Why is My Angle Grinder Running Slow?

Why is my angle grinder is running slow?

Your grinder is running slow because you are using the wrong disk or your disk is unbalanced. A worn carbon brush or a low pressure are other reasons your grinder is running slow.


angle grinder running slow


Wrong or unbalanced disk

An angle grinder often features various  grinding wheels and disks to accommodate its many uses. If you are using the wrong or unbalanced disk, your angle grinder will start running slow. Make sure you are using the right disk for the job in size and type.

You should  also examine the disk for signs of wear, such as dull blades, chipped edges, cracks, or uneven wear. Once you’ve checked it and the disk has any of these sign, then you should replace the disk.


Worn carbon brushes

The carbon brushes can be shortened or worn out if the angle grinder doesn’t run at a steady pace. In an electric motor, the carbon brushes are the two components that connect the commutator to the armature, allowing current to flow from the former to the latter as the armature rotates. The motor’s efficiency can drop if its carbon brushes are worn.

If the carbon brush is worn-out, you need to replace it. Please refer to the manual if you need clarification on how to change the carbon brush.


Low pressure

Your angle grinding will keep running slowly if the pressure is low. A tool’s motor won’t be able to operate the abrasive at maximum speed unless the pressure and flow are just right (for rated speed, always verify the abrasive manufacturer’s suggested speed).


How to fix a grinder that is running slow?

You can fix a grinder that is running slow by replacing the carbon brushes. Setting the right pressure or tightening the nut is another way to fix a grinder that is running slow.


Replace the carbon brushes

A worn carbon will make your grinder run slowly. Replacing this brush is very essential for your grinder to start working effectively. Here is how to replace it;

  1. Remove the handle and remove the top section.
  2. Remove the handle by removing its top section.
  3. Remove the paddle unit.
  4. Remove the button that locks the door.
  5. Split the field case from the handle.
  6. Use long-nosed pliers to disconnect the brush wire from the terminal
  7. Use long-nosed pliers to separate the brush spring from the brush arm
  8. Lift (rotate) the brush arm assembly to access the brush.
  9. Remove the brush from the arm assembly.
  10. Repeat this process to remove the second motor brush (on the opposite side of the grinder).
  11. Insert the brush lead (wire) through the opening in the brush arm.
  12. Seat the new brush into the brush arm assembly.
  13. Spin the brush arm assembly until it reaches a lower position above the armature.
  14. Reinstall the brush wire.
  15. Reconnect the brush spring with needle-nose pliers.
  16. Install the second brush in the motor similarly (on the opposite side of the grinder).
  17. Simply rejoin the handle unit to the field case.
  18. Reinstall the lock-on button.
  19. Reinstall the paddle assembly.
  20. Reinstall the top half of the handle assembly.
  21. Secure the handle with the screws.


Set the right pressure

Without the right pressure, your angle grinder will keep running slowly. Setting the right pressure is the only fix for this issue. Here is how to set the right pressure;

  1. Use the flat part of the wheel.
  2. Maintain a 20° to 30° angle between the tool and the surface you’re working on.
  3. You should face the back of the blade guard toward yourself.
  4. Move the flap disc back and forth in a fluid motion to smooth the fabric.
  5. Let the wheel work, but push hard enough to ensure you’re getting things done.

Note: Depending on the tool and grinding wheel’s ratings, an industrial grinding application’s ideal pressure draws between 8 and 10 amps.


Tighten loose nut

Angle grinders are useful not only because of the disc’s surface but also because of how fast it runs. When the wheel gets too loose, it prevents the angle grinder from running effectively. Here is how to tighten it;

  1. Check how the nut is attached to the main wheel’s center spindle.
  2. If it’s loose, use pliers or a wrench to tighten it.
  3. If you need to, clean the parts of the center spindle and add a little oil to keep it moving.


Why your angle grinder is spinning slowly?

The reason your angle grinder is spinning slowly is because of a worn-out spindle. A worn carbon brush or excessive dirt in the field is another reason your angle grinder is spinning slowly.


Worn-out spindle

The spindle is housed in a separate box. The spindle is threaded on one end to attach the grinding wheel. The armature gear’s bearing and spindle gear, which receive power at a right angle, are located at the opposite end.

A worn-out or broken spindle won’t sit properly in the housing. If the spindle no longer sit properly in the housing, your angle grinder will start running slowly. You need to replace the spindle to solve this.


Worn carbon brush

Carbon brushes rotate on the commutator to transfer current to the armature. When the carbon brushes of a motor are old, dirty, and worn, they demand more current, spark more, and cause the angle grinder to run slowly. You need to examine it first by taking apart the machine’s parts: the back cover, the brushes, and the tension springs.

If after examining it and you notice any wear, you need to replace the carbon brush.


Clogged field

The field is an electromagnet that makes a magnetic field. Over time, this part can get a lot of heavy dirt on it, which can cause the motor to run slowly. If you don’t fix it, it will lead to bigger problems, like a short circuit, smoke, and the field failing.


How to adjust the speed on a grinder?

You can adjust the speed on a grinder by using a router speed control. Fitting a belt pulley or using a variable frequency drive is another way to adjust the speed on a grinder.


Router speed control

If the motor on your angle grinder has less than 1HP, you should be able to use a router speed control to regulate the tool’s speed. Here is how to use it;

  1. Use low settings of around 2000 RMP for burnishing metals
  2. High speeds in the region of 5000 to 7000 for cutting hard materials.
  3. Change the router’s speed so that there are no vibrations.


Fitting a belt pulley

You can change how your angle grinder works by putting a belt pulley in place of the wheel. Here is how to fix it;

  1. Connect a V belt to a secondary shaft with a larger pulley wheel.
  2. The gear ratio would then be the diameter of the small pulley/diameter of the large pulley.


Variable frequency drive

A variable frequency drive is a piece of electrical and mechanical equipment that can change the speed of an angle grinder by changing the frequency of the power going into the motor. Here is how to adjust it;

  1. J1 (upper board) – 230V/115V – This jumper lets you switch between 230 and 115 VAC input voltage. It’s already set to 230V.
  2. J1 (lower board) – 50/60Hz – This jumper lets you switch between motors with ratings of 50Hz and 60Hz. It’s already set to 60Hz.
  3. J2 (lower board) – 2x RPM: This jumper lets the motor spin up to twice as fast as its rated speed.


Why your Makita grinder is running slow?

The reason your Makita grinder is running slow is because the brush holder is clogged with dirt. The holders protect the brushes and springs and ensure that they may move freely up and down on the commutator. The holder’s ability to maintain uniform pressure on the commutator can be compromised by wear and tear or a buildup of debris, leading to your Makita grinder running slowly.


Replacing the holder is essential for your Makita grinder to start running effectively again. Here is how to fix it;

  1. Unscrew and remove the side handle from the grinder.
  2. Loosen the lock screw on the guard assembly.
  3. To remove the guard assembly from the housing, rotate it counterclockwise.
  4. Rotate the guard
  5. Remove the guard from the grinder.
  6. Remove the screw from the rear cover.
  7. Slide the rear cover away from the motor housing.
  8. To remove the brush spring from the carbon motor brush, carefully pry it up with a pick.
  9. Reposition the brush spring alongside the motor brush (against the brush holder).
  10. Adjust the spring
  11. Pull the wire from the brush holder’s terminal.
  12. To remove the brush from the motor, slide the brush holder to the side.
  13. Get the brush holder wired field disconnected (this wire is often black).
  14. Lift and reposition the brush spring back into the (now empty) slot on the brush holder.
  15. Take the brush holder’s screws out.
  16. Bring up the brush holder and take it away from the motor.
  17. Replace the old brush holder with the new one inside the motor.
  18. You may need to reposition the brush spring to access the mounting hole.
  19. Put the two screws in the brush holder to keep it in place.
  20. After installing the new brush holder, reconnect the field wire to its termination.
  21. You may need to reposition the brush spring to reach the motor brush slot.
  22. Set up the motor brush by inserting it into the brush holder.
  23. Join the holder’s terminal and the brush’s wire.
  24. The brush spring must be repositioned to press against the motor brush.
  25. Repeat (as necessary).
  26. The two motor brushes in your Makita grinder look like this: (and two brush holders). These can be found on the motor’s outer and inner casings. Methods on both sides are equivalent. Look at the other brush holder and see if it needs to be replaced (as necessary).
  27. Put the back cover back on.
  28. Check the wiring for any obvious “pinch places,” and tuck or reposition the wires as needed.
  29. The rear cover slides onto the motor housing.
  30. Insert the screw to fasten the back cover.
  31. The guard must be re-set.
  32. The guard assembly’s mounting plate can be engaged by rotating it 90 degrees.
  33. Screw into place to tighten the guard.
  34. Put the side handle back in place.