To oil or not to oil

Following the fantastic advice I received yesterday, I thought I would ask the next question that I’m struggling with. When should I be using cutting fluid and what fluid should I buy?

I bought a bottle of general purpose cutting oil from machine mart. For general use. For alloy a lot use WD40 as it helps keep the cutting edge lubricated. With HSS tooling i usually use my cutting oil. If using insert cutters then not so much unless doing a finish pass. More experts will be along shortly with a more in depth answer.

Steve.

If I use carbide tipped tools I usually run dry. I also don't use any cutting fluids when machining Cast Iron and brass. For aluminium kerosene/parafin may be used. When machining hard/tough steels I use a thin machine oil applied with a small brush. If your machines have a proper flood coolant system an emulsion is usual when machining steels. None of my machines have flood coolant systems, I have tried but coolant tended to be thrown all over, if your machine has good covers that might not be a problem.

Thor

Edited By Thor on 12/02/2021 15:12:28

I always use a cutting fluid when turning steel, phosphur bronze and stainless steel but none on brass and cast iron.

My Boxford has a coolant tank and pump and I use Alusol from Castrol which is available in small amounts and I dilute with water at 10 to 1 to give good cooling and better cutting.

As its name suggests Alusol was developed for aluminium but it is also suitable for steels and someone on here recommended it so I gave it a go.

It doesn't develop a smell unlike the traditional suds.

For tapping and milling ops I use a straight cutting oil, also available in small quantities from our M.E. suppliers and applied with a plastic sauce bottle, the kind you get in cafe's.

Others will, no doubt, have their own favourites.

Brian

Assuming HSS.

Brass and Cast-iron, not required.

Aluminium - Paraffin or WD40, always.

Steel - almost any oil, or suds. I use CT90, which I have for threading because my local emporium keeps it, or neat cutting oil as used to make suds. Suds is an emulsion of oil in water; the water removes heat and the oil lubricates the cut. Commercial fluids work better than home-made, but at a pinch soapy water, Chip Pan, 3-in-1m or Engine Oil are all better than nothing.

Mostly I apply cutting fluid with a brush because most of my cutting is modest - I don't remove lots of metal at high-speed, or work continuously. My mill can be flood cooled with a pump but I only use it for heavy work on steel: it's messy, and I have the daft idea the water might cause rust. (It doesn't!) The pump system was a waste of money - I don't use it enough.

With Carbide, I find cutting fluid is usually unnecessary on any metal. Sometimes it improves the finish. If cutting fluid is used with carbide, apply generously and avoid splashing the insert directly. Carbide is brittle and thermal shock can crack it. Carbide's quite happy taking brutal deep high-speed cuts that spray the operator in red-hot steel chips, but a spot of cold water can ruin it.

Chief exception: I always apply a squirt of CT90 when threading with taps and dies.

Dave

Like this Brian.

Steve.

For steel, aluminium and bronze I use a neat cutting oil, usually CORA B from Morris Lubricants. I only use HSS tooling. Brass and cast iron are obviously machined dry. For thread cutting with a tap or die I use Morris's thread cutting grease

Neat cutting oil has two advantages over suds: It does not have a limited shelf life (nasty things can grow in suds) and you can leave it safely on the lathe/milling machine metal work. It does cost more but is almost infinitely recyclable.

On second thoughts I actually use a mixture of mainly CORA B plus some ISO 32 & 68 oils and white spirit (all the liquids that drain into the coolant/cutting fluid tank).

JA

Thank you everyone, probably a stupid question but as I have a mini lathe what is the best way to apply the fluid and how often should I apply it while working?

Just have a small pot of oil and a little brush, about 1/4" , 6mm diameter. For steel, using HSS just a dampening each pass, and similar for aluminium. With carbide, you can cut dry with steel and maybe dampen the work for finishing cuts.

Not a stupid question at all!

Good news, in a home workshop fluids aren't particularly fussy. Damp rather than soaking, but overdoing it doesn't effect cutting. I use a ½" paint brush, squirt from an oil can or squeezy bottle, or spray WD40 & CT90 from an aerosol. Basically a little of the right kind of liquid splashed on - enough to keep the cutting area wet.

Liquids flying off the spinning job are a good reason for keeping the volume down. Messy, and wildly overdoing it at high speed might get some in your eyes. Dabs, not pints!

Industry is different; they value high-speed cutting a perfect finish every time. They often flood cool, maintaining a continuous heavy flow over the tool and work. Partly because it increases tool life and partly because the flood washes swarf away. But flooding means dealing with gallons of dirty liquids and tons of wet swarf: a right pain unless it's needed, and what about the electrics! More recently industry have moved to compressed gases and carefully metered spray systems. Work very well but are expensive to set up and have the disadvantage that the machine should be enclosed to protect the operator. Breathing in coolant fog all day or being hit in the eye by jet propelled swarf is no joke. Always exceptions, but generally not worth the trouble in a small workshop.

Don't be afraid to experiment. Much depends on what's done in your workshop.

Dave

Does anyone still use milk?

An addition to my earlier post.

On the milling machine I use a small decorator's paint brush to apply the cutting oil. The fluid is in a plastic bottle that is refilled from the lathe coolant/cutting fluid supply.

JA

I generally don't bother and usually cut dry unless:

1. There is excess heat or noise

2. There is build-up on the cutting tip

3. I am doing a finishing cut

+1 for all the above. for my uses ...

Brass & Cast Iron - dry

Steels - with HSS Light cutting oil, SAE32 or similar. if using carbide inserts - mostly dry

Aluminium - WD 40 or parafin ( Kerosene ).

Threading - RTD or similar, I have used a heavier grade oil ( gearbox oil ) , on Aluminium I use WD40

Application - I use a kiddies non spill paint pot with 1/2 " brush ....

George.

Afraid not Steve, that's very McDonalds, mines more like a very cheap greasy spoon.

Brian

I find just intermittent brushing of soluble oil is frequently very inefficient as it flows along the bar, away from the contact area.

So often, when using the self-acting feed, I use an old paint-brush about an inch wide, dipped into a small tin of suds then held from behind the work so the bristles trail over the work, and span the cut.

'

For lubricating deep drilling, I sometimes use a pump-action oil-can to squirt suds into the hole when I have withdrawn the drill to brush the chips off and cutting-oil on.

(Industry can use drills with internal coolant channels opening onto the cutting edges - obviously on machine-tools equipped for them)

'

I have used spray-can cutting fluid but this is very wasteful. I am not trying to machine the workshop wall!

Using taps and dies - cutting gels on steel, and a more liquid cutting-oil or WD-40 on aluminium.

Draw-filing steel - a little WD-40 or thin oil can prevent "pinning" and help produce that lovely satin sheen. (It was chalk when I did metal-work at school - blackboard "chalk", not the raw rock chalk, which can contain fine particles of silica a lot harder than a steel file).

Hacksawing - I have tried sawing with and without cutting-paste, with mixed results. Its main aid perhaps is in lubricating the blade flanks rather than the cutting edges, and may even help slightly worn teeth simply slip over the metal. I would not use any cutting lubricants on the bandsaw, with its rubber-covered wheels.

When I bought my first lathe about 10 years ago (maybe more) full of enthusiasm and memories of my apprentiship shop floor days, I also bought a 'suds' pump. Used it a few times but got fed up with the mess and haven't used it for some time. Sometimes use suds oil in an old ketchup squeezy bottle or even just a squirt of oil from my oil can. Difference between model engineering and industrial scale heavy machining.

Machined a lot of cast iron in those days (imagine a 16 year old tramping up the road on the way home, had it been Barnsley rather than Brum I would have been mistaken for a miner) which is pretty much self lubricating, lubricant creates one hell of a mess I can tell you and especially drilling the mixture of fine dust and a liquid would quickly jam the drill.

I have found my early days of working to the book on this and cutting speeds have pretty much gone, I just judge what seems to be the correct speed, like most people I guess.

Bill D.

On light finishing cuts I sometimes use a squirt or two of WD40 when it seems advisable. For slow or heavyish cuts I sometimes use tapping fluid - as well as when tapping steel, of course.

But if the fluid is getting splashed about, cutting dry is an option in most conditions for model engineering. Even HSS will still cut at dull red heat, and you'd have to be doing something pretty cruel and greedy to be getting there.

I believe it's undesirable to use any fluid on cast iron. Some of the fines coming off the iron are hard and sharp, and can form an abrasive slurry with oil, which will stick to slideways and thread flanks. OTOH, the graphite inclusions will provide self-lubrication on dry-cutting, as per Bill Dawes' post above.

Edited By Mick B1 on 12/02/2021 18:30:33

Patient to Doctor: Doctor I keep being ignored!

Doctor: Next!

Seriously does anyone still use milk for machining copper or aluminium? I have an old Frederick Bates, Stirchley, Birmingham (phone Kings Norton 2266/7/8!) tap and die set which lists the following lubricants and materials for tapping:

Wrought iron, steel 0.1% through to 0.6% -> rape oil, paraffin, lard or whale oil (I take it that lard is also known as Russian Fat)

Cast iron(!) malleable and cast steel -> soluble oil and water emulsion

Tool steel -> As Wrought iron

Nickel / Chrome and stainless steels -> Turps or emulsion oil, or Turps and white lead

Copper -> Milk

Bronze -> Rape oil or Emulsion oil

Brass (soft, medium or hard) -> Rape oil or emulsion oil

Aluminium or Silium -> Methylated spirit, paraffin, milk, or paraffin + rape oil

Bakelite -> Paraffin

Some interesting old lubricants there as well as materials, love the Bakelite and Silium! Now where can I find some whale oil?

Martin

In simple terms neat cutting oils provide lubrication and not much cooling, whereas soluble oils provide cooling and not much lubrication. Soluble oils are used for general machining whereas neat cutting oils are used for relatively slow but high pressure cutting, such as gear shaping. I only use soluble oils.

I never use coolant for plastics, brass, bronze and cast iron. On the centre lathe I normally cut dry (inserts and HSS) and only use coolant for drilling/reaming with HSS tooling. The exception is parting off - I always use coolant, apart from the aforementioned materials. On the repetition lathe I normally use coolant as tooling is all carbon steel/HSS.

On the vertical mill I never use coolant, apart from WD40 on aluminium as needed. That's partly due to not needing it and partly not having a drip tray underneath, so much of the coolant ends up on the floor. On the horizontal mill I mostly use coolant as I only carbon steel and HSS tooling with heavy cuts by hobby standards. On the CNC mill I mostly use coolant, but primarily to wash away the swarf rather than for cooling.

I always use coolant when cylindrical grinding to cool the work and reduce glazing of the wheel.

Hand and machine tapping is mostly done dry, with some exceptions. I use WD40 on aluminium and coolant on the repetition lathe where I'm tapping at speed - normally 500 to 1000rpm. If the tap is large, >3/4", or the material is difficult (stainless steel) I use Rocol RTD compound. I avoid RTD where possible as it's a pain to clean the work and tap afterwards.

I used to use Biokool14 from Hallett Oils, but now use Hysol XF from Castrol which is a general purpose coolant, formulated for hard water areas. Modern coolants are much better than those of old. I never have a problem with corrosion on the machine tools, but I regularly check the mixture with a refractometer and keep within the recommended dilution. I also never have a problem with nasty nifffs even though the coolant sits in the tanks for months, or years, at a time.

All my machine tools have their own pumps and flood coolant. Dabbing, or dripping, on by hand doesn't achieve anything useful.

Assuming that the OP is in the early stages of learning I'd say forget coolant. On a mini lathe it simply isn't going to achieve much, other than possibly paint a nice streak up the wall behind the lathe. There are many other things to learn that have a far bigger effect on the work produced than using coolant.

Andrew