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Lathe - Turning - Finish

 
 

 

 
 
Black finishes (Sep 10, 2002) Finish problem (Apr 10, 2004)
Surface Finish (Jul 4, 2003) Machined finish expectations (Sep 24, 2004)
Finishing (Jan 26, 2004) Bright, shiny finish on stainless steel? (Apr 4, 2005)
 
Black finishes
Good question Mario, When I complete a tool I usually degrease it in a solvent like alcohol to remove dirt and fingerprints. Tie on some bailing wire that has a loop on it for retrieving. Then either put it on the stove gas ring or in the wood stove. If I don't care to harden it, I'll let it go to a dull cherry. Then remove it and dunk it into a bucket of cold 30wt. motor oil. Use the kitchen stove top for small stuff. For big stuff, I put a piece boiler-plate on top of the coals to keep the tool out of the ash. In your case charcoal will do fine. It can be used to heat-treat as well as anneal and color. A small 5 gal. garbage can, (metal of course!) with a lid and expanded screen double-bottom; along with 2 vents will do fine. We can design a coloring chamber from this later if you want. Now if all you want is a rainbow finish instead of black put the piece on a fire brick and dance a large hot flame over it until you achieve the desired look. If you want to do an 'apartment-finish', buy enough 'Perma-blue' to cover the object in a glass vessel. Be sure you pre-clean it to remove every bit of oil, dirt, and above all finger-prints! Put it in the drink and leave it there for a day before checking it. Professional gunsmiths will have an exhaust hood over the vat so they can heat the brew to accelerate the process. You can do this only if you have the proper equipment and can do this OUTSIDE. You will have an odor to deal with so I hope any house-mates like the smell of 'Ode To Forge'! regards, Ron (6297)
Anybody have a good recipe for blackening brass parts? I think there used to be a selenium solution that gave a brown color. MSC sells some stuff - two part product Anybody tried it? Frank (6298)
Any of those finishes you fellas been talking about work on aluminum? Or know of some easy anodizing method for the home shop? Thanks for the response on my turning question earlier this week. Alphawolf45 (6299)
Frank this suggestion that I have for you to try is not what you're after but it is interesting science and if you putter with brass often enough it could prove useful to you sometime. I used to restore antique radios and often got an old radio that some fool had put a buff shine on the brass dial covers or other trim parts. To age the brass ( sort of a controlled tarnish), I would suspend the part over a bowl of ammonia and let the fumes turn the brass black. Don't like the look? Soak the part in the ammonia and it will return to the original finish. Weird huh? Alphawolf45 (6302)
Ron, That sounds like fun! For my purposes, the oil quench will probably do just fine. I have an old smoker that I don't use; it might be just the ticket for a coloring chamber. Do you have any references as to where I might read a little more about these processes? By the way, I'm not familiar with the technical term "apartment finish"!? Mario (6303)
Ron Newman wrote the definitive online guide to anodizing here: http://www.focuser.com/atm/anodize/anodize.html A friend of mine followed his instructions and has turned out some beautiful work. He did a few of my parts too and they look great. c (6304)
Corey The anodizing instructions look very comprehensive. I will need to be a bit more rested to read and comprehend the instructions but i thank you for the link. Alphawolf 45 (6307)
Surface Finish
I've been machining an arbor on my 9" model B out of prehard 4041, this is for my Burke #4 mill. Using a negative raked tool, with indexable carbide insert, I attained a surface finish that looked beautifully polished. Unfortunately, this was not the final cut. Thereafter, the finish was not nearly as good. In fact it was smooth but dull, and needed polishing to give it that proud product appearance. This is the usual finish for me. I tried to duplicate this seldom obtained wonderful finish with my Aloris tool holders, various inserts, high speed steel, and by varying speeds, feeds, tightness of the work piece between centers, etc, all to no avail. I have yet to figure out how to get consistently superior results. BTW, I use no coolant of any sort and prefer to cut dry. So to those for whom a superior surface is commonplace, would you be so kind as to share your magic, tips, and skills. Al (12506)
Al: One thing I find with Carbide tooling is that surface finish is better with heavier cuts. Carbide does not like small finishing cuts ( .005 to .010 on diameter ) but performs better with heavier cuts. Alas are small machines cannot sometimes take the heavier cuts with Carbide and sometimes are inexperience does not allow us to take a .050 cut for finishing and still keep size tolerances. Ron (12507)
Al, I have found that a freshly sharpened bit that has also been run across a sharpening stone always gives me a nice shine. Therefore, I rough cut with one bit, and fine cut with another one. Philip (12512)
When it comes to the chromolly steels you need to either polish to get your finish or take a heavier cut as a finishing pass. And as stated above the heavy finish pass may not be possible with your machine. Cutting dry is only for quicky jobs your tool will last longer and run cooler if you use a coolant or cutting oil. Kerry (12526)
Finishing
Thing is all we do on a lathe IS cut screws, or spirals. Just a matter of how to deal with their paths. Even cylindrical grinders do this. The question isn't what feed necessarily, so much as finishing AND accuracy. Most tools for finishing are of a broad-nose variety. Flat tools can chatter on machines that are either small or loose. Notice I didn't say old. A follower-rest may be needed for long thin work. For bench-top or tool-room lathes, a 3/8-full radius tool is all the tool you'll need. Unless you have a very tight machine, a flat 3/8 is not recommended. To much chatter, IMHO. If a lathe is in good trim, you can turn a finish on alum and have the chips resemble very fine cotton-wool. My finishing tool is the one described above. After rough grinding with the stage set at 5 degrees, I go to my expanding 8" belt-sander and finish it on 600 grit. Then change belts for a leather one and charge it with 50,000 diamond paste. This puts a mirror finish on anything. Even under a loupe it looks good. Keep this tool in its own box. That way it won't get chipped like all the other tools. A word on expanding belt-drum sanders. The word is indispensable. Built for the lapidary trade, the 8" expanding drum belt sander can do a lot of work in a shop. The sanding belts come in 20 and 100 grit intervals. They can be diamond or alum.-oxide. Changing one takes less time then reading this sentence. A can of water dripping through the guard and on to the wheel keeps even carbon steel cool. A 3/4" or 1"arbor is standard. This allows you to change-off for a diamond saw blade. Now your cutting carbide into shapes. You can sand stone, wood, or metal. The grinders that promise to sharpen any tool are dedicated to do just that. They cannot sand wood or polish metal; let alone cut carbide. Build an arbor To handle this belt sander and diamond saw. The cost should be less and you'll do more with it. Go to tile stone floor stores and see if they have any old diamond blades about to be thrown out. If they do, you can try out a diamond saw on HSS or carbide. In water, a diamond saw runs cool, almost no sparking. Imagine the file-steel you can shape without losing the temper? Now back to finishing. For super-finishing *,I'd use a wet silicon carbide 600 grit with an old file to back it up. Keep it wet. At these grits, you won't take off but a few tenths, but do check your progress. It is a good way to get a grind tolerance with a jewelers finish. A piece of leather charged with rouge will be as far as you can go practically. For bores, I'd make up a set of hones out of copper tubing. A t-split near the end will give you some spring against the bore. Use 600 grit in light mineral oil to hone with. regards, Ron *super-finishing is discussed in a book written by the chief engineer for the SR-71 project. I'll discuss this in more detail when there is time. Ron (16836)
I forgot to mention little things like rigidity. Anything you do on the lathe requires a no-flex set-up. Keeping the tool close to the holder is important. However removing all flexing is near impossible. Knowing how to use it can be a help. Like the 'spring cut'. If your cutting a shaft with the tool nice and sharp, and close to mamma tool post, you still have spring. Just re-cut without moving the crossfeed dial over the same stock. You will see how the tool and work-piece 'relax' against each other. As for CRS, there is a way around a bad finish. Because it is so troublesome to finish...don't. Use a coarse feed to put thread-like tooling marks on the work. It'll make the part look like it was turned in some huge circa 1900's lathe. A regular tooled finish actually draws the eye along its length. If you were to cold blue, (as in perma blue) the finish, it will look even better. Ron (16879)
Thanks to everyone for their comments on finishing tool geometry, rigidity, and the effect of steel type. It may be of interest that the link in FAQ that is listed first only refers to grinding a very specialized tool for deep boring, unless I missed a more general section. http://groups.yahoo.com/groups/mwhints  Will use the sugs made and check the other two sites plus HTRAL. Thanks, Steve (16890)
Finish problem
I thought I had fixed my finishing problem, not. It seems my lathe has developed a spiral finish on any turning I do. From one end to the other, all my turning work has developed this spiral or 'barber-pole' finish. Is it a vibration somewhere? Any takers on this one? Ron (18341)
Ron- are you using powerfeed? try 'helping' the handwheel. i found that sometimes the clutches aren't grabbing right. if I put a little preload on the wheel it goes away (I am putting off tearing into the carriage). else: worm gear, swarf ? dennis (18342)
Ron, Far be it from me to offer you advice, but I too had this spiral/harmonic finish problem on cuts anything over half bed length.. umm, 3ft usable bed. I found my problem was bed twist and a very small (downward) offset of the tailstock. A mate also advises me that being just a touch too low with tool height can cause the same symptom (similar to, but not, chatter). A fairly simple (though a tad dangerous) way to tell if its vibration is to grease up your palm and every inch or so of cut along to bed, give a gentle push on the work and observe the finish. push/pull/up/down. Garry D (18347)
Even if they are both within tolerances, their relative values may set up a resonance in that spindle. By simply changing one of the settings (within tolerance) you may eliminate the problem. RC (18367)
Machined finish expectations
A question was posed to the Southbend and 7x10 groups this morning as to what one can expect in a turned finish with carbide or ground cutting tools. The normal finish to be expected from cutting tools on a lathe or mill is called 120 and is to the eye and touch rather coarse and rough. The best one can expect from a lathe or mill in careful turning with very sharp tooling is a 63, good finish but not what the person posing the question wants. Now to get a finer finish than a 63 micro one needs to go to other methods than cutting tools and proceed to grinding and and/or lapping. Now grinding with lubrication and a hard fine wheel can get with care and light cuts down to an 8 micro finish, but still not the mirror finish the person posing the question wants. A mirror finish is called and shown on the micro finish comparator as a 2 micro finish and can only be obtained by turning on the lathe or mill to about .003 to .005 thousandths of an inch over the desired finish size. You would then grind with a coarse wheel or lap with say 180 wet/dry paper and oil to .001 oversize. The next steps would be straight lapping with first 220 grit, then 440 grit and finally 600 grit to .0002 oversize. The final step would be with polishing rouge or a good automotive car polish to desired finish size and desired mirror finish at 2 micro finish. Archiving a mirror finish and a dead on size slip fit part is doable but requires intensive work to produce extremely tight fits and high brightness finishes. Also these extreme high finishes are not very good for rotating shafts where lubrication of bushings or bearings is needed. High micro finished parts used in rotating or reciprocating will usually gall and fail rapidly because there are no low places to retain lubricants so wear is rapid and failure certain. JWE (21078)
Bright, shiny finish on stainless steel?
I am new to working with metal, and have no clue about finishing. I have been turning decorative wine bottle stoppers using 3/4 inch stainless steel round stock. I have no trouble finishing to a finely brushed appearance, but cannot raise a bright, shiny surface. Any advice on polishing compounds / technique would be welcome. Cam (26669)
Cam, I like to first pick up any shavings that have been cut off, and use them like a pile of Steel wool, while the machine is turning very quickly and some light oil. This works especially well when using carbide insert tooling since the chips are more likely to be hardened or close to hardened, and are a proportionately harder that the metal you are cutting. Then some OO or OOOO Steel wool or Scotch-Brite pad still with some light oil. If you go really crazy, you can take two thin and wide pieces of Basswood or other stiff wood and make a bracket to grab the workpiece. You put lapping compound inside, while turning the lathe at high speed. Bernie (26693)
Lots of info here: http://www.caswellplating.com/buffs/buffman.htm Pat (26683)
Cam, Bernie's suggestion is good. What I do is use a buffer with stainless compound then white rouge compound with a loose sewn wheel. You could mount an arbor in the lathe to drive a buffing wheel if you don't have a buffer, but the speed would be a bit low (which may not be all bad for delicate finishing - just takes longer) Don't use the same buffing wheel for the different compounds!! I got my buffing wheels and compounds from Eastwood www.eastwood.com and they have a chart in their catalog about which compounds to use for polishing, coloring, etc. George (26686)
Cam, forgot to mention if you do buff in the lathe - protect the ways!! Nothing worse than getting compound grit on the machine ways. BTW I get mirror finishes on SS. It's like sanding, use more aggressive compound to start then finish with the finer rouge. You may want to start by using fine emery cloth with oil when the part is still in the lathe before going to buffing. George (26687)
 
     
 

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