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What’s it gonna be? Feed or Speed?

For a given production rate of metal removal, better tool life is obtained by using heavy feed and low speed.
 Sorry, Flash.
Less horsepower per cubic inch of metal removal is required for heavier feeds (see the diagonal lines on the chart below.)

This also means  fewer revolutions of the work (or tool) to get the job done.
This reduces wear on the tool.
Slower speeds results in less friction, less heat.
Surface finish declines as feed rate  increases, but  it is usually acceptable until a critical rate is reached (see  the numbers along the curves above- they are the values for surface finish in RMS).
In steels, grades that are rephosphorized and renitrogenized can take heavier feeds than steels that are not. (That’s why I’m showing C1213 at 0.07-0.012 phosphorous compared to C1215 at 0.04-0.09 Phos.)
Here is another graph to illustrate the effect of feed rate and surface finish.

As feed rate increases bottom (horizontal) axis so does surface roughness (vertical) axis measured in RMS.
The contract shop industry remains seduced by the siren song of speed to reduce cycle time.
Perhaps the proper use of the feed approach can make you some new friends among your customers…

These data are based on HSS tools. Obviously using carbide one needs to have sufficient speed to take advantage of the carbide.
Bottom Line: Increased feed rather than speed can result in longer tool life and less problems than increasing speed and  dealing with the heat that results.
What is your approach? Speed for cycle time? Or feed for  minimizing HP for removal and longer tool life and fewer problems?
Feed or speed? What’s it gonna be?
Photo credits:
The Flash:
The Incredible Hulk:
Playstations’ genius image of  Finger of the Hulk beckoning link:

5 thoughts on “Feed or Speed?

  1. Mike says:

    I find it very interesting that most of this type of data is based on HSS tools. I know in Swiss turning, most of the tools used are carbide, either off the shelf or ground. Carbide and cermet tools make a world of differance and are not always used “by the book” when it comes to speed, feed, surface finish, and tool life. We strive for the maximum tool life at this shop, because we like to tryu and run everything lights out. That still makes cycle time important, but not as important as tool life management.

  2. speakingofprecision says:

    Mike, thanks for the thoughtful comment. Tool life management is an important aspect of what I call ‘predictable production.’ Trying for maximum tool life is a strategy that aligns cost, quality (reduced variability) and reduces shop “management by crisis.” Thanks for sharing your comments.

  3. Kevin says:

    Well, I guess if you have to choose, choose Feed; since feed=money. You are paid to remove material! However, as you mentioned, carbide likes higher Speeds – being able to handle more heat and less pressure than HSS tools; and in most cases, carbide is the choice for high performance machining.
    It has been our experience, that when customers are struggling with their machining process (low tool life, poor part surface finish, etc..), increasing the Speed has solved the problem more often that not; maybe it’s because they have already tried reducing the speed and if it hasn’t helped then they call us…
    So Miles, obviously the answer is “it depends” (on the situation); but, once again, you got your point accross in a rather enlightening fashion.
    Absent of having to ‘choose’, and with the luxury of the proper resources for study, I would suggest increasing both Feed and Speed – all-the-while monitoring the effects on the process – and let the chips go a flyin’.
    Kevin Johnson

  4. speakingofprecision says:

    It’s always nice to “hear from one that’s doin,” Kevin. Thanks for sharing your experience. As you point out, it may in fact be both Feed and Speed, and if carbide, it’s very likely Speed.
    But as you noted I was trying to help people reconsider their focus on cycle time vs material removal.
    Folks Kevin is with Fischer Special Tooling and has more than a little experience in these matters.

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