lathe cutting fluid.

[SteviegtrParticipant @steviegtr]

Can anyone verify my theory about the cutting medium melting into the work, where oil does not.

[Anonymous]

Compounds like Trefolex and Rocol RTD do indeed tend to melt as they get hot. But that's a convenience, not a key part of their performance. It means they stay where they're put until needed. Whereas oil tends to drain away. They often contain high pressure additives which helps with tapping in particular. I use Rocol RTD tapping difficult materials like stainless steel and tungsten, and larger taps, say bigger than 1/2" depending upon material. I don't think the behaviour or performance of drilling/tapping compounds has any significant bearing on turning.

There are a myriad of cutting fluids available for turning, but two basic types, soluble oils and cutting oils. Soluble oils,when diluted, are mostly water. So they're excellent at cooling, but not so good at lubrication. Conversely cutting oils are good at lubrication, but not so good at cooling.

For general machining (turning/milling/grinding) I use Castrol Hysol XF, which is a soluble oil. Provided one keeps the concentration correct I have no problems with rust or staining. I do a lot of my machining dry, so the coolant sits in the tanks for many months at a time. I've never had a problem with bacterial growth and no niffs of any sort.

Andrew

[Ed DuffnerParticipant @edduffner79357]

Steviegtr,

I used a lot of tallow and trefolex during my time as an electrican. I think also as a cutting aid for drilling with a holesaw but it smoked quite a bit and would probably be the same on a lathe and mill. There would also be some difficulty adding tallow to a rotating work-piece.

Tallow was always hard going when threading by hand until the workpiece got warm.

Ed.

[SteviegtrParticipant @steviegtr]

Posted by Ed Duffner on 05/01/2020 16:12:58:

Steviegtr,

I used a lot of tallow and trefolex during my time as an electrican. I think also as a cutting aid for drilling with a holesaw but it smoked quite a bit and would probably be the same on a lathe and mill. There would also be some difficulty adding tallow to a rotating work-piece.

Tallow was always hard going when threading by hand until the workpiece got warm.

Ed.

Yes totally agree with you. My main point was on the occasions when we had no cutting aid, we would use oil. When we did that it was hard going especially on large conduit. 1 1/2" was a cow to screw. All the shopfitters on site used to have a lamson's tube shuttle filled with tallow for screwing large woodscrews into timber.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Steviegtr on 05/01/2020 15:26:19:

Can anyone verify my theory about the cutting medium melting into the work, where oil does not.

Doesn't sound likely to me : very few liquids 'melt into' metals, and if they do they're nasty!

Cutting fluids have three or four jobs to do, and what works best depends on the circumstances. With cast-iron, the main purpose is removing dirt: no help is needed in the way of lubrication. Lubrication isn't needed much with brass either, and it's not dirty. Steel is harder to machine and gets smoking hot: lubrication, swarf removal and cooling become important. Aluminium cuts best with a thin oil which lubricates whilst preventing welding. More difficult materials like Stainless and Titanium demand lubricants that will take extreme pressures and high temperatures – an oil performing well on mild-steel might not cut the mustard. The fourth job of a cutting fluid is a long list of don'ts: don't mark the work, don't damage the machine, don't poison the operator, don't make a mess; don't cost a fortune, don't pollute the planet etc. Quite a few traditional cutting agents work well apart from failing one or more of the "don't" tests. For example, an old-fashioned emulsion unacceptable in a modern factory because of mess and health issues, would probably be fine splashed around in small quantities at home.

Threading with taps and dies and manual sawing is something of special case. Hand-driven multi-point tools need all the help they can get, swarf is tiny, and slow cutting puts extraordinary pressure on the lubrication. On the other hand heat and cleanliness aren't problems. For manual purposes I find CT90 works better than the cutting oil I use on my lathe and mill, which is otherwise good stuff.

One of the reasons I like carbide tools is the reduced need to worry about cutting fluids; very often it's possible to cut dry.

Dave

[David George 1Participant @davidgeorge1]

I have a favourite cutting oil called Kutamatic liquid 500. I use it where there are problems with parting off, drilling reaming etc especially stainless and pre toughened materials. it's magic and gets me out of problems evan aly that picks up is no problem with a drop or two. I think it is better than Rocol RTD.

David

Edited By David George 1 on 05/01/2020 16:59:50

[the artfull-codgerParticipant @theartfull-codger]

I usually use castrol hysol "white water" for turning & only mix small amounts & apply with an oil can so doesn't get time to smell[like it used to when I had it in the sump & pumped it] & about 20 yrs ago I bought 5 gallons of rocol rtd for a few quid [shared it with all my mates] downside was it was the heavy type so I just mix it with a little white spirit to make it runny for the oil can,

Graham.

[old martParticipant @oldmart]

At the museum, we have some Rocol soluble oil for diluting. We mix at 10% which is stronger than normal, but reduces the problem of fungus when the oil is old. We have not used the pumped coolant in the lathe, but prefer to use a squeezy bottle. Most of our turning is done dry for steel except for drilling and parting off as we usually use carbide inserts.

Edited By old mart on 05/01/2020 18:13:59

[Mark RandParticipant @markrand96270]

Posted by Steviegtr on 05/01/2020 16:22:55:

Yes totally agree with you. My main point was on the occasions when we had no cutting aid, we would use oil. When we did that it was hard going especially on large conduit. 1 1/2" was a cow to screw. All the shopfitters on site used to have a lamson's tube shuttle filled with tallow for screwing large woodscrews into timber.

Almost any vegetable or animal oil/fat will work better than an unmodified mineral oil for cutting. This is because the triglycerides in the plant/beast oils break down to form chemically active bits, which help to keep the cut surfaces separate by binding onto those surfaces. The Mineral oils, being mostly unreactive alkanes don't do that. Mineral based cutting oils tend to be modified with chlorine or sulfur (note use of official IUPAC spelling ) in order to give them the chemical reactivity that's needed for the job.

At least, that's the way that I see it!

[GreensandsParticipant @greensands]

A rarely mentioned cutting fluid option these days but one which I have used with great success for turning silver steel is a 50% mixture of Neats Foot oil and paraffin and does lead to a superb finish. The only minor downside is that like all animal based oils in will oxidised over time which can lead to surface staining of the lathe bed. If you have access to the oil available from any horsey outlet it is well worth giving it a go.

[not done it yetParticipant @notdoneityet]

Greensands,

Were you making point application, or flood cooling, for your silver steel?

[Nigel McBurney 1Participant @nigelmcburney1]

Its nearly 5 years since this thread started,in that time I have downsized from the large turret mill to an 00 omnimill and have not used the pumped coolant ,just using a mug and brush, the coolant will go off in the mug if left for a week,I still have the Colchester master and still use castrol soluble oil,it goes off in less than a month,3 years ago the coolant tank leaked,removed the tank after a struggle,the bottom of the tank had severe corrosion,the sides were ok so a new thicker bottom was mig welded on,the pipe system and pump was cleaned and flushed,after a while the bacteria came back and the coolant goes off after a month or less. I live in a very hard water area and just wonder if this makes bacteria growth worse ,do people who live in soft water areas get the same problem? The soluble oil at first goes a bit muddy and if left too long the soluble turns to a murkey water with oil content gone.this liquid is quite corrosive.I have never tried rain water or distilled water.

[Bryan Cedar 1Participant @bryancedar1]

To avoid staining of equipment, is it wise to use soluble oil neat. I have an almost full 5 liter can so it will last years assuming it does not go off.

[Henry BrownParticipant @henrybrown95529]

My experience with soluble oil when I was working was that it needs circulating. We used t have a centrally based sump that pumped the suds to individual machines and it drained back for straining and filtering. I don't remember there was an issue. As time went on it was deemed that this was too expensive so then each machine had its own tank and it was the responsibility of the operator to keep it maintained, great in theory but when shifts are involved it didn't happen so there were issues with smell and oil separation. Incidentally, we had a temperature controlled gear shop that only used cutting oil, it was a horrible place to work as the mist of 30+ gear cutters and grinders using it in heavy flood mode caused an oil residue everywhere. This wasn't a back street company, they were a world leader in large high speed epicyclic gears.

I haven't got my coolant system set up on the mill yet, when I do I will put a timer into the power supply that will run the pump for a couple of hours each day to keep the solution mixed and see how it goes.

[GreensandsParticipant @greensands]

Hi not done it yet – Brush application at the cutting edge is all that is necessary to give a lovely finish.

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