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I am very new to machining.

I have access to a metal lathe that was once part of a small commercial engineering workshop. The available spindle speeds are in the range 65 to 2000 r.p.m. The existing cutting tools are all replaceable insert tools, all carbide. I'm wanting to machine a piece of aluminum round bar 1 inch in diameter.

When I look at the recommended surface cutting speed for a high-speed steel tool, it is in the range 500 - 600 feet/minute, which converts (given the 1 inch diameter of the stock) to a spindle speed of 1910 - 2292 r.p.m, or, in other words, just at the upper limit of the available spindle speeds on the lathe. For a carbide tool, the recommended speed in around 2820 feet/minute, which converts (again given the 1 inch diameter stock) to a spindle speed in excess of 10,000 r.p.m., which is well above the capacity of the lathe.

What would be the typical way in which a commercial shop would deal with these limits? I can think of several possibilities but have no idea whether any of them are correct.

  • Never machine small diameter aluminum
  • Only use high-speed steel tools
  • Use a kind of carbide of other tip that has specifications that fit within the capabilities of the lathe (Does such a thing even exist?)
  • Something else?
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  • $\begingroup$ Why are you asking what a production shop would do? You aren't a production shop. You two have different priorities. In other words, is this question out of curiosity or are you asking how you, yourself, should go about machining 1" aluminum stock? You can afford to run HSS or run uncoated inserts with high positive rake for aluminum at a slower surface speed. A production shop can't afford to run HSS or slower surface speeds. And if your lathe is manual, production would be using CNC lathes which can spin much faster for how large they are. If your lathe is CNC, 1800RPM seems real slow. $\endgroup$
    – DKNguyen
    Jul 15, 2022 at 13:36
  • $\begingroup$ Technique also depends on how many parts are being made , a few or a hundred thousand ? And alloy, some high silicon aluminum alloys are abrasive and cause more tool wear. ASM has books on metal machining that would be helpful. $\endgroup$ Jul 15, 2022 at 15:08
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    $\begingroup$ HSS tools would be a good investment. You could also cut slower, minding how hot the tool gets and whether chips are getting stuck to the tool. It is just aluminum after all... $\endgroup$
    – Abel
    Jul 15, 2022 at 18:23
  • $\begingroup$ The reason I'm asking about a commercial shop, which is where the machine came from, is because I'm interested (as I had hoped I made clear in the question but obviously didn't) in how a commercial shop would deal with the (apparent, but perhaps not actual) limitations the machine imposes, especially given that this kind of machine, is still sold as being suitable for a commercial environment. $\endgroup$ Jul 16, 2022 at 7:08
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    $\begingroup$ recommended speeds are for optimum metal removal at maximum temperature. If you haven't got that speed, go slower for (normally better tool life). You will get poor surface finish and may chip your tool if you go too slow, but that is well bellow "optimum" speed. Aluminium is cheap, so commercial shops will just try it and see what the result is. $\endgroup$
    – david
    Jul 27, 2022 at 8:17

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Use tools etc within the capabilities of your lathe and the materials that you will be working on.

Whatever has the lowest limit is the limit to be followed.

There are books with lots of machining info which give that sort of data. I would just ask my sons as they know most of the limits etc from memory as they did machining apprenticeships.

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  • $\begingroup$ I think that may be overly cautious in this case. He probably can turn the aluminum at a slower than optimal speed, with slightly poorer results. I personally agree with davids comment that a commercial shop would likely just try it, and see what kind of results they can get at a lower speed. $\endgroup$
    – Drew
    Dec 13, 2022 at 9:59

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