Cutting or tapping oil

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Neeves

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I am machining, drilling, some hard steel (Bis 80) and slightly less hard aluminium alloy 7075 for marine fittings (to be galvanised or anodised). Drilling upto about 14mm diameter holes is surprisingly easy, normal drill bits. Larger than 14mm I have some 'special' drill bits, a bit like hole saws, specifically for drilling hard steels. I used to have special oils for tapping but have run out and I know, or think I know, there are special oils for machining. What is special about machining oils - why are they better then any other oil for drilling hard steels? Will they make my life easier, in terms of drilling :), and in the future tapping. Will they extend the life of my fancy drill bits. Or can I simply use some engine oil, which is cheap and I have lots. I do need to keep the aluminium cool as the temper temperature is surprisingly 'cool' (normally it would be water cut - but that' a bit beyond my resource/budget for a prototype).

Jonathan
 
Cutting oil is usually an oil/water emulsion. It utilises both the heat transfer properties of water and tool tip lubrication of oil, reducing heat generation and then transporting that heat away.
Plain engine oil will do, but you won't be able to work as fast as if you were using cutting oil. The result may be that you need to stop occasionally, but not as frequently as if you were using no fluid at all.

Water is significantly better than oil at heat transfer, you might experiment with water only cutting fluid or even try to make your own emulsion.

High end cutting oils also have additives to manage very high tool tip pressure.
 
Dougal, 3rd Engine and Down West. Thanks for the speed of reply and the detail. I had not realised there were so many permutations. I'm back on the straight and narrow.

Jonathan
 
I have always used oil mixed with a bit of water and washing up liquid. I have no evidence that it works. But it does mean that any steam will indicate that things are getting a bit hot.

Do you have a pillar drill? The problem with using a hand drill is that you have too little pressure and too much speed. So the drill bit is rubbing not cutting which means more heat and less progress.
 
I imagine you need an oil with plenty of EP additives, as cutting with a hole saw or similar uses boundary lubrication rather than hydrodynamic. I keep a small bottle of EP gear oil as a cheap and readily available substitute for any 'proper' stuff. Oil with molybdenum disulphide should be good.
 
Ruffles said:
I have always used oil mixed with a bit of water and washing up liquid. I have no evidence that it works. But it does mean that any steam will indicate that things are getting a bit hot.

Do you have a pillar drill? The problem with using a hand drill is that you have too little pressure and too much speed. So the drill bit is rubbing not cutting which means more heat and less progress.
Click to expand...

Yes large heavy duty pillar drill, bolted to a concrete bench. Multiple speeds through an amazing combinations of pulleys. I operate, must of the time, at the slowest speeds.

I learnt, very quickly, that hand drills are waste of time (for this sort of work)

Thanks for the comment and that from Vyv.

In addition to completing what I'm doing I'm anxious that when I finish I do not destroy all my drill bits, including hole saws (the largest of which is 27mm diameter).

Jonathan
 
I'm lucky to have a mate with a tool and cutter grinder. So I can get an edge back on things if needed.
But if you've annealed your drill bit by overheating, it's all over.
Hence I have a great belief in water based coolant, the latent heat of steam will keep things to 100degC and you'll know when it's getting heated.

Then again for a 27mm hole, I might use a carbide boring tool on the mill.

With your large pillar drill, you should have no issues I'd have thought, but a quick look at the bisalloy info on the web suggests you want at least Cobalt bits to drill Bis80, and carbide is your friend.
 
Just to clarify, the mix with water is 3% of the oïl, 93% water so a 5lt jug lasts a long time. Probably Axminster can supply smaller quantities. It really makes a difference to the life of drills and speed of cut.
 
Yngmar said:
This is what the stainless fabricator at Brighton used: https://www.cromwell.co.uk/shop/lub...ounds/mcc-cutting-compound-450g/p/MLY7034040B

I said I like to see how he does that when he said he'd come and drill some 6mm holes through 22mm solid A4 stainless rod with a hand drill. No special drill bits or anything. He gave me a tub of it. It makes all the difference.
Click to expand...

That stuff is great, but it's only a lubricant, not really a coolant.
Drilling big holes with a powerful machine there is a lot of heat, which the workpiece may or may not absorb.
Tapping and hand drilling is a different game.
 
Neeves said:
..... including hole saws (the largest of which is 27mm diameter).
Click to expand...

Huh! Call that a hole saw? :(

THIS is a hole saw......

29232883388_548725feb2_b.jpg








Extra points for the source of the 'quote'..... ;)
 
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