Achieving fine finish on turned parts

I have been practicing with my lathe a little bit. This included making a few things that I actually needed, such as bushings etc.
While I had some minor successes making parts that actually ended up functional, I am not very happy with the final finish. I would hope that there is a technique that would make turned parts to be nicely smooth. I am sure that I am missing something.
What seems to help a little, is using carbide inserts with rounded corners (square so far), higher speed, and automatic feed at the lowest feed rate.
So... if you turn steel parts... and want nice finish... what do you do?
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On Jul 29, 9:41 am, Ignoramus31137 <ignoramus31...@NOSPAM. 31137.invalid> wrote:

I avoid CRS. O-1 drill rod and Grade 5 bolt shanks usually give me a good finish with honed HSS bits, cutting oil and fine feed. If I want a polished finish I use a single-cut file and then sandpaper.
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On Tue, 29 Jul 2008 06:52:39 -0700 (PDT), Jim Wilkins

Scotch-Brite pads also work well. You can try some from the grocery store to start and if these work for you, these come in different grits from mill supply stores. For example http://www.use-enco.com/CGI/INPDFF?PMPAGE&2&PARTPG=INLMK32
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Ignoramus31137 wrote:

1. Get the speed and feed right. 2. Get the cutting geometry right. 3. Choose a material that's highly machinable.
I got a head start on these when I took a night class at a local technical college. I've followed up with lots of reading of old books and just plain experimentation.
Pete
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Don't forget rough/finish cuts, and that sometimes in some situations, it's possible to take *too fine* of a finish cut. Sounds weird, but I've experienced this.
Sandpaper, emory (which comes incredibly fine, 1200 grit I've seen), and various grades of Scotchbrite--or kitchen scouring pads/steel wool.
Also a steady tailstock. A trick I use is to put the tailstock crank at 3 o'clock, and load it with heavy rings, keeping pressure on the work. I find this to work better than the lock on the tailstock. Also, a positive stop at the chuck some kind of way is helpful.
Ahm certainly no 'spert, just what I do to get thru the day...
Of course, don't forget the erl. I use both a flux brush and dropper.
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On Tue, 29 Jul 2008 08:41:06 -0500, Ignoramus31137

1: get some free-machining steel stock, e.g. 12L14. Some "junk" steel, as found in water pipe and imported tricycles, is about impossible to machine to a nice finish.
2: Carbide tools have their place, but HSS toolbits work very well on mild steel in a home shop setting where production is not an issue. How the bit is ground and honed can make a huge difference. Experiment!
For other steels, another useful trick is 1" wide emery paper -- it comes in rolls. Applied in the lathe, it can clean up a rough surface in seconds.
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wrote:

12L14 is wonderful, cuts like aluminum, but it rusts very easily.
The water pipe I got at Lowe's recently turns cleanly except at the weld. I was only removing the zinc to weld it and not trying for finish but it came out smooth and shiny. It was also within a few thousandths of round. I mention this because it's so unusual.
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Don Foreman wrote:

This matches my (meager) experience.
1. I haven't splurged yet on free-machining stock, but among the bits and pieces of 'mystery metal' that I use some work quite well and some are very hard to get a good finish on. If I ever get to the point of feeling that finish is more important than just getting a part that works I may buy some.
2. For a good finish I use a large radius bit (1/16 or 3/32, if I can get away with it), slow feed, and lots of lubricant. As a counter-example, consider that if you use a really pointy tool and high feed rate you're just making threads...
2a. Make the tool sharp, then hone it by hand on a fine stone. It seems that the finish on the tool transfers to the finish on the part, so make the tool as smooth as a baby's butt (I always thought that was hyperbole, until we had kids...). I do the final sharpening by stroking the round face across the hone, crosswise to the direction of the cut, to knock down any angles. I also touch up the tool every time before I put it in the holder, to make sure it's sharp and smooth.
3. I generally don't use sandpaper or files unless accuracy doesn't matter (I'm not that good!). So if the cut has to be accurate I have to achieve the finish with the tool.
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OK. I think that the mystery metal that I tried, was not as good at achieving a good finish. I have some brass stuff that I will try turning down a little and see how good finish I could get with that.
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Ignoramus31137 wrote:

Brass is a useful metal any time your self-esteem is flagging, at least if you use the right alloy. That stuff is just made to machine easily, and it's a nice color to boot.
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wrote:

Brass works very nicely for some projects. See http://users.goldengate.net/~dforeman/COLgage /
This project didn't take much more than an hour ... and it worked!
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Don Foreman wrote:

Oh ... that's nice! Isn't it satisfying to have the tools & *skill* to do that?

Yeah, for _you_! It would be more like a week for me & then it wouldn't look nearly as nice. <G>
Bob
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I had some progress on this yesterday..... I used "highly machinable steel" 12L14. The result is markedly better than the mystery metal shafts that I tried turning before. What I found out is that the final pass, even at the lowest feed rate (using the slotted shaft, not screw cutting), was still not great. So I did one more pass where I moved the carriage manually, very slow. The result, if not perfect, is at least very good and the machined part feels "smooth". Still had no opportunity to grind HSS, yet, and used carbide for now, but HSS grinding is the next item on the list.
i
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Oh that sounds like a nice project. One more thing to make.
So you tap each case to fit your clamping system. How did you get a nice square to base hole and threads in your cartridge head?
What cartridge was it? If it was a bottleneck shouldn't you have retained the shoulder?
Keep doing your cardiac workouts.
Wes
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Seat cartridge in (cylindrical) caseholder from Wilson case trimmer. Chuck that up in lathe, drill and tap.

.22-250. If you mean the neck, then the bullet would stick in it. The rod is stiff enough that the bullet doesn't droop much, and the fit of rod to hole has no perceptible wiggle. So the bullet stays pretty well centered and square, and the rifling lands have enough of a taper on the start to sorta guide the ogive into place. I use just light finger pressure on the end of the rod, set the rodlock. A series of measurements repeated to a bit over a thou, close enough for my purposes.

Yah yah .... I am.
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I thought about that after I posted, using a reloading die held in a chuck and taking a very light cut drilling while keeping the exposed case head from rotating in the die would likely work also.

http://www.neconos.com/22-250.jpg
Seems like you could have kept the shoulder but if it is working for you, it solves the problem.
Thank you again for giving me one more idea of things to build.

Beats the alternative. Take something interesting with you to read or listen to as they torture you.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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You have Quickdesign! Are you doing wildcats?

A friend is getting interested in making a case neck annealing device, which I'd think might be real useful when working with wildcat cartridges. He's studied the ones offered by Ken Light and others. I'll be goin' on a scrounging mission next week for rawstock.
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On Sun, 03 Aug 2008 22:23:01 -0500, Don Foreman

Do it right and make an induction heater....<G>
Gunner The hottest places in hell are reserved for those who in times of great moral crisis maintain their neutrality", John F. Kennedy.
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Tool geometry is very important and it is different for every material. The rule is to use as much edge support as possible without inducing material drag on the tool. Some material is tougher and stickier than others. This defines relief. Second, there must be enough surface speed to induce the plastic temperature of the material you are cutting at the cutting edge., no more, no less. This defines the durability of the tool. Thirdly, some materials work harden when being cut, like some types of stainless, chrome molybdenum alloys and cast iron. With these, your feed must be fast enough so the cutting edge is in front of the hardened surface. The most important consideration in machining on any machine and a lathe is no different is chip control. If you watch the tool closely when your finish is poor, you will see the chip is getting caught behind the cutting edge between the tool and the work just cut. It is these chips that are scraping the work and marking the finish. Tool geometry and back relief solves that problem. Another rule is to observe is the width of the cutting tool nose must equal 1.5 times the feed rate. This bridges the spacing caused by the tool advance across the work. Be careful with this because it is easy to overwhelm a small machine with too great a load. When it comes to which tools to use, there is a lot of junk out there, but in my experience cobalt HSS alloys are the best for the hobbyist. These have an enormous advantage over carbide and indexed carbide tools on the small machines, because you can control machine load with geometry changes and that is an issue with commercial production tools, as these are expected to be used on heavy, high horsepower production equipment. Cobalt alloys are very durable like M35(5%) and M42(8%) and will cut all but the very hardest material. As a hobbyist, production speed is not an issue, so cooling is not normally used and these tolerate high tool temperatures much better than normal HSS. Steve

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So, Steve, if I understood you right, you can use M42 and M35 bits without coolant, as long as your speeds are within a certain range. Right? I would prefer not to use coolant for obvious reasons.
i

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