How do you change the grinder disk. I have the tool with the two pronges that slide into the nut but the wheel keeps spinning. There must be a trick?

Contact Nutool directly to inquire.

Mine came with a special wrench that fits into the "nut" that holds the wheel on. Make sure the grinder is unplugged. Mine also has a button I push in that locks the shaft.I lock the shaft put the special wrench into the nut and spin it off.

Unplug the grinder. Remove the guard on the side you want to change. Grasp the wheel with one hand while you turn the nut with a wrench. Remove the nut and arbor washer from the arbor shaft, pull the wheel from the shaft and replace it with a new wheel - DO NOT remove the paper label! Put the arbor washer and nut back on, spin the nut down snug, grasp the new wheel with one hand while you tighten the nut with a wrench. DO NOT overtighten the nut.

It may help to grasp the SECOND wheel (which should still be tight) with one hand while you tighten the nut on the new wheel. It may also help to loosen & tighten & adjust the new wheel several times until it runs as straight as possible before you really tighten it.

After tightening down the nut, dress the wheel with a wheel dresser to get it to run as balanced as possible and give you a smooth round wheel so your workpieces don't bounce against the wheel and so it cuts freely. Repeat as necessary to keep the wheel cutting freely, and to keep the grinding surface flat.

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.

1 Check the grinder before you begin. The newer discs on rotary grinders have patented buttons that allow you to remove the disc without any tools. You may have one like that. In models like this, there's usually a spot to depress and then remove the disc.

2 Turn off the grinder before you attempt to remove and change the disc on your rotary grinder. If it's battery powered, put the grinder in lock position so you can't accidentally turn it on. If it's electric, unplug the grinder from the wall.

3 Look for a nut in the center of the disc. This is a give away that you need to use your special wrench. Sometimes the grinder comes with a tool necessary to loosen and remove the nut. Other times you need to use a wrench.

4 Lock the wheel into place before you begin. You can find a button or switch at the side or back that allows you to do that. When you lock the wheel in place, the disc remains still as you loosen the nut in the center.

5 Remove the nut in the center with either the tool provided with the grinder or a shop tool and lift the disc off your rotary grinder.

6Lift the disc off the rotary grinder. If you have different discs, remember to check for the best fit. Put the nut back on a different way for different discs. Check for a rim and indentation on one side of the nut and a flat side on the other. A visual inspection of the disc for the rotary grinder gives you information about the side to use.

Here is a diagram of your grinder and the tool you are looking for is number 50...

http://www.ereplacementparts.com/images/dewalt/DW402_TYPE_6.pdf

If its a hand held grinder, on the back or the side of the grinder itself there is a button in which you must depress. While depressing it you must turn the wheel at the same time until it locks in place. You have to keep the button pressing to get it to lock.

Once it locks into place, you need a spanner wrench to loosen up the nut (counterclock wise). If you have a grinding wheel on it, some just screw on without a nut. And if this is the case, then just grab a hold of the wheel by hand and turn it counterclock wise and it should come off.

Make sure you unplug the tool before doing any of the above.

Make your own wrench out of a piece of wood stock,with 2 screws or nails spaced out to 2 opposing holes in the retaining ring/nut.HarborFreight sells a 'spanning wrench' online .

on a grinder the nut that holds the wheel on has left handed threads.....that means it has to be turned in the opposite direction than conventional nuts do..there should be a button on the casing to hold in..this keeps the grinding wheel from turning wheel being removed....remember to unplug first..thanks and have a great day

There is a nut that you release from the middle of the grinder wheel, (grinder blade)
This nut is flat and has four holes in it.

You will see you are providing a spanner wrench to remove this nut. The wrenches' actual name is Lock Nut Wrench. It has a U shaped end with two pins sticking out. On on each side of the U shape.

The pins are inserted into the holes in the flat lock nut, located in the middle of the grinding wheel. The wrench is laid flat against the grinding wheel, with the two pins of the wrench going into any two holes of the nut.

At the top of the Makita grinder you will see a Black button. The button is pushed down to keep the grinding wheel from spinning. Holds the grinding wheel in place, as you turn the lock nut loose. When you release the button, a spring inside pushes the button back up out of the way.

As you view the Makita grinder, Release Button towards the Back, grinding wheel towards you, the nut is turned to the LEFT, to loosen. It is a Left threaded nut.

The grinding wheel spins to the Right. Using a left threaded nut insures that the nut will stay tight, due to the direction the grinding wheel spins.

without having the model number I can only go from experience on other grinders. First you would have to unplug tool and remove outer guard housing to expose the hex nut, one side of the tool would have a left hand thread and the other standard so you would need to hold both the hex nuts at the same tme and try both ways, when you get one off put a GOOD pair of pliers or similar device on the shaft and remove the other wheel