Speaking of Precision Blog

Speaking of Precision

Speaking of Precision is a knowledge preservation and thought leadership blog covering the precision machining industry, its materials and services. With over 36 years of hands on experience in steelmaking, manufacturing, quality, and management, Miles Free (Milo) Director of Industry Research and Technology at PMPA helps answer "How?" "With what?" and occasionally "Really?"

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Feed or Speed?

Posted May 06, 2011 8:30 AM by Milo

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: http://www.ramasscreen.com/wp-content/uploads/2009/07/Flash-Adam-Strange-Aquaman.JPG

The Incredible Hulk: http://keneller.typepad.com/photos/uncategorized/2008/06/14/lou_ferrigno_as_incredible_hulk.jpg

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which originally appeared here.

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#1

Re: Feed or Speed?

05/07/2011 12:18 AM

Work-hardenable materials like stainless also benefit from relatively deep cuts and slow speeds--another reason to be in Milo's camp rather than Flash's.

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#2

Re: Feed or Speed?

05/07/2011 5:49 PM

Thanks Milo,

As a hobby machinist I need all the help I can get.

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#3

Re: Feed or Speed?

05/09/2011 2:02 PM

Tool wear is least with the depth of cut, then feed and finally speed.

Hence maximize the depth of cut, optimize the feed and use the lowest speed possible to get the highest tool life

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#4

Re: Feed or Speed?

05/11/2011 7:32 AM

There is another factor - the surface finish, which almost (not totally) contradict with the statement.

In fact we carry out lot of studies for a given material to optimise the process parameters (speed, feed and of course depth of cut) for different materials (which thankfully are not many types). The speed here of course is the cutting speed (which we convert to RPMs for specific jobs for operator's ease)

For rough machining your argument is OK. For finishing there is an optimum go too fast and you have tool rubbing instead of metal shearing and resultant frictional heat (and poor surface finish). Too slow the cutting parameters not achieved and you have again poor finish. Same with the feed too (High = lines or grroves, Too Low = rubbing). The depth of cut of course again has the dependence on bit nose radius and so on.

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#5
In reply to #4

Re: Feed or Speed?

05/12/2011 3:45 PM

My comment is only for rough machining. There is no question of taking a large depth of cut while finishing, which in itself is a contradiction.

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