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Why is a pneumatic grinder spinning too slowly?

Your tool stalls or is not working to its expected performance and you find yourself asking ‘why is my angle grinder spinning too slowly?’, or ‘why has my pneumatic grinder stopped working?’, read on.

March 24, 2019

Material removal Tools Maintenance Grinders Tools Air line Accessories

In this scenario, it’s all too easy to blame the tool itself. However, there are two other fundamental factors that could be causing it to fail – the air line set-up and the maintenance regime – and these are often overlooked.

Linkedin - expert article - airline setup with angle grinder

If your pneumatic angle grinder’s abrasive spin starts to slow down, or the motor stalls when you apply force then this is a tell-tale sign that the tool is not operating at full performance. It is vital to look out for these indicators, otherwise there will be a significant negative impact on productivity.

To try and prevent the tool from stalling, it is common practice to apply less force, but this means more time to complete the job, which results in reduced efficiency. If efficiency is affected, this will have major financial consequences and lead to a decrease in global production.

Let’s take a closer look at the two most common reasons affecting a pneumatic grinder’s performance.

1. Air line set-up & air line accessories

A pneumatic tool’s motor needs two things to work properly and at maximum speed:


  1. A dynamic air pressure of 90 psi / 6.3 bars at the tool inlet 
  2. Air flow as recommended by the tool manufacturer

Without the correct pressure and flow, the tool’s motor will not have enough energy to run the abrasive at full speed, resulting in a suboptimal efficiency (for rated speed, always check the abrasive manufacturer’s recommended speed).

How to get the right dynamic air pressure and air flow?

The choice of the right air line accessories (such as hose, couplings, FRL) is critical to ensure your tool’s performance.
To demonstrate how performance can be affected, we have set up a CP3650 industrial pneumatic grinder with two different hose set-ups:


  1. One with the manufacturer recommended hose diameter (in this case: ½”) 
  2. One with a smaller hose diameter (in this case: 3/8”)

See the difference in performance for yourself – it’s astounding!


To ensure accessories fit the tool perfectly and deliver the best performance level, always refer to the tool manufacturer’s recommendations.
There are four key values to consider when selecting your air line accessories:


  1. air line size, 
  2. air inlet type, 
  3. maximum air consumption at load, 
  4. recommended hose diameter/length.

To get tips on making sure you have the right air line set-up and good habits (such as air lubrication), download our guide Is your air tool installation right? This guide includes a valuable check list to help you do your own air line set-up evaluation.


2. Tools maintenance

Just as you would perform regular maintenance on your car, it is vital to carry out routine maintenance on your tools – to ensure they are kept in excellent working condition, and delivering a consistent high performance. After all, pneumatic tools are mechanical systems comprising wear parts that need regular inspection and changes (as required).

The parts that wear most frequently in pneumatic industrial grinders, and need regular maintenance are:


  1. Blades, with inspection recommended every 500 h
  2. Bevel gears (angle grinders and sanders only), with the maintenance interval specified as every 1000 to 2000h depending on the tools

Information relating to proper maintenance is available in the tool’s operator manual and you can read more about pneumatic tools maintenance in our blog: How to maintain pneumatic tools and optimize performance in industrial applications.


Get in touch with a manufacturer’s authorized repair center.

If the problem remains after you have checked the air and referred to the tool’s maintenance instructions, only then can you consider the problem to be with the tool itself and you should get in touch with a manufacturer’s authorized repair center.

“ Ultimately, by having a good setup, the tool will work well to a high performance, and you will be able to remove more material, which enables you to save time and operate more efficiently. ”

Lucas Bryk , Global Product Marketing Manager, Material Removal