HSS versus carbide inserts, etc.

[Tinkering_Guy]

I haven't done much work with carbide tooling, other than the boring bar I used in my boring head to make my lens-cutting tool (scroll down).  And that left me with a chipped tool (no wonder, really, since it had to hammer at the work).

So I'm curious about carbide, and in particular inserts.  What I've read about it indicates it should be used at higher speeds and with deeper DoCs than HSS, and that HSS is often preferable.  However, most inserts seem to be carbide rather than HSS.  Why is that? 

And what about chip breakers?  Look at this set of indexable turning tools from LMS.  The supplied inserts are carbide TCMT, but the compatibility note says you can use HSS TCMW inserts.  Why the different geometry?  I can see using TCMW HSS on brass, but in general?

Thanks!

[Bernd]

So I'm curious about carbide, and in particular inserts.  What I've read about it indicates it should be used at higher speeds and with deeper DoCs than HSS, and that HSS is often preferable.  However, most inserts seem to be carbide rather than HSS.  Why is that? 

Here's a very well written article that may help at Gaget Builder's Website. Click on "About Carbide" in the upper left of screen.

Bernd

[Lew_Merrick_PE]

So I'm curious about carbide, and in particular inserts.  What I've read about it indicates it should be used at higher speeds and with deeper DoCs than HSS, and that HSS is often preferable.  However, most inserts seem to be carbide rather than HSS.  Why is that?

And what about chip breakers?  Look at this set of indexable turning tools from LMS.  The supplied inserts are carbide TCMT, but the compatibility note says you can use HSS TCMW inserts.  Why the different geometry?  I can see using TCMW HSS on brass, but in general?

Tink,

First of all, you need to learn about the grades of carbide.  Machinery's Handbook or a good supplier website (MSC leaps to mind) will provide the basics.  The next thing to realize is that cheap inserts usually have a reason for their lower price.  Purchasing good carbide tools and inserts will save what's left of your mind some wear and tear.  Carbide tools do not take hammering or chatter well.  They are very hard -- which means (mostly) brittle.  They do take "wear" better than HSS.  They have earned their place in our repertoire.

HSS can be sharpened more keenly than carbide.  That makes a real difference in materials such as (most) aluminums.  (Be aware that 6061 aluminum that has been allowed to sit for any length of time as a surface comprised of aluminum-oxide -- the same stuff you find in good sandpaper.)

NASA "got behind" tungsten carbide back in the mid-1960's.  The government "encouraged" companies to get into the carbide business.  Many thousands of man-years of government funded research has been put into carbide (and its derivatives) tooling.  HSS tooling was considered passe until quite recently.  It has not enjoyed the "encouragement" of government R&D money the way carbide has.

I spent the summer of 1975 doing comparison drilling for DoD while in college.  I was paid to take a Pratt & Whitney Hol-O-Matic drilling machine and compare: HSS, tungsten carbide, selenium carbide, and boron nitride drills for efficiency and length of life.  There were (about) 250 of us spread out across the U.S. doing such work that year.  In 1984, I oversaw a similar program (using BYU students) repeating that work to compare "coatings" on various drills.  Sintered HSS inserts did not start appearing commercially until a few years after the Swiss and German governments underwrote a program aimed at making them.  This is the way such things work.