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  1. #1
    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 ?


  2. #2
    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.
    Last edited by JAZZCNC; 03-01-2013 at 12:32 PM.

  3. #3
    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)
    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.

    EDIT ,
    JAZZ Beat me to it.

  4. #4
    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

  5. #5
    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.


  6. #6
    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.


  7. #7
    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.

  8. #8
    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.

    Click image for larger version. 

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    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.
    Last edited by Shinobiwan; 06-01-2013 at 12:02 AM. Reason: Fixed broken link

  9. #9
    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


  10. #10
    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 . 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 .
    Cheers - Rob

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