Grinder: Grinding Wheel Wobbles

A worn out bearing on the spindle can cause the grinding wheel to wobble. To replace the bearings on the spindle, remove the grinding wheel with the inner and outer flanges and then remove the wheel cover and handle. Separate the gear box assembly from the grinder and then separate the spindle assembly from the gear box assembly. Depending on your angle grinder, there are a couple different ways to replace the bearing on the spindle.

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

Method #2: Using a bearing puller, or a bearing separator, remove the upper bearing from the spindle. There may also be a lower bearing on the spindle as well, but not all models do. To access the second bearing, remove the retaining ring, spindle gear with the woodruff key, lower retaining ring and second bearing. Place the new bearing on the shaft and use a socket that only makes contact with the bearings inner race to avoid damage to the bearing. Tap it in place with a hammer. Reinstall the lower retaining ring, spindle gear with the woodruff key – making sure the woodruff key stays in place during installation. Reinstall the upper retaining ring and the upper bearing. Reattach the spindle box assembly to the gear box assembly and then reinstall the gear box assembly back on to the grinder. Reattach the wheel cover, handle the grinder wheel with flanges and secure with the lock nut.

The flanges provides strength on the wheel. If a flange is broken, it will cause a wobble and will not be able to sit flush against the grinding wheel. Remove the locking nut and take out the flange, grinding disc and inner flange. Inspect the flange for damage, equal size, relief around the wheel’s hole and the correct diameter. The diameter of a flange must be equal to, or greater than, one-third of the wheel’s diameter. Replace flanges as needed and reinstall. Install the inner flanges, grinding wheel and outer flange and then tighten with a lock nut.

The spindle gear transfers power from the armature gear at a 90-degree angle. Over time, gears wear down, especially if they get used for heavy-duty jobs. If the center hold of the gear wears, or the keyway wears, it can produce a wobble on the spindle and can transfer the wobble to the grinding wheel.

This procedure will vary slightly between different makes and models. To replace the spindle gear, remove the grinding wheel, with the inner and outer flanges, and then remove the wheel cover. Take out the screws securing the spindle box assembly to the gear box assembly and separate. Remove the bearing with the bearing separator or puller. Take out the retaining ring that secures the spindle gear on the spindle and then the gear with the woodruff key.

Install the new gear onto the spindle with the keyway – always install a new keyway with a new gear. Make sure the keyway stays in place during the installation. Install the retaining ring and then the bearing. Place a socket on top of the bearing, making sure it only makes contact with the inner race of the bearing to avoid damaging it. Tap in place with a hammer. Reinstall the spindle box assembly to the gear box assembly. Reattach the handle and the wheel cover, followed by the flanges and grinding wheel. Tighten with the lock nut.

The spindle is located inside the spindle box assembly. The spindle is threaded on one end in order to mount grinding wheels. The other end houses the bearing and the spindle gear that transfers power at a 90-degree angle from the armature gear. If the spindle is warped from too much pressure being applied, then the grinding wheels will wobble and the spindle will require replacement.

To check and replace a warped spindle, remove the grinding wheel with the inner and outer flanges, followed by the wheel cover and the handle. Take out the screws securing the spindle box assembly to the gear box housing and then separate. Depending on your model, the bearing and gear placement may be in reversed positions on the spindle. Remove the spindle bearing with a bearing separator or a bearing puller and then take out the retaining ring – and the wave washer, if your unit has one – and the spindle gear. Remove the gear, with the woodruff key, and then the spindle housing from the spindle and take out the labyrinth ring. Take one gauge, held perpendicular to the surface of the spindle, and slowly move it across the surface of the part axially as the part is rotated. If the gauge varies at any point by more than the total run-out tolerance, the part would be out of spec.

Install the parts in reverse order into a new spindle, making sure the woodruff key stays in place when installing the spindle gear. When installing the bearing, place a socket that only makes contact with the inner race of the bearing to avoid damage. Use a hammer to tap the bearing in place. Reattach the spindle assembly box to the gear box housing. Install the wheel cover, inner flanges, grinding wheel and outer flange onto the spindle and tighten with the lock nut. Reattach the handle to the grinder.

If your unit has flat washers and wave washers, make sure the faces of the flat washer are smooth and not rough. Check that both the flat washer and wave washer are not broken or damaged. Ensure the center holes of the washers are not too big on the shaft. These symptoms can cause the grinding wheel to wobble.

Remove the grinding wheel, with the inner and outer flanges and then remove the wheel cover. Remove the handle as well as the screws securing the spindle box assembly to the gear box housing, then separate. Depending on your model, the bearing and gear placement may be in reversed position on the spindle. There also may be one or two bearings, depending on the model. Remove the spindle bearing with a bearing separator or a bearing puller. Remove the retaining ring and wave washer. Inspect the wave ring and replace if damaged, including play inside the center hole. Take out the spiral bevelled gear, with the woodruff key and inspect the flat washer for damage and for play in the center hole.

Reassemble all the parts in reverse order of removal. Reattach the gear box housing to the gear box assembly. Install the wheel cover back on to the housing and reinstall the inner flange, grinding wheel – with the outer flange – and tighten with the lock nut. Reinstall the handle.

The first thing you should check is the grinding wheel, since it is the easiest thing to check and takes all of the abuse. It is also the first thing to cause the wobble. As grinding wheels get used, and with age, they will go out of round. Install a new grinding wheel first to see if this solves your problem. Check the expiry date on the grinding wheel. Grinding wheels can fly apart during operation from fatigue, causing serious hard. To install a new grinding wheel, remove the lock nut with the wrench. Remove the outer flange and grinding wheel. Install the new grinding wheel and outer flange on the spindle and tighten the lock nut. Be careful not to over tighten. Some grinding wheels have the but and flange built into them as an all-in-one-unit.