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The heresy of cutting oil?

DocsMachine

Titanium
Joined
Jan 8, 2005
Location
Southcentral, AK
Simple question with, I'm sure, a not-so-simple answer: What sort of issues might I face using cutting oil, rather than water-based coolant, in a small VMC with a 10K RPM spindle?

Parts are small, aluminum, relatively low complexity, and only moderate accuracy.

Part of the reason for using the oil is the machine will only be used a limited number of hours per month. I'm not a high-volume shop (yet) and I figure the thing will only see 10-20 total hours of use a month.

Oil eliminates evaporation issues, smell/rancidity, rust, and the need to frequently adjust concentrations.

On the other hand, I know it's nowhere near as good as a coolant, and heat issues may be a problem.

Is there anything else of significance I should know about? Reduced tool life? Reduced surface finish?

And, now, for the real heresy. :)

I've been using Mobilmet 426 cutting oil in my other machines (including a CNC lathe) and it appears to be working fine. But, being in Alaska, a single bucket costs me $260 including shipping.

I can get hydraulic oil locally for less than $70 a bucket. I know that's probably false economy, but just for the sake of the argument, what would be different about it as a cutting oil? I read about guys being able to tell when their soluble coolants get off-spec for concentration, and can tell the difference between brands.

One would presume the cheap hydraulic oil wouldn't have the proper additives to make a good cutting oil, but I guess the question is, how bad would it be? Chip welding? Insert breakage? Endmills lasting less than ten minutes?

Doc.
 
Most of those problems go away with experience. I get no rust and don't have to adjust concentration.
Aluminum needs more cooling than lubrication. The oil will fry and aerate, you will breathe it and people will think you smoke 3 packs a day.
Friend had a shop years ago that ran a couple Hardinge CHNC with oil. The wall AC was caked with oil. Think about breathing that

HOw much coolant are you buying a year? If you are not that busy, get an aquarium pump to aerate, rinse your chips to recover coolant and I would be surprised if you use a bucket a year.

Yes you can do it.

Few do
 
Doc, I'm not so sure how it would work in a flood coolant environment, but diesel fuel works really well with aluminum, but I'm pretty sure it would be much better than hydraulic oil. Yes, there is a fire hazard, but I think it would not be so high. I think it would be worth a test.
 
I'm not so sure water is a much better coolant than oil. Maybe a little. But given your use, I doubt you're gonna heat up gallons of oil to the burning or vaporization point.
 
Your 426 oil will have antimisting and other additives that promote cutting. If hydraulic oil makes a mist at those RPMs it could pose a fire danger. Any way of getting a full drum hauled in unconventially? If so you would have multiple years supply at the cost of a couple of pails. I am still using a drum of Nu and bought a drum of 427 just to know the difference. Primary difference is the 427 is almost clear Nu is considerably darker. The way the drops coalesce you can see both have anti misting additives. Could tell no difference in cutting properties. You coolant guys can call me Dinosaur if you like.
 
When I worked for Doosan, we were telling folk in the strongest of terms to NOT use straight oil in the CNCs. In fact, it would void your warranty. We had several customers burn their shops to the ground because of cutting oil fires in CNC machine tools. Not recommended.
 
When I worked for Doosan, we were telling folk in the strongest of terms to NOT use straight oil in the CNCs. In fact, it would void your warranty. We had several customers burn their shops to the ground because of cutting oil fires in CNC machine tools. Not recommended.

You would void the warranty ?

on what grounds other than a claim for fire ?
 
On the flip side using water based coolant in my Ewamatic grinder would void the warranty. One big place that starts with "S" tried it and the machine died in 6 months.
Many carbide grinding shops have gone to oil as it keeps things so much cleaner and of course using oil with a high flash point.
My insurance company made me put a fire suppression system in the machine.

From what I've seen in metal cutting oil seems to work better than water at low surface footage and when using HSS.
Part of what coolant does is provide lubricity for the chip flow at the tool surface. This often more important than it's theoretical cooling capability at reducing heat where it counts.
It is the tool/chip interface and not the cooling the part or the tool that counts. This is why all water based have so many additives.
As an rather simplistic example in AL. On a B-port a squirt bottle of WD-40 will out run a squirt bottle of any water based by a long stretch.

Downside is that everything is oily. If the door opens and it drips some water on you this is different than if it drips some oil on you every cycle.
The parts are covered in oil which is harder to clean.
Upside, none of that maintaining concentrations or having to put in a bubble thingy so that it does not go stale.
Bob
 
. . .From what I've seen in metal cutting oil seems to work better than water at low surface footage and when using HSS.
Part of what coolant does is provide lubricity for the chip flow at the tool surface. . . Bob

That's a good point to bring up, and may be what GregSY was getting at in post #4. The heat of cutting is generated by friction, some of which is internal to the chip but most of which is at the chip/tool interface. Lubricating that does indeed reduce, but does not eliminate, the generation of heat. The water-based coolants try to take advantage of the properties of water and oil.
 
a good question, I look forward to the answers.

I have noticed where ever I've seen oil run - horizontal mill, gear hobber, lead screw mill come to mind, they were slower revolving operations than a cnc mill or lathe with carbide cutters. I think oil would be easier on the machine but I've never had a clear understanding why it was chosen for some applications and not others, other than the slow/fast thing and it smoking with the heat generated by carbide tools at speed.
 
There is no lubrication with water based cutting fluids and some of the water based ones I have used sure do strip the paint off the machines.
 
Properly maintained coolant will be just fine, even with intermittent use. Just keep the concentration correct, and aerate it to prevent anaerobic bacteria from growing. The coolant has bactericides in it to help keep life.

If my machines sit for more than a few days, I just turn on the coolant pump set on flood to recirculate for an hour or whatever.


I would NOT use hydraulic oil as a coolant/cutting oil. It isn't designed for it, and you're asking for trouble.

As far as the cost, you need to build that into your overhead. Living in Alaska doesn't exempt you from math. The cost of doing business in your area needs to be reflected in your hourly rate. If a 5 gallon pail of coolant is enough to make you not profitable anymore, then you need to charge more.
 
There is no lubrication with water based cutting fluids and some of the water based ones I have used sure do strip the paint off the machines.

I disagree. What I use is a water-soluable oil (Rustlik WS5050) and it definately has lubricating properties. I use it 16:1 with water, which is stronger than most but even at that concentration I consider it a water-based coolant.
 
"Water is a much better coolant. Per unit volume, water will absorb much more heat and do it quickly."

How much better?
 
"Water is a much better coolant. Per unit volume, water will absorb much more heat and do it quickly." How much better?

Well, the specific heat of water is almost double that of, say, vegetable oil. There are many variables, but starting there I'd say a lot better. I know there are chemists and others here who could quantify it, but for me, it just comes back to experience and common sense.
 
I disagree. What I use is a water-soluable oil (Rustlik WS5050) and it definately has lubricating properties. I use it 16:1 with water, which is stronger than most but even at that concentration I consider it a water-based coolant.

Last place I worked did this. I ran a huge Poreba lathe and the soluable oil was great. I had an aquarium bubbler in 3 of my tanks, and that kept the big 'rubber vomit' from growing on top.
Another thing that added to bacteria was people spitting tobacco, an dumping coffee in it.
I preferred the oil, because the coolant mixes they used would eat up my hands. I still have skin problems 20+ years later. We even used a refractor to mix it.
 
I disagree. What I use is a water-soluable oil (Rustlik WS5050) and it definitely has lubricating properties. I use it 16:1 with water, which is stronger than most but even at that concentration I consider it a water-based coolant.

I use the same stuff, at about that concentration. It most definitely does lubricate, as well as cool. And it works just dandy on aluminum.

It does not tend to stink when neglected. I do have to purge all the old coolant in the pump sump once a year, as the coolant slowly thickens, probably slowly polymerizing or something.

I do have MobilMet on hand, but apply it only with a brush.
 
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