A physics question.

[Steve_D]

Oil is used to reduce friction.
So why does a drop of oil make a drill cut better when drilling steel rather than make it slip?

Steve

[227bhp]

It doesn't make it cut better, it helps cool the drill .

[stevieturbo]

and it helps it cut better into the metal with less friction ?

The bit isnt designed to slip over the piece it is drilling into.

[Dr Jekyll]

I did see a theory that punctures are more common in the wet because the water lubricates the nail and allows it to go deeper into the tyre.

[227bhp]

Thinking about it some more, after the sharp edge has cut in, the chip or swarf then has pass over the parts of the drill immediately after the cutting edge, maybe that is where the lube comes in, to help them glide along as they are parted away.
Lathes and mills don't use oil though, just a water based coolant so maybe my first point is more correcter

[anonymous-user]

Steve_D said:

Oil is used to reduce friction.
So why does a drop of oil make a drill cut better when drilling steel rather than make it slip?

Steve

consider what a "cut" actually is.

Lets make things easier and consider a soft thing, being cut with a hard thing, lets say a carrot by a steel knife.

You press on the knife, and at some level for force, the surface pressure at the tip of the narrow (small area, pressure = force/area) blade exceeds the sheer strength of the material it's cutting through. For our carrot, that's not a huge pressure. The carrot therefore splits apart right where the cut starts. But the rest of the knife, the sides, have to slide into the material. For our carrot, it's soft, so the hard, slippy steel just pushes the carrot apart.

But, for say a drill, cutting steel, the friction between bits of the drill that aren't the actual cutting edge (ie most of it) is significant. The high pressure at the cutting edge of the drill will squeeze any oil out, but other, lower load parts will get a friction reduction from sliding past a layer of oil

[mr.man]

Please all now Google search CUTTING FLUIDS

Everything you need to know. Also Dry Machining and Air Blasts

[CrutyRammers]

227bhp said:

Thinking about it some more, after the sharp edge has cut in, the chip or swarf then has pass over the parts of the drill immediately after the cutting edge, maybe that is where the lube comes in, to help them glide along as they are parted away.
Lathes and mills don't use oil though, just a water based coolant so maybe my first point is more correcter

Normally a soluble oil, or oil / water emulsion.

[Steve_D]

CrutyRammers said:

Normally a soluble oil, or oil / water emulsion.

I use a soluble oil elsewhere in the workshop but have always considered that as a 'coolant'.

What I was using in this case was just a dab of engine oil which made the drill really bite and start producing significant swarf.
I think the reduced friction on the other surfaces of the drill bit may be the answer.

Steve