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Old 25-10-2011, 21:38   #1
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Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

So, I'm preparing to refit the Steel boat I just bought. As part of this, I need a better grinder, and probably a sander and definitely a needle scaler. So I have decided to go with some air tools.

Since I have a steel boat that needs work, and since I know welding is a sellable commodity while cruising, and since I need this stuff anyway... I'm thinking it would be cool to set up the boat to be able to do some actual fabrication.

So, to that end, finding a compressor that I can hook to a motor is not all that hard. But is there a reasonably sized compressor that has a decent flow rate of 4-6 CFM?

In order to gen any usage out of these tools, if I have a tool that can use a 3 gal tank to run 90psi for 5 min, will 180 psi run the same tool for 10?

IOW is there a way to do away with the sheer volume of a large tank?

Can I get a scuba compressor that's smaller sized and can also run tools?
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Old 25-10-2011, 22:44   #2
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Re: Need some compressor advice from the full of hot air blowhards

Most air tools will run 40-60 psig and a few CFM each. for 4-6 SCFM you will want at least a 2-3 HP compressor with an ideally 20 gallon tank or larger.

Probably 90-100 psig is all you really need. Above 125 psig your getting into ASME code type tanks which cost quite a bit more. 3-4 times more if I recall. You do NOT want to run a cheap tank at higher then about 100 pressure.

The scuba compressors are generally very high pressure low volume type which is the opposite of what you really need.
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Old 25-10-2011, 22:55   #3
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Re: Need some compressor advice from the full of hot air blowhards

If your looking at an engine driven compressor, it might be easier to get a gas powered contractors type air compressor then to adapt a low pressure compressor to a inboard engine. You would need a method to unload the compressor and of course a safety relief valve, and probably an electric clutch.

You need the tank volume as 2.6 cfm is about 20 gallons or about one minute of usable air (80 psig down to 40 psig) in a 20 gallon tank for one tool, there about anyway. As you only have the 80-90psig down to 40 psig usable or whatever your grinder, etc require.
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Old 25-10-2011, 23:03   #4
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Re: Need some compressor advice from the full of hot air blowhards

Many air tools require more than the 4-6 scfm you quote. You need tankage to make up for that. You use the higher flow air tool then give the compressor a chance to fill the tank again. Do not expect to run a decent sized grinder with that sort of a setup.
Going higher pressure will improve efficiencies but you are looking at a two stage compressor ($$$) and a heavier air tank.
Excessive cycling of a compressor causes all kinds of wear issues as well. There isn't any substitute for tankage.
There are lots of things you can do with a little pancake compressor but running air tools that require a large amount of air isn't one of them. Don't expect too much life out of one of these and whatever you do, do not waste your money on a little oil-less unit unless it is for a very short duration one-of kind of job.
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Old 26-10-2011, 01:06   #5
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Re: Need Some Compressor Advice from the Full of Hot Air Blowhards

I'm familiar with pneumatic tools and steel work (building a 42' steel cutter). A pneumatic needle gun will work well. A pneumatic grinder big and powerful enough to be useful will take a LOT of air, a lot more than you are budgeting. Look up the tools and their consumption figures. If you are going to really do any steel work you are going to want at least a 7" grinder. It will be much more practical to either power this off an inverter or a 110VAC generator.

Your best set up for on board welding will be a high output alternator set up for welding. Zena sells an excellent one, or you can build your own, Brent Swain has plans in his book. The high output alternator, say 150 amps, will also provide the current required to keep up with the inverter powering electric tools.

Pneumatic tools excel for compact, light weight with reasonably small power requirements. They are not well suited to providing significant power. And a practical grinder for steel work definitely requires that.

Regards, Paul
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Old 26-10-2011, 16:38   #6
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

Working with bare metal, air grinder would not be my first choice. On the outside of a hull it would be OK, but inside or topside it could blow the debris into the nooks and crannies (do you think you could find it all?). Additionally air tools are condensation makers, blowing all that water laden air on freshly ground metal. For it's versatality I would go electric.
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Old 26-10-2011, 21:44   #7
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

Thanks for all the advice. I am planning on a zena-type alternator setup at some point in the future. Condensation and blowing debris are things I hadn't considered.
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Old 27-10-2011, 15:09   #8
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

maybe consider a blaster too? i just blasted the interior of my steel boat with a 3hp compressor and a 2.5mm nozzle. the results are significantly better than grinding. it is excellent for spot blasting rusty spots on the exterior too.

if you do it, try using garnet abrasive. the results are impressive.
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Old 27-10-2011, 21:36   #9
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

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Originally Posted by Honey Ryder View Post
maybe consider a blaster too? i just blasted the interior of my steel boat with a 3hp compressor and a 2.5mm nozzle. the results are significantly better than grinding. it is excellent for spot blasting rusty spots on the exterior too.

if you do it, try using garnet abrasive. the results are impressive.
Yeah, I'm definitely going to have to do the exterior at some point. I was thinking of doing the interior in just a few spots.

Tell me: what are you planning on insulating with?
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Old 27-10-2011, 23:57   #10
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With regards to air powered tools. I did my apprenticeship and four and a half years as a tradesmen (Boilermaker - Metal Fabrication) working for the state based railways using only air powered tools. The workshops were steep in history with air tools being the only real way to work. It made for a very safe scenario with no 240v leads greeting sliced up my steel!....the fact that they seemed less "torquey"...if you will...did not matter. They were more than adequate.
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Old 29-10-2011, 09:01   #11
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

re insulation; after weighing up the pros and cons of spray foam versus hard pre-formed slabs, we decided to combine the two.

at present, my plan is to spray foam the ceilings so that there is absolutely no chance of any condensation forming and then dripping through the tongue and groove on the ceiling or down the sides. with the hull i intend to cut and loose fit hard slabs of kingspan between the horizontal and vertical stringers, and then to spray foam the joins and all the seems. this way i can get them out relatively easily for inspection. this method has the added advantage of cost saving as the hard slabs work out to be about half the price of the spray foam. the downside is that any air that is trapped between the slabs and the hull has the potential for condensation, but i have drilled limber holes in the horizontals, and the steel has been blasted and then coated with the ameron epoxy paint system. any condensation should run down into the bilge. as for the bilge, we have dug out a deep pit in the existing concrete and pig iron ballast and will create a small area for any water to accumulate, into which will go the pump. we intend to shape the large flat bilge section with new concrete in such a way that all water runs into the bilge pit, so there should be no standing water except for the small amount in the bilge pit. we will look at a strum box on the pump so that it will be as dry as possible. that's the plan!
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Old 15-12-2011, 20:52   #12
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

One possible solution for a compressor might be a commercial vehicle compressor (Highway truck). Bendix Tu-Flo 550 or 750 come to mind and there are larger ones also. I've seen these set up on tow trucks and tire trucks to run off the engine via an electric clutch arrangement.
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Old 15-12-2011, 21:01   #13
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

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One possible solution for a compressor might be a commercial vehicle compressor (Highway truck). Bendix Tu-Flo 550 or 750 come to mind and there are larger ones also. I've seen these set up on tow trucks and tire trucks to run off the engine via an electric clutch arrangement.
You do have to be careful with crankcase oil getting into the air, it's a no no.
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Old 15-12-2011, 21:07   #14
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

Being in the business, most large shop compressors have wet crankcases..and separators for the paint gun lines... as far as shop tools ie grinders etc, water separators are called for.
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Old 15-12-2011, 21:22   #15
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Re: Need Some Compressor Advice from the Full-of-Hot-Air Blowhards ;-)

Oops! Got over zealous, Thought we were talking diving compressors.
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