Sulfurized (IUPAC changed the international correct spelling from sulphurated) and chlorinated oils create extremely active chemicals when subject to high shear loads. These bond to 'recently' cut metal and lubricate that metal. In other words, they make the chips separate from the stock far more easily, reduce cutting forces and improve the finish that can be obtained.

WD40, being mostly kerosene, has no effect whatsoever on steel, other than making it smell. On aluminium, it can have a positive effect that is similar to other light alkanes and alcohols. Silicone compounds are not useful cutting lubricants at all, since they are poor lubricants in general and have no enhanced activity in high shear conditions.

WD40 is as it name implies (Water Displacement #40) is not a lubricant, it is designed to get rid of water from wet metals. After that it does absolutely nothing except get sticky as the volatile constituents evaporate. It is handy for short term rust prevention and machining ali as previously mentioned.

In the bush I use something like this if nothing else is available, rendered pig fat (tallow) works pretty well although it does smell a bit. You can get some here **LINK** or hunt the pigs with a suitable calibre. I like a .444 Marlin with 12G O/U loaded with bb's as backup. Eating the rest of the pig is a bonus but cook it well as they carry parasites. Use a meat thermometer!

As you do not give a location you could be anywhere in the world so consider this as general advice!l

From reading your other thread though, it appears that you may have picked a difficult to thread lump of stainless steel wire so then I would just consider replacing with the correct bits as probably cheaper in the long run.

* Danny M *

Buy yourself a 500g tin of proper tapping compound, something like Rocol RTD(stands for reamer tap and drill) paste ( I use a cheaper brand but can't remember the name) it will last you for years and is good on all steels. I also use it on some aluminium just because it holds the swarf on the tap and is easier to wipe off than blowing a lot of mess around. As well as the above compound I use a spray of metal cutting compound from "Sterling" Other brand are available and have their uses.

I believe Duck Oil is similar to WD40 in being a carrier fluid with a grease component which I use as a quick spray on the working parts of my machines after use to keep corrosion at bay in my damp garage workshop. It has been successful at this for 6 years.

For tapping I use CT 90 tapping fluid available from EKP Supplies in the UK (amongst other suppliers, I expect). After breaking numerous small and expensive taps, usually while turning backwards to clear the swarf, while using the cheap and readily to hand oils I tried CT90 and have had no breakages since. I use it in all metals as apart from easing the thread cutting it sticks the swarf to the tap making it easier to clean.  Although it looks expensive, a drop goes a long way and  I expect the bottle I have will see me out.

Jim

Edited By Jim Nic on 04/01/2018 10:23:41

I see that WD40 is now being used as a brand for a range of specialist lubricants including a cutting oil for tapping etc. It looks as if we will need to qualify the product when referring to WD40.

Mike

Edited By Mike Poole on 04/01/2018 10:58:58

The MSDS states C9-C11 alkanes and isoalkanes with a flashpoint of 46°C. Pedantically, that's white spirit in the UK, but it's still a light kerosene/paraffin.

Typical Mercan obfuscation! They love to dress everyday substances up behind the protection of "trade secret". So perhaps technically it's not "kerosene" as such. But it's clearly based on a simple derivative from the fractional distillation of crude oil – one that is possibly even cheaper to source.

I've got some of the funky new WD40 "multipurpose cutting oil" and I have to say I've only used it a couple of times. Main reason being that it is a filthy brown colour and it stinks of a sort of nasty sulphurous pong. For tapping etc I use Rocol and for turning without flood lubricant I just use std WD40. Unlike said "specialist" WD40, it gets the job done without threatening your sense of smell.

Despite Mark Rand's explanation above (which I'm not arguing with), I find that WD40 can help with some steel turning operations such as parting off. I'm now down to my last 2 gallons which I acquired for peanuts in Canada.

Murray