You have a very old product that was in development by 3M in the early 1990's but was discontinued - maybe because, as I recall, the developer lost a finger while testing a version of this wheel (not fact - I do know he was injured but do not recall all the details.
I would not use this wheel if I were you. But I would like to buy it from you to show some of our R&D people what 3M was working on.
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First of all I must warn you of the dangers bench grinders can represent. Here in Britain no one connected with a business is allowed to carry out any maintenance on any none-portable grinding machine unless they have attended and passed a course on the subject and every employer must keep a register recording what maintenance has been carried out and by whom. Grinding machines have been responsible for many industrial "accidents".
Householders and private individuals are exempt from the Law but cannot afford to be less well informed even though the five and six inch bench grinders sold to the domestic user represent a somewhat reduced risk, great care and precautions are still required, not the least of which is the use of good eye protection even if the grinder is fitted with shields.
The first problem about dressing the grinding wheel of a grinder intended for the domestic market is the tool rests are usually too small and insubstantial for the vibrating star-wheel type wheel dressing tool to be used correctly.
A demonstration would be the best way to learn how to dress a grinding wheel and there are many available on Youtube and here is a link to a particularly good video.
Finally, it is best to be aware of one little thought about problem. There is an optimum speed range when a grinding wheel works efficiently and small domestic grinders barely turn fast enough for them to be properly efficient, probably because it is reckoned price and user safety takes priority over efficiency.
The speed that is of concern is the surface or peripheral speed of the grinding surface rather than the rpm of the spindle and should that speed fall too low the wheel will not be able to operate efficiently, will become dull more quickly with a greater tendency to clog and the wheel will become hot in use and hot grinding wheels soon become dangerous.
I hope you will be able to see that by reducing the diameter of a grinding wheel by dressing it also reduces the surface speed of the grinding surface even though the spindle speed remains the same. The relationship between surface speed and spindle speed is why small grinding points need to spin at 20,000 rpm and an eight foot wheel at just a few hundred rpm - in both cases the surface speed is similar.
A domestic grinder should not be used for heavy work but as the size of the wheel is reduced it should be used only for increasingly light work and if it is desired to carry out "normal" grinding operations it would be better to replace the wheel sooner rather than later.
There is a left handed thread and a right handed thread on the arbors.
Right Hand Side (RH)
Wrap a piece of rubber or leather around the threads on the LH side of the arbor & hold with pliers, while turning the RH nut CCW.
Left Hand Side (LH)
Wrap a piece of rubber or leather around the threads on the RH side of the arbor & hold with pliers, while turning the LH nut CW.
Note: Hand tighten the nut, then 1/4 turn.
Right Hand Side (RH)
Wrap a piece of rubber or leather around the threads on the LH side of the arbor & hold with pliers, while turning the RH nut CW.
Left Hand Side (LH)
Wrap a piece of rubber or leather around the threads on the RH side of the arbor & hold with pliers, while turning the LH nut CWW.
For grinding stones:
ring test the stone
discard the stone if it has been dropped
be sure the paper washers are installed on the wheel
Once you get them snugged a little, you will probably have to hang onto one wheel while you tighten a nut. It's easier if you tighten down one wheel with the other wheel dismounted so you can really grab the arbor shaft.
Do NOT overtighten either wheel - it doesn't need it, and overtightening increases the risk of a catastrophic wheel explosion.
Use a wrench on the nut, and hang onto the wheel with one bare hand while you turn the nut in the same direction as the wheel normally spins. If you have a lot of difficulty doing that, jam the wheel with a piece of wood.
It sounds like the motor is burnt out. If the case can be opened, unplug it and check around for signs of too much heat, especially at any wire connections. You may be able to resolder or replace a wire to fix it
The angle things on the grinder are usually set up for drill bits and never moved again. If you need to sharpen your shovel, I would get a 4 1/2 grinder with 80 grit disc in there and grind away from the edge, Not into it, it cuts 10 times faster, cleaner, straighter, than the grinder, use fit or the lawn mower blades too, and the machete, use the grinder for your drill bits and other precision type stuff, don't let the wheels get rounded off or uneven, use a wheel dresser if they do. I have a couple grinders set up in my shop, one wheel for finer stuff, then a wire wheel, then a green wheel for carbide, and then another wire wheel. I use a 1 inch belt for knives and finer stuff, and a 10 disc for serious stuff along with the 48 inch belt. So you can see, I use them a lot. But if you need to use the grinder for your shovel, I would not use the angle stops, I would do it freehand and you can only cut the outside edge, and it will be hard to get it around there. You might have to take the angle stops off. Hope this helps.
Goggles or safety glasses need to be worn to protect the operator's eyes from the sparks and metal filings that result. Depending on the workpiece and time of exposure, hearing protection may also be required, the dust produced is also potentially hazardous. The toolrest (or workrest) should be mounted slightly below the center of the grinding wheel with less than 3 mm clearance from the wheel. This prevents the work from jamming between the toolrest and the wheel. Grinding wheels designed for steel should not be used for grinding softer metals, like aluminium. The soft metal gets lodged in the pores of the wheel and expand with the heat of grinding. This can dislodge pieces of the grinding wheel. Wire brushes require particular attention for the safety of the operator and bystanders as the metal wires may become dangerous projectiles as they could bind with the object being brushed and so throw it away with great energy. The machine needs to be securely mounted to a pillar or a bench to be used safely and effectively, often with an emergency stop switch or pedal fitted close by the machine, for use in emergencies.