"Rex B" wrote in message
...
A comment on surface finish. Mild steel, which appears to be the
topic
of discussion, is amongst the worst of materials to machine in that it
loves
to tear. Only when carbide is employed along with a high surface speed
and
proper depth of cut and feed will it cut otherwise. The addition of
lead to steel makes it machine beautifully----so if you'd like some
success
with surface finishes, try machining some of it. Your metals supply
house
could provide you with proper designations.
Harold
OK, so for us stateside folks, if I want a free-machining leaded steel
round 1.25 diameter, what do I ask for, and where?
Rex B
You've noticed that 12L14 has already been mentioned a few times. It's not
the only free machining mild steel, however. There are others, commonly
known as screw stock, or material for screw machines. 1213 and 1215 are
two more numbers to keep in mind. These two are resulphurized and
rephosphorised to improve their machining qualities, and contain no lead.
They are rated @ 136% for machinability, based on 1212 @ 100%. 1018 has a
machinability of only 78% as compared to 1212, so it's clear that these
materials are far superior for machining, although they may suffer in
mechanical areas. They are not recommended for parts subjected to severe
fatigue stresses.
In addition to 12L14, there is another leaded material, 11L17, which is a
high manganese alloy. It has good machining qualities and can be
carburized, in spite of the small amount of lead in its makeup. 1117,
without lead, isn't quite as good for machining (rated @ 91% based on 1212
as 100%), but is still far better than 1018.
If you require a tough material with excellent strength, but don't want to
heat treat, consider using Stressproof (1144 Hi Stress) or Fatigue -Proof.
These materials have excellent machining qualities, along with tensile
strength far superior to the other materials. Stressproof and Hi Stress
have a tensile strength of 100,000 PSI, and Fatigue-Proof is greater at
140,000 PSI. All of them are rated at approximately 80% machinability as
compared to 1212 @ 100%. These materials cut very well, without tearing,
and tend to cut better with HSS than carbide, at least from my personal
experience.
Where? Large supply houses have them. I used to buy from Jorgensen Steel,
now known as EMJ.
http://www.emjmetals.com/emjonline/index1024.htm
Harold