Mist Coolant (Fogbuster)

I'm all set to build myself a mist cooling system based on the Fogbuster to go on my almost finished SX2.7 CNC conversion (do these things ever really finish?). In all the excitement I completely ignored the fact that I need to run some sort of coolant through the thing! I'm having trouble finding mist coolant in the UK. Can anyone recommend a suitable coolant? Lots of people seem to use Koolmist 77, 50 quid for a jug of the stuff and another £50 for postage from the US... plus any import fees???

Any help greatly appreciated!

James

Google comes up with one from Force Suppplies **LINK** for £30 plus tax for 5 litres which might well do.

One from Saws UK just down the road from me is more expensive **LINK** at £70 odd plus tax.

Or you can get 25 litres of Terralus, made by Morris, off E-Bay for £35 (at the moment) in a auction ending at 3 pm tomorrow 6 th Feb. I'm almost tempted to buy and break up as that's not far away either. List is about £325 for that. Yikes!

In practice you can use most oil-water mix systems, not suds, providing you keep the oil concentration low and direct it away from you. Air pressure has to be low enough not to create mist bounce back. Set up right the air blows the coolant away from you.

The biodegradable ons are said to be a good choice but I don't know about shelf life.

Clive

Edited By Clive Foster on 05/02/2021 21:12:13

Thanks Clive. I was struggling to get anything useful out of google.

I'm hoping to be able to run at a nice low pressure to just push the chips away, and I may add a second air blast for a more aggressive puff when required. I don't have an enclosure yet so I would like to keep mess to a minimum.

It will be a big step up on trying to hold a hoover in one hand and WD 40 in the other whilst nervously glancing over to the ESTOP every few seconds.

James

I use XtremeCut 250C in my FogBuster on my Tormach 440 and my Myford lathe. It seems popular with many of the YouTube machinists. UK sales are from Lubriserv near Bristol, just up the road from where the Bristol Exhibition used to be held. Dilution is 4-12 % for machining. I use 8%. Cost in 2017 was around GBP100 for the 20 litres.

I bought the 20 litre drum in 2017 and am still using it and I reckon my great great great grandson might still be using the same drum such is the dilution and low consumption in the Fogbuster.

If you want a litre bottle full to try (which will last you ages) send me a PM with your shipping address.

Alan

Smith and Allan sell one at £125/20litre but that quantity might be more than you want.

My Bijur spraymists run at about 24 psi which seems fine on my manual machines, two lathes and a Bridgeport.

Most important points seems to be to ensure the spray is pointing away from you and rely on the "sniff test" to detect bounce back. You will smell the coolant if any comes back. Fugging up the workshop or anything more than a slight niff when close to the machine means you are running far too much coolant. There will always be a slight niff hanging around the machine even when not running. If the niff is significantly more when running look to reduce the coolant load or change the direction of the nozzle.

What are you planning to uses as a control / nozzle set up. I'm not completely sold on the whole Bjur set-up and have considered using one of the "£10" (ish) import mister set-ups as the basis for a fog buster style system fed from the Bjur reservoir. Basically only the nozzle to make (I'm lazy).

Clive

I thought the who idea of a Fog buster was that you don't get mist as the coolant is not atomised.

I've just set up one based on an air tool lubricator but not had much need for lubrication yet though I'm not sure it will flow enough with the 5psi that I need to keep the chips away. This system was suggested to me by Ketan at ARC as it it what they and the late JS use on their CNC machines. see my last post here

Jason

Mister, Fog Buster and Microdrop aren't really specifically different systems. More different points on a continuum.

The all work by entraining "just enough" lubricant inside an airstream. The lubricant mist / droplets stream should be comfortably inside the actual airstream so the lubricant is surrounded by a "wall" of air helping to control its distribution.

They will all produce an unholy fug if set up wrong with too much air driving too much coolant. My Bjurs can be spectacularly awful!

Generally, whatever the system, if you can see significant drops or fluid layer on the workpiece surface you have too much lubricant. Hafta confess that I run my modified Bjurs a little too rich but the overbored nozzles produce bigger, more like fog buster, droplets.

Oversimplifying

So called mist systems, more of an aerosol than true atomisation, produce the smallest droplets in a distribution which doesn't need to spread out much to cover the cutting area. Theoretically you can operate at lower pressures to, theoretically, have no bounce back. Supposedly the very small droplets instantly wet the surfaces and shouldn't be blown off by the airstream so the lubricant pretty much stays on the work and tool. Drawback is the low inertia of the tiny drops so the nozzle has to be close to the job to work at low pressures. At longer distances the aerosol tends to spread past the work.

Its very difficult to see when you have the required tiny amounts of entrained coolant so its tempting to open up the air and lubricant feeds so you can really see whats happening. Usually blasting huge amounts of mist past the job into the shop atmosphere for instant fug. Plenty of adjustment so plenty of opportunity to get it wrong.

Fog Buster basically uses a larger nozzle than mister so bigger drops are produced which carry better and don't spread into the air so easily. Being bigger the drops don't wet and spread quite so easily over the cut and tool so you may need a little more lubricant. But the higher inertia of the bigger drops makes it easier to control the distribution in the air stream so they carry further than mist without spreading out dangerously. Much more tolerant of variations in nozzle to cut distances and the bigger drops are easier to see. Too much air and too much lubricant leads to bounce back and drops being blown past, or off, the workpiece into the air where they break up into fug. The big advantage of a (DIY) fog buster is that its simple to make and pretty tolerant with a reasonably wide spectrum of "works well enough" conditions. The bigger drops make it easier to see whats going on and its pretty obvious when the set up is wrong.

Fog buster set-ups tend not to be very versatile. Lubricant to air ratios tend to be pretty much fixed by design. Which can be a limitation for industrial use. Great for DIY because, if you make it to design, it does what it says on the tin. Someone else has already done the hard work of figuring out a set up that works well enough. Generally you have to work quite hard to produce a fug.

Micro drops release small, individual, droplets into the centre of a well defined airstream. With truly independent control of drops and air they can be set-up to specifically match exactly what is needed for any given cutting conditions and nozzle orientation. Effective, versatile and expensive but, if you are determined they will still produce an unholy fug.

Opening out the exit nozzle on a Bjur system gets quite close to Fog Buster performance.

Clive

Edited By Clive Foster on 06/02/2021 11:43:46

I use pumped mistic on my machines but I have often thought that I'd give misting a try sometime. John Bogstandard designed and made his own version of a nozzle to keep the mist to a minimum but I can't find reference to it any more.

If I ever do get round to it I'll re-read this before I do anything.

**LINK**

Consideration needs to be given to the air supply capacity when running a Fogbuster. I have a Bambi PT50 'silent' compressor that has a 65% duty cycle and gets very warm on a long machine run at 10psi. The air supply feeds the Fogbuster fluid reservoir and onward to twin Fogbuster nozzles.

The nice thing about a misting installation is that you have the choice to just run air or air with coolant unlike flood coolant where it is all or nothing (and messy).

Clive, not sure which fog busters you have been looking at but they don't have a fixed air/lubricant supply. Unlike mist systems the Fog busters have the liquid container pressurised and then a valve is used to adjust the amount of fluid being pumped into the air line a long way from the nozzle. As the mist systems use the venturi effect to draw up the liquid they atomise it in the process. You can even get them with full electronic control to solonoide valves so that the flow can be controlled by the machine shutting it off or turning the pot on the control box.

Flow being adjusted about 14mins into video

For those who live vaguely in the middle of the UK, it might be worth seeking out Pennine Lubricants; when I lived in Sheffield it was easy, and they'd fill a 5l container of anything, ready for collection.

They supply a wide range of lubricating and metalworking oils at reasonable prices.
For my own homebrewed air/oil coolant lash-up I used Multisol SS, but mainly because my local Buxton stockist had a 5l container on the shelf, and some of their more specialist products are normally only available in larger quantities.
It's not listed as one of their mist coolants, but did for the job I had in hand.

Bill

When i was at work i had to maintain these systems as there were problems with bacteria growing in the coolant and system and as a result they were abandoned as to costly. The extractor system to remove the mist in the machine enclosure and the extractor to remove the coolant and from the extracted air from the pipework before releasing it to outside atmosphere was getting to much. we had previous visit from health and safety officer after two cases of lung problems and had notice put on the system to upgrade and in the end the system was abandoned.

David

These type of systems should not be referred to as 'Mist cooling systems' - The ones that have earned similar system the bad reputation do just that - generate mist - and that is NOT what you want. If a mist results, very little of it ends up at the cutting tool tip, a lot ends up all over the work area and in your lungs, etc. If mist is being created it is a sure sign of excessive air velocity at the mixing nozzle. The aim is to have micro-droplets of the fluid trapped in the airstream, certainly no mist. If you see fog at all, and it floats about, the fluid has been atomized and that is not desired and hazardous to your eyes and lungs.

I built such a system and posted here about the build - A pressurised fluid chamber with the fluid entering the mixing nozzle where it met with and was entrapped withing the low velocity airstream. It works very well, but only did so once I fitted pressure regulators in both air feeds. A single air line feeds both regulators, with a air solenoid in line, activated by spindle on. When turned off, the solenoid vented fluid tank pressure to air so the fluid flow stops right away. The fluid tank outlet to the flow line is via a needle valve to be able to set fluid flow volume to suit fluid viscosity, etc. - I use only neat cutting oil, no water soluble types, so viscosity plays a bigger role.

The nozzle design was a bit of effort too..

All in all, a bit of a pain to set up, but once running, a pleasure to use.

Don't know how to post a referral to my specific posts on this, and don't want to repeat the whole thing here, but here are some photos..

1 'drop' per sec with air

1 'drop' every 2 sec, with air

1 'drop' every 5 sec

3 drops per sec with air.

Flow stream , no air.

Nozzle. Air flows around it, inside the blue tube in the background. Fluid flows from a small hole in the nozzle tip.

Hol is 0.7mm OD

Joe...

Jason

I did say oversimplifying!

Was thinking more about the simple DIY versions of the Fog Buster rather than the commercial variant in your video. That one is basically the same as my Bjur Spraymist systems. They also have a pressurised coolant tank and solenoid valve control of air and lubrication but the air / lubricant mixing is done differently so Fog Buster droplets are larger.

Objectively nobody in their right mind would use a simple venturi effect system using airflow to draw up lubricant through a small nozzle from an unpressurised tank. That is basically a carburettor and pretty much certain to produce a wide airstream completely full of at least very small, probably fully atomised, droplets.

Which is seriously not what you want. The ideal is to deposit just enough lubricant in the cut zone via a stream of droplets in the centre of the airstream with most of the airstream, carrying essentially no lubricant, devoted to blowing chips away.

A major problem with any misting / fog buster or micro droplet system is that they give very little cooling to the cut. The main benefits are easy, low friction, chip flow, prevention of built up edges and low pressure air blast clearing of modest amounts of chips. Great for ME level cuts and similarly lower levels of chip production, providing you can keep the drop size up, lubricant quantity down and avoid atomised mist.

For our purposes its probably sufficient to define drops as being like paint overspray, so they splat onto surfaces and largely stay there, and atomised droplets as being so small that they hang around in the air like, um, mist.

Turning up the wick in an attempt to deliver enough mix to approach the cooling effect of conventional full flood liquid systems is an exercise in futility.

As David says the results are pretty bad for all concerned. If you need a serious mist extraction system you are doing it wrong. On a high speed machines even full flood systems produce some mist along with lots of droplet splashing so you need a ventilation system to clear the air in the enclosure. Really the only satisfactory way to deal with mists is to intercept the flow with a surface and wipe off. Think fogged up window or mirror.

Clive

Joseph

Lovely job.

I think I'm going to steal your design and retro-fit my Bjur systems. The standard set up is just too hard to get reliably set at the right flow level. Probably crud build up in old age.

Bjur use a slightly smaller nozzle, about no 75 drill I think, and slightly different mixing arrangements. Only one regulator so air and tank run at same pressure but I don't thik thats a great issue as there is a needle valve to regulate the oil flow. Supposed to run at around 22-26 psi but open the valve wide and up the pressure and the results are lethal!

Clive

A large part of success lies in the nozzle. I can turn up the air volume high enough to blow chips out of a groove being milled, without mist developing. The trick is to have a large area of air exit at the nozzle, and to have the fluid exit hole well past the airflow nozzle tip, ie, the fluid outlet tip in my nozzle is about 6 to 7 mm outside the air nozzle outlet tip. That way the venturi effect is almost negated and the fluid is transported down the center of the airstream . The fluid outlet must not be at an air expansion point within the airstream, as it is at that point that a drop in air pressure occurs, and the possibility of atomization arises.

Joe

If using mist coolants isn’t there a problem with bacteria buildup, legionella springs to mind, it is more prevalent than we imagine. I know some will argue that the chemical makeup of the liquids will combat bacteria buildup, the problem is that bacteria can thrive in most extreme conditions, the water circulating in central heating systems for instance and bacteria also thrive in the fuel inside aircraft fuel systems. In respect of legionella they thrive in liquid systems that are used infrequently and kept at a steady temperature. Ordinary Suds coolant is prone to bacteria build up if not changed frequently. Generating an aerosol form of the liquid when misting will spread any bacteria build up very quickly. I can see that using misting in a production environment would appear to be much safer as in all probability the solution would be used fairly quickly and presumably the environment would be monitored by the dreaded Health and Safety in respect of adequate ventilation, we might not be so fastidious in our own workshop environment. Dave W

The point is that you are NOT supposed to be generating a mist - the objective is achieving micro droplets of coolant carried in the airstream.

Joe

You also don't tend to recycle at least not on the hobby machines, it just gets chucked out with the swarf. So only any left in the tank or pipework would be a lot less likely to be affected than something that is being exposed to the air time and time again.