How does oil get there

[refinery mike]

I have wondered this for years, and someone else, at work, brought it up yesterday. How does cutting oil get to the cutting edge of a lathe tool. I mean so long as it is cutting continuously it would seam that the edge would only see fresh, unlubed metal all the time.

[f350ca]

Good question, especially true when using a parting tool.

Greg

[Harold_V]

That's why it's a good idea to keep an acid brush on the cut. Everything stated is true, but an acid brush keeps a supply where it's needed.

Remember, lubrication of the cut plays a role in more than one way. One of them, often overlooked, is to limit chip welding on the tool. That's critical when machining mild steel.

Harold

[lakeside53]

Good question, especially true when using a parting tool.

Greg

A great deal of the lube is used for the SIDES of a parting tool - no new metal cut but a lot of friction especially if the tool isn't perfectly square to the cut (and has the common "no side relief").

[ken572]

I think there might be a little bit of wicking effect
taking place as well, caused by the pore's of the
cutting tool surface, and the material being cut,
opening up and causing the cutting oil to move
toward the heat source.

Ken.

[SteveHGraham]

So you're saying I can stop leaving cat food out for the elves.

[dly31]

I think that if the oil is to do any good it just 'stays there'. If one assumes that the oil is always squeezed out during cutting then it can't be doing anything to start with. The oil has to have enough film strength to stay in place in order to be effective. There could be areas where the oil is not effective and others where it is due to the differences in temperature and pressure. At least, that's how I see it. YMMV.

[BadDog]

I was told that during the cut, depending on the tool profile, cut (depth, speed, feed) and material, there is opportunity for small amounts to get under the chip from time to time with most materials. That the movement of the material sometimes (basically) creates small gaps with resultant lower pressure that pretty much sucks a bit of oil in, and that the tiny amount is generally "enough". It was further stated that (particularly with flood or at least "plenty") the remarkable differences in finish and performance on a given material and cutter with differing speeds and feeds was a result of how well that process worked to get lube into position. Of course similar things about responding to changes in feed/speed are said of dry cuts too...

Not sure how absolutely accurate, but that's what I was told when I asked the same question some years ago.

[JTiers]

Strikes me that Harold hit it on the nose when he mentioned built-up edges.... if the surface is "poisoned" with oil, then it doesn't get the welded-on lump of material on the tip.

Then also, since that built-up-edge tends to shed bits back onto the surface, if there is a decent amount of oil around, it "poisons" the work surface also, preventing a lot of re-welded-on bits there.

The amount of oil that gets under the chip into the space at the cutting edge where the shearing action is occurring is probably little to none. That is newly cut metal, so unless the oil was in the metal it could not get there at all.

But if it gets onto the surface behind the cut, it prevents shedding bits. And because the bits don't stick to the tip, they can't be shed. Even if they do, they will have enough oil on them that they won't stick in any case.

[BadDog]

But if the oil is just on the surface and spiraling (or curling) away with the chip, how does it "poison" the tool rake or fresh metal surface? True it would be nearly (completely) impossible to get to the cutting edge, but I can maybe see that it could work in tiny amounts to the rake surface and/or fresh cut surface, thus poisoning as described.

[Harold_V]

Do as I suggested and none of these issues are a problem. By keeping an acid brush in the cut, there's a steady flow of oil. Keep the brush deep in, in contact with the surface as it's being reduced. In spite of all the negative attributes, oil does get where it needs to be, and it takes very little to do the job.

I generally have more than one acid brush in my can of oil. I also generally power feed when parting (although not always, as I used to do a lot of very small work, which didn't require much of a cut). If you're using power feed, you can keep one brush in the cut, and reach for the second brush. The cut never goes dry.

Not too long ago (a few days), one of the readers of this board posted that they always part dry. I'm sorry to say, I do not recall his board name.

Sir, my hat is off to you. I've been in the trade since 1957 and have found almost no materials that will tolerate a dry parting cut. Leaded brass, leaded steel, 2024 aluminum and magnesium are about all I can think of. If you've had luck parting mild steel when running dry, there is much you can teach me.

Harold

[pete]

There's a few Youtube videos, and no I don't have a link. But think small, very small, the videos I'm thinking of show high magnification photography of the cutting action, you really can see a plastic flow of the metal being cut. There's a massive amount in common everyday life going on right in front of us we just don't see because of just how reduced the scale is. Splash lubrication in the cut from very tiny droplets, metal flow that helps draw it in from directions it's not even being supplied from directly, and no doubt other reasons I haven't even thought of also. We know it works. Somewhere somebody has done a video showing how and why it works. Sometimes? I've had to do that cutting fluid application much differently that what normally works. No real idea why, but something is different to a level I can't pinpoint why. But why it works is probably excess fluid in and around the cutting tools / cutting area that are enough to help it get sucked into the cut that helps the most. At the cutting tool tip, you'd have to be running ultra dead slow to not have tip temperatures way past what it takes to boil any normal cutting lube off instantly, that flashing off would help pull more in. Any and all of the above would create flow patterns were really not observant enough to notice.

My guess. The above certainly isn't 100% factual. But I think it's somewhat logical that some or all of that is at least helping.

Pete