Air compressor buying tips?

[WelderMick]

Hi, I'm after an air compressor for general home workshop use - workshop tools, paint spraygun, plasma cutter. I don't know the first thing about air compressors and was hoping someone could help me out with a few tips on what to look out for and what to avoid. I'm thinking around the $500 mark. Thanks - Mick

[SurfinNev]

Avoid the ones with alloy bores. They are cheaper for a reason. If you want to run air tools go for at least a 12 CFM. Long time since I bought a compressor but I don't think $500 will get much. Might pay to look for second hand.

Nev

[eskimo]

what ever you think you need double it...and then you might be close to what you wanted

[malb]

Haven't used one but from what i have heard plasma cutters need a huge amount of air so it would pay to establish the demand for that and try to size the comp so that can supply about three times that at free air delivery. This way the comp will have a duty cycle of about 35-40%.

Reduction drive comps have a better pumping efficiency than direct drive ones, so will be better able to cope with high demand loads.

Have a 3HP twin cyl belt drive 13CFM unit with a 100L tank, it copes well with most of the things that it faces but runs at about 35-40% duty cycle on a blower nozzle due to the lack of restriction. Generally very happy with the unit but beware of units with an plastic oil level sight glass housing. The only sign of an oil leak on my unit is the sight glass thread but it has cost me one set of bearings after about 8 years of work.

[jatt]

The single phase plasma cutter I recently looked at purchasing specified 14 cfm. With that in mind think I will buy a 17 cfm for the shop.

Biggest unit I have seen that will run on 15 amp single phase is 17 cfm.

Cant see $500 bucks getting u far, at least as far as purchasing a new unit.

My supercheap baby unit is handy as its sml and lite, but of course high volume air demands are beyond its capabilities.

[WelderMick]

Guys, thanks for your replies so far. My plasma cutter (40amp) hasn't got a nominated rate, but the supplier recommended 7-10 cfm. I haven't got any air tools at the moment, so not sure what their requirements are but by the sounds of it this is on the low side. Malb - thanks for your rule of thumb regarding this.

I'll have to head to the shops and ask a few questions:
- air tool flow requirements and recommended flow rates
- bore type (so what's the alternative to alloy? are they stainless steel?)
- drive type
- oil indicator

Any other general questions I need to ask? Apart from how I can get a $1000 machine for $500? Anyone prepared to go out on a limb and recommend brands for home workshop?

Thanks

- Mick

[malb]

I selected the plasma as the basis for my information as I suspect that it is generally the highest flow user. Next would be sanders and sprayguns, because once in use they tend to be used for fairly long runs. Much easier to handle are intermitant use items like drills, nailguns, rattleguns, rachets and rivet guns, where the device might do a a small set of units then gets time for the comp to recover. My 3HP unit was sized to be able to handle medium demand sprayguns and sanders, and copes with lesser items with ease, but I have never had to play with a plasma.

Industrial/commercial use comps are always cast iron bores, either in an alloy crankcase/cylinder or as pure cast. I know of 50 plus year old comps that have worked factories all their life and still do it well, but may be on their third or forth motor.

[WelderMick]

Malb - thanks. The dealer noted that the the plasma cutter has a similar orifice to common spray guns and therefore similar air requirements. I'll look for cast iron bore machines, and have yet to hit the shops, but I'm already pessimistic that I'll find one anywhere near my budget.

Machinewong - OK good point I'll have to find out the pressure requirement too. I had assumed that all compressors would be above the required level, but maybe not. Thanks.

[RayG]

Any other general questions I need to ask? Apart from how I can get a $1000 machine for $500? Anyone prepared to go out on a limb and recommend brands for home workshop?

Thanks

- Mick

Hi Mick,

I saw a catalogue today which had a scorpion XRS1750 3hp 270 l/min (9.5 cuft) compressor for $869, I don't have one, but they look to be ok, as far as specs go.
Italian made alloy compressor with cast iron cylinders. Of course it all depends on whether 9.5 cuft/min is enough for what you want to do.

Try googling for scorpion XRS1750.

Regards
Ray

[jackaroo]

Last time I saw Cosco has the Mcmillan AF12 for $800 or so (cosco in Dockland, Vic)

[matthew_g]

Most air tools run arounnd 90cfm, That said try to avoid the drirect drive type of unit, Not only are they cheap but they just won't do what you require. H/F have fairly good 3hp 3cyl compressors at a reasonable price...(not affiliated and all that stuff) My 17cfm is a PUMA and I have had it over ten years now and it has never missed a beat but it also cost me $1290.00 + sales tax back then..I also have a 20cfm that I only just picked up in the last 2 months for $300.00...It was an EX service station unit and is in perfect running condition, And is single phase, There are many options out there you just need to look..
Hope this has helped a little.....Matt

[franco]

Most air tools run arounnd 90cfm, .....Matt

Matthew, did you mean 9 cfm, or were you referring to high consumption tools like jack hammers, railway track maintenance tools etc?

FWIW I have an ancient 10 cfm twin cylinder workshop compressor. This is just adequate for running small air tools like die grinders etc. I certainly would not go smaller than this, and if I ever have to replace it the new one would be at least 12 cfm.

I agree with Matthew's suggestion to avoid the small direct drive compressors - I have one of these too. They are very noisy, and I have heard they have a fairly limited life, though I've had no trouble with mine yet. It only gets limited use inflating tyres though.

For anyone looking to buy a new compressor this thread is a must:

Air Compressors for Newbies- by Forrest Addy - Practical Machinist - Largest Manufacturing Technology Forum on the Web

Frank.

[matthew_g]

SORRY fellas, I ment 90psi.......So if you want to run say a die grinder you would need to be able to run 90psi constantly, I generally run my big 20cfm with my sandblasting cabinet and I run the 17cfm for all the other jobs...

[Harry72]

You will need most of that 20cfm just to run a die grinder properly...

[WelderMick]

Guys, this info is great and really helps

Ray and Jackaroo - thanks for the tips on specific models - it's always good to have a benchmark to compare all the options to. Both of these look pretty close to what I need.

I reckon you're right on the money with sizing Matt (not the 90cfm though !) and general specs. I don't think I'll be going for air grinders etc. I can't recommend enough the Forrest Addy article - very informative - look it up if you are a newbie. thanks heaps for this and your other comments Frank.

Cheers - Mick

[matthew_g]

You will need most of that 20cfm just to run a die grinder properly...


How do you work that out ??? A die grinder only needs 90psi @6cfm roughly...
Well thats the rating on mine and they are all pretty close in there requirements
Matt

[Dingo Dog]

Get a Clisby if u can.

DD

[Harry72]

How do you work that out ??? A die grinder only needs 90psi @6cfm roughly...
Well thats the rating on mine and they are all pretty close in there requirements
Matt

If your DG only needs 6cfm @90psi it must be micro sized, my DG's rating is 6cfm too yet my 14cfm Clisby will not support it without a pressure drop to 70psi, dont believe the rating its a con because its ratted in free air not under load... its like putting your car up on stands and claiming 100mpg:D
Check this decent air DG out read the spec's (http://www.mytoolstore.com/ir/ir301-k.html?source=google)

[rathkool]

Welder Mick,

Are there any compressor repair shops relatively close by? I picked up a reco'd 17CFM/80L tank upright machine years ago for $500.

cheers

Kevin

[Yonnee]

I picked up a brand new Ingersoll Rand 17cfm compressor a few years ago, with a 20M hose thrown in for around $750 at a trade night at a local compressor place. Its capacity has yet to let me down, but it does kick in and out more frequently when the pneumatic drill is going. I've yet to spray with it, but it should cope fine.

A Plasma Cutter... that's on the wish list.

[matthew_g]

If your DG only needs 6cfm @90psi it must be micro sized, my DG's rating is 6cfm too yet my 14cfm Clisby will not support it without a pressure drop to 70psi, dont believe the rating its a con because its ratted in free air not under load... its like putting your car up on stands and claiming 100mpg:D
Check this decent air DG out read the spec's (http://www.mytoolstore.com/ir/ir301-k.html?source=google)


Thanks for that Harry72, But you also need to remember that earlier on in the thread I mentioned that I am running 17cfm and a 20cfm depending on the job I am doing..My 17 will run a DG all day every day at 90psi....
I would have to agree that if a compressor was a little smaller it would probably need a pressure drop..
Matt

[WelderMick]

Are there any compressor repair shops relatively close by? I picked up a reco'd 17CFM/80L tank upright machine years ago for $500

Kevin, thanks - I haven't come across any but hadn't thought of that so that so'll have to hit the phone book. An upright tank would suit my situation pretty well I reckon. How mobile is it? Cheers - Mick

[WelderMick]

Yonnee, thanks I'll check these out too. cheers - Mick

[rathkool]

Mick,

Not very mobile, being rather top heavy but if I do need to move it, a sack or better a fridge trolley does the trick.

cheers

Kevin