Air cooling

[Peter HallParticipant @peterhall61789]

I am looking into small-scale cnc milling (think Taig/Sherline). Is it feasible to use a compressed air jet as an efficient coolant?

Any info or suggestions would be much appreciated.

Pete

[Peter HallParticipant @peterhall61789]

[Anonymous]

Hi Peter,

Yes and no! You can certainly use air blast on small mills; see for instance this thread:

**LINK**

As I'm sure you're aware, air blast is used extensively in industry instead of liquid coolant. However, the main purpose of the air blast is to remove swarf, not to act as a coolant. Many coated carbide cutters can, or need, to run hot to work efficiently, so cooling is not an issue. If you look at the heat capacity of air versus water you will see that water has a higher heat capacity and is therefore better at removing heat.

So, if you're looking for an efficient coolant then I suspect that air blast will be ineffectual, however for swarf removal it is pretty good.

Regards,

Andrew

[Peter HallParticipant @peterhall61789]

Thank you, Andrew. I was sure I had seen video of small mills with air jets directed to the cutting tool; now I know why it was done. I have a background in woodwork, so am pretty much ignorant of industrial practices where metalwork is concerned. Swarf removal would be good though, so if I go this route, I'll probably use it.

If you have any links to information on the use of small carbide rotary cutters, that would be very useful. I'm starting from scratch with cnc, but have some hobby experience with HSS and indexable carbide tools on small lathes and mills.

Pete

Edited By Peter Hall on 20/09/2012 20:53:51

[Steve GarnettParticipant @stevegarnett62550]

Posted by Peter Hall on 20/09/2012 18:33:11:

I am looking into small-scale cnc milling (think Taig/Sherline). Is it feasible to use a compressed air jet as an efficient coolant?

Any info or suggestions would be much appreciated.

There is one other possibility – although I believe that in operation, it's quite noisy…

Hilsch Vortex Tube

It's certainly been used in the past as a cutter cooling method. A google search will also reveal a lot more about how to make them, and optimise the efficiency. In an idle moment, I wondered whether using the cold side as a feed to an oil mist system would be any good?

[KWILParticipant @kwil]

Peter, as Andrew said coated carbide cutters can be run (and I do) without any coolant, indeed they are advertised as dry cutting. Look at Cutwel Tools site, I have used them from 3mm dia upwards.

[Anonymous]

Peter: I don't have any specific links for using carbide cutters. I've settled on uncoated 6mm and 10mm carbide cutters for general work on both CNC and manual vertical mills. I run flood coolant on the CNC mill, primarily to wash away swarf rather than for cooling. Now that I've bought a compressor I might consider air blast, as it'll be less messy. I run dry on the vertical mill. Generally carbide can be run hot. In steel I'm happy if the chips are coming off blue to yellow coloured and the cutter isn't actually glowing red.

I limit the use of coated cutters to tougher materials, such as stainless steel, where I normally use a TiAlN coating.

There is only one rule for cutters: Don't buy cheap cutters!

Regards,

Andrew

[John Stevenson 1Participant @johnstevenson1]

The biggest enemy of cutters on milling machines, manual or CNC is recirculating the already cut chips.

If you think about it it makes a lot of sense when you realise that a lump of chip getting stuck into the leading edge of a cutter will deflect the cutter off it part before it either gets recut or wedges itself past the tooth.

So the trick is to keep the cut clear, coolant works but for it to work effectively you needs loads of it, not a drip or a dribble, all that does is cools the job down a bit and provides a bit of lubrication but the chips are still there.

You need enough to completely was the job clean. However unless you have shrouded machines like in industry you are on a looser as regards mess.

Air blast does the same job and is not quite as messy, you don't need to work in a wet suit but it still throws chips all over.

You have to address guarding / screens as much as chip removal.

The smaller the cutter the more problem recutting chips is, you only need a slight deflection on a small cutter for it to snap.

[Bill PudneyParticipant @billpudney37759]

Must second JS' comment about recirculating chips.

When I was working I had some dealings with machine tool companies. When the company I worked for was making the leap into high speed machining several companies (well, DMG, Mazak, Makino) impressed on me the importance of not "recutting" (as they all put it) chips. They all used a combination of HP coolant and HP air to blow and clean the area adjacent to the cutting face.

One of the last projects that I never got to progress was to investigate the value of using HP air alone to clean and cool.

cheers

Bill

[TerrydParticipant @terryd72465]

Posted by Steve Garnett on 20/09/2012 21:28:43:

…………………………, I wondered whether using the cold side as a feed to an oil mist system would be any good?

I don't think that I would use an oil mist system on an unshrouded machine. My lungs are much too valuable to risk.

Regards

Terry

[Peter HallParticipant @peterhall61789]

Thank-you, Gentlemen. Plenty of useful advice there. A shrouded machine with an air supply will be the way to go I think.

Pete

[Steve GarnettParticipant @stevegarnett62550]

Posted by Terryd on 23/09/2012 13:01:02:

I don't think that I would use an oil mist system on an unshrouded machine. My lungs are much too valuable to risk.

I must admit that I have wondered about that myself. Doesn't appear to have killed off Bogstandard yet though…

[David ColwillParticipant @davidcolwill19261]

I made an oil mist for my triac using an old diaphragm compressor. It filled the workshop with choking fumes and was unusable. I found that the chip clearance was a useful feature and having abandoned the spray mist concept found that running just the compressor made a huge difference to tool life. I had thought that this was due to the air cooling the work / cutter but I'm sure that John S has it right. I still use the setup pretty much as was and would recommend the idea as it is fairly cheap to implement and does very quickly pay its way.

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