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mountainman
January 21, 2009, 20:07
OK, I have been calling all teh pawnshops and what not. I need a decent air compressor for sand blasting and It's gotta be portable ( It's gonna be stored in my bedroom). So my neighbor who has been lending me his says that his boss bought a belt driven one that barely makes any noise for $200 about 30 gallons craftsman. It's an oiled system which I don't mind ( any possibility of it leaking on carpet?) anybody got any input and good suggestions? I plan on using a gravity fed gun so I can save on air consumptions (Is it worth it?)

Prototype Services
January 21, 2009, 21:13
In my opinion....

You can try to make any compressor work for small jobs or temporarily, but if you ever get a chance to use a real blast cabinet w/compressor, you will realize you need about 20+ CFM to blast very much. Otherwise your compressor just runs constantly trying to catch up to your consumption. Lots of air storage like multiple tanks, etc will allow longer blast sessions, but your compressor will still be the weak link.

Gunplumber had a great post about compressors long ago.

RottenII
January 21, 2009, 21:17
+1

(oh, and I would keep something under your compressor besides just the carpet.:biggrin: )

delloro
January 22, 2009, 01:25
the older belt-driven oil-lube types are quieter than the alternatives. look for low rpm, IIRC 1800-ish is good. they are quieter and last longer. but they are heavier and they cost more.

I have the 26" or so harbor freight cabinet, and my 5 hp (advertised) craftsman barely keeps up at 6 scfm. and it is LOUD, as in you will get evicted from an apartment with the sears oil-free compressors.

a too-small compressor will slooooooow you down badly. find somebody with enough air and buy them some beer.

Ron Walker
January 22, 2009, 13:26
I consider 10-12 cfm @ 90 psi the absolute minimum for the compressor itself, and a 30 gal or larger tank. My current one is a rollaround 20 gal and it works but as the man said I have to wait on it at times. Ron

Prototype Services
January 22, 2009, 22:08
Mine is a 5hp 80gal about 14cfm, and it is not enough to do much blasting.

My buddy's compressor is about 25cfm, and I have to stop sometimes and let the compressor catch up if I am blasting large parts. Or remember to blast in "bursts".:D

But sometimes you have to go with what you can afford or have room for.

Ron Walker
January 23, 2009, 13:43
Prototype, even the big setups in commercial shops will run down if you stay on the trigger(I know from personal experience). Short bursts is the way to go, no matter the size. Also, remember compressors have two ratings, one low pressure cfm, and the other high pressure, which is the one I quoted. My compressor is 12 cfm, but my tank is small, so short bursts work best for me, and it cleans up stuff just fine with 80 grit. My compressor itself is a two cyl. oil type. Usually takes me about 30-45 min or so to do the major parts of a rifle. On really bad ones an hour or little more.Ron

ggiilliiee
January 23, 2009, 13:59
orafice ....orafice ...orafice.....hehe
might get more consistancy with a smaller exit port on the gun ....rather than big burst then fizzle out ...
just a sugg indigestion ......for your smaller CFM system .....:wink:

Jaxxas
January 23, 2009, 14:56
Here's what you need ......:rolleyes:


http://www.daveycompressor.com/beltdriveba.html

ggiilliiee
January 23, 2009, 15:34
you buying ....????hehe i think he wants to sand blast not cut the rifle in half ..ehhehe ..nice unit ...aww ya aint seen anything till ya hold 1800 psi 400 cfm ....do rifles from 30 feet away ......:wink:

JColdIron
January 23, 2009, 15:48
My compresor on wheels (4hp 30 gal tank)would blast sand but only for about 20 seconds until it kicked on. It actually had to run longer to fill than it took to empty. It is a short term solution at best. I blasted an entire Truimph Spitfire frame but it took FOREVER and was loud

I picked up a 5HP 8o gal two stage from a friend that came from an industrial shop. 17.3 CFM! I was able to run one of my air hogging die grinders at full bore and the comp never ran down. Kicked in but it caught up and kept ahead of demand. True bliss

:biggrin:

Now for Tech! Oiled system is better than oilless and not as noisy. They can leak especially if older. You can check the HP and what it will produce CFM wise. Most are falsely overrated on the tanks. I think I found a link at Practical Machinest for the calc.

Prototype Services
January 23, 2009, 20:16
I do agree, I think there is a big discrepency with CFM ratings of compressors and tools. My die grinders run my compressor down quickly....

fastback65
January 24, 2009, 18:24
One more thing to consider. Where I live it is very humid and the compressor needs to be drained periodically. This might be difficult to do in a bedroom without making a mess. Consider placement and a water tight connection for a drain hose.

Rick

JColdIron
January 25, 2009, 11:51
Good point.

I hope he is just storing it in the room and taking it outside for sandblasting. Blasting in a house without a cabinet would get messy fast. :eek:

I guess he could keep the comp in the house and run the hose outside for the sandblaster.

RG Coburn
January 25, 2009, 12:35
Originally posted by ggiilliiee
orafice ....orafice ...orafice.....hehe
might get more consistancy with a smaller exit port on the gun ....rather than big burst then fizzle out ...
just a sugg indigestion ......for your smaller CFM system .....:wink:

dittos.
Only problem being clogs when re-using blast media. Gotta be strained and dry,very dry.

RG Coburn
January 25, 2009, 12:42
Originally posted by fastback65
One more thing to consider. Where I live it is very humid and the compressor needs to be drained periodically. This might be difficult to do in a bedroom without making a mess. Consider placement and a water tight connection for a drain hose.

Rick

Dittos again. When I built my first blaster,I relied solely on the tank drain for moisture control,and it just wasn't enough. I then went to the local rental place,took mental pictures of their unit,and did a copy with improvements. Like putting on a point-of-entry dryer,along with a dryer at the exit point on the compressor. I still have to pick my days by humidity in Michigan.Clear and sunny being the best. My current blaster is made from a 40 lb. propane cylinder,and will hold about 160-odd lbs. of sand.

Old Guard Dog
January 26, 2009, 18:38
My compressor is too small (about 5 cfm at 90#), but I use a #4 nozzle on my gun (smallest one supplied), with about 80 psi pressure. I use 80 grit silicone carbide and get a super job on gun parts in a blasting cabinet from Harbor Freight. It is their large one (36" wide), which I got on sale with everything for $219.00. It has a light, and I use a shop vac to draw out dust. I take my time, and "burst" blast, instead of constant blasting. That way the compressor can keep up. I can do a complete long gun in about 1/2 to 3/4 hr. Be sure to keep the air dry and free of oil. Filter as necessary. This finish is prefect for parkerizing or coating with DuraCoat. I don't think it is smooth enough for blueing, but if I do any bluing, I'll try #120 grit or glass bead. The media is easy to change, as there is a trap door on the bottom of the hopper. I am careful to degrease before blasting to keep oil out of my grit.

Deltaten
January 27, 2009, 09:17
For what a good, high-capacity electric compressor would cost....
Find a nice used tow-behind Rand-Aire or construction/demo/jackhammer unit !

Park it behind the bldg and run the line ta where yer working! ;)

PLus, ya could rent it out to contractors! :D

Last time I got one; they were about $50 a half day without all the accessories.
Hmmmmmm?????

L Haney
January 30, 2009, 22:28
This ain't portable, and ain't mine, but it's what I get to use for the blast cabinet. It's the air supply for the dry seals in our turbine engine. Instrument grade air.

http://i362.photobucket.com/albums/oo63/lch1428/AirSystem.jpg


Lowell

JColdIron
January 31, 2009, 11:06
Originally posted by L Haney
This ain't portable, and ain't mine, but it's what I get to use for the blast cabinet. It's the air supply for the dry seals in our turbine engine. Instrument grade air.


Lowell

LOL, I guess it will be hard to top that! What is the CFM on that:bow:

L Haney
January 31, 2009, 11:25
Not sure, it's got twin 2 cylinder compressors with a 10 hp motor driving each. Nominal 145 psi delivery, if it drops to 135, the second compressor kicks in. The conditioner/dryer can keep up with it at any flow I've asked of it. It also runs the air motor on the crane in the engine room. That's a pretty high flow rate I think. We just finished refurbing the conditioner/dryer this past week.

Lowell

erhauser
January 31, 2009, 12:16
For my first few projects I used an old home made compressor. I increased the storage capicity by adding a second storage tank. I used a WWII B17 oxygen tank. This allowed me to let it pump for 15 minutes, blast for 5 etc. until the job was done.

Later I purchased a 5 hp cheap compressor. Noisy, but adequate air. The problem then was that in the humid Midwest, the hot compressed air quickly started to add condensed water to the blast. Instant rust.

I purchased 20 feet of copper tubing, and bent it into a coil. The air goes from the compressor, into the coil of tubing, then into the B17 Oxygen tank, then to the gun.

The coil of tubing is placed in a cheap picnic cooler, filled with ice and water. This cools the air, condensing the water. The condensed water accumulates in the second tank, which has to be emptied periodically.

I know that B17 oxygen tanks are no longer on the market, but you can get rigs to convert a propane tank into an air storage tank. A suitable modification to make sure that the incomming air and water had to go into the tank should work.

RG Coburn
January 31, 2009, 15:57
For painting,whether gun parts or Jeeps,I don't monkey with compressed air.Too many problems with water or oil contamination. I just get a 300cubic foot cylinder of nitrogen,and regulate it to whatever I want. I think its like $17 a tank,no compressor noise or lag time,zero moisture or oil,and one tank will paint a whole Jeep.

NoNotAgain
January 31, 2009, 19:04
Originally posted by RG Coburn
For painting,whether gun parts or Jeeps,I don't monkey with compressed air.Too many problems with water or oil contamination. I just get a 300cubic foot cylinder of nitrogen,and regulate it to whatever I want. I think its like $17 a tank,no compressor noise or lag time,zero moisture or oil,and one tank will paint a whole Jeep.

For our metal bonded parts, we also use nitrogen to propel the primer onto the surface. The added benefit is that you can use nitrogen as a shield gas so that you can leave the primer in a pressure pot without the primer starting to oxidize.

For agitation of process tanks, we use "Blower air", basically nothing more than a large vacuum cleaner motor, though rated @ 1200 CFM. Its got volume just does not develop much pressure, (less than 20 PSI).

mountainman
February 01, 2009, 09:04
Originally posted by gunplumber
based on your criteria, you may be better off renting a blaster with compressor at another shop - until such time as you have the space.

You can get away with a small compressor for painting, but not for any significant blasting. What kinds of shops should I stay away from and what kind of shops should I try? Whats a reasonable rate?