Cutting brass with a coolant

Just for the experience, I tried cutting a 0.625" diameter brass rod off with a BXA-7 cutoff tool, both dry and wet, even though all the books
say that brass is best cut dry.
Dry, it squealed loudly but cut nicely at ~800 rpm, yielding random piles of little brass needles as long as the cutoff blade was wide.
Wet with oil emulsion (Rustlick WS-5050), it squealed very quietly at the same speed, but yielded mirror surfaces. The wet piles of little brass needles sitting on the top of the cutoff blade were not random, instead looking like stacked firewood, and the needles ended up in neat piles rather than going everywhere.
A better lubricant might eliminate the brass squeal entirely. Steel cut off in the same setup does not squeal at all.
So, cutting brass wet actually helps, at least with an oil emulsion. This ties in with the historical use of whole milk as a cutting fluid for brass and copper, milk being an emulsion of butterfat in water.
At least WS-5050 doesn't turn rancid.
Joe Gwinn
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Lots of non-recommended methods work, just not quite as well as the recommended ones. Often for one-off jobs it doesn't matter. The Cincinatti "Milling & Milling Machines" book from Lindsay describes cutting speed and coolant tests on cast iron, for example. There wasn't much difference with or without oil, so they suggested milling dry to avoid the mess (pp. 123-4). Textbooks present that as a hard rule with no explanation.
I start with the same cutting oil on everything including aluminum and brass and only change to the recommended fluid when there's a problem that sharpening the bit doesn't solve, which isn't often.
Jim Wilkins
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Right on, Jim. The "dry brass" rule is amended esp. for cutting off (parting) in most of Sherline's literature. It doesn't seem to make a lot of difference when working with small stuff; but real cutting fluid such as Tap Matic is best. Just about any oily fluid is much better than nothing at all when cutting off brass.
Bob Swinney
Lots of non-recommended methods work, just not quite as well as the recommended ones. Often for one-off jobs it doesn't matter. The Cincinatti "Milling & Milling Machines" book from Lindsay describes cutting speed and coolant tests on cast iron, for example. There wasn't much difference with or without oil, so they suggested milling dry to avoid the mess (pp. 123-4). Textbooks present that as a hard rule with no explanation.
I start with the same cutting oil on everything including aluminum and brass and only change to the recommended fluid when there's a problem that sharpening the bit doesn't solve, which isn't often.
Jim Wilkins
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Good to know.

Oddly, I found that the WS-5050 oil emulsion makes a pretty good lubricant for hand tapping, actually working better than LPS Tap-All. And I have gallons of WS-5050 emulsion, which is cheap enough to use once and discard.
Does Tap Matic work better than Tap-All?
Joe Gwinn

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Joseph sez: "Does Tap Matic work better than Tap-All?"
dunno Joe, anything oily works better than dry. I'm sure on a production basis, some level of superiority might show up among various commercial cutting fluids. On a hobby basis, there is no discernible difference. I have a sneaking suspicion the guys that rave about some certain cutting fluid are swept up in the moment of their first departure from cutting dry.
Bob Swinney

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I'm milling the semicircular radius on sheet metal brake hinges on a rotary table. Milling the steel dry is giving me a better finish than a little oil does as long as I hold a brush on the back side of the end mill to remove adhering slivers.
Jim Wilkins
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In article

I've had the same experience with brushed oil. The problem is that the oil keeps the chips in the action. A mister with enough airflow to blow the chips away yields a considerable improvement, as does copious flood cooling.
Joe Gwinn
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They do, on machines made for it. The tee slots on my Clausing are open-ended and no way do I want the curved slivers from cutting with the side of an end mill blown on the floor, then tracked upstairs, and permanently stuck in the rug.
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The curved slivers are a real problem.
Make some endplates, one with a drain fitting, and use flood coolant?
Joe Gwinn
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I have been alternately welding steel onto the hinges and milling most of it off again all day with maybe a drop of oil a minute brushed on when the smoke lightens up. And it works fine that way. The finish is good enough for the purpose and I haven't had to resharpen this end mill in 3 years. (The tips are beveled and they don't wear down nearly as fast as sharp ones.)
If the mill had automatic feed it would need an automatic way to apply oil but it doesn't, I have to be there anyway to turn the crank, so brushing on oil with the free hand is entirely practical.
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To see what would happen I started drilling the hinge pin and the sleeve around it without oil. The sleeve is annealed water pipe and drilled like butter without oil, but the drill bit demanded oil for the O-1 hinge pin.
Jim Wilkins
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Umm. I'm reporting that cutting wet (a non-recommended method) in fact works a lot better than cutting dry (the recommended method).

I have not read this book, I think. I'll have to check.
My report is about brass, not cast iron, but I did read somewhere that some companies cut cast iron wet to keep the iron dust under control. Apparently the wet mess was less a problem than the dry mess. Or at least the mess stays in one place, and doesn't get into everything. With flood cooling and a filter, the problem would certainly be controlled.

I'm certainly going this way. I have yet to run the experiment on cast iron, but I will. But it may not be soon, as have to get some cast iron first.
Joe Gwinn
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The 1919 book said that coolant stopped heat distortion of odd-shaped or fragile parts but the grit damaged machine bearings. I don't cut fast or deep enough to overheat the tool or work and a little oil (or tapping fluid) from a brush or needle oiler seems to be enough. Maybe my old, slow, worn machines mask effects that would be important for more aggressive cuts on newer ones.
Jim Wilkins
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My recollection is that the book that suggested wet cutting of cast iron said that it didn't improve the machining, but the iron dust in the factory got into everything, man and machine alike, and was very annoying, in the same manner as sand in a sandstorm. The sole reason given to cut wet was to trap the dust.
As for the grit getting into the bearings, that sounds like a machine design issue either way. The flow of air or fluid should be arranged to move the grit away from critical areas.
I've been using a Noga mister on the lathe, mainly so I don't get blue emulsion flung everywhere. The drill press is set up for flood cooling with the same emulsion. The problem with misters is that breathing the mist doesn't feel good, so I wear a 3M dust and mist mask.
Joe Gwinn
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The machine designers didn't have synthetic rubber for seals in 1919. Some of our old home machines may have the same concerns. My 1965 South Bend lathe is an update of a 1920's model.
I read their long discussions to mean that a little lubricant is enough to improve surface finish and a flood of any cheap coolant greatly improves high speed production. For intermediate amounts, "The average small stream as usually provided, is by no means sufficient to secure ample cooling." The book contains many observations and test results but generally expects the reader to decide how to apply them.
Jim Wilkins
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