Makita MAC5200 Compressor - CFM enough to trump small tank?

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Old 07-11-13, 11:33 AM
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Question Makita MAC5200 Compressor - CFM enough to trump small tank?

Hi,

Newbie, here. Found several threads on the site regarding compressors, so thought someone out there would have a strong opinion on what I'm looking at.

I want to buy a compressor to be primarily used for:

- Nailing (finish, brad, framing)
- Die Grinding
- Light Auto Work (1/2" impact, 3/8" ratchet, inflator)
- Winterizing sprinkler system

I doubt I would ever use an air sander as I already have an electric. A cut off... not sure. Maybe, but I've never needed one thus far. Generally, everything I've been looking at puts me at a max 90 PSI SCFM requirement of about 4.2 to 4.5.

Not super flush with cash, I find this Makita on HD's website and Amazon. @ 90 psi it's supplying 6.5 cfm. It can be used on my existing electrical, and outside of an issue with the wheels (seems to have been fixed) and some crappy packaging, it seems the thing is showing up as a really good unit.

The only thing holding me back at this point... it only has a 5.2 gallon tank on it. It seems that this doesn't matter for nailers (the only pneumatic tools Makita makes) or other lower air consuming tools. However, I'm wondering if using 4 to 4.5 cfm tools, like impacts or what have you, is going to drive this thing to run all the time to keep up, which will in turn drive me nuts, possibly the neighborhood nuts, and overwork the motor and shorten the life of the compressor?

Any guidance you guys could give would be greatly appreciated.

Thanks!
 
  #2  
Old 07-11-13, 01:04 PM
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By the published numbers that compressor should work fine for you. However, you must understand how air tools are rated to know the full story.

Pneumatic tools are rated in average air consumption in standard cubic feet per minute (SCFM) but they use far greater airflows than stated when actually in use. Take as an example a standard 1/2 inch rattle gun (impact wrench). The specifications will state that it uses an average of 4 CFM but what they don't tell you is that is when the gun is used for a ten-second burst. During that ten seconds the gun is really using 24 SCFM and everything needs to be sized for that if you want optimum performance.

If your compressor is pumping 6 SCFM into the receiver and the tool is taking 24 SCFM then it is clear that the receiver pressure is going to fall during the time the tool is actually in use. If you are using the wrench to remove lug nuts you might be able to remove all four (or five) before the pressure drops too low to properly operate the gun or you might have to remove two or three nuts and then wait for the receiver pressure to rise again.

You most definitely need to use a pressure regulator so that the receiver pressure is always greater than the hose/tool pressure. You need to use a pressure regulator that is of sufficient size to pass the required air flow (in this case 24 SCFM) without excessive pressure drop. You need to adjust the regulator to the desired pressure with the tool running to allow for this pressure drop. You also need to use a large enough air hose to supply the air without excessive pressure drop. Most tools suggest no less than a 3/8 inch ID hose.
 
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Old 07-11-13, 08:20 PM
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Seems that you already know the answer to your question - that Makita would be undersized for any kind of rotary tool. The 3HP rating on it is imaginary, given the 13.8 amp draw on 120 volts. Buy a 60 gallon unit with a 240 volt motor for only a $100 or so more.
 
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Old 07-15-13, 10:28 AM
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@ Furd

I'm not sure I follow how something that averages 4 cfm in usage can jump to 24 cfm usage. I understand it's not static, and that burst draws and startup are very different from maintenance volume in fuel requirements. But that's really surprising.

I will say this, your post helped me understand that I've been shopping for this all wrong. I was told and I read on my own as well to focus on the cfm output of the compressor and to match that up with the highest consumption tools I was looking at. Because of that, I could not understand how someone would pair a compressor like a big oilless craftsman that only puts out 2.5 cfm from the compressor with a craftsman impact that averages 4.1 cfm in consumption. Now I see how people are getting away with that (because there's 30 gallons of stored air once the compressor tank reaches pressure).

So, basically, the cfm output of the compressor (on it's own merit) has little-to-no correlation with supplying the tool with air and the tool's performance. A compressor with a lower cmf output will simply take longer to reach pressure on initial power-up and take longer to reach pressure when re-pressurizing the tank when that is required, where one with a higher cfm will do both functions more quickly. And that's it.

correct?

And if that's the case, then it is more important to focus on the appropriate supply of air available and the proper sized supply lines/fittings to deliver a that supply of air to the tool to satisfy its demands... correct?
 
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Old 07-15-13, 10:46 AM
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@ markiz37

No... I didn't know. I was starting to worry, which is why I asked.

The 3hp rating on the motor is peak. It is listed at 2.1 for a running HP. But, honestly, I don't see too much of a reason to focus much on HP anyway?
 
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Old 07-15-13, 06:37 PM
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2.1.. maybe if the motor was 100 percent efficient. But by the time you add up all the loses, you may get about 1.5 horse at the output. Which is in line with its cfm rating.

But you're right, don't focus on hp. Let's focus on the CFM. As Furd had explained - rotary tools are rated for short, 10-15 second bursts. I don't know why it's called average, but it's common practice. As an example, if a grinder is rated at 4 cfm average, it means it'll eat up 4 cfm in 15 seconds. If you have to run it for a minute, it'll use up 16 cfm. Compressors, on the other hand are rated for straight cfm, no average or any other commercial trick. So, with a 6 cfm compressor there is no way to keep up with a 16 cfm grinder. After a short time the pump will run constantly, pressure will still drop, pump will overheat and bad things will happen.
 
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Old 07-15-13, 06:50 PM
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I'm not sure I follow how something that averages 4 cfm in usage can jump to 24 cfm usage.
It doesn't "jump to 24 cfm usage" it was ALWAYS using 24 CFM. The average usage is calculated over the time frame of one minute. If you are flowing 24 cubic feet per minute for ten seconds and then no flow at all for the next fifty seconds then the AVERAGE flow over that sixty second (one minute) time frame IS 4 cubic feet per minute. Ten seconds is one-sixth of a minute. Four is one-sixth of twenty four.

This is pretty typical usage for an impact wrench but other tools will have different "duty cycles" and that must always be taken into consideration. A pneumatic chisel may have a duty cycle approaching 50%, a die grinder 80%, a "sidewinder" grinder or polisher close to 100% and the like. This is why what tool is being used and HOW it is used is so important. A smaller compressor with a large reservoir can often supply a tool with a CFM rating (actual, not average CFM) larger than the compressor output IF the tool usage is fairly intermittent. On the other hand, a tool with just slightly higher consumption than the compressor output WILL drain the reservoir if the tool is used continuously.

One thing that far too many people misunderstand is that most pneumatic tools are designed to operate with 90 psi AT THE TOOL and will try to get a little bit more from the tool by jacking up the air pressure. In most cases this does nothing but add to the wear and tear on the tool and in some cases could be quite hazardous to the tool user and any bystanders. In conjunction with this, far too many people add additional hose to the compressor without ever thinking about how it adversely affects the flow rate and pressure at the tool. Most pneumatic tool manufacturers strongly suggest nothing less than 3/8 inch inside diameter hose be used yet most compressor kits have only 1/4 inch hose. About the ONLY tool that can effectively use a 1/4 inch hose is a pneumatic nail gun. Increased hose lengths, especially undersized hoses, will cause an excessive pressure drop at the tool and also decreased flow. The end result is a tool that performs poorly.
 
 

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