Face Milling




Law of the Rubber Band – and Metal Machine Cutting Theory.

Growth stops when you lose tension between where you are and where you could be, John Maxwell. Oddly enough, I have witnessed this concept for years in the world of metal cutting or machining. Obviously the term, “machining” is used for the Mechanical cutting of metal. In the theory, a harder metal, alloy combination or more currently, a powdered metal composite (carbide) is used to cut or shape a softer metal. This can be on a drill press, lathe, milling machine, shaper, band saw, etc. The “cutter” needs only three conditioned in order to cut;

1) tool geometry

   Sharpness, cutting angle, rake angle, clearance relief angle

metal cutting

2) motion

     Rotating cutter, like a drill, or a stationary cutter with the material moving, like on a lathe or planer or combination, like on a milling machine where the cutter is rotating and the material is moving


3) pressure – load

     The cutting pressure, chip load, force necessary to engage the cutter into the work material.

Of course many more options can improve the cut; coolant, machine rigidity, proper work holding techniques, improved cutter geometry and material including high tech coatings etc. the list goes on but because this is not a machining post but a leadership concept, we’ll leave it at that. The point is that those three critical elements are absolutely necessary for any material cutting.  Where Maxwell says that we need that tension in our lives for growth, I see it as pressure, the number three element or condition for effective cutting. Here is the concept as I and every other machinist has noticed; I’ll use an example from my past.

I was on a large plate machining job. When I say large plate, I mean around 10″ thick 1018-1020 steel. This one was 60″ square. Used as a base plate for a large drop testing machine in the electronic testing market. The plate must be machined to a flatness of +/-0.010″ over the entire surface. We normally achieved much tighter tolerance than that. My machine passed its face cutter (a wheel that holds many carbide cutters and spins around 300-500 rpm via a 20 hp motor) over the plate in over 20 stripes or overlapping passes, back and forth removing small amounts of metal with each pass. Pete, my boss at the time let me in on a great secret. I was cutting material necessary to achieve the flatness spec and at this point I was just allowing the tool to remove a modest amount of material (perhaps .015” – .025”) because I didn’t want to overload the machine. In essence, only the very sharp tips of the cutters were engaging in the metal. What this does is for the first few passes, the cut looks amazing. The tool marks left on the plate are mirror like. The super sharp tips are smoothly cutting the material leaving a beautiful finish. The problem is that as the cutter travels across the plate, in time, because just the tips are in the metal, they wear and can chip easily. The issue here is not that the carbide is the wrong class, the plate is not the wrong material, the speeds and feed rates of the machine are not the issue, it’s the way the cutter is being used. Its condition # 3! You must understand that cutting tool design is much like the Law of the Rubber Band, and much like our lives. Here is the fix; go deeper, push harder, and engage the tooth! As the cutter makes a deeper cut, you might think that it would wear out sooner but the opposite is true. The tip of the cutter is tapered down to a fine point, the deeper the tooth is cutting, the thicker the profile of the tooth is. The deeper the tooth, the more pressure is needed, but the more support for the tip of the sharp cutter is in use and the tip stays sharp for longer. Think of it this way. My family has 4 girls; we go through packs of toilet paper like crazy. When my daughter goes to rip open a new pack of rolls, she may start with a sharp finger nail to cut through the thin layer of plastic, right? Maybe she makes a couple unsuccessful passes, then out of frustration, she jabs her whole finger into the package. Her freshly painted fingernail actually pierced through but not without the strength and support of her finger. She could scratch all day at that thin plastic but until she adds the appropriate (or even over abundance of) pressure, all she is doing is wearing out her pretty fingernail. Maybe a poor example but the concept is similar to me. John Maxwell thinks of it as tension, I think of it as load or pressure. I’ve seen it many times, the machinist is unaware, fearful or unmotivated so he adds the slightest amount of cutting pressure, the cutter just slips along the top of the surface, wearing out the sharpest points. There is zero load on the cutter so the machine is basically freewheeling. The part gets nowhere and the tool becomes dull and chipped. The answer is to lean in, push down, burry the cutter into the material. You will hear the load on the machine, the RMPs go down a bit while the load pulls the motor slower. The beautiful result is the cutter tooth is deep, pushing metal up the face of the cutter where it’s thicker, heavy and able to pull the metal chip up off the plate and fling it through the air revealing a fresh shiny machined cut.

I know in times of my life when I was just skipping along on the surface, not much cutting engagement, some level of comfort but in the grand scheme of things, was going nowhere. We cannot be afraid of the tension, the load. According to Maxwell, that’s where the growth happens. In Machining, that’s where effective cuts take place. I believe we were created to develop under load, to grow under load and to innovate under load. Obviously more effort is required to be effective. It’s my mission to see this load or tension as a desired state, not something to run from. I know I am hard wired to avoid any discomfort but I have seen time and time again, that’s not necessarily where I need to be.


Where do you lean into this load or pressure in your life?

Where do you avoid it?

What would be possible if you did decide to take on the tension, or load?

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