Why is a pneumatic grinder spinning too slowly?

Your tool is stalling, 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

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.

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. 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

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Grinders & Sanders

For maximum material removal with minimum effort and high-quality finish, Chicago Pneumatic delivers robust, durable and lightweight easy-to-handle tools.

Surface applications from heavy material removal to fine finishing. Tools designed to bring better comfort and increase your productivity. The range provides random orbital sanders, rotary sanders, pistol sander & polishers, and belt sanders. Secure payment, Afterpay, nationwide delivery. Buy now, pay layer.

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Their combination of power, compactness and light weight gets the job done. Better operator comfort comes with a unique vibration dampening body.
The range provides industrial chipping hammers, weld flux chippers, needle scalers, long reach scalers and rust & weld scalers.

With drilling capacity from 6mm (1/4”) to 50mm (2”), various speeds and power, our drills are designed to handle both your tough and smooth operations. The range provides straight, angle and pistol drills. Secure payment, Afterpay, nationwide delivery. Buy now, pay layer.

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The range provides saws, high speed cutters, nibblers, shears, engraving pens, riveters, caulking guns, air files, and blow guns. Secure payment, Afterpay, nationwide delivery. Buy now, pay layer.

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The perfect solution for all your nailing needs, from framing to decking and more. Our range of professional-grade brad nailers offer precision and durability to ensure you get the best results possible. As a professional tradesperson, our brad nailers are the ideal choice for any nailing task.

Explore our range of staple guns. Our brand of PIT TOOLS by Ash Air heavy-duty staplers we supply are trusted by tradespeople all over NZ.

Our Brad nailers and Staplers are suitable for a range of applications: Bedding and furniture, Cabinets and joinery, Fencing, Framing, Prefab housing, Wall lining, floor covering, cabinet making, trellis and boxes, interior decorative trim, cabinetry, cabinet backing, crafts and hobbies.


The use of the latest technologies and materials, such as composite housing or steel housing for the toughest materials, makes CP Industrial impacts the best in each class. Our versatile line features different clutches such as rocking dog, 2 jaw, pin, single dog or twin dog clutches.

We offer a range of powerful pneumatic ratchet wrenches from ¼’ to ½” square drive for every task.
Due to their small size and light weight, pneumatic ratchets are an excellent choice for fastening in tight or cumbersome applications. Secure payment, Afterpay, nationwide delivery. Buy now, pay layer.

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Ash Air has been around in New Zealand since 1979, and we’ve grown into a nationwide company with international support and a reputation for quality and reliability.We look after all things compressed air for your business!

  • Rotary Screw and Piston Air Compressors
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Ash Air's range of Chicago Pneumatic, ALUP, Pneumatech, and Atlas Copco products are used extensively around the world in industries ranging from oil and gas to food, automotive and farming, and we bring you these world-class compressors here in the land of the long white cloud.Our technicians are compressed air equipment experts and are dedicated to addressing customer needs. Supported with nationwide coverage, Ash Air offers one of the widest selections of compressed air, vacuum pump, and industrial gas equipment and parts available today in New Zealand.

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With Ash Air, you can count on reliability and high performance for even the most demanding applications. We focus our efforts on the following:

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