Grinder: Smoke From Tool

The armature, located inside the field of the motor, is the power-producing unit of the motor. If your grinder is smoking, you should check the armature for any build up of dirt and debris, shorts and performance. Remove the screws securing the gear box assembly to the grinder. Remove the lower cover to gain access to the brush holders.

For some models, you will remove a side cover, paddle, lock button and a second side cover. Move the tension springs to the side and remove the brushes. For some models, remove the brush caps on the side to take out the brushes. Separate the armature from the field by pulling the armature out. Check for a heavy build up of dirt and clean it with electrical contact cleaner. Inspect for any burn marks, indicating a short, and replace if needed. Check the commutator for missing bars. If there are missing bars, the armature needs to be replaced. Clean the commutator with 600-grit aluminum oxide sandpaper only in the direction of travel, to avoid damage. Use a plastic scribe to clean out any debris in between the bars on the commutator that can cause a short.

Next, test it for continuity to make sure the armature is in good working order. To check for a bad armature, you can perform the 180-degree test. With the armature removed from the unit, stand it up on a bench. With an ohmmeter, attach the two ends of it to both sides of the commutator to measure the resistance of the windings. As you move it around the commutator, the reading number is not important. You are looking for a consistent reading, indicating all the windings are good. If it varies radically, reading zero or open circuit, then the armature is not good. Another rest is reading. If the ohmmeter reads zero, or open circuit, then that indicates a bad armature. The last test is a bar-to-ground test, which is done by placing one lead of the ohmmeter to the tip of the shaft of the armature and the other end to the commutator. If the armature is bad, install a new one.

Remove the nut securing the armature gear and remove the gear. To remove the gear box cover and bearing, place the cover on top of a bench vice and open the bench vice enough for the cover to sit on it. Now, tap the top of the armature shaft with a rubber mallet to remove the bearing and cover. Install the cover and bearing onto the new armature and use a socket that makes contact with the inner bearing race, to avoid damage. Tap in place with a hammer. Insert the armature into the field. Reassemble the gear box housing to the grinder and reinstall the brushes back into the holders. Reapply the tension springs and then reinstall the lower cover.

The carbon brushes ride on the commutator, supplying electricity to the motor. As the carbon brushes wear down, they will produce more sparking. This can cause a heavy carbon build up between the brushes and the commutator, resulting in smoke from the grinder. Remove the lower cover. For some models, you will have to remove a side cover, paddle, lock button and a second side cover. Move the tension spring to the side. Remove the brushes and inspect them for wear and damage.

On certain models, the brushes are located inside the caps, positioned on the side of the grinder. Use a screwdriver for removal. Carbon brushes getting close to 1/8 of an inch, or less, require replacement as they are worn. Clean the brush holder with electrical contact cleaner. If the brush is in good working order, clean and resurface the face on the brush by lightly sanding it with very fine sandpaper. Install the brush back into the holder, reinstall the brush caps and then reapply the tension spring. Reassembly the lower portion of the grinder in reverse order of how you removed it.

The field is an electromagnet used to generate a magnetic field in an electro-magnetic machine. Over time, this part can build up a lot of heavy dirt and cause excessive heat in the motor. As a result, this can lead to shorting out and smoke. To inspect the field for shorts and damage, you will have to remove it from the grinder.

Remove the gear box assembly from the grinder. Take off the lower cover and remove the tension springs from the brushes and then pull the brushes out of the brush holders. Pull the armature out of the field and then remove the baffle plate. Remove the power switch by holding it in the OFF position and pressing the switch lever forward. When you hear the click, you can remove the power button. Disconnect the wire connections and remember where they attach to for when you reassemble. Remove the field from the grinder housing. For this part, you may have to bang the housing on a table to free the field as it may be secured tight.

Clean the field with electrical contact cleaner. Once cleaned, check the field for burn marks, indicating sparking and shorting out, which may have caused the motor to produce smoke. If you notice burn marks on the field, it probably needs to be replaced.

You can perform one simple test on the field to check for continuity, using a multimeter. Set the multimeter to the ohmmeter and place a lead on each end of the field. If the reading is infinity, the field is bad and requires replacement. Install the field into the body of the grinder in the correct position for the wires to reattach to their proper connections. You may need a long screwdriver to position the wires with the openings during the installation of the field.

Reconnect all of the wires back to the switch and brush holders. Push the switch lever forward and reinstall the power switch, making sure the lever on the switch catches the lever. Reinstall the baffle plate and then slide the armature back into the field. Reinstall the gear box assembly back on the grinder, followed by the brushes back in the holder. Reapply the tension springs and the lower cover.

The switch controls the power to the motor. Over time, and with use, switches wear out. To check and replace a switch, remove the lower cover. On some models, you will have to also remove the side cover, lock button and paddle. Remove the power cord clamp and then locate the switch. Pull the switch lever away from the switch and remove the switch from the grinder. Remove the wires – make sure you take note of where they go.

Inspect the switch for any burn marks, or melting, indicating a short. Attach an ohmmeter to the switch wires to check continuity. Press the switch in – the ohmmeter should then give you a reading. Now, release the switch; it should say infinity or O.L. If you are not getting these readings, the switch is inoperable and requires replacement.

Attach the wires to the new switch at the appropriate terminals. Install the switch back into the housing and make sure to reposition the switch lever to the button on the switch. Tuck the wires away. Reinstall the cord clamp. Reattach the lower cover or, on some models, reinstall the lock button, paddle and side cover.