Motor oil for cutting fluid

[JimEb]

I have a few unopened quarts of 5w-30 sitting in my garage. Leftovers from back in the days I used to do my own oil changes.

I dont even own a vehicle that uses this oil anymore. Was thinking of using it as a cutting fluid just to use it up. Any harm in that?

[plumberzpieco]

No sulphur, not going to work very well. I'd rather use butter

[refinery mike]

motor oil is just the kind of oil NOT TO USE. the purpose of motor oil is to prevent metal touching metal and wearing out the engine. Even for drilling or tapping it is just barely better than nothing. better go to enco and order a proper metal cutting fluid. Or even thread cutting oil from a home depot or the like. even bacon grease will work but it tends to go rancid if not cleaned up real well.

[spro]

I could use that oil in my engine so how could it be a cutting oil?
Back in the day and we saw someone uses "oil" for drilling, it was because they knew not to drill or cut dry. That was it. The term should be cutting Fluid and oil is Oil.

[steamin10]

Harm, no. Just stinky, and wrong for application.

Bacon fat, rendered well, is ideal, free as breakfast, and easily replaced. Smells like potato chips in use instead of Ode to Exxon. Put the oil in your mower or vehicle, and forget it. Kerosene is real good for aluminum, but works for other things. Water based fluids are good, but get smelly with age, so pipe threading blackoil is best for long term. Available at most any plumbing supply, a gallon will last you forever. Dont use diesel, it stinks too much and lingers. Beware of any lite oil/solvents, brake cleaners, etc. They tend to be flammable, or toxic, or both. WD 40 if nothing else, very common, and available in quart bottles.

Its what I do.

[revrnd]

I was taught to use isopropyl alcohol when drilling aluminum. Our shops used Anchorlube for tapping.

[earlgo]

Well I tried to insert a .pdf but was incompetent.

What was intended was a section from the HANDBOOK ON POWER THREADING by the engineering department at Teledyne-Oster that was written about 1986.
It describes cutting fluids and the 4 factors that are critical: Lubricity, Heat Capacity, Viscosity and Wetting Properties and Consistency.
The important part that was trying to be conveyed is in the section on Lubricity where it states that there are both LIQUID film and METALLIC film lubricants in a good cutting fluid. The liquid film lubricants are like motor oil.
Quoting from the pamphlet:
"The metal film lubricants are forms by the oil when it combines chemically with the surface of the material being cut. Generally, this is done by adding elements to the oil which will rapidly form intermetallic compounds on the surface being cut. These compounds are easily machined and have very low coefficients of friction. Typical additives for forming metal film lubricants for threading are sulfur and chlorine."

So good cutting fluids contain materials that form intermetallic compounds. These are not found in normal motor oil.

--earlgo
(mfg engn at T-O in another former life.)

[ctwo]

The oil you have is typical for many modern passenger cars, at least the ones I have. It may fall within your vehicle's viscosity range and still be usable.

[10 Wheeler Rob]

Modern lawn mowers will use it also.