Tuesday, April 30, 2019

Grinder 101

I’ve previously talked about a tool called an angle grinder. However, with all that talk, I’ve never gone into what one is, how it works, or how not to be maimed using one. Today, I will correct that omission.

At its more drilled-down definition, an angle grinder is a hand-held motorized tool that spins an abrasive wheel of some sort at very high speed. It is primarily driven by either air or electricity, and the electric models can be either battery-operated or use a cord that plugs into a standard outlet.

Wheel Types 
There are a wide variety of abrasive wheel options, and the wheel you choose will be determined by the work you are doing.

Cut-off wheels are very thin, approximately 1/16”, and are far too fragile to do any kind of surface grinding. Made of an abrasive material bonded to a fibrous mesh, they are used to make slicing cuts clean through metal or other materials.

Grinding wheels are made of the same kind of material as a cut-off wheel, but are much thicker (usually 1/4”). Their thickness makes them a bad choice for slicing cuts, but their rigidity means they’re great for surface grinding, which means that they’re best used for removing burrs and thick rough spots on metal surfaces. They also shine at cleaning up areas to be welded, as well as post-welding to prepare for paint or other surface finishing.

Wire wheels employ fine wire strands bonded to a center hub. These strands can either run straight away from the hub individually or be twisted into groups. The grouped-strand type wheels last far longer than the individually-stranded ones, but cut far more aggressively and can damage a work surface if the user isn’t careful. Wire wheels are ideal for paint and rust removal, or for removing rough metal areas that are a bit less coarse than those that require a hard grinding wheel.

Flap wheels are the most forgiving of the abrasive wheels. Basically comprised of layered pieces of sandpaper bonded to a backing disc, a flap wheel removes paint and other light surface materials, but has a bit of “give” to it, so an aggressive user doesn’t damage the work piece as easily.

There are a wide variety of other specialty wheels available. They allow for working stone and other materials, polishing surfaces, and innumerable other specialty tasks. Whatever kind of wheel you use, it will attach to the grinder either with a threaded hub that is a permanent part of the wheel, or a nut that comes with the tool. Make sure that whichever attachment method your wheel uses, it is tightly secured to the tool.

I won't mince words here: an angle grinder can eat your lunch and come back for seconds if you're not careful! When wheels are spinning in excess of 10,000 RPM, small pieces of metal and sparks can go flying everywhere. It's a situation with all sorts of opportunities for danger, so take all appropriate precautions and don't skimp or you might get the opportunity to make friends with your local first responders.

Clear the area of flammable materials. This includes fabrics, dry grasses, oily rags, or anything else that can burn. Having a fire extinguisher handy is also prudent.

Wear all appropriate PPE. At a minimum closed-toed shoes, long pants, gloves, and safety glasses are needed. If a face shield and long-sleeved shirt are available, they are a wise addition. Button the shirt to the top of the collar if possible.

Make sure that no people or animals are in the path if the material you’re cutting falls or the grinder binds and leaves your hands. As a much younger and bolder man, I was nearly on the receiving end of a grinder that bound while cutting a piece of metal and flew towards me. Luckily for my pretty face, I was out of range and escaped injury, but it was a closer encounter than I liked.

Next time, I’ll demonstrate proper use of a grinder on a project on which I’m working in my garage.


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