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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What About the Chips?

Posted August 06, 2019 12:00 PM by Milo
Pathfinder Tags: chips machining manufacturing

Our customers are interested in what is left after we remove the chips. But it is up to us as operators and engineers to understand that there are differences in our chips based on process, material and tooling factors- and what those differences mean.

The infamous “Bird’s Nest Chip”

Process Differences

Turning can result in a long continuous chip, while sawing or milling processes result in shorter chips because of the interrupted nature of the cut. Drilling can result in the chips being recut depending on how the tool is fed and the nature of it’s spiral and means of chip evacuation.

Different materials can drive differences in the chips as well. I’m a steel guy, so my comments are based on that experience, but similar differences will be found in other materials, just based on different factors than Carbon.

Material Differences

Plain Carbon, Low Carbon Steels (C1008, C1010) tend to generate a more Continuous, Soft Chip. Plain Carbon, Medium Carbon Steels (C1030, C1045) can give a Continuous, Semi-Soft Chip. Plain Carbon, High Carbon Steels yield a Continuous, Hard Chip. Adding alloys can result in a Continuous, Semi-Hard Chip at lower carbon contents (4120) while higher carbon alloy steels can result in a Continuous, Tough Chip (4150) Very High Carbon Alloy steels (52100) give a chip that is both Continuous and Springy.

Having said that, I do not mean to say that all of these steels will result in long stringy chips- it is just that compared to Resulfurized Steels, such as 1117, 1144, 1215, or 12L14, the chips are far less likely to fracture into nice short pieces- often called “6’s or 9’s” or “C’s.” These chips can be described as Broken Semi-Soft (1117) or Broken Semi-Hard (1144) or Well-Broken Semi Hard (12L14, 1215)

Process Parameters

Finally, having the speed, feed, depth of cut, and angles on the tools is critical if we are to optimize material removal, minimize chip volume, and keep our process stable and maximize our uptime. Chip control features can also play an important role. ISO 3685 characterizes chips into 8 types- Ribbon, Tubular, Spiral, Washer-type Helical, Conical Helical, Arc, Elemental , and Needle chips. These can then be further described by length (short, long, or snarled).

Source ISO 3685

The ISO 3685 standard is a bit pricey, but it will help you to better understand what is going on in your turning process.

Of course you can look at the part, but to learn about your processes may I suggest that you take a really good look at the chips?


Editor's note: CR4 would like to thank Milo for sharing his blog, which can also be read here.

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Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

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#1

Re: What About the Chips?

08/07/2019 10:50 PM

Early on in my machinist apprenticeship was training on the proper grinding of cutting tools to get the desired chip while removing metal using various machine tools. For example, I was not allowed to use pre-made inserts on lathe tool holders. I was required to hand grind my own tools from cutting tool stock. For milling we hand ground end mills as necessary. Long strings of single "chips" was a no-no in my shop due to the obvious potential danger. And, being a research shop, we cut the entire gamut of materials; from plastics, to copper, to aluminum, to inconel, and everything in between.

Has this knowledge been lost with the disappearance of apprenticeship training programs?

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#2

Re: What About the Chips?

08/08/2019 8:09 AM

Although I did not attend a formal school or program, I was also taught to hand grind with a dip for breaking the chip. We were taught this way because store bought cutting tools aren't always available at sea.

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