Grinder: Bad Vibration

A worn out bearing will have play in it, which will cause a bad vibration inside the grinder. To replace the bearing, remove the grinding wheel with the inner and outer flanges, then remove the wheel cover and handle. Remove the screws securing the gear box assembly to the grinder and then separate the gear box assembly from the grinder. Remove the screws on the spindle assembly and separate it from the gear box assembly. Depending on your angle grinder, the next steps may vary according to how the bearing and gear are both positioned on the shaft as it is different between manufacturers and models.

Method #1: Remove the retaining ring, securing the spindle gear on the spindle. Remove the spindle gear with the woodruff key. Once the gear is removed, there may be another retaining ring or screws securing a cover, holding the bearing in place, that will need to be taken off to access the bearing. Once you have access to the bearing, clean out the old grease then press out the bearing with your fingers. Install the new bearings in, evenly by hand, and then apply new grease. Reinstall the cover, or retaining ring to hold down the bearing and then install the woodruff key, spindle gear, and retaining ring. Make sure the woodruff key stays in place during installation. Reinstall the spindle box assembly to the gear box assembly and then reinstall the gear box assembly to the grinder. Reinstall the wheel cover and then reinstall the grinder wheel, with flanges, and secure the lock nut.

Method # 2: Use a bearing puller, or separator, to remove the bearing on the spindle shaft. There may be a second bearing on the lower part of the spindle, depending on the model. Therefore, you will have to remove the retaining ring and gear to access the lower bearing. Place the new bearing on the shaft and use a socket that that only makes contact with the bearings inner race, to avoid damage to the bearing, and tap it in place with a hammer. Reinstall the spindle box assembly to the gear box assembly and then reinstall the gear box assembly to the grinder. Reinstall the wheel cover, handle and then reinstall the grinder wheel, with flanges, and secure with the lock nut. There are two bearings on the armature: one of the front and one at the rear. To replace a bearing on the armature, remove the gear housing from the grinder. Remove the lower cover and locate the brush holders. Move the tension springs to the side and remove the brushes. For other models, remove the brush caps, located on the side, and pull the brushes out. Pull the armature out of the grinder. Remove the retaining ring and the armature gear from the armature, if replacing the front bearing. Using a puller, or bearing separator, remove the bearing. Install the new bearing on the shaft by using a socket that only makes contact with the inner race of the bearing, to avoid damage to the bearing, and tap it in place with a hammer. Reinstall the armature gear and retaining ring. Slide the armature back in the field, inside the grinder. Reassemble the gear housing to the grinder. Reinstall the carbon brushes and reapply the tension springs on the brushes and reinstall the lower cover.

The carbon brushes supplies electricity to the motor. In some conditions, the commutator slots may become filled with foreign material. This can cause the brushes to vibrate, or cause a ring fire, by allowing current to leak through, from one bar to the other. To fix this, remove the gear housing from the grinder. Access the carbon brushes by removing the bottom cover. Move the tension springs aside and then take out the brushes. Some models have brush caps, located on the side of the grinder. Remove the caps to take out the carbon brushes.

Pull the armature out of the grinder and inspect the commutator slots for any build-up. Then, inspect the brushes. If the brushes are 1/8 of an inch, or less, then they need to be replaced. If they are in good shape, gently sand them down, with fine sandpaper, to get them nice and smooth on the surface that makes contact with the commutator. Using only an electrical contact cleaner, spray the commutator and clean with a soft-bristle tooth brush to remove oil, grease and dirt build up. Next, cut a piece of only 600-grit aluminum oxide sandpaper and wrap it around the commutator, rotating it only in a full-direction motion – never back and forth, to avoid damage. Rotate the commutator in the direction it travels, only. Clean in-between the bars, using a plastic scriber to avoid damage.

Reinstall the armature back in the field, inside the grinder. Reassemble the gear housing on the grinder. Reinstall the carbon brushes and reapply the tension springs, or reinsert the brush caps, followed by the lower cover.

Flanges must be in perfect condition as they spin at a high rate of speed. Any damage on a flange will cause a vibration. Remove the locking nut and remove the outer flange, disc and inner flange. Inspect all around the flanges for any signs of damage, such as cracks, chips or anything else out of the ordinary. Replace any flanges showing signs of damage. Install on the grinder and tighten the lock nut.

A worn out, or damaged gear, will make a grinding noise, not spin true and will cause a bad vibration from the grinder. To replace a gear, remove the grinding wheel, with the inner and outer flanges, and then take off the wheel cover and handle. Remove the spindle box assembly from the gear box assembly. Inspect the spindle gear for any signs of damage and replace if necessary. This procedure will vary between models. Using a bearing separator, or puller, take out the bearing and then remove the gear with the woodruff key. Install a new spindle gear into the spindle with the woodruff key, making sure the woodruff key stays in place during installation. Install the retaining ring.

Reinstall the bearing, using a socket that only makes contact with the bearings inner race to avoid damage to the bearing, and tap in place with a hammer. With the spindle box assembly removed, you can inspect the armature gear inside the gear housing. To replace the armature gear, remove the gear housing off the grinder. Remove the retaining clip, or the nut, and pull the gear off and then install the new armature gear. Reinstall the retaining ring or nut. Reassemble the gear housing onto the grinder. Repack the spindle housing with grease. Reattach the spindle box assembly to the gear box assembly and then reinstall the wheel cover, handle, followed by the grinder wheel, with flanges. Finally, secure the lock nut.

The grinding disk takes the most amount of abuse as it spins at a high rate of speed, making contact with objects. The disc should be the first thing to check when experiencing a vibration as they wear down, causing the disc not to spin true anymore. Replace the disc as needed by removing the lock nut and outer flange and then installing a new grinding disc, with the outer flange and tighten down the locking nut.