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downunder 06-28-2008 08:13 AM

Lubricant for drilling in metal
A quick poll of experiences in drilling holes in metal. We have a new shop foreman (in his twenties) who thinks that using sae 30 motor oil is OK to use as a cooling lubricant when drilling holes in metal. I prefer to use a low speed- 300-400 rpm- whether or not I have CUTTING OIL available. I have the idea that the lower speed is more useful for preventing burning the bit. I am talking about 1/4 inch to 1/2 inch range holes. This particular project is bolting down some benches in a park; drill through the legs and bolt into the concrete.

FYI- I am in mid-fifties and started using a 1/4 inch single speed maybe 45 years ago with my dad who was a mechanic.
This mechanic is the shop foreman because local governments pay such crappy wages they have to pay supervisor pay ($12.00 hr) to get any kind of mechanic.

Anyway, am I really that old and set in my ways (my apologies to you younger posters) or is this kid full of shtuff?

Termite 06-28-2008 08:46 AM

I agree with you and the kid! Slow speed is critical to drilling holes in metal. I use motor oil as a lubricant when drilling holes in beams and such. It doesn't take more than a couple drops and it makes a little smoke, but I think it helps the bit cut better and stay sharp longer.

HandyMac 06-29-2008 09:17 AM

Mtr oil works - but my preference is Cool-Tool cutting fluid. I hope this helps.

downunder 06-30-2008 07:34 PM

I should have maybe explained in just a little more detail. You see, I was always taught starting with my father and others along the way who were true mechanics, craftsmen, etc. to use the right tool for the job. I extend this to cutting oil vs motor oil. They are two different products made for two different uses. If I was in the field, had to have something to cool the bit because somebody else wanted to drill too fast, I could see using motor oil. I once put a chewing gum wrapper on a blown fuse to get home, but.... More likely I would have an extra quart of oil in the toolbox than cutting oil. But that is why I took the job back to the shop in the first place. I use WD-40 or similar when I chasing old threads just to clean and lubricate before re-installing. But then very few people take the time to clean threads as part of the job. Not the same as cutting new threads. By the way, my dad would not allow any form of permatex type gasket product in his toolbox. "If you clean it right and put it on straight, it won't leak." Never saw anything that did, although it looked clean enough to a 12 year old the first three times!
This incident was AT THE SHOP and there was cutting oil available. Not to mention that he knocked over half a quart of oil all over my tailgate where we working and then walked off with no offer to wipe it off, knowing it's going to be my gass on the ground the next time I step into the bed.
Just never was taught to use motor oil to cut threads, drill holes or for anything thing else that didn't run.

micromind 06-30-2008 11:16 PM

In any machining operation, fluid applied to the cutting tool does basically two things.

1) It aids in removing chips. This is especially true in softer abrasive metals, like aluminum, copper, and stainless. Even when cut with a very sharp tool, the chips are somewhat jagged, and tend to wedge themselves between the remaining stock and the cutting tool.

2) It acts as a coolant. Even a sharp tool operated at low speeds will generate very high temperatures on the cutting edge. In fact, no tool actually 'cuts' anything. The cutting edge of a tool must, on a molecular level (VERY small) heat the stock enough to cause it to melt, and thus the molecules can be separated. The trick with fluid here is to cool the bulk of the cutting tool, but not cool the very edge of the tool.

I usually carry some cutting oil in the truck, and find that dipping cutting end of the bit into the oil before drilling makes a world of difference. Bits last alot longer too. Motor oil would certainly be better than nothing, but cutting oil is formulated specifically for cutting tools.


downunder 07-02-2008 06:46 PM


In fact, no tool actually 'cuts' anything. The cutting edge of a tool must, on a molecular level (VERY small) heat the stock enough to cause it to melt, and thus the molecules can be separated.
From whence cometh this knowledge?

Docfletcher 07-06-2008 09:35 PM

Try this...

For cutting metal, a cutting emulsion is recommended. It prevents the cutting edge(s) from overheating and thermally damaging the tool and also reduces friction. You can make a suitable emulsion by mixing water : vegetable oil in ratio 4 : 1 and adding soap and mixing well until it becomes homogeneous.

If you can't make emulsion, use vegetable oil instead. Do not use plain water as it will corrode the cutting edge and render it useless.

Vegetable oil is better than mineral oil because doesn't damage your skin and also makes more pleasant stench when gets overheated.

Apply the emulsion/oil with an old paintbrush or a syringe.

Info found at :laughing:

homework 07-06-2008 11:12 PM

TAP-MAGIC cutting fluid for steel iron etc.
ALUM-TAP for aluminum

the harder the metal the slower the speed

downunder 07-07-2008 06:52 AM


A quick poll of experiences in drilling holes in metal.
As I stated in the beginning, I was just curious about others' experiences. The conflict in question, if you want to call it that, is with someone who is not even 30 years old but thinks he knows everything and no one else knows anything.

Now thats thinking outside the box. Cutting oil is less than $10 for a bottle that will last forever, amd I have some, but I would probably rather spill this formula in the toolbox. Great idea!:thumbsup:

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