-
Shorten the tips of center drills. (See Fig. 7-24)
F
IGURE
7–24
The tips of center drills
have less tendency to break if they are ground to about half the factory ground
length.
How many times have you inadvertently broken
the tip off a center drill? It doesn’t take much does it? A little bit of
run-out is generally all that it takes to break a factory ground tip. If you
grind the tip of a center drill to about half the factory ground length, it
will be much harder to
break.
32. Be aware that
HSS
will cut withless pressure than carbide.
This is one of the great mysteries of the
universe. Given identically ground cutters of
HSS
and
carbide under identical cutting conditions, carbide will cut with more pressure
for some reason.
-
Use a left hand lathe tool to make a right hand lathe tool.
(See Fig.7-25)
F
IGURE
7–25
A left hand brazed
carbide lathe tool is ground as a right hand tool. Tools ground like this
resist chipping and are easy to sharpen.
This is a trick I learned not too long ago.
The picture shows a left hand brazed carbide lathe tool ground to be used as a right
hand tool. Cutters ground like this work great, are more resistant to breaking
and are easier to sharpen than conventionally ground lathe tools.
34. Is it OK to grind
HSS
with a diamond wheel?
I’ve been finishing
HSS
cutters with diamond wheels for years and
have never had a problem. I like to use diamond wheels for finishing
HSS
because of the smooth, sharp edges they
produce. Smooth sharp edges promote cutter longevity and efficient machining.
Some people claim that grinding
HSS
with
diamond wheels loads up the wheels and renders them useless. I’ve never seen
evidence of it. Just to be safe, avoid using diamond grinding wheels to rough
off
HSS
.
35. Use “middle of the road” grade carbides
for the majority of your machining.
This is a complex subject that I prefer to
keep simple. Under laboratory and high production conditions you could probably
increase material removal rates and tool life by experimenting with different
grade carbides, coatings and chip breakers. For “run of the mill” low
production and prototype machining, good quality straight tungsten carbide
works well. “Micrograin” carbides seem to hold an edge a little better when
machining hard materials. Hard grade carbides such as C8 are very brittle and
chip easily. Since I am an advocate of high feed rates for removing metal
quickly, I prefer the softer but tougher grade carbides such as C2 and C5 that
don’t chip so easily.
Assuming reasonable feeds and speeds, the
rigidity of your setup, part and cutter and your ability to avoid “crashes”
will have more to do with how long your cutters last than just about anything
else. Another important factor regarding cutter life is chip packing. Chips
that can’t easily escape are destined to be recut which can significantly reduce
cutter life.
36. Use a piece of ejector pin to make boring
bars and other tools. (See Fig. 7-26)
F
IGURE
7–26
Ejector pins are ideal
for making cutter extensions, boring bars and other tooling. To drill and tap
through the side of an ejector pin you must first grind through the case
hardened surface.
The rigidity, accuracy, and hard surface of
ejector pins make them ideal for constructing boring bars, and cutter
extensions. To drill through the side of an ejector pin with a
HSS
drill bit, you must first grind through the
case hardened surface of the pin.