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Saracen
03-01-2013, 12:00 PM
Any experience as to what size of PSI/CFM compressor would be needed to provide a chip blower to clear alu chips ? It's only a desktop machine, so not taking deep cuts in one go.

I'm thinking that the size of the nozzle will determine the pressure/size/reach of the jet, and hence the overall air loss, but don't own a compressor so don't know what say 20psi equates to in terms of an air jet.

Also thinking that a decent (50l ?) size reservoir will keep the duty cycle to a minimum ?

Last question - can you use a coolant output switch to control the compressor, so that a job left running will kill the compressor when the cutting has finished ?

Adrian.

JAZZCNC
03-01-2013, 01:02 PM
It takes a fair bit of air to blow chips completely clear but your correct the nozzle and pressure is the secret.
The problem lies not so much with the DOC but more has you get deeper the chips become harder to clear the slots so more pressure needed.
Can't advise on either I'm afraid has the Nozzle used will determine PSI needed and my straight blow setup is very crude being a length of car break pipe with end nipped with pliers.?
It's not has bad or crude has it sounds and I did used to have a purpose built pipe which used motorcycle main jets for nozzles but found them restrictive and too direct. This setup works much better and I can change spread very easily by just crimping the end with pliers on the fly if needed.

I also have a mister which works very well but can't help with that has it's a commercial component with a quite complex venturi system and multi nozzle system. It also eats air and needs a far sized CFM and tank.
Also on my system I just leave the PSI on Comp set to 90psi and control the blown air on machine with 2 valve's. One for each system.

If you want to have blown air under machine control then don't have it turn the comp on/off directly has there's too much surge and the load will be high. Instead use a 24v solenoid valve to cut the air thats controlled thru a low power 5v relay from an input. The coolant or spindle relay on a BOB would work fine or any 5V external relay.

Edit: This would also give the added benefit of being controlled thru G-code M8/9 commands and air flow will stop for cutter changes and automatic resume when hitting cycle start again. You can also choose which tools in the code use air and which don't.

Sorry can't give more specifics but with trial and error you'll get it right. My only advise is the bigger the comp/tank the easier it will be.


A can tell you a 50ltr Hobby Comp will empty faster than you realise if you want to keep the slot clear and it will be working hard and often, like almost 100% duty if you don't get the nozzle setup correctly.

BedlamRik
03-01-2013, 01:19 PM
Hi Adrian, First and foremost to consider is cost, What you need to factor in in this decision is, Where is it going to be used?,
Is Noise a factor? ( Am I going to off ps the significant other or Neighbour).
can the compressor be enclosed? (this can lessen the noise, but needs ventilation and access to service the compressor, IE you need to get at it to drain the tank occaisonally).
Generally the bigger the tank/ more CFM the motor is capable of generating means the more expensive it is, so like everything, a happy compromise needs to be reached.

I'd love the space/ cash for a 200ltr tank, but I just don't have it, so at the moment, I'm playing with a 50ltr Aldi Jobby, which for its purpose ( pressure casting resin) is spot on.
Yes its noisy, but it lives box in my shed, out the way of the other half, so jobs a gud un.
(Roll on Finishing the Garage and bigger compressor here I come, Just Don't tell my missus:witless:)
as for Duty cycle, thats dependant on the amount of flow from the nozzle, 20 psi = plenty for blowing small debris, and the size of the aperture in the nozzle, so yeah smaller nozzle, more concentrated "jet" of air.

Last question, I dont see why you could'nt put a solenoid on the airline to control it switching on/off. Assuming that a "Coolant output switch" is a signal input.
if it is , then instead of coolant it would be controlling air flow.
most "tank" compressors have pressure switched duty cycles anyway, so when the tank reaches its desired pressure the motor switches off, placing a soleniod valve in the output airline controlled by the coolant input would have the desired effect, it just means you'd have to turn off the mains for the compressor when your done.

if that makes sense.
Rick.


EDIT ,
JAZZ Beat me to it.:friendly_wink:

blackburn mark
03-01-2013, 03:12 PM
as far as nozzles go iv found using a length of straight brass pipe (1.5mm id on mine) helps
I think it makes the first couple of centimetres of air laminar... better for getting into those deep slots
not a problem if you have an abundance of air like jazz but worth a play if you want to maximise a small compressor

I'm mostly cutting plastics and using a glorified fish tank type pump, the low pressure/volume is not so good for getting jagged alli chips out of narrow slots

Saracen
03-01-2013, 11:47 PM
Thanks for all the points to consider. It will be going in a garage at the bottom of the garden, and it's quite built up around here, so it may well annoy the neighbours as well as attract unwanted visitors.

Space is at a premium, so I think the best bet will be to measure under the work bench and get the largest I can fit in. I would like one for sand blasting and spraying as well, so it will be a compromise between these three roles.

Adrian.

cropwell
04-01-2013, 02:47 PM
I use a Hailea AC-208 piston air pump, which at 35 litres/min is a little less than ideal, but it works. You can get the 80 litre one for 35. The usual garage type compressor won't run all the time without overheating as they are not intended for continuous duty. The pond pump is also quieter, and as my den is in the house, it means I can CNC into the night without waking SWMBO. Using a worshop vac at the same time keeps the debris under control.

Rob

martin54
04-01-2013, 05:40 PM
If your wanting to use it for chip removal, grit/sand blasting & spraying then a 50 ltr tank isn't very big at all even though it may sound it. All 3 functions would benefit from a larger tank & don't forget there may also be times when you want to do more than one thing at a time, say you have a job to cut that takes a few hours, you may want to do some spraying or blasting while the job is cutting.

Shinobiwan
05-01-2013, 06:15 PM
Most of the 50L models out there are poor. I had a Sealey 50ltr 2hp that lasted about 6 months before developing a loud knock on the piston. Bought a cheapie 2.5hp 50ltr from Netto for about 80 as a stand in and that did exactly the same. They use cheap materials and cut corners anywhere they can with these low end compressors. They're really made for occassionally blowing up the odd tire, a quick spray paint here and there etc. Problem is the duty cycle is low and if you run these regularly and for long periods the heat kills them. Things that need lots of air such as spraying or blowing off chips will have your compressor cycling often with the combination of small motor and small tank.

I eventually bought one of these.

7874

Surprisingly quiet since its really made for dental work, great if you have to run for long periods or have neighbours. That was about 6 years ago and have absolutely hammered it. Its just starting to get tired now with the teflon coating on the pistons all but gone(its an oil free type) so it tends to get very hot quickly but there hasn't been a week where it hasn't run and sometimes I'm using it all day week long when busy.

I'm looking around for a replacement and the next one will be a 150ltr possibly 200ltr if I have room. This one on ebay is a good price Air Compressor 3hp 150lt Belt Driven Motor 230v SUPER QUALITY | eBay (http://www.ebay.co.uk/itm/Air-Compressor-3hp-150lt-Belt-Driven-Motor-230v-SUPER-QUALITY-/290813003059?pt=UK_Air_Tools_and_Compressors&hash=item43b5ce4533).

Saracen
05-01-2013, 07:02 PM
Hmm, interesting. The pond pump idea sounds good as they should be rated for continuous 24/7 running. Looking at the 80l/min one, it only provides 18psi, but that will depend on the nozzle size at the cutting tip.

I doubt I have the room for a 3HP compressor, and at 180kg (!) it would have to be pretty much static wherever it landed :concern:

Adrian.

cropwell
05-01-2013, 10:10 PM
I have a friend who uses one of the three motor Clarke Shhh compressors in his garage at home for sand blasting and another who has a hydrovane compressor for his glassblowing studio. Both of them are quiet and high volume output. At about 1,500 and 3,000 each these would do the job nicely :thumsup:. I on the other hand have ordered an 80L pond air pump for 35 as I feel that the 35L one at 19 was underpowered (but it does the job OK-ish). I have got an old Clarke Tiger with a 50L tank, which has served me well for spraying, air tools and nozzle blast cleaning, but run it continuously for 10 mins and it starts to smell of hot oil and frying electrics, but there again I am at an age where the same happens to me :chargrined:.
Cheers - Rob

Shinobiwan
06-01-2013, 01:04 AM
I doubt I have the room for a 3HP compressor, and at 180kg (!) it would have to be pretty much static wherever it landed :concern:


Sup with ya, its got wheels! Stick a couple of steppers on there and you've got a remote control bomb lol

martin54
06-01-2013, 02:46 AM
I'm guessing I have just been lucky with mine then, had my 50ltr machine for 8 or 9 years now & it's still going Strong. OK it's not run on a daily basis in fact some weeks it doesn't run at all but it has done a lot of work over the years although I haven't used it to spray anything since I got the HVLP machine 6 months ago.
I got it because I needed something portable that I could throw in the car/van & this one fitted the bill but if I was buying a dedicated machine for the workshop I would buy something with a bigger tank.

Saracen
06-01-2013, 11:18 AM
Sup with ya, its got wheels! Stick a couple of steppers on there and you've got a remote control bomb lol

:hysterical:

Looks like I'll need to be more drastic with the workshop clearance then :friendly_wink:

Adrian

John S
06-01-2013, 01:00 PM
There are some cheap hydrovane compressors out there.
This one sold for 155.

Hydrovane 6PU air compressor | eBay (http://www.ebay.co.uk/itm/Hydrovane-6PU-air-compressor-/281040295378)

Best to get the tank mounted ones but many can be had single phase for under 450.

My shop is about 50 foot away from the house but it against my neighbours house so I can't run anything really noisy late at night. I often forget to switch the compressor off and due to small leaks it often starts up a couple of times during the night.
Never had any complaints from next door.

There are differences in the models, the tank mounted ones are like normal compressors and use a pressure switch to cut off at a pre determined pressure.
The tripod mounted ones have an unloader valve built into the compressor that stops it pumping, the motor carries on running. These can be uses as a normal compressor when fitted to a tanked system if the pressure switch is set to say 10 pounds below the unloader pressure.

One way to save a lot of money is work out what the max pressure needs to be. Mine is set to run to 120 psi but I only use it for general use, no power tools etc so I have dropped the pressure to 95 pounds because it takes 5 minutes to get to 95 but 8 minutes to get to 120, that extra 25 pounds cost a lot of money as it has to do more work. It's also less strain on the compressor.

Shinobiwan
06-01-2013, 03:11 PM
One way to save a lot of money is work out what the max pressure needs to be. Mine is set to run to 120 psi but I only use it for general use, no power tools etc so I have dropped the pressure to 95 pounds because it takes 5 minutes to get to 95 but 8 minutes to get to 120, that extra 25 pounds cost a lot of money as it has to do more work. It's also less strain on the compressor.

Great advice John. I forgot to mention but after killing 2 compressors in the space of a year I hunted around on the spraying forums for advice and found this is fairly common practice on smaller hobby to light trade models. I adjust the pressure switch on my last one in a similar way and that's been good for all these years, might have something to do with that.

Ricardoco
07-01-2013, 04:32 PM
I went through all the same pains when i first got my workshop, in the end i purchased a higher CFM unit, it is only a 50ltr but with 13cfm it fills the tank in no time instead of being on all the time, this is not a particularly noisy unit but ist not a whisper system either but the high CFM means its not on constantly either. Ive had it for two years now and its had two oil changes and its fine, i run a blaster cabinet and that will push any compressor to its limit, but its fine. Ive seen V configuration systems but they are running in the 80-90db region, thats way too noisey, mine runs at about 40db so whils not quiet its half as noisey as those. mine is a Wolf, from china i suspect but its not let me down yet!!

Rick

Shinobiwan
12-01-2013, 04:28 AM
Ive seen V configuration systems but they are running in the 80-90db region, thats way too noisey, mine runs at about 40db so whils not quiet its half as noisey as those. mine is a Wolf, from china i suspect but its not let me down yet!!

Half the actual acoustic output is a 6dB drop but due to the none linear way our hearing works we perceive more like 10dB as half the level.

Jonathan
12-01-2013, 02:06 PM
Half the actual acoustic output is a 6dB drop

Half is surely -3dB as log(3)=0.48.

Either way, no distances specified for these measurements so they don't really mean much without making assumptions. Plus the frequency response of the human ear isn't flat, so if one operates at a higher speed that would make a difference...

Ricardoco
12-01-2013, 05:51 PM
Half is surely -3dB as log(3)=0.48.

Either way, no distances specified for these measurements so they don't really mean much without making assumptions. Plus the frequency response of the human ear isn't flat, so if one operates at a higher speed that would make a difference...
From my point i was talking dbm, as i thought everyone was but still it is right to clarify this, the difference with my workshop is i can hear 80dbm outside quite clearly, i can also hear 40dbm outside, but hardly.

Rick

Shinobiwan
12-01-2013, 08:55 PM
Half is surely -3dB as log(3)=0.48.

No its 6dB for half the sound pressure output. Consider it the otherway around and you get the idea ie. 3dB increase is only half rather than double.


Plus the frequency response of the human ear isn't flat, so if one operates at a higher speed that would make a difference...

Not only that but also with a higher mean sound pressure level there is some compression of this. The fletcher munson curve is the commonly accepted equal loudness curve used to describe the frequency response of the ear when considered as a transducer.

Jonathan
12-01-2013, 09:17 PM
No its 6dB for half the sound pressure output.

Fair enough - at first you said 'acoustic output' which I took to mean acoustic power (which would be 3dB) not sound pressure, which as you say it 6dB for twice as loud (when neglecting our ear's response) which is a more meaningful comparison in this context.