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Old 09-17-2006, 10:19 AM
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What kind of compressor?

It looks like I will have to bite the bullet and get an air compressor. I don't do a lot of painting and I don't have any air tools, but I can't find a way to shoot 2k epoxy primer without a compressor. I browsed Habor Freight and found a bunch of compressors that might work, but being a total rookie I have no idea what I need. Can anybody tell me how many PSI and what size tank would I need to do some light painting (primer spots mostly)

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Old 09-17-2006, 10:39 AM
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PSI and tank size are irrelevant. What you go by is how many CFM it can produce. The minimum you need for most things will be around 12-15 CFM @ 90 PSI, but the more the merrier. So buy as much of a system as you can afford. The one I use I bought at HF on sale for like $320 but was regularly $500 and it puts out about 13 CFM. However, I also have one of my old compressors tied into the system also, in case it cant keep up. But if youre only doing real light stuff, you might could get by with less. The problem with marginal compressors is they hafta run non-stop to keep up, thereby creating heat, which will cause moisture problems. With compressors, the "Bigger is Better" rule usually applies
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Old 09-17-2006, 05:36 PM
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I would take a look at eaton compressor's site, even if you don't buy your compressor from them there is a lot of useful information on what to look for, stay away from, ect in a compressor. I have the 5hp 2cyl upright which according to the site is 19.5cfm at 100psi. It will keep up with all my tools and will pump up while running the 1/2" impact. There is a 4.5hp 3 cyl which is rated at around 14cfm which would probably outdo the ones you find at home depot, sams club, or similar places. Before I bought mine I called up the owner Matt Cain and he answered all the questions I had, nice friendly guy. Do yourself a favor & get a better compressor than you think you need now, you'll never say "I wished I got the smaller one." This is from a guy who was going to get a 26 gal 5.7cfm IR portable but was stubborn enough to hold out for what I really wanted. Lots of good advice on this forum, do a search for "compressor" and read what Oldred says, I've learned a lot just from reading his posts.

Good luck,
Steve
a compressor newbie
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Old 09-18-2006, 11:02 AM
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Quote:
Originally Posted by CDJr
PSI and tank size are irrelevant. What you go by is how many CFM it can produce. The minimum you need for most things will be around 12-15 CFM @ 90 PSI, but the more the merrier.
I was looking at some ads for compressors and they said SCFM, What's the S for?
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Old 09-18-2006, 12:23 PM
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Lincoln, SCFM is what you want, S-tandard C-ubic F-eet per M-inute. Be very careful when shopping for a compressor because there are MANY misleading specs listed on most these of things that are nothing more than sales gimmicks designed to make the buyer think he is getting more compressor than he really is. You may find one listing ACFM which is ok IF the "A" is for "Actual" Cubic Feet per Minute however the latest trick they are using is "Assisted" CFM which means "Tank Assisted". These big numbers look impressive but they are pure garbage and mean exactly nothing as to how well the compressor will keep up with your tools so if you see a "tank assisted" CFM rating you would be well advised to pass it up and keep looking. Also HP numbers are usually grossly inflated by using "peak" or "maximum developed" numbers and are sometimes double or even more than double the actual true HP produced so look at the AMP rating on the motor data plate. A true 5 HP motor will be rated at about 23 AMPs or more and a 6 to 7 HP "peak" will be rated at about 15 AMPs which makes it really only around 3 HP. I know it gets confusing and the manufacturers of these things are taking advantage of that by listing all those big but phony numbers just so they can sell that junk. Just remember that big HP numbers and a big tank do NOT make a big compressor no matter what the salesman tells you and the bottom line is that you need VOLUME and that is what the CFM rating means, if that volume (CFM) is low then nothing else will make up for it, not HP numbers, big over sized tanks or ridiculous performance claims, NOTHING! If you don't plan on using something like a high volume (HVLP) paint gun then you may ok with one of the very common 3 HP single stage outfits like those sold at Harbour Freight or Lowes/Home Depot just be aware that the performance is almost always exaggerated so allow for that. The outfits I mentioned are usually rated at about 6-7 "peak" HP (3 actual HP), are single stage and on a 60 gallon tank and these should work ok for most home shops.
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Old 09-18-2006, 01:51 PM
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[QUOTE=oldred]Lincoln, SCFM is what you want, S-tandard C-ubic F-eet per M-inute. Be very careful when shopping for a compressor QUOTE]

I bought a Lowes IR 6.5 peak Hp/30 gallon tank to run my air tools. It does a good (well, an OK) job of doing that. Then I decided after getting some $7 to $10K quotes to paint a '31 Model A roadster, that I could do the job myself. Quite frankly, now I think need a bit bigger unit. This is supposed to put out 10.5 SCFM at 90 PSIG and 13.5 at 40 PSIG, but since it is only a 50% duty cycle, it really huffs doing it. As a minimum, I really need a 60 gallon tank and 14 + SCFM @90 PSIG, an 80 gallon tank would be perfect. But, then I run into another problem - I would need a bigger electrical circuit. I'm now temporarily plugged into the 30 amp dryer circuit, using 10ga wire as my "extension cord just in case". And then again, it might just go to compressor heaven in the midst of my paint job.

So, to echo oldred, if you can afford a compressor like I just described, save up some more bucks and get the bigger unit - you wont be sorry
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Old 09-18-2006, 02:32 PM
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Ireland, I think you are placing too much emphasis on the tank, it will make no difference on how well your compressor will keep up and in fact you would be unable to tell between a 60 gallon and an 80 gallon. This has been covered before and to make a long story short the only thing the bigger tank would do is to make the compressor start up fewer times but run longer each time, it would not help keep up if the tool CFM is too high. This is a VERY common misunderstanding and all too often someone will look at HP ratings and the size of the tank and make a decision based on that which is just what the manufacturers want you to do but this is the wrong criteria for choosing a compressor. With a bigger pump and a bigger motor to pull it that little 30 gallon tank would keep up just as well a 60 with the same pump/motor combo but that is going too far to the other extreme and although it would keep up it would also cycle on/off too much. If the pump/motor combo is capable of around 11-14 CFM and that is going to be the approximate demand then a 60 gallon tank is about right, 15-20 CFM would be better with an 80 but not enough to warrant spending much extra money on. On a larger compressor the bigger tank will not increase performance but it will offer some advantage in decreased pump wear and slightly lower power consumption because of the fewer(but longer run time) high load start-up cycles but on a smaller compressor the opposite can be true with a larger tank because the longer recharge times will make for higher pump temperatures leading to accelerated pump wear and decreased efficiency.

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Old 09-18-2006, 05:08 PM
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I agree

Quote:
Originally Posted by oldred
Ireland, I think you are placing too much emphasis on the tank, make for higher pump temperatures leading to accelerated pump wear and decreased efficiency.
Oldred,
I guess I didn't explain myself well enough because I was trying to equate a bigger tank, compressor and motor to the less on-off operation, increased pump (compressor) output and heat generated by that compressor - just as you pointed out . As far as my little 30 gallon tank, yes, I could have a bigger compressor and output but the on-off operation at some rated output would change very little - the tank will still be only 30 gallons, a larger compressor would run as often, but obviously not quite so long each start.

I happened to be in Tractor Supply today and looked at their $399 special 60 gallon tank. Nice size - but smaller motor (5Hp - peak)with less SCFM output than my "baby" unit. It wasn't until you coughed up over a thousand hard earned dollars there did a compressor equal mine in SCFM at 40 and 90 psig. While that compressor had 2 separate cylinders, my guess is that the compressor output was way down.

When it is all said, big tank, big compressor and high output motor - if you can afford it - I'm retired - fixed income. If it blows, then it will be replaced, probably with something a bit bigger but only after a good job of research. When the unit I have now was purchased 6 years ago, it was about the best available - HP, SCFM and tank size as well as cost effectiveness. And would still be if I hadn't decided to paint my own car in a moment of insanity. At least it is better than the 1 Hp, 30 year old Craftsman 12 gallon unit it replaces (which still runs and is my tire inflater now).
Dave

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Old 09-19-2006, 12:34 PM
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Here's the thing. I am NEVER going to paint a car, I have no air tools. The only thing I am going to use an air compressor for is to apply some 2k primer to a bunch of bare metal spots. I understand the concept of bigger is better, and I certainly understand the benefits of quality over junk. But I don't want to go buy a tractor to farm my little garden patch. All I'm looking for is a decent paint system that I will use only occaisionally to prime a few spots. Or if someone can recommend an alternative to the compressor, a spray can solution I'd be really grateful.
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Old 09-19-2006, 01:22 PM
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I NEVER thought I would recommend an oil-less compressor to anyone but one of those little 3-4 gallon CH compressors from Wally world or Harbor Freight may be just what you need. It would be handy for pumping up tires and such and would power a small spray gun for what you have described. You could not paint a car with that thing but it sure would beat rattle cans for primer and would not cost much at all. I think Wall Mart has some compressor kits with a spray gun that would spray primer ok and a couple of other tools and since you say you will never attempt to paint a car this may be the cheap way out for you.
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Old 09-19-2006, 01:26 PM
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oldred,
Thanks for the reply. Do you have any idea what I would need in the way of a spray gun to shoot some 2k primer?
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Old 09-19-2006, 02:36 PM
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Lincoln, I shoot 2k with a HVLP primer gun that has a very large tip and most of the 2 part primers are supposed to be used with this type of gun but they require a lot of air. I have had good results by over thinning some primers and shooting them with a small 1.4 tip but it would depend on the primer. Some of the guys in the paint and body section know a heck of a lot more about the different types of primer and their characteristics than I do so if you pose this question there you might get a better answer. I would think that one of the cheap Harbor Freight guns for less than $20 would work fine for epoxy primer but most of them have a 1.4 tip so you would need to thin it properly. Since you are just trying to replace rattle cans to do some spot spraying (VERY good idea BTW) this can be made to work with that little compressor and a cheap gun. HF has a gun that is on sale most of the time for only about $12 that has very low air requirements that may be what you need for a really small compressor, I will try to locate a link for you.

Don't get the wrong idea about that gun from that price as you may be surprised at that thing. I have a couple of them that we sprayed mine equipment with and I don't see how they can sell something like that so cheap
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Old 09-19-2006, 02:45 PM
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My compressor system seems to keep up well with my spray guns ( conventional, siphon feed, 1's a touch up like what HF sells for $10 ) that's what I sprayed the green tractor paint with. it's 2 small compressors running in tandem, with 1 aux tank plumbed in
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Old 09-19-2006, 03:20 PM
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Is this the HF spray gun? http://www.harborfreight.com/cpi/cta...?Itemnumber=86

or this? http://www.harborfreight.com/cpi/cta...emnumber=93270

and how about this for a pump? http://www.harborfreight.com/cpi/cta...emnumber=90385

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Old 09-19-2006, 04:17 PM
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for primer this is the gun I would buy http://www.harborfreight.com/cpi/cta...emnumber=93205 as it has a 1.8 tip.

that touch up gun would be a hassle to prime a car, I have it but from a diffrent company ( same manufacture tho ) which is American Tool, it does keep up to my compressors well which is a 7 gal 2 horse ( 4.2 SCFM @ 90 ) and a 2 gal 1/4 horse ( 3.3 SCFM @ 90 ) but, it has a small holding cup and runs out fast. I put 1 coat of tractor paint on a truck tail gate and it ran out.
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