Die grinders and accessory bits
(Image/Wayne Scraba)

Die grinders are the perfect tool for many jobs such as porting and polishing, cutting, and of course, grinding. Die grinders were first used to finish and match profiles of dies for metal stamping, die-casting, forging, and plastic molding. They’re typically small, powerful and easy to control (at least with practice). 

Die grinders are available in electric (corded), battery-powered, and pneumatic (air-powered) versions. Some folks prefer electric and battery die grinders because they’re not quite as powerful as an air-powered tool. That means they can be used with more precision. Air-powered grinders are light, powerful, and less costly than their electric counterparts. Many have a voracious appetite for air, requiring a good size compressor to keep up.

Rotary tools can also be considered die grinders. They’re small and compact, but don’t expect them to do the job of a bigger die grinder. Rotary tools are best for small project and detail work.

There are three die grinder configurations–straight, 90-degree (right angle), and 45-degree. Straight die grinders are the easiest to handle and the best choice If your budget permits just one tool. 90-degree die grinders allow you to get into spots you can’t access with a straight die grinder. They also provide some flexibility when using the die grinder with a cut-off wheel. The same applies to 45-degree tools.

Straight die grinders are also available in ‘mini’ sizes, roughly one-half to two-thirds the size of a standard die grinder. They’re useful in areas a regular grinder can’t fit. Extended nose die grinders are also available. They typically have five- or six-inch extension on the nose that allows you to reach deep inside something like a long cylinder head or intake manifold port. Keep in mind control lessens when you’re dealing with an extended nose die grinder. That’s one reason why good pro head porters earn their keep.

Noise is an issue with air tools. Manufacturers have spent considerable engineering time working on the exhaust end of their die grinders and other air tools. By tuning the exhaust you can reduce noise; some pneumatic die grinders are rated at 82 decibels or less. That’s downright quiet compared to the sound of a compressor pounding away in the background.

There are all sorts of bits for die grinders–burrs for grinding, cutting stones and rolls for light grinding and polishing, flapper wheels and cross buffs for polishing, and cut-off wheels for, well, cutting. Most are made for tools with 1/4-inch collets. There are adapters that allow a conventional die grinder to accept an 1/8-inch collet, but it’s best to avoid those if you have a very high-power tool. Big power plus a small diameter spindle can quickly spell trouble. 

As you can see, there’s much more to die grinders than first meets the eye. Check out the accompanying photos for a more detailed look.

AIRCAT air die grinder, straight style
If you can only budget for a single die grinder, go for a straight type like this AIRCAT air-powered grinder. They’re the easiest to control. (Image/Wayne Scraba)
AIRCAT air die grinder, 90-degree style
Die grinders with 90-degree or 45-degree angle heads are ideal for cutting and polishing chores in spots a straight grinder can’t reach or is too awkward to use. This one is a AIRCAT air-powered tool. (Image/Wayne Scraba)
Full size and mini die grinders
Compared the full-size AIRCAT die grinder at the top, the well-used mini die grinder is quite a bit smaller. It’s also way louder and burns through a lot of air very quickly. At around 82 dB’s or so, the AIRCAT tool is pretty quiet so you can hear yourself think when it’s running. (Image/Wayne Scraba)
Milwaukee M12 FUEL 90-degree grinder
It’s hard to beat a cordless or battery-powered die grinder for versatility and ease of use. This Milwaukee M12 FUEL 90-degree grinder features a four-mode speed control to dial in the correct RPM for the job. Other features include a variable speed trigger, a 0.3 horsepower brushless motor, and a 24,500 maximum RPM rating. You can get just the tool or a kit with two batteries, a charger, and carrying case. (Image/Summit Racing)
Dewalt electric die grinder
While air- and battery-powered tools are the most popular, corded electric die grinders are worth considering. This Dewalt die grinder is a professional-grade tool with a high performance 4.2 amp motor that delivers 25,000 RPM. That makes it ideal for working on frames, suspension components, and thick sheetmetal. The tool has AC/DC capacity so you can plug it into a welder or a generator. (Image/Summit Racing)
AIRCAT die grinders with different trigger types
These die grinders have different trigger styles. The straight example has an easy-to-control “feather” trigger. The 90-degree job has a conventional trigger with a safety lock—release the trigger and it locks in the off position. The 90-degree die grinder also has a variable speed selection switch. (Image/Wayne Scraba)
AIRCAT die grinder with two collet wrenches
Most die grinders require two wrenches to loosen and tighten the collet, as shown here. (Image/Wayne Scraba)
AIRCAT die grinder with single collet wrench
Some die grinders like this 90-degree tool have a spindle lock button that requires a single wrench to swap bits. (Image/Wayne Scraba)
Die grinder with air coupler arttached
Air-powered die grinders use a male coupler that locks into the female coupler on the hose from the air compressor. This one is a Milton 1/4-inch coupler. (Image/Wayne Scraba)
Astro Pneumatic Tools die grinder bits
You’ll be using rotary burrs a lot with your die grinder. This set from Astro Pneumatic Tools comes with two “pine tree” shape carbide burrs, two ball end carbide burrs, and four cylindrical carbide burrs. There are special burrs for non-ferrous materials like aluminum and plastic, but carbide burrs will work provided you use cutting fluid. (Image/Wayne Scraba)
Summit Racing™ Porting and Polishing Kit
Cartridge roll sets are another must-have accessory for your die grinder. This Summit Racing™ Porting and Polishing Kit includes an assortment of 60, 80 and 120 grit rolls along with a couple of 1/4-inch mandrels. You can also buy cartridge rolls in individual sets. (Image/Wayne Scraba)
Summit Racing™ Cut-Off Wheel Set
Die grinders are also very good at cutting. They’re less bulky than a common angle grinder. You’ll need a set of cutoff wheels along with a dedicated mandrel. This Summit Racing™ Cut-Off Wheel Set includes five 3-inch x 1/16-inch cutoff wheels. They’re designed to work with a 3/8-inch arbor that fits a standard 1/4-inch collet. (Image/Wayne Scraba)
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Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.