Short answer: Let the disc cut at full speed with light pressure, keep it square to the work, and never lean on it. Most people burn through discs because they push, and pushing is what makes a wheel shrink, glaze and eventually shatter.
Why do cut-off wheels disappear so fast?
An abrasive cut-off wheel works by sacrificing itself. Every cut grinds away part of the wheel, which is why it starts at 4 inches and ends up the size of a coin. That is normal for abrasives, and it is why a box of them empties so quickly.
There are two problems with that. A shrinking wheel loses cutting speed at the rim, so each cut takes longer than the last. And a thin, worn wheel is fragile: it is the one most likely to come apart under side load.
A diamond disc works differently. The grit cuts, the steel body stays. It keeps its diameter, which means the last cut runs at the same speed as the first. That is what the Indestructible Disc 2.0 is built around: a turbo rim on a diamond steel body, made for steel, aluminum, copper and brass.
What is the right technique?
Let it reach full speed before it touches metal. Starting a cut against the workpiece kicks the tool and stresses the disc.
Use light pressure. Your job is to guide, not to press. If the disc is not cutting, the fix is never more force. Check that it is the right disc, check the speed, check the angle.
Keep the disc square. Cutting discs are strong in the direction they spin and weak sideways. Twisting in the cut is the single most common way to break one.
Cut in a straight line. If the line needs to curve, make a series of straight relief cuts instead of steering the disc through the arc.
Pull the trigger less, not more. Let the tool stop between cuts on thin material. Heat builds fast in sheet metal and warps it.
Does the metal type change anything?
Mild steel and rebar. Straightforward. Steady pressure, let sparks fly away from you, and cut all the way through rather than snapping the last bit off.
Stainless. Cuts hotter and work-hardens if you dwell in one spot. Keep moving. Do not stop halfway and restart in the same groove.
Aluminum, copper, brass. These are soft and gummy. They load up an abrasive wheel quickly, clogging the grit until it stops cutting and starts rubbing. Take lighter passes and back out often to clear the cut.
Sheet metal. The thinner it is, the more it flexes and grabs. Clamp it close to the cut line so it cannot flutter.
Why does the disc grab and kick back?
Kickback happens when the disc binds in the cut. Metal closes on the wheel, the wheel stops, and the tool has to go somewhere: usually toward you.
Prevent it by supporting both sides of the cut. When you cut a bar in two, the offcut should not sag and pinch the wheel as it separates. Support it, or let the cut end where the piece can fall free.
Also keep both hands on the tool and stand out of the plane of the disc, not directly behind it.
What does the guard actually do?
If a disc comes apart at 12,000 RPM, the guard decides where the fragments go. It is the difference between a bang and an injury.
Plenty of people take it off because it gets in the way. It takes seconds to fit a quick-lock guard, and there is no cut worth the alternative.
Add safety glasses for the sparks and fragments, cut resistant gloves because a fresh steel edge is a blade, and ear protection because a grinder on steel runs well past 100 dB.
Will this disc fit my grinder?
The Indestructible Disc 2.0 is 4 inch outer diameter with a 5/8 inch arbor hole and 0.04 inch thickness, which is the standard size for common angle grinders. It runs up to 12,225 RPM, so check that your tool does not exceed that.
The short version
Light pressure, square to the work, full speed before contact, and both sides of the cut supported. Do that and the disc lasts, the cut stays clean, and nothing comes apart.
Get the disc built for metal: Indestructible Disc 2.0
