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Die Grinder, Pneumatic... Are all underpowered? Answered

So, it's compact.  Nice.  But it is so easy to stall it out. It cuts sooooo slow.
I'm using it today because I dont wanna use the electric die grinder in the rain.

It is from harbor freight, so I'm gonna take my initial aversion to the tool with a grain of salt. Perhaps a more expensive one would have more power?  Or is there a way to soup it up a bit?


Harbor Freight stuff is low quality. That's a bigger problem. I had one of their electric right-angle die grinders and it was scary to use. Extremely loud and no quick stop if you dropped it or it slipped while using it. It also blew up early. Way too much power in a small package.

http://www.harborfreight.com/air-angle-die-grinder... This was made to cut muffler pipe and remove rust, and not much else. One reviewer said you need at least a 26 gallon tank for 4 or 5 minutes of steady use.

1 cubic foot is 7.5 gallons. This 4 inch die grinder needs 6 CFM at 90 PSI. That means you get about 30 seconds use with a 26 gallon tank.


This Harbor Freight compressor almost has enough output to supply the 4 inch air grinder, with 5.9 CFM.


The 1st few seconds ought to indicate its power, regardless of smaller tank. Wimpy tool.

Tell the truth, I bought it as a toy with no specific job in mind. My intent was to play with it, disassemble it to satisfy my curiosity, then attempt reassembly. Why not? $10.

Like gizmologist said, did you oil it? Plus, the diameter of the supply line makes a big difference. For a tool that need 6 CFM you should be using at least a 3/8" line and properly sized adapters.


Plus you can add a regulator/oiler at the tool and raise the compressor pressure without damaging the tool. If you have 120psi in the tank and a regulator set to 90psi, you will get 90psi at the tool until the tank pressure drops below 90psi.

You are oiling the tool according to the instructions, right?

my experience was low power straight out of the box. Dont think it has to be oiled before 1st use. But maaaybe i should look at instructions...

All of those mechanic type air tools(impact wrench, metalworking tools) need a big compressor to run or one with a reserve tank bigger than 10 gallons. I have a good 6 gallon pancake compressor but even that is not rated for a spray paint gun. Look up the recommended SCFM air requirements and most likely your compressor is not big enough. Bumping up the pressure a tiny bit may help but can be dangerous.

ive had success with wrenches, air hammer, etc.

The air grnder(cutoff tool) however, doesnt even work well when the airtank is full. Some tools work nicely for several seconds when tank is full. This indicates that cfm is the issue. But a hacksaw would cut faster than this tool, even when tank is full.

That might be it then. Rotary tools that run continuously spit out the air as soon as you feed it. Impact tools just take one blast of air and the compressor has time to recover and build back up the pressure and volume. You might have to ask the lady of the house if she will let you get a new compressor.

:) im not certai, but think that a grinder is a bit like a waterwheel, pinwheel, or turbine, while the impact tools are more like a piston steamengine. Easy to stall the former, tough to stall the latter.

That is a really good point!
In some cases you can compensate with a old gas tank attached to the compressor.
It takes forever to fill with a small compressor but gives you a chance to reach the air volumes required.
Only works till the pressure drops and the compressor needs to fill again but if you are not constantly using the tools it might be enough.

Problem with air tools is that you actually need pay a bit more to get pro tools.
An air grinder is usually not very powerful anyway, especially the small models.
They basically works as clean up tool but not really for cutting steel.
Only way I found to make them work at least to a usable stage is to only use so pressure that they don't slow down too much.
Even with electrical grinders people tent to use them with massive amounts of pressure to cut faster.
Truth IMHO is that the only thing going down faster this way is the diameter of the grinding disk.
For serious work it might be better to get a good sized tarp to cover your work area from rain.

Ill have to check max pressure for the tool. Still, thatll only help if i replace compressor.

With electric tools, Im nervous about wet ground. Even with gfi, and double insulated tools, Id rather find an alternative.