Achieving fine finish on turned parts

Ignoramus31137 wrote:


For hobby-level machining, you never need coolant, like flood-style. But, brushing on some thread cutting oil from the local hardware store can make a huge difference. It prevents the chip from welding to the cutting edge, ie. "built-up" edge.
I use retired toothbrushes to apply the oil.
Jon
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wrote:

I found the brush method a bit awkward, especially when cutting off, as I couldn't get the fluid to where it was needed, down in a deep narrow groove. A simple mister which sprays soluble oil emulsion works well. I have been using Rustlick WS-5050, but there are many alternatives. Emulsion makes less mess than black sulfur oil.
People have also used homebrew gravity drip cans to apply coolant.
In both cases, the trick is to attach the applicator to the lathe carriage, so the coolant is applied at the cutting point no matter what.
Joe Gwinn
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I use a needle oiler to put the oil down in the cutoff groove. Very little oil is needed but the bit will jam within seconds if I stop.
Filing is accurate if you use the tool marks as a guide and stop as they disappear. One light stroke with a fine file only removes about a ten-thousandth so with a little practice and measuring you can calibrate your feel for it.
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In article

That would certainly work, but requires a hand. I prefer that the coolant application be hands-free, so the hands are free to run the lathe. A compressed-air driven mister has no problem keeping the groove wet, even if alignment isn't precise. I've been using a Noga unit, and have been looking at a Trico unit.
Noga: <http://www1.mscdirect.com/CGI/GSDRVSM?PACACHE0000062954483>
Trico: <http://www1.mscdirect.com/CGI/GSDRVSM?PACACHE0000062955402>
The Noga unit I have is a cheaper version that has a simple magnet, rather than the on-off version shown.
The Trico unit shown is the one with the metal armored line. No way to hold the Trico sprayhead in place is shown, so I assume that the user is expected to provide the magnetic holder assembly.
Joe Gwinn
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Does mist settle all around the room, with this mister?
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If one is too aggressive, vast amounts of mist hangs in the air visibly, and mist is not pleasant to breathe, so I'm very stingy with the mist. I set it up to produce a small amount of a heavy, wet mist that won't stay in the air for long.
The airborne mist does settle out around the room, but this has not been a problem. I suppose it would not be good if one also was trying to paint in the same space, as the oil from the emulsion would wreck the paint job. But I paint outside, and clean things with acetone first.
There are expensive systems (Trico Micro Drop) that spit a slow stream of large drops at the workpiece, carried by a lot of compressed air. By all reports this works very well, but they are too costly for my blood.
My first spray mister had only one control, and it was impossible to get the right mix of air (to blow chips away) and coolant, leading to a fog-filled workshop. The replacement mister (the Noga) has independent air and coolent valves, which is essential. The problem with the Noga is getting the spray started, and random variation in spray. The hope is that the Trico sprayer will be more controllable and predictable.
If I get motivated, I'll set up some kind of gravity drip, with a tank on the wall near the ceiling and tubing from tank to drip nozzle on a little stand attached to the carriage.
For facing and boring, the mister would still be needed.
In the meantime, if I am doing something that fills the shop with mist fog, I wear a half-mask respirator, even though it makes me look like a Preying Mantis, to the eternal amusement of my wife.
Joe Gwinn
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On Thu, 31 Jul 2008 09:27:14 -0400, Joseph Gwinn

I have found that using a 390ml or 600ml coca cola plastic (PET) bottle with a small length of hospital oxygen cannula plastic tube through a tight hole drilled in the screw on lid makes an absolutely excellent coolant applicator.
I originally thought that these would be quite temporary and would need replacing occasionally but mine have been in use over 2 years now.
the beauty of them is that you can vary the application of coolant just by changing how you squeeze the bottle. using transparent tube means that you can see when the application is about to start.
the original one was brewed up in desperation one night when I kept melting the tip off a hss tool. I was amazed at how well the 5 second job worked.
I should patent it :-)
Stealth Pilot
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So, you hold the bottle in hand while machining, and use it as a big squeeze squirter? Yes - mentioned below.
I don't know where I would get cannula tubing.

Using what kind of coolant? Oil?
The emulsion coolants don't seem to bother plastic.

I was looking for something that I didn't need to hold in hand while machining. One thought I had was to pressurize a reservoir so the fluid would climb up from floor level to the applicator tip, which would direct a thin stream of coolant onto the cutting point. But having compressed air to also blow chips away is very useful.

It is a good idea.
Joe Gwinn
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On Fri, 01 Aug 2008 10:22:58 -0400, Joseph Gwinn
<snip>

Maybe one of the generic pesticide sprayers in the one to two gallon size would work? See:
http://www.amleo.com/index/item.cgi?cmd=view&Words=lcs2
It just so happens I bought a similar type one gallon today on sale for ~$11. I wouldn't be surprised if you already had one with some yard chems in it.
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    [ ... ]

    It helps if you know what a cannula is. It is that oxygen source which hooks over the ears and into a clip which sticks into the nostrils -- one to feed oxygen, one to give feedback whenever you inhale to turn on the oxygen. It is used both in hospitals (connected to a central supply of oxygen) and for individuals with respiratory problems, bottles for travel, concentrators for sitting around in the home.
    Go to a *good* medically oriented drugstore. I've gotten one in the local Rexal, after the CVS didn't have them -- but suggested the Rexal. (I needed it for the smaller tubing which goes over the ears to the nostril clip, not for the larger tubing which goes from the junction point under the chin to the oxygen bottle.
    They're not even as expensive as you might expect for something made for medical use. And I've seen distilled water labeled "Federal law prohibits dispensing without Prescription". :-)
    Enjoy,         DoN.
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On Fri, 01 Aug 2008 10:22:58 -0400, Joseph Gwinn

I use a cutting oil that has no water component. When I squirt it on most eventually ends up in the swarf tray which drains into a can. I periodically pour it back into the bottle. My cutting oil is gradually being augmented with Tellus 46 slideway oil but it still seems to work. Stealth Pilot
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I have been doing something similar, actually. I have a big (one quart) pump oilcan full of Mobil DTE 24 hydraulic oil (used for the lathe headstock and apron) and I use it as a cutting oil on small jobs, where setting up the mister is too much trouble. DTE 24 works pretty well as a cutting oil. I've used Vactra #2 as well, but DTE 24 works better, probably because it is thinner but is a very good lubricant.
Joe Gwinn
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On Sat, 02 Aug 2008 14:16:33 -0700, with neither quill nor qualm,

Does Ed's Red work for cutting/drilling/tapping, too? Do what you feel in your heart to be right - for you'll be criticized anyway. You'll be damned if you do, and damned if you don't. -- Eleanor Roosevelt
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On Sun, 03 Aug 2008 05:35:24 -0700, Larry Jaques

Id imagine that it would, but it would be right expensive. ATF bought at the 99c store works well enough
Personally..I use high sulphur oil at home in the shop. Stinky, smokey and attracts dust on the machines between uses here in the desert..but is really hard to beat for most everything.

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And it smells good.
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On Sun, 03 Aug 2008 13:18:41 -0700, with neither quill nor qualm,

Ah, good sourcing/pricing tip there. Danke, seor.

I hear that sulfur is like lead and softens the contact a bit.
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On Tue, 29 Jul 2008 11:47:48 -0500, Ignoramus31137

But coolant does more than cool the tool and the work. Coolant or some other type of cutting fluid used properly will prolong tool life and improve surface finish. One way the finish is improved is by lubricating the surface so that if the chip coming off the tool rubs against the work it does less damage to the work. ERS

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On Tue, 29 Jul 2008 18:38:00 +0200, "Steve Lusardi"

All good advice but the nose radius/feedrate ratio relation can be solved a different way.
In pretty well all my fine finishing requirements I feed from right to left so I use an assymetric tool with a plan view that is near square with almost zero corner radius (less than depth of cut).
It is presented to the work with the forward cutting edge about 15 deg off square so that the chip curls nicely away from the work. The straight front finishing edge is a few degrees off parallel to the work so that it bridges the feedrate spiral.
The forward edge provides near ideal cutting conditions. The straight front edge behaves as a large radius nose but with the advantage that the equivalent radius is easily varied by trimming the bridging angle,
Jim
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On Wed, 30 Jul 2008 11:55:44 +0100, snipped-for-privacy@yahoo.com wrote:

That works for me too. It isn't the only strategy that works, but it works very well for me on ally, brass and free-machining steel.
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Ignoramus31137 wrote:

Ohh, this topic goes round and round (so to speak!)
First, some metals turn like mirrors, and others turn like concrete, tearing and spalling off chunks. It is a characteristic of the metal. High speed, a little cutting oil, and just the right feed rate and depth of cut are important, too. Go too slow on the feed and the work hardens ahead of the cutter. Go too shallow and the tool can ride up on the work, intermittently. The cutting tool can develop a "built-up edge" of workpiece material. As this varies, the diameter changes, leaving rings. You're in over your head, now, and well on the way to becoming a "metal head".
Long parts need to be supported at both ends, or possibly with a follow rest, otherwise the work deflects and causes rings.
Jon
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