Buying guide for Best die grinders
Die grinders have long been popular in professional metalworking, welding, and auto shops. They’re relatively easy to handle and offer plenty of versatility for grinding, shaping, and finishing tasks. They’re sometimes confused with rotary tools like the Dremel, but most are considerably more powerful. They have a greater range of power options and can use larger, more aggressive accessories. That said, they’re capable of fine detail work, and while perhaps most often used for metal, they can also grind wood or plastic.
While heavy-duty die grinders are still largely the tool of the professional, there are lighter, more user-friendly tools for home and hobby workshops. These can be useful for everything from vehicle restoration projects to works of art.
Key considerations
Power source
Pneumatic die grinders get their power from an air compressor. These are usually high-performance tools and with no motor in the tool itself, they can be light and compact. There is little to go wrong, so they’re also very durable. And even high-quality models are not expensive.
However, high-pressure hoses are quite stiff, which can make the pneumatic tool a little awkward to maneuver. It’s also important to check the air demands of the tool (given in cubic feet per minute, or CFM). If you don’t already own an appropriate compressor, the additional cost can be considerable.
Corded die grinders would seem like an obvious solution for those who don’t own a compressor, and there are high-quality models available from a number of top brands. The motors are usually sealed to prevent damage from dirt and grit. Many kits include accessories, which isn’t always the case with pneumatic die grinders. With no need for a compressor, a corded die grinder is much more portable.
However, given the length of the cord on the tool, you might sometimes need to use an extension cord. And compared to air-powered tools, corded die grinders are quite expensive, and your choice is much more limited.
Cordless die grinders offer the user complete freedom of movement. They are very popular with home users and great for light- to medium-duty grinding tasks. Brushless motors maximize battery performance.
However, cordless models aren’t as powerful as pneumatic or high-end corded die grinders. And a spare battery is usually something of a necessity for extended work periods. These are often sold as bare tools, meaning the battery and charger are not included. This adds to what is already a premium-priced option, and it’s possible to buy a modest compressor and pneumatic die grinder for the same money as a cordless model plus battery and charger.
Staff Tip
With cordless die grinders, a higher ampere-hour rating for the battery means a longer run time. If you’re getting a spare battery, this is the feature to maximize.
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Features
Performance
It isn’t easy to compare die grinder performance across different power options. Pneumatic tools are sometimes rated in horsepower (hp) but usually in cubic feet per minute (CFM). Corded models use amps and/or watts, while cordless models rate the battery power in volts.
Pneumatic die grinders rely on the power of the compressor. Entry-level tools start at around 2 CFM. General-purpose tools are 5 to 10 CFM. Heavy-duty models can exceed 40 CFM, though these are rare.
Corded die grinders run from 3.5 amps for light- to medium-duty tools up to 10 amps for high-performance models.
Cordless die grinders are either 18 or 20 volts, which are actually the same: 18 volts is the nominal output when the tool is running normally, whereas 20 volts is the surge demanded at start-up. Some manufacturers choose to use one figure and some the other, but there is no real difference.
Speed
The other figure often used with these tools is revolutions per minute (rpm) which can run anywhere from 2,500 to 25,000 rpm. While high numbers sound impressive, wood and plastics cut better at relatively slow speeds, so it’s important to think about the intended use.
Air die grinders are controlled by a trigger, and while skilled users can “feather” this, they are effectively either completely off or on at full power. Some corded and cordless models have variable speed control which might appeal to less-experienced users.
Configuration
The head of the grinder is either straight (in line with the body and motor) or at 90° to it. It isn’t a question of one being better than the other, rather, which design suits the user's purpose better. Some kits include both.
The method used to grip accessories is a collet, which is a simplified version of a chuck. They have little adjustment: they’re either open or closed to grip the bit. There are three sizes:
1/4 inch: This is by far the most common size.
1/8 inch: Some die grinders have this as an option, which allows them to use the smaller accessories sold for rotary tools like the Dremel.
1/2 inch: Very heavy-duty models are this size and are really the preserve of specialists.
Body
Body design varies little, and it’s clear to see the difference between pneumatic tools (with an air inlet at the rear) and corded or cordless tools. The latter are physically bigger because they need to contain the motor.
Some pneumatic die grinders are designed specifically for use in cramped spaces. While the bodies have a similar shape, the material of the casing varies.
Chrome or polished metal bodies are tough and easy to keep clean in a busy workshop, but they can be difficult to grip, especially when cold.
Composite (usually fiberglass and/or plastics) bodies offer a more positive grip, as do those with textured or rubberized areas. These also reduce vibration, making them more comfortable to hold for long periods.
Pencil grip
An interesting variation on the standard is tools that offer a pencil grip option. This is a slender extension with an internal cable that transmits rotary power from the standard collet, along a cable, to a pencil-type head. It allows you to reach into otherwise inaccessible areas, and it’s much easier to control for detailed work.
If you’re considering an air-powered die grinder, check that your compressor delivers sufficient cubic feet per minute. The necessary figure should be mentioned in the tool’s specifications.
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Accessories
Grinding burrs: Wokesi Burr Set
Cheap grinding burrs can wear out quickly, while tungsten carbide is very hard and maintains its cutting edge far longer. This ten-piece set from Wokesi has a 1/4-inch shaft that fits most die grinder collets and a variety of different profiles. A plastic case keeps the burrs organized.
Abrasive disk holder: Ram-Pro Roloc Disk Holder
This is a low-cost yet durable holder for standard 2-inch quick-change abrasive disks (known as either Roloc or roll lock). It has a 1/4-inch shank suitable for use in die grinders and drills, and it’s rated for up to 20,000 rpm.
Pricing
Inexpensive: The cheapest of these devices are air-powered tools. They cost around $25 to $35 for lightweight, aluminum-bodied models that are perfectly adequate for occasional DIY and hobby use.
Mid-range: There are some highly-rated air die grinders in the bracket between $35 and $70. They are ideally suited to home use, auto enthusiasts, as well as professionals.
Expensive: Heavy-duty air tools and corded and cordless grinders run from $70 to $200, though with cordless models a battery and charger are unlikely to be included at this price, and they could add another $100.
Staff Tip
With electric die grinders, the cable length is often overlooked. Some can be frustratingly short, making an extension cord a necessity.
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Tips
- Secure your workpiece in a vise or clamp. While you can sometimes hold the workpiece in your hand, using a clamp or vise on small pieces is safer, more secure, and allows for more accurate grinding.
- Move the tool around as you work if possible. This ensures that you use different parts of the grinding burr or abrasive, which makes for more efficient cutting and distributes the wear.
- Don’t force the tool. It won’t cut any more quickly, and it will put unnecessary strain on components.
- Use the correct burr for the job. Generally speaking, coarse, open burrs are designed for cutting wood and plastic, medium burrs are for soft metals like brass and aluminum, and fine burrs are for steel and cast iron.
FAQ
Q. Can you cut with a die grinder?
A. It is possible to buy an arbor and mount cut-off wheels. However, many experts avoid the practice because the cutter is unguarded. A proper cut-off tool should be used, and there are very affordable models available.
Q. What is the difference between a die grinder and an angle grinder?
A. Die grinders are generally smaller and operated with one hand. The abrading or polishing attachment can either be in line with the body or at right angles to it. Angle grinders are larger, frequently more aggressive (requiring the use of two hands), and use disks at 90° to the body.
Q. Is it the same as a rotary tool?
A. They are very similar in basic design and function. However, rotary tools have comparatively modest power and are often seen as craft or hobby tools. Die grinders are a more general-purpose tool, capable of both detailed and heavy-duty tasks.
