# Carbide bits/end mills and lubrication



## ChooChooMike

More of a newbie question, but that's why we're here !!

I've used carbide bits on the lathe on aluminum without any kind of cutting/lubrication oil. Now I'm trying that on (probably plain old) steel. Should I be using any kind of lube/cutting oil on the lathe bit ? 

I successfully turned a 1-1/2" bar down to 1" w/o any kind of oil, thinking I don't need it per my very limited prior experience. Of course the steel and resulting chips were quite hot on my Sherline, taking 0.005 - 0.010 passes (1/4" lathe bit, carbide insert). Got a decent finish, but with some tooling marks, think the insert may need to be replaced. Nothing that a little sandpaper or light filing won't take care of.

Ditto question for end mills.

Thanks,
Mike


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## tel

I rarely use cutting fluid/coolant for anything - too durned messy in my opinion. Most things will cut dry if you fiddle with the speed/feed a bit.


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## Lew_Merrick_PE

ChooChooMike  said:
			
		

> I've used carbide bits on the lathe on aluminum without any kind of cutting/lubrication oil. Now I'm trying that on (probably plain old) steel. Should I be using any kind of lube/cutting oil on the lathe bit?


First comment: Using carbide on aluminum is usually wasteful. The nature of tungsten carbide is such that sharpening it to a truly keen edge takes more than than it is worth. Also, a truly keen edge in tungsten carbide is, by nature, a weak one. I find that a well sharpened HSS cutter does me better in aluminum.

Cutting oils serve two purposes: (1) to lubricate the cutting edge and reduce friction in the cut which can prevent all sorts of mishaps during machining. (2) to cool the cut which reduces the chance of localized hardening in higher carbon content steels.

The main advantage to using a lubricant when cutting aluminum (cooling is rarely an issue here) is to keep the chips moving away from the cutting edge. Aluminum will gall to a cutter (flutes, especially) at temperatures as low as 275°F (depending on the alloy). A light "spritz" of something such as WD-40 (just about the ONLY use *I* have for it) or "Simple Green" (I cut my "Simple Green" by 3:1 with tap water and add about 3 drops of dishwashing liquid soap per pint) helps to prevent this from happening. I keep a "plant mister" by my lathe. [I use a mist-spray system on my mill.]

My other "trick" is to polish the chip flow area (lathe bits) and flutes (end mills) using fine polishing compound on a linen wheel. Keeping that area well polished makes for fewer problems with galling. This is especially true when working with nickel-bearing materials such as stainless steels.


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## Deanofid

Hi Mike;

Whether you might need some kind of lube, or not, depends on what you are cutting, and the type of tool you are using.
Mostly, I'm with Tel, in that I rarely use any kind of lube, but there are situations where it's needed.

For aluminum turning, I always use sharp HSS tool bits, and the type of aluminum you are cutting will tell you if you need lube. Some types machine very well dry. The gummy types, like 6061, work better with a lube like kerosene, or similar, such as WD-40. 
You will know fairly quickly if you have one of the gummy types, as it will stick a small nib to the tip of your tool, and immediately stop cutting well. When that happens, get that nib off the tool tip, and use some WD.

For steel turning, I use mostly HSS, and the tool needs to be sharp. With leaded steel and drill rod, lube is rarely needed. For stuff like HRS, you will find a few drops of some commercial cutting fluid like Tap Magic useful.

For turning steel with carbide bits, I hardly ever use a lube, unless I'm threading. I don't use carbide that often for turning, simply because it doesn't give as good a finish as HSS with the small machines I have. When I do use it, I rarely use a lube. Just not necessary.

For milling, I usually use carbide end mills. Unlike most carbide lathe tools, good carbide end mills are very sharp. The edge on the flutes will draw blood.  
Carbide is great for milling aluminum. So is HSS. The same thing about gummy types of aluminum that applies to turning goes for milling.

For milling steel with carbide, I rarely use a lube, but a few drops of cutting oil won't hurt. I don't use any lube that contains water, as I don't flood or mist, and I don't want to have a mess to clean up. Just a drop or two of what ever kind of cutting oil you like will do, if you think you need it. It helps some with steels that tend to be stringy, like HRS. 

If you're using HSS end mills on non leaded steel, you will probably want to use enough cutting oil to keep the tool slightly wet with it. You can use HSS mills on steel dry, but the tools won't last as long. 

If you use small machines, and your chips are coming off blue, you either:
need some lube, or
your tool isn't sharp, or
you're taking too much of a cut, or
you're turning too fast, or some combination of these.

These are not suggestions made with production in mind. I'm assuming you are working at the home shop level, like most of us here.

Dean


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## Blogwitch

This is what can be done with very expensive tungsten cutters (these cost over $200 apiece. Luckily, I get them for nothing. Used once, then discarded by the machinists), but cheaper grades won't normally do this, they will just either go blunt or break on the tips. This was a setup shot, to show what can be done with the right cutters when cutting very hard materials.







A good flood coolant or spraymist situation is normally required if you want to be that silly. 

As shown here.






As everyone else has stated, for normal use on aluminium, you really do need something to stop the swarf bonding to the cutter tips. Again everyone else has mentioned the usual. I used to mix up my own paint on lubricant out of white spirits with a bit of 3 in 1 oil mixed in, but have now gone over to buying WD40 by the gallon (works out to a small percentage of buying it in spray cans) and putting it on with a spray, usually using the free spray bottle that comes with the WD40.

There are no hard and fast rules in a home shop to using lube and coolant, it alls boils down to whether you want to clear up the mess afterwards, and the quality of tooling you use.

But you must remember, even cheap tooling can can way outlast expensive stuff if coolant/lube is used. 

It is a balancing act between how much it costs in time to clean up the mess, and usually a better finish and longer lasting tools, compared to how much you will spend on replacing blunt and broken tooling in the future.

I am going down the coolant route on all machines by making my own spraymist units, unfortunately you can't go down that route unless you have piped air in your shop. But most small shops can get away with a tin of coolant/lube and a paintbrush.

My personal view is to use it whenever you can, it does make a huge difference.


Blogs


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## IanN

Hi,

A lot of sound advice has bee given about the use of coolant/lubrication, to which I would add that there are two serious issues with using soluble oils:

First, the oils wash away the lubrication on the machine beds, ways, screws, etc, so constant re-oiling is necessary.

Second, the oils contain anaerobic bacteria which feed off the oils and produce corrosive by-products as a result. These by-products cause black stains on steel and eventually cause pitting. When exposed to the air, there is no problem, but when trapped under cross-slides, saddle, tailstock, machine vices, or soaked into the felt wipers etc the corrosion takes place very quickly unless the machine is cleaned down thoroughly after use.

This corrosion problem is not an issue in a production environment where tools are used 24/7 but is a real pain for the hobby user - you need to strip, clean and re-oil all your kit and it makes it impossible to leave that vice setup on the milling machine (you know, the one you spent half an hour carefully setting up in exactly the right place......)

Another point - when using carbide tipped tools, the cutting oil should be full flood or none at all - if you feed the fluid in as a series of drips, the tool will heat up between drips and the thermal shock of the sudden cooling effect of each drip will cause the carbide tip to chip and fail.

Ian.


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## Maryak

IanN  said:
			
		

> Second, the oils contain anaerobic bacteria which feed off the oils and produce corrosive by-products as a result. These by-products cause black stains on steel and eventually cause pitting. When exposed to the air, there is no problem, but when trapped under cross-slides, saddle, tailstock, machine vices, or soaked into the felt wipers etc the corrosion takes place very quickly unless the machine is cleaned down thoroughly after use.
> 
> Ian.



Ian,

It's my understanding that no soluble oils actually contain bacteria.

Bacteria which are capable of utilising the emulsifier and hydrocarbon components can breed in soluble oil emulsions.

Most common of the aerobic bacteria are of the genera Pseudomonas and Nocardia. These thrive in well aerated systems at elevated temperatures. Pseudomonas at bulk fluid temperatures around 30C where they reduce the pH to around 6.5 increasing the acidity and promoting corrosion. Nocardia at higher bulk emulsion temperatures, (55-60C), reduce the pH to around 4.5 creating an even greater corrosion problem.

Anaerobic bacteria, (those which thrive in the absence of oxygen), normally Desulphovibrio desulphuricans, detected by the presence of Hydrogen Sulphide occur in stagnant soluble oil systems, particularly where the emulsion has a surface layer of oil which tends to exclude oxygen.

Good quality soluble oils have a pH in the range 8.5-9.3. Below 8.5 rusting is likely to occur, above 9.3 skin irritation is likely. If the pH of the emulsion is maintained within this range then bacteria of either type are unlikely to survive and corrosion is minimised. These soluble oils also incorporate bactericides.

Hope this helps.

Best Regards
Bob


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## Blogwitch

> Another point - when using carbide tipped tools, the cutting oil should be full flood or none at all - if you feed the fluid in as a series of drips, the tool will heat up between drips and the thermal shock of the sudden cooling effect of each drip will cause the carbide tip to chip and fail.



I will agree with that, but no mention is made of spraymist systems, it is the air that continually cools the cutter and the liquid gives the lubrication.

Yesterday, I parted off, under power, two three inch diameter discs of cast steel, about 1/4" thick, using my own very low consumption cheapo home made spraymist system, and a tipped parting tool. In fact, as the discs fell off, they were cool enough to pick up straight away. Maybe this is the way people should go. No oil in big puddles, and after an hours use, just hoover the slightly wet chips away.

With regards to damage caused by coolant. I have been unfortunate to have to stop and start work in the shop for weeks on end recently, and have never removed any of the flood coolant from my mill table, it is just left sitting there, what doesn't drain back to the tank, evaporates off the surface. Not one sign of rust or staining, not even any detectable residue. The table top is in exactly the same condition now as when it was installed 18 months ago. Even the steel swarf left down in the T-slots doesn't go rusty.

Any good modern cutting fluid prevents all that. In fact the stuff I use, which is designed for use on auto grinding machines, at 100 to 1 mix water/oil ratio has been in the mill tank for well over a year now, and it comes out of the nozzle as though it was just mixed, and no sour smells you used to get with old style cutting oils.

One thing I do agree with you on. Lubrication. I religiously over lubricate all my machines. 20 squid a year spent on oils far outweighs the cost of replacing worn out parts. Your machines will also cut a lot more accurately and smoother as they are running on a film of oil rather than a metal to metal contact.


Blogs


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## ieezitin

Choo Choo

Every piece of advice already given to you is true. We are not a commercial workshop so we have different needs. I believe tool care is our main concern, people who do not use lube produce fine work as people who do. I personally do a little of both.

I use HSS 95% of the time for the stock I usually work is Brass, Aluminum, Steel and stainless steel. The finish is so far superior than the carbides and ceramics on our home shop machines. But as stated the tool has to be sharp. This is the key!

I form my HSS tool bit and rough out by digging in as hard as my machine will tolerate. ( your little treasure will inform you of abuse it does not like ) if the tool blunts it not too much of a problem, unless your spitting sparks and your ears are exploding, carry on leaving around .050 for finishing. Then re-grind and hand hone the tool bit, finishing off the bit is so important for your results of the finish you get. Up the speed and lick your passes.

Grinding!. its a pain in the A)*^% , my eyesight is getting worse and holding bits of steel up to the wheel hurts my fingers. I have hand ground all my bits all my life and its only now I am right at this moment making myself a fully operating 3 Axis grinding jig for cutting tools. Just by removing my blunt bit and zipping it through on a jig will increase my time and I will get better value from my tooling stock.

End mills. Well without spending fortunes on special grinding machines to sharpen them this is my only solution to this problem.
End mills should be treated with care. I buy only top quality new mills, again I rough out with semi sharp mills and finish off with a sharp less used mill.

All the best.  Anthony.


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## doc1955

If you want you carbide cutters to last you either, flood coolant and keep it on the cutter or air blast never put liquid coolant on a hot carbide cutter the edges of the cutter are very susceptible to thermal shock and will crack and you can ruin a cutter that way. I find the best is to use a cold air gun but at home in the shop I just use a cheap mist coolant but with no liquids only air and that is sufficient for carbide. A cold air gun would be nice but they are spendy. We use them in the tooling shop here and you cant beat them. I think they run around 200 to 300 bucks.


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## IanN

Hi Bob,



			
				Maryak  said:
			
		

> Ian,
> 
> It's my understanding that no soluble oils actually contain bacteria.
> 
> Bacteria which are capable of utilising the emulsifier and hydrocarbon components can breed in soluble oil emulsions.
> 
> Most common of the aerobic bacteria are of the genera Pseudomonas and Nocardia. These thrive in well aerated systems at elevated temperatures. Pseudomonas at bulk fluid temperatures around 30C where they reduce the pH to around 6.5 increasing the acidity and promoting corrosion. Nocardia at higher bulk emulsion temperatures, (55-60C), reduce the pH to around 4.5 creating an even greater corrosion problem.
> 
> Anaerobic bacteria, (those which thrive in the absence of oxygen), normally Desulphovibrio desulphuricans, detected by the presence of Hydrogen Sulphide occur in stagnant soluble oil systems, particularly where the emulsion has a surface layer of oil which tends to exclude oxygen.
> 
> Good quality soluble oils have a pH in the range 8.5-9.3. Below 8.5 rusting is likely to occur, above 9.3 skin irritation is likely. If the pH of the emulsion is maintained within this range then bacteria of either type are unlikely to survive and corrosion is minimised. These soluble oils also incorporate bactericides.
> 
> Hope this helps.
> 
> Best Regards
> Bob



Sorry if some detail about the exact origin of the anaerobic bacteria in my original comment was incorrect, it was the issue of corrosion caused by the bacterial by-products that was my main point.

I think we will just agree to differ on whether this is a real problem or not, but it seems that others in this group have noticed the staining effects - see this thread:

http://www.homemodelenginemachinist.com/index.php?topic=5359.0

Ian.


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