Machining question

Hello, I'm getting ready to turn some small parts out of aluminum. The parts I'm making are basically discs of about 24mm diameter and 3mm
thickness with a few holes drilled for lightening. The most important criteria are beauty (looks good with no gauling) and machinability.
I've seen all sorts of grades and am confused as to which is the better grade to use. What grade aluminum should I get and what type of tool. HSS or Carbide?
Any other tips I could use?
Thanks
James
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You didn't mention if you're interested in starting with round stock or sheet material-----and they can be made from either one easily. It might be more helpful in getting an opinion in keeping with your project. Shooting from the hip, though, I offer this:
For beauty in machining, there's nothing quite like 7075-T6. It cuts with a bright, smooth finish, assuming you have sharp tools and apply them properly. Next choice would be 2024-T351 or T4, but it doesn't cut with the nice, bright shiny surface you get from 7075. My last choice would be 6061-T6, but it would be a better choice than 2024 if you expect a shiny surface. 2024 tends to cut with a somewhat dull surface, somewhat resembling cast iron, but without the graphite. In all cases, use kerosene or some WD-40 to lubricate your cuts. You can apply it with an acid brush, or a small paint brush.
If you're adept at hand grinding turning tools, there's absolutely nothing wrong with using HSS with some serious positive rake. If not, and you're uncomfortable sharpening toolbits, I'd suggest a positive rake carbide with a chip breaker. Choose a corner radius that is in keeping with the surface finish you desire and doesn't cause chatter, say 1/32". You don't need carbide for aluminum and I'd encourage you to learn to grind toolbits if you don't already. Nothing will set you free when running a lathe more than that will.
Harold
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If you want the best possible finish, a diamond tool is it for aluminum (PCD tipped tool). Get the largest radius your part geometry will allow. 6061 or 7075 for the material.
--
Anthony

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You can get 6061 to a mirror fish with the dish soap and polishing with a fine wool. I use a good mixture of water and dish soap, rub or turn with steel wool and it will shine very nice.

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    [ ... ]

    Agreed -- though PCD diamond can be rather expensive. And *never* use them on steel or iron. They are hard enough, but hot steel or iron tends to dissolve carbon (including diamonds) into the alloy, making it harder.
    Don't confuse PCD (PolyCrystalaine Diamond) with the so-called "diamond tool holder", which holds a HSS lathe bit at an angle which presents a diamond-shape cutting surface.
    And if you use carbide inserts (one of the suggestions in Harold's branch of the thread -- if you are not up to grinding your own HSS toolbits), *don't* use TiN (Titanium Nitride -- a yellow-gold color) coated carbide. TiN coatings rounds the edges slightly, making for duller tools. Aluminum wants the sharpest edge that you can get. The best of the carbide inserts are the ones which have been ground to final dimensions, instead of just formed as sintered to final shape which is common. (I've got some very small ones, in 55 degree diamond shape which fit the tool holders for my Emco Maier Compact-5/CNC which I sometimes use when I need a really sharp carbide on my larger machines, as they are ground to final dimensions.
    TiN coatings are good for other materials, such as steel, where they avoid BUE (Built-Up Edge -- an accumulation of metal which welds itself to the edge and destroys the resulting finish.)
    Good Luck,         DoN.
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I'm gonna quibble with this a little. Although I'm sure Anthony already knows this, someone else might find it interesting. A PCD tipped tool won't give you the best possible finish in Aluminum. PCD or Poly-crystaline diamond is made up of many diamond crystals. A single crystal diamond, usually a natural low grade gemstone, will give the best possible finish, since the cutting edge can be lapped to a flawless condition. With a PCD tool there is some "un-eveness" due to the multiple crystals. I have a polygonal mirror on my desk that was face milled in Aluminum with a natural diamond tool. Also, video tape recorders have drum heads that are turned with a single crystal tool. Look inside a VCR. The head is aluminum and that is a turned finish. Pretty amazing. Thing is, you need a damn good spindle and a very good servo system.
Dan
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Agreed Dan, however, within the budget of just about anyone, PCD would be the next choice. Monocrystal diamond tools in any useful size are *extremely* expensive. We do use some, but only in applications where the specific advantages they offer are absolutely required.
PCD grain size (PCD Grade) will determine, to a large degree, the surface finish you get. Using a fine grade (say GE 1500), will provide a better finish, but really should only be used for light finishing cuts, as you have much smaller diamond crystals which are easier to rip out of the binder along the edge. However, you do get a much smoother edge on the tool, with smaller binder gaps between crystals, hence better surface finish. You want to use a very coarse grained PCD tool for roughing operations. The crystals are larger, but the binder has a better grasp on the crystals, so they aren't as easy to rip out. You will have a rougher surface due to the larger gaps of binder between crystals, however.
Unless you are doing mirrors, or some automotive/electronics/NASA type stuff, the differences are unnoticable to the average machinist. You can really only see the differences when doing microscopic inspections of the surface.
--
Anthony

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<snip>

Anthony, I got a quick question for you. I read an article in IDR (Industial Diamond Review)a couple of years ago, where DeBeers did some test cutting in Titanium using PCD tooling. The economics looked pretty good. Have you had a chance to try them in Titanium? My Kennametal rep was going to get an insert for me, it was the same tool used in the study, but it wasn't available yet. I'd forgotten about it until now. I'd like to hear from anyone cutting Ti with diamond tools.
Dan
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Not cut any Ti with them....I'm wondering though, DeBeers brought out a 90 micron crystal size diamond for a while, a couple of years ago, mostly for testing. The results of our tests looked very good, but they claimed the demand wasn't there for them to produce it. I wonder if this is the same thing you are talking about.
--
Anthony

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I'll bet that was the tool. I showed the article to our Kennametal rep. to see what he thought of it. We have a really good rep., most tooling companies put their best guys servicing OEM accounts. Anyway he ws familiar with the tool as they were doing some testing with it and considering it for a new grade, IIRC. He was never able to get one for us to play around with. It seems every time I find something new for titanium it never pans out.
Dan
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Dan, Get in touch with your local Sumitomo rep. They have a large crystal pcd chip. Not the same as DeBeers, and more costly (Sumitomo is more expensive in general, but they do have better quality on some products). This might work for Ti, you'll have to discuss that with the rep. What kills us on Sumitomo is lead time. Most of the tools are made in Japan, so lead time can be an issue, if it isn't a stock item. The majority of what we use is custom made.
--
Anthony

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I've ordered some 2024 and 7071 stock. I have some 6061 already. Will try all three. I'm using a Taig lathe and the parts are small. 24mm in diameter and 6mm thick with a few holes drilled for lightening. I'm looking to buy some tools. Will these work OK? I have yet to find a source for PCD tools on the internet.
http://www.grizzly.com/products/item.cfm?itemnumber=G5639
Any place else to get something that will be better if these aren't up to the job?
Thanks! James
Anthony wrote:

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I am too impatient to wait for some tool bits to arrive. For aluminum I would use a steel tool bit and grind in more relief than you would use for steel. If you don't need lots of these parts, you can always finish them to a high polish using sandpaper in various grades. Walmart has sandpaper finer than 600 grit.
Dan
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Try Kennametal, Iscar, Vertex, Citco Diamond, and a host of others. They may not be shown in the regular catalogs, but about any style insert they have can be ordered PCD tipped.
--
Anthony

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