Chris Adams
Well-known member
- Joined
- Oct 21, 2007
- Messages
- 2,117
Or, how a cheap die grinder can conquer most compressors.
Been doing a little welding, and as I am new to MIG welding (grew up with stick, now learning MIG as an old man,) I've needed to use a flap wheel quite a bit.
Since I was working outside my shop, I could ignore my compressor. Then the cold came and I pulled the project into the shop.
My 60 gallon, 3.2 running horsepower compressor started to drive me nuts.
Any of my 6 die grinders could beat it and keep it running indefinitely.
In fact, they soon drop the tank down till the grinder slowed.
So I figure, heck, treat myself to another cheap compressor.
Picked up an almost new HF compressor. Almost no hours on it.
Couldn't test it as no power, and it was fairly cheap.
Got it home, pinholes in the tank.
Yes, I tapped on it, yes I shoved the bore scope down it's throat before buying. I only saw only a very light coat of rust.
The weld itself around the bung on the bottom had become porous.
Decided to snag another tank, rather than risk/bother welding. Didn't think it would work anyway. (It didn't.)
Started scouting for tanks.
Ended up buying two more compressors and a tank.
People sell compressors when they need 8 dollar parts, it would appear.
Two years ago I went through a compressor for a friend. His buddy gave it to him, as 'it's scrap'. It needed a D-switch, check valve and safety valve. He's been painting cars with it since.
Well, with the tight economy, people aren't giving them away anymore. But they are not fixing them much either...
So for 300 bucks I filled my shop for about ten days, until I could cheaply and correctly fix three broken compressors.
However, as I had two 80 gallon and two 60 gallon tanks that were good, I decided to test the times to fill, and the CFM of the four motors.
I used the simple formula from this site;
http://www.about-air-compressors.com/fill-an-air-tank.html
and correcting for my 3000 foot altitude.
I was interested in finding that three Husky (Campbell Hausfield) units and the HF compressor all tested pretty close. One CH was a small amount under specification, coming in at about 10 CFM, while rated at 10.2
Figures, it was the one I was using... and had about 3 years of use, some of it pretty steady.
The Two stage compressor from CF, from a 4 running horsepower 80 gallon, made 12.8. Rated at 12.6 so pretty good.
The '7' horsepower (draws exactly the same amps as the 3.2) produced 10.4, rated at 10.3.
Incredibly, the HF was underrated. It made better than 16 CFM even above the factory set 165. I have it running at 175 lbs per square inch, as the tank it is now on exceeds the safety factor of the old tank by 30 lbs.
So I went from a 3.2 horsepower 60 gallon, 10.0 actual CFM compressor with a max pressure of 135 to a 5 horsepower, 80 gallon, 16+ CFM with a max pressure of 175.
Should cure that die grinder problem, right?
Not so much.
Any of my die grinders can keep the compressor running till my head hurts.
Even at 16 cfm, the compressor never catches up unless I stop grinding.
So the six, 7-10 CFM rated die grinders all draw on the close order of 15-16 CFM.
Still have to listen to that compressor while I grind.
For those who wonder, it takes about 91 seconds to 'catch up' if I let off the grinder.
The old system took 128 seconds to catch up. To about half the volume of air, of course.
I sold the leftovers for enough that I'm satisfied the job was worth doing, so that's a win, anyway.
I wear shooting muffs when die grinding, which I could have done in the first place...
