Buying guide for Best air die grinders
Air die grinders are remarkably versatile tools. You’ll find them in garages and workshops everywhere, used for everything from shaping plastics to carving wood to polishing metal.
Air die grinders have no motor of their own — they’re powered by a compressor. That means the unit can be more compact and lighter while producing equivalent or greater power than its electric counterparts. There’s also less that can go wrong, which results in minimal maintenance.
Given the advantages, it’s no surprise that air die grinders are very popular, and manufacturers have responded with dozens of different models for you to choose from.
Key considerations
What air die grinders can do
Perhaps paradoxically, air die grinders (also called pneumatic grinders) owe much of their versatility to their simplicity. Basically, they're a tool with a head that rotates very fast, but because you can fit them with many different bits, they can be used to sculpt, cut, grind, or polish all kinds of materials.
That being the case, you’ll find them in the shops of professional woodworkers, engineers, auto technicians, welders, and a host of other trades and crafts. They’re also very affordable, which helps to make them suitable for people with home workshops that already have a compressor or who are thinking of investing in one.
Features
Almost all air die grinders have a similar design: a steel or aluminum body has a lever trigger/throttle on the side. It’s a simple and ergonomic design. You wrap your hand around it and squeeze. The only disadvantage is that it’s easy to operate accidentally, or when you put the tool down, and that could be dangerous. Good models have a safety lock to prevent this from happening.
Tool head
The tool head is either straight (in line with the body) or at a 90° angle. Which is the better choice very much depends on the work you need to do. An angled head can get into spaces a straight one might not, but the straight tool is often preferred for precision. If you can’t decide, or you think you need both, there are some very cost-effective twin-packs available.
Expert Tip
When using a grinder, give yourself plenty of hose length. You don’t want to minimize performance or safety.
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Power
It can be difficult to assess power, and often figures aren’t easy to find. Sometimes the horsepower (hp) is given, but it doesn’t mean much when a 1/4 hp tool is quite powerful in these circumstances. The best indication is air consumption, given in cubic feet per minute (CFM). Generally, this runs from around 1.5 CFM for pencil-grip precision air grinders, to 6 CFM for heavy-duty models. For the technically minded, it’s not air pressure — which is probably a constant 90 pounds per square inch (psi) — it’s actual volume of air.
Speed
You’ll also get speed ratings, usually between 20,000 and 25,000 revolutions per minute (rpm) Precision types go higher. It’s important to note that this is “free speed,” in other words, without a bit attached, because the type of bit (and the material you’re working on) will make a huge difference to actual operating speed. That’s where the difference in CFM will make itself felt, with higher airflow providing increased drive.
Insulation
High rotational speeds can make air die grinders vibrate quite a lot. Not a problem if you’re only using one for short periods, but uncomfortable if you’re working with it all day. Some of the top models have rubber casings that provide insulation. With those that don’t, it’s worth checking customer feedback to see if real-world users think it’s a problem.
Collet
Most air die grinders have a 1/4-inch collet. The range of bits available is enormous. However, for delicate work, a bit with a 1/8-inch shank might be preferred. Some air grinders come with an optional 1/8-inch collet, but not all, and adapters may or may not be available, so this is actually quite an important factor.
Expert Tip
As with all power tools, secure loose clothing and long hair when using grinders.
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Exhaust valve
An exhaust valve is necessary to allow the air to escape. Where this is positioned is another point to consider. You don’t really want it in your face, but having fast-moving air blowing across the workpiece might be a problem. Having said that, for someone else, having the debris blown away could be a bonus!
Weight
Although none of these tools is particularly heavy, the weight is worth thinking about if you’re using one for long periods. It will also have a minor impact on maneuverability.
A note about safety
Compressed air doesn’t seem dangerous, but it can be lethal. If a tool is pressed against the skin, air can penetrate and cause an embolism — an air bubble in the bloodstream. If it reaches your heart, it can kill you.
Used properly, there isn’t any risk, but never mess around with these tools. Take the same precautions with an air die grinder that you would with any power tool. Wear gloves, safety glasses or a face shield, and respiratory protection appropriate to the task you’re performing. Compressors and die grinders can be noisy, so earplugs may also be needed.
Expert Tip
Use a bench vise if the project piece is not already secure.
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Accessories
Disc holder: Protool Roloc Disc Pad Holder
This is a cheap but indispensable tool for increasing the versatility of your air die grinder. A hard-wearing rubber pad with a 1/4-inch steel shank accepts 3-inch-diameter disposable sanding, grinding, and polishing pads. Screw-in fitting ensures you don’t get the fly-off problems associated with hook-and-loop pads. A 2-inch version is also available.
Mandrel: Weiler 56490 Mandrel for Type 1 Cutoff Wheels
Another low-cost accessory. Takes 3-inch aluminum oxide cutoff wheels used to slice through plastic, fiberglass, iron, and steel. Made of tough carbon steel, with a standard 1/4-inch shank, this mandrel accepts wheels from 1/16- to 1/4-inch thick.
Grinding burrs: Osidu Carbide Rotary File Set
Made from extremely hard tungsten carbide blanks, these high-quality burrs have a unique double-cut tooth angle that grinds metal and wood with remarkable efficiency and stays sharper longer. There are ten different shapes and sizes, each with a 1/4-inch shank, supplied in a convenient stand.
Air die grinder prices
Inexpensive
The cheapest air die grinders we found cost around $20. They offer useful features and adequate performance for the occasional user.
Expert Tip
As many of these tools do not have lock-off safety switches, use care when handling them, and be sure to cut the power when changing bits.
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Mid-range
Between $30 and $60, you’ll find a wide choice of durable, high-quality tools for home and trade use, including models from many of the industry’s leading names. Few users will need to spend more.
Expensive
Heavy-duty and specialized air die grinders can exceed $60 (long-reach models, for example), but of the dozens we looked at, only one tool topped $100.
FAQ
Q. What’s the difference between an air die grinder and a rotary tool?
A. In a nutshell, performance. While they both do similar jobs in terms of providing drive for various rotating bits, a compressor-driven die grinder is much more powerful than the electrically powered rotary tools from Dremel and similar devices.
Q. What about the difference between an air die grinder and an angle grinder?
A. OK, the angle grinder is another step up in terms of power: rotary tool, die grinder, angle grinder, if you like. However, the angle grinder is limited to circular discs, and because of its high performance, mostly requires two hands to hold it. The die grinder is a more versatile tool, easier to control, and capable of greater precision.
Q. How do I know if my compressor is big enough to handle an air die grinder?
A. All these tools (in fact, all air-powered tools of any kind) should have a CFM (cubic feet per minute) rating, which is the amount of air they consume while operating. If your compressor matches or exceeds that figure, you’re good to go.
