Sanding and the Compressor
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Junior User
Joined: Sep 2003
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From: WA
Sanding and the Compressor
I am new at this sanding stuff. I have been trying to sand my hood, because it has at least five layers of paint. But I am having trouble gettin my 5.5 HP Craftsman Air compressor to stay above 90 psi. I set it to 90 psi then I start to sand for about three minutes then the pressure drops down to about 45 psi. During them three minutes I can get alot sanded, then I hear the motor kick in and am back to 45 psi and can barely get anything done. So I have to keep waiting till I get back up to 90 psi. I have even tried to set it at 120 psi. No luck. I am about to throw the #@^& out the window.
Please someone help me.
Thanks,
JAck
Please someone help me.
Thanks,
JAck
Elder User
Joined: Mar 2003
Posts: 999
Likes: 1
From: Willamette Valley Oregon
<br>
Your p.s.i. reading is the symptom, not the disease.
The drop in air pressure occurs because the tool you are using demands more air than the compressor can provide. Although the compressor can produce 120 p.s.i., it does not produce the volume (measured in C.F.M.).
Craftman makes a good air compressor. There is nothing wrong with the brand. Your compressor is just too small. I didn't get my air compressor purchase correct until I bought my 4th machine. It was an expensive learning curve.
Air tools like sanders, die grinder, impact wrenches, and etc. use a great deal of air. Most of them require more than what your compressor can supply. It's not usual to see C.F.M. (cubic feet per minute) requirements of 12 - 18 at 90 p.s.i. I would hazard a guess your compressor is putting out about 6 C.F.M. at 40 p.s.i. At 90 p.s.i., you are probably getting around 4 C.F.M. The actual figures are probably listed on the compressor.
Your p.s.i. reading is the symptom, not the disease.
The drop in air pressure occurs because the tool you are using demands more air than the compressor can provide. Although the compressor can produce 120 p.s.i., it does not produce the volume (measured in C.F.M.).
Craftman makes a good air compressor. There is nothing wrong with the brand. Your compressor is just too small. I didn't get my air compressor purchase correct until I bought my 4th machine. It was an expensive learning curve.
Air tools like sanders, die grinder, impact wrenches, and etc. use a great deal of air. Most of them require more than what your compressor can supply. It's not usual to see C.F.M. (cubic feet per minute) requirements of 12 - 18 at 90 p.s.i. I would hazard a guess your compressor is putting out about 6 C.F.M. at 40 p.s.i. At 90 p.s.i., you are probably getting around 4 C.F.M. The actual figures are probably listed on the compressor.
Posting Guru
Joined: Sep 1999
Posts: 1,022
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From: Pensacola Florida
My five horse couldn't cut it any longer (wore out) so I bit the bullet and bought a 7.5hp that really gets the job done. It isn't the best brand and it may fail sooner than some but I can sandblast all day and it doesn't drop below 90 psi. I am very pleased with it. You can get it at Sears as a Cambell Hausfeld or at Home Depot as a Huskey. Same compressor. The final word is that my neighbors ears burn no more as I don't have to cuss while using the air compressor.
Thread Starter
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Junior User
Joined: Sep 2003
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From: WA
Thanks
Thanks for the help. Not what i wanted to hear, but I guess it true. I guess I will be at sears or somewhere buying a new aircompressor.
You guys are great. Thanks for the help.
Thanks,
JAck
You guys are great. Thanks for the help.
Thanks,
JAck
Posting Guru
Joined: Sep 1999
Posts: 1,022
Likes: 3
From: Pensacola Florida
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Posting Guru
Joined: Dec 2002
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From: peoria, az
I don't know about that, my 5.5 craftsman will keep up with my blaster but with my da sander it won't even come close.
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Elder User
Joined: Sep 2003
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From: indiana
WHEN I STARTED OUT I WAS USING THE SAME COMPRESSOR AND HAD THE SAME PROB. THE ONLY FIX.....BUY A NEW AIRCOMPRESSOR. I HAVE A 60 GAL 6 HORSE AND IT KEEPS UP WITH EVERYTHING I USE BLASTERS CABINET AND PORTIBLE AND ALL THE AIR TOOLS THEY MAKE.
Posting Guru
Joined: Dec 2002
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From: peoria, az
You will get no argument here. Bigger is better. I've been rebuilding mine about every 2 years for a 35 dollar kit The wife can't understand why I want to go buy more tools if I can keep doing that. I guess it will just have to expire for good. Maybe it'll have an "unfortunate incident"
Posting Guru
Joined: Sep 1999
Posts: 1,022
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From: Pensacola Florida
Stepman,
What size nozzle are you using? It must be small if if 11 cfm is all that is required. My glass beader has a 5/16" nozzle and needs at least 19 cfm and my sand blaster uses a little less.
Sand blasting my frame did my last compressor in. Not terminally but I had to rebuild it twice in two weeks so my better half suggested that a better compressor was in order. I'm a lucky guy.
What size nozzle are you using? It must be small if if 11 cfm is all that is required. My glass beader has a 5/16" nozzle and needs at least 19 cfm and my sand blaster uses a little less.
Sand blasting my frame did my last compressor in. Not terminally but I had to rebuild it twice in two weeks so my better half suggested that a better compressor was in order. I'm a lucky guy.
Posting Guru
Joined: Dec 2002
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From: peoria, az
darkman, My nozzles are 1/8". My beadblaster is also bigger but it keeps up pretty good. My sandblaster works good until it wears to about 1/4", Then I have to wait on the compressor or change tips. It doesn't remove a lot at a time but it does okay. When I bought the compressor, the bigger ones cost about twice what they do now so my next one(which shouldn't be too far away) will definately be alot bigger.
Posting Guru
Joined: May 2002
Posts: 1,495
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From: Northwest Fl
It's true CFM is the determining factor in most air tools because even the little compressors can pump up to 100+PSI, but be also aware that different tools vary considerably in operating CFM. The same size die grinder can range from 3.5 CFM to 9CFM depending on power and quality.