CNC Coolant Easy Guide [ Mist, High Pressure, Through Spindle, Flood ]

Cooling: CNC Coolant #3 Priority

Material Considerations for CNC Coolant

Feeds and Speeds with Different CNC Coolant Options

It may surprise you to learn that very few recommend different feeds and speeds for mist versus flood coolant.  The reason is that there is a baseline expectation that no matter what you do for coolant, you will make sure that chips are adequately cleared.

Baseline Coolant:  Clear the Chips!

The baseline role for any would-be CNC Coolant system is to clear the chips.  Recutting chips is bad for the cutter, bad for your part’s surface finish, and is to be avoided.  Therefore, let’s start with the assumption that whatever you’re doing about CNC Coolant it is clearing the chips.  For example, manual machinists often make use of chip brushes to periodically sweep chips away.  This is way too cumbersome and ineffective for CNC, but in that sense, the chip brush is a form of “Coolant”.

A step up would be spritzing the area with an air gun.  Perhaps you will even have rigged a continous air flow from a nozzle of some kind.  Or, maybe you’re on a CNC Router and you’ve got a vacuum system sucking up all the chips as fast as they are made.  Now we’re getting into the realm of the real baseline for CNC Coolant.  A baseline provides no advantage, rather, it is the minimum acceptable level of Coolant to be usable and reliable for CNC work.

There’s one more thing called for from a baseline CNC Coolant system and that’s the ability to lubricate the cutter and material if needed.  Certain materials, such as aluminum, require lubrication or they will tend to weld onto the cutter and disaster follows not long after–broken cutters, globby taffy-like aluminum clinging to cutter, and ruined part.  Clearly avoiding this has to be a part of our baseline.

Folks can stand by giving an spritz now and then from a can of WD-40, but like the chip brush, that’s really not adequate if you plan to cut much of whatever material demands the lubrication.  There are some cutter coatings that eliminate the need for lubrication, but be aware the coatings wear and the failure will be sudden when there’s no long enough coating to keep going.  You can sometimes make due if your chip clearing is prodigious enough and you keep your cuts extremely shallow, but you’re probably living on borrowed time for your cutter the deeper you go and the more chips escape extraction and wind up being recut.

Flood versus Mist: Which CNC Coolant Option is Better?

This may come as a surprise to many, but the difference is almost entirely a function of which one will clear the chips better.  Let’s do a simple thought experiment.  Suppose you have a simple low-performance Flood Coolant system.  It’s putting out a slow trickle of CNC Coolant.  Maybe you’ve even turned it down so you don’t have to wear a pancho when running the machine because you have no enclosure.  Imagine your machine cutting a deep pocket or slot with your trickle of Coolant.  The pocket is full of cutting fluid.  There’s no question the cutter is immersed in it.  But are the chips being cleared?  In a word, “No!”  They’re sitting under that pool, and the pool is almost protecting them from removal because the force of the Flood is not strong enough to blast them out of there.

Now consider a good Misting system.  There’s no pool to hide under.  You can easily see whether the chips are being cleared and crank up the air pressure if not.  You’re less worried about the mess because Mists are much less messy.  It should now be more obvious that Mist is going to be a better CNC Coolant option than a mediocre Flood Coolant!

While we’re on the subject of Misting, there are basically two kinds of Mister–plain old Mist systems which produce a coolant aerosol:

Misters produce a coolant aerosol…

Plain old Misters work great for machining, but they use more coolant than they need to and they fill the shop air with the mist–not the world’s best thing to be breathing all day.  There is an alternative called the Fog Buster that focuses on propelling larger droplets without creating an aerosol mist:

Fewer larger droplets from the Fog Buster…

By launching fewer larger droplets, the Fogbuster makes sure they don’t travel all over your shop–they mostly land on the workpiece where the thing is pointed.  Better for you and just as good for the machining work.  They cost a little more, but for a premium Mist system they sure are worth it.

How do we make sure our Flood Coolant system isn’t mediocre (else we may as well use Mist)?

There are a couple of parts to the answer.  First, we need to make sure we can generate sufficient pressure on the Flood system to make sure the chips are cleared out.  When it’s cranked up good, you almost can’t see what’s going on there’s so much CNC Coolant flying around.  Second, we need to make sure the Coolant is properly aimed to clear the chips.  That can be a little harder.  Different tools are different lengths.  Things move around as the work progresses.  Typically, we want to either aim for the bottom of the cut or the top of material if the nozzle can’t “see” the bottom of cut.

By now you’re probably realizing there’s another reason not to give Feeds & Speeds bonuses for flood coolant: it’s hard to properly identify whether a flood system is really clearing the chips.  Operators assume they are, but most are not paying close enough attention to it.  How the coolant is aimed matters tremendously.

Good chip clearing and lubrication where needed are the baseline assumptions that our G-Wizard Calculator makes about your CNC Coolant.  However, while we don’t recommend slower feeds and speeds as the answer to poor coolant, G-Wizard does know how to take advantage of premium coolant options such as programmable nozzles, through spindle coolant, and high pressure coolant.

To calculate proper feeds and speeds with premium cnc coolant options, just click the boxes in the machine profile that tell G-Wizard your machine has these capabilities.  Then, you can operate the check boxes on the Feeds and Speeds Calculator to take advantage:

Performance Recipe: Aiming CNC Coolant for 5% Higher MRR

Performance Recipe: Through Spindle Coolant & High Pressure Coolant

Programmable Coolant Nozzles are great, but they can’t guarantee the coolant goes to the optimal place every time.  Some places are just not accessible, for one thing.  Consider the bottom of a deep hole you’re trying to drill.  No way to aim the nozzle there–it’s below the surface of the material and there is no access.  Or is there?

Through Spindle Coolant (abbreviated TSC) gains access by feeding coolant through your spindle like the name says, and from there is can exit via passages inside the tool.  You really can have a nozzle built into the bottom of your drill bit, for example:

Through Spindle Coolant: Like a Nozzle in your tool’s tip.  (Image courtesy of MC Machinery Systems)

TSC ensures the cnc coolant is going to exactly the right spot to make the most difference.  BTW, there are lathe equivalents that go through the tool rather than the spindle, but the principle is exactly the same.

With Through Spindle Coolant, performance can be greatly increased.  Even higher chip loads can be tolerated, holes can be deeper, and peck drilling can be all but eliminated due to the improved evacuation of chips.  Of course, G-Wizard Calculator has an option for TSC too.

Another advantage for TSC machines: you can often run more flutes, particularly when profiling.

Once you have Through Spindle Coolant, you’re still not at the pinnacle.  To go further, you’ll need a High Pressure Coolant system.

High Pressure Coolant

With Through Spindle Coolant, you’ve made sure the cnc coolant is being delivered to exactly the right location where it will do the most good.  The next level of benefit comes from dramatically increasing the pressure and volume of coolant delivered to that sweet spot.  Of course this improves chip evacuation, hence the reduction in the need for peck drilling, but High Pressure Coolant (abbreviated HPC) is where there’s a chance for the cooling capabilities of “Coolant” to really shine.

The trouble with Coolant’s cooling is that it can be spotty.  A droplet hits the tool here, another hits the workpiece there, a third bounces off a chip, and there’s just not enough consistency.  Mist and air blasts do almost as good a job cooling as a result.  The exception is on materials like Titanium that don’t conduct heat very well.  For those types of work, flood coolant is essential.  But aluminum, for example, conducts heat extremely well.  It’s hard to tell a difference between flood and mist unless you’ve really got a great flood system going.

There’s another problem with liquid coolants too.  It’s called “shock cooling.”  Unless there is enough coolant to keep carbide from really heating up, what happens is those random droplets cool the carbide randomly.  One moment it’s very very hot, the next a big droplet lands (splat, sizzle!) and it is shock cooled back down to low temperature.  This leads to micro-cracking of the carbide which can severely reduce tool life.  Always check with your tooling manufacturer, especially on high performance insertable tooling, whether there is a point where the coolant needs to be turned off and a pure air blast used to prolong your carbide’s life.

High Pressure Coolant can provide an alternative.  By using very high pressures, 1000 psi or more, as well as high volumes, it’s intent is to deliver so much coolant that nearly all of the heat will be carried away before it can ever build up.  Practically speaking, what this means is higher surface speeds, more rpms at the spindle, higher material removal rates, and longer tool life.  You can trade some of that off as well.  For example, let’s suppose you’ve got a job drilling thousands of holes in some material that requires carbide drill bits.  You might very well sacrifice a little of the ultimate rpm potential in exchange for longer life so you don’t break a bit and have to scrap a part.

Performance with a High Pressure Coolant system can be amazing compared to running without.  G-Wizard is set up to give appropriate SFM bonuses when you have HPC, so go ahead and check it out.  You can literally use G-Wizard to figure the ROI (return on investment) for an HPC system by calculating what sort of increase in feeds and speeds the HPC will enable for you.

Horizontal Mills and Lathes Have Gravity Helping Clear Chips

Don’t overlook the benefits of gravity for machining. On vertical mills, gravity makes it harder to pull chips out of deep holes. On lathes and horizontal mills, gravity makes it easier. Kinda makes you wonder why nobody has a machine that cuts from underneath. You’d need a pretty crazy palette loader so you could drop the workpiece onto the table and then flip it for cutting. Too far out, I thought, but then I discovered such machines actually exist. They’re called “Inverted Spindle Lathes” and are a potent alternative to bar fed lathes.

Here is a link to an MMSOnline article about them.

Exotic Recipe: Alcohol as Coolant Datron uses an ethanol alcohol mist as coolant for its HSM machines. They make a good case for it: It is ideal for high-speed, micro-tooling of non-ferrous metals and some plastics due to a thinner-than-water viscosity that allows the ethanol to quickly cover and cool more of the surface area on fast-moving parts. The low evaporation point of ethanol makes it an efficient cooling and lubricating solution. Since the ethanol simply evaporates, disposal, recycling and their associated costs are a thing of the past. Plus, ethanol coolants leave no residue on machined parts, which makes costly secondary operations, like de-greasing, obsolete — maximizing throughput, increasing efficiency and ultimately improving a manufacturer’s bottom-line.

Conclusion

For many high performance applications, machinists can focus on chip clearance and lubrication and ignore the cooling issues. Above a certain surface speed, many tooling manufacturers recommend turning off the flood coolant and using an air blast (perhaps with mist for lubrication) to clear chips. Materials that don’t transfer heat well like titanium will require flood coolant regardless.

One last tip.  Coolant and chips are messy.  Most machinists like to use an air gun to spray them off the part before removing it from machine.  You can automate that task with a chip fan.

Additional Information

Selection of Cutting Fluids in Machining Processes: Good overview of some of the factors involved in selecting coolant type.

DIY Flood Coolant: Need to put together your own flood coolant system? Check this article out.

Tramp Oil Skimmer: Easy to build but powerful tramp oil skimmer.

Turning Down the Heat in a Cut