece / cutting tool on a metal lathe is generally flooded with coolant. The operations are similar - removing metal, but the probabilities of potential events occurring are quite different.

Most OHS authorities recommend guarding of metal lathes with interlocked guards so that the work piece cannot be accessed by the opperator while the lathe is in opperation. In fact it is a mandatory requirement in many jurisdictions now.

[Ned Ladner]

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Wow. I've pocket dialed before but never pocket posted on a forum.

My apologies.