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Thread: Engine oil as cutting fluid
04-02-2009, 06:15 AM #1
Engine oil as cutting fluid
I'm new to machining and also to this forum so I'd like to say hi to everybody and apologise for a potentially stupid question - I have a 9x20 small lathe and engine oil is much more available and cheaper than cutting oil to obtain in my country. Is it permissible to use ordinary automotive engine oil as cutting fluid or would I get bad results, tool life etc?
Thanks for all the answers.
04-02-2009, 06:31 AM #2
04-02-2009, 06:33 AM #3
I've never tried it but I knew one fellow who used old motor oil for threading pipe. He was quite busy and threaded a lot of pipe; he seemed happy with the results but that's a pretty vague report.
Proper cutting oil isn't really that expensive, especially compared to the price of motor oil in Europe, and for home shop and occasional use a liter can last a very long time. From personal experience it pays to use decent stuff. You'll also have a much easier time if you get some good dedicated tapping fluid for threading- I've been amazed at the difference this can make: regular cutting oil= torn threads/ good tapping fluid= beautiful threads on the same part with same die.
04-02-2009, 09:57 AM #4
There seems to be quite a variety of cutting fluid formulations being sold, so apparently it is not a simple problem. If motor oil is what is readily available, experiment a little and determine if it is good enough for the task at hand. I've heard reports of good results from some odd sounding choices, like bacon fat (lard), kerosene, grain alcohol, milk (yes, from a cow), and others. But personally, I'd recommend a good quality commercial cutting oil specifically engineered for the type of material being cut. It can make a tremendous difference in finish quality, and as Screwmachine wrote, a small amount will last a long time for hobby usage.
04-02-2009, 10:07 AM #5
MY Dad used to mix vegetable oil and crisco to the consistency he liked, I have used plain old engine oil(used or new) on a tap when I had nothing else avail and it was indeed better than nothing.
1 quart of cutting oil goes a LONG way for tapping if you use an acid brush to apply it, and you may be able to beg or buy some from your local hardware store of they thread pipe, which most due.
04-02-2009, 12:03 PM #6
As another post said, motor oil has been extensively developed to keep two metal surfaces from touching. It will do its best to keep your tool bit from touching the work. I once borrowed a Sunnen cylinder hone and spent hours and hours and hours honing a cylinder in an engine. I asked Hans Fisher, who was one of the Sunnen honing gurus, why it took so long. He had a good laugh at my expense, then explained that by using motor oil that I had around, I had picked about the worst possible lubricant. Then he gave me some Sunnen honing oil. I hope I have learned a little in the ensuing 50 years, but I am still learning about cutting oils. What I do know is that motor oil isn't.
04-02-2009, 12:37 PM #7
You won't be happy at all with motor oil. Put some on a hand file and go to work on a piece of stock. You will FEEL the difference in a heart beat. The cutting edge will spoil, and you still won't move much metal.
I use Canola oil (vegie) for many purposes around the shop. NOT LUBRICATION though, it dries out gumms and gets nasty. Animal oils work too. (Milk for copper anyone?)
So just say NO too MOTOR OIL!
04-02-2009, 12:49 PM #8
Oils don't know when they are supposed to 'hold apart' or 'bring together'. No way is a film of oil going to keep the tool away from the material it is cutting, unless the edge clearance is gone from the tool.
Metals are not cut like cheese, they are bulldozed off by brute force of a harder material engaging a softer material. The metal fractures along the weakest planes within its crystal structure. It piles up like a stack of tilted dominos. Oil lubricates the slip planes between 'dominos' and this is what eases the process of chip formation.
While I do not recommend motor oil because it smokes and stinks like crazy, its lubrication function is similar to any other lubricant that will stand up to the temperature in the cutting zone.
100% my opinion. Fire away
04-02-2009, 12:55 PM #9
LOL Fire away!!!
Serious use a mix of engine oil and wd40 or a very small amount of minerla spirits together. The main issue with engine oil is the film thickness. A good coolant for machining will use a very thin film layer. If you use engine oil use the LIGHTEST oil you can find and USE IT SPARINGLY!! (0w10 or 5w only with a brush) Remember it is flammable and will catch fire if you arent carefull. Sometimes we will use 5w synthetic for tapping harder steels or better yet Moly-D tapping fluid.
04-02-2009, 01:06 PM #10
"...Oils don't know when they are supposed to 'hold apart' or 'bring together'."
This is totally incorrect.
Lubricating oils have strong bonds between the atoms
which are depended upon to keep the molecules from shearing
in operation. Think lots of teeny ball bearings between
the metal surfaces. Strong ball bearings. Oil manufacturers
go to great lengths to keep their oil from shearing under
high pressure and temperature.
Now cutting fluids are an entirely different matter.
Cutting fluids are designed to carry heat away, and to
allow the molecules to shear into pieces so metal-on-metal
contact can happen, and cutting can occur. One way this
is done can be seen in my favorite cutting fluid, lard
oil. It's an animal fat with weak interatomic bonds.
But make no mistake, there are *huge* differences in
chemistry betwen lube oils and cutting fluids. Motor
oil is an especially bad choice for a cutting fluid.
Look around at any shop you see, how many professional
shops use motor oil as a cutting fluid, and how many
use a purpose-engineered material for this?
You can use it. It'll work like $hit.
04-02-2009, 01:15 PM #11
Jim correct me if I am wrong here
Cutting fluids and engine oil both carry away heat. Cutting fluid is so good because the viscosity is low and they dont have high-pressure additives like phosphourus and zinc and it doesnt start on fire.
04-02-2009, 01:19 PM #12
You need something that prevents particles of metal being threaded or tapped from being welded to the cutting edge. You need an oil containing animal fats, vegetable fats, or a petroleum based oil with sulfur added to prevent the chip welding to the cutting edge. It does not seem possible to generate enough heat for this to happen with hand tapping, but it does. If you don't believe it, take a look at the cutting edges of a tap after trying to tap without cutting oil with a magnifying glass. This is the reason that you get a ragged finish, because the built-up material on the cutting edge is doing the cutting, rather than the cutting edge of the tool.
MOTOR OIL DOES NOT HAVE THE PROPERTIES TO PREVENT BUILT-UP EDGE WHEN THREADING IRON OR STEEL.
CAST-IRON IS DIFFERENT, YOU CAN THREAD IT DRY, BECAUSE THE GRAPHITE IN CAST IRON PROVIDES THE CUTTING LUBRICANT NEEDED.
Last edited by Bruce Nelson; 04-02-2009 at 01:25 PM. Reason: Left something out.
04-02-2009, 01:20 PM #13But make no mistake, there are *huge* differences in
chemistry between lube oils and cutting fluids.
04-02-2009, 01:33 PM #14
HFD Yep! Just like axel grease. love it!
But.....Lube oils and cutting oils are MILES apart. It's all about chem mystery and co-valence bonds and magic stuff.
Mostly, We all have our experiences. Mine says KEEP MINERAL OILS AWAY FROM THE CUT ZONE! Animal oil, Check. Vegetable oil, Check. Formulated cutting, sawing or grinding oils, Check. Waxes ???? Solvents like LPS or DOMS? Sometimes.
Now how does Tri-chlor (Banned! Banned! EPA says NO!) Work so well as a tapping fluid? Not a drop of "lube" in a barrel of that solvent!
Secret> psst,,pst.... creepy stuff, very creepy.
I know, I'm all wet.
04-02-2009, 01:35 PM #15
For occassional use on at home on a mill or lathe - a qrt of motor oil is a whole lot better'n nutt'n. I have used some on the engine lathe on the odd occassion and I have 250 gallons of cutting oil sitting in an Acme right beside it. I generally use the cutting oil - but I guess it never seemed bad enough to go too far outta my way to look too long for the oil can if the other happened to be close by.
A drill and tap are not equiv of a honeing stone or a fine file.
The drill and tap need some lube, the stone needs an agent to carry off the debris.
Think Snow Eh!
04-02-2009, 01:37 PM #16
Oils do know if they are supposed to keep things apart, although I doubt that it is a conscious decision by the oil gods. It is true that once a cut is started, the contact point is on top of the tool back from the point and the chip is more like wood being split than something like flesh being cut by a sharp edge, but the film strength of the oil can stop the edge from penetrating to start the cut. Having the point skate on the work is almost always a loser. There is another effect here, the triboelectric electrical current between the cutter and the work. The fluid acts as an insulator to prevent work material from, in a sense, plating itself onto the tool. See
Electrophysical and Electrochemical Phenomena in Friction, Cutting, and Lubrication by S. N. Postnikov, Gorky Polytechnic Institute, USSR ISBN 0-442-26624-3
One of the things he suggests, that I haven't tried yet, is insulating the tool from the machine so there isn't a current path.
04-02-2009, 01:41 PM #17
I like using the sulferized cutting oils for tapping, pray tell, what is the base oil type which they sulferize to make this formula?
04-02-2009, 01:57 PM #18
Triboelectric? Is that when the hydro plant is on reservation land?
Would ceramic inserts act as electricl insulators? Or are they really "semi-metals"?
HFD Base stock and modifiers for sulfur oils? Petroleium engineers are of highest compensation of all engineering. You ask us? I don't make enough to know '=)).
04-02-2009, 03:21 PM #19
Use cutting oil for cutting and threading and lube oil for lubing and you will get good results. It's all in the chemical additives.
04-02-2009, 03:23 PM #20
Yum. Axle grease. My fave.