Last month we covered a simple overview of what edge
preparations are, plus we went into a little bit of detail about the main
types. In this installment, we are going to delve deeper into the details of
each edge; we will cover some of the what's and why’s and give a bit of insight into how to tell what is on
your tools currently.
The first edge we are going to talk about is a simple razors
edge. The “sharpest of the sharp.” Great for slicing and dicing but is it
really what you want on a tool? According to the Oxford dictionary the term
razor comes from the French word “raser” which means; to shave closely. We in the tooling industry need a definition
that is more…descriptive. In order to “shave” or take a little off you need to
have a small thin edge. You see, an edge is when two angles come together to
form a point. A razor edge would imply that the angles involved are very steep,
creating a sharper edge, but the material to reinforce it would naturally be
thinner. Below, is a picture of a razor edge taken with our Walters Helicheck
Pro at 1000x magnification. As you can see, the line running diagonally across
the photo is the actual edge. All the areas that go from light to dark are
chips along the edge. Your naked eye would never see these, but they exist.
This is where edge prepping becomes important: if you leave a straight razor
edge with little reinforcement, depending on the material that you are trying
to cut, the results could be catastrophic. Blown out tool, scrapped workpiece,
and possibly damaging the work holding device. All those micro chips in sharp
cutting edge can fracture to create larger chips, which of course result in
poor performance of the tool.
(Razor Edge 1000x Mag)
So, if you are cutting plastic, rubber or wood with a
carbide drill, a razor edge should be acceptable with proper chip evacuation.
Generally speaking, if you are cutting any form of metal or any material that
is 40 or higher hardness on the Rockwell B scale, then we recommend using an
edge preparation of some sort.
(Razor Edge Chart)
The above chart comes from our Helicheck Pro. What you are
seeing is the measurement of the edge from the tool previously pictured. In
this chart, we see that the edge radius on a “sharp” tool is an incredibly
small 0.0003”.
Before we delve into the two other types of edge preps, it
should be mentioned that the size of various edge preps have a wide range -
from as small as 2 or 3 tenths of a thousandth (0.0002” or 0.0003”) up to 4
thousandths (0.004”). The size of edge prep you need will depend on the
application and feed rate being used. You will want to speak with your tooling
representative concerning the specifics for your application. We as Komet
Service providers know that the reps at Komet are required to go through
extensive training on edge preparations and their applications. Knowing this
information will also help to increase tool life in the regrinding arena. Not
all regrind shops can match a specific edge preparation, and even fewer can
check them. CountyLine-Tool is one of the few regrind service providers in
North America that have the ability to check specific edge preparations.
The most common edge prep, and probably the easiest to
understand, is referred to as a hone. This style of prep creates a radius at
the edge that serves two primary purposes. First, it strengthens the edge. In
reference to the image of a “sharp” tool, non-honed edge looks like a miniature
mountain, very jagged. These jagged features are micro chips in the cutting
edge, and grow exponentially upon impact with a work piece. By smoothing the
edge, the problems created by micro-chipping are reduced dramatically. This
smooth, solid surface has major advantages in increasing the ability of a
coating to adhere to the cutting edge, thus retaining the properties and
benefits of the coating. The hone is going to be the edge preparation with the
most structural integrity. Hones are recommended for most general-purpose
machining - especially in non-production shop environments where job types and
materials may vary between uses.
(Hone at 1000k)
(3d Image of the same hone)
As we discussed about the razor edge the hone is much more
smooth. This allows for better adhesion by coatings that are applied. Another
advantage this smoothness offers is that the work material is less prone to
stick to the edge, allowing for greater feeds. So if you are cutting a gummy
type of material a hone combined with a chip breaker on your tool would help
with chip evacuation and allow for better cuts. You will also notice that the
edge is rounded very much like the razor edge, the difference is the thickness
of the material. This thickness is the reinforcement that was discussed before,
with additional material backing the edge, it is able to handle more abuse
before succumbing to chipping.
(Hone Chart)
You may notice that the shape of the edges are very similar
from the razor edge to the hone but the SIZE is the factor to look at. In this
hone, the radius is .0012 – four times thicker than the razor edge. While not
always noticeable to the naked eye, this micro detail makes a big difference in
the life of your tools.
Finally, we have a K-land – completely different in size and
shape. The intent of a K-land is also completely different. When you are new to
tooling we all think that drills are the same, they are not…at all. To put it
in perspective when dealing with the geometries of these tools vs. something
you buy at a big box store and even the standard tool steel drills, it is like
comparing a Focus to a Caddy, to an F-1 Racer. High performance drills with a
K-land are basically your F-1 racer, they are intended for high production,
high volume. They have been specifically designed for the material they are
recommended with.
K-lands have a very specific use: to breakup chips into
smaller pieces to aid evacuation. This will allow for more efficient cuts and
faster feeds. Obviously, this style of edge prep is designed specifically for
production environments. Not only do you get the benefits of reinforcement of
the edge but you still get the smooth surface to adhere coating to plus there
is that final benefit of extra chip removal making it the prime candidate in a
production environment.
(K-land at 1000k)
(3d Image of
a K-land)
If you look at the shape of a K-land it is obviously
different from the other two, K-lands have a specific “flat” this acts as a
mini chip breaker and is what gives the K-land its advantage over the
competition. Now unlike the hone it is very important to know the material you
are cutting and what speed/feed you will be using in determining the size of a
K-land you need.
K-lands obviously range in size but your tooling expert
should know what size should be used based on what you are trying to do. With
just a little information that specialist will be able to hone down and
determine what size will be most helpful for your use. In the chart below you
can see the K-land is 0.0028” this size of a K-land would likely be a general purpose
usage, to cut into gray iron or steel. When you are talking to your tooling rep
make sure you have all the pertinent information ready and available so they
can best assist you in what will give you the best results. But how do you
identify if there is an edge prep on the tools you are currently using?
(Chart of K-land)
All of this information is pretty useful but unless you can
tell what your tooling has it really does you no real good. So you need to be
able to identify what type of edge your tools have. You will want to purchase a
loop of some sort, doesn’t have to be super fancy but a light and small
magnifying glass. From there you can look and see a general shape. IF there is
a flat you may be able to see the light reflect off the tool with out a loop.
For a hone it will be rounded and thicker than if you have a razor edge. Now go
get your loop and take a look!
