Pardon me for hijacking this thread. I hope to answer Bobw, and a few other person's questions. If the moderator disagrees, please delete, or move my responses. I am not up on board etiquette.
Bobw; high speed inserts are superior to carbide in many applications. A good use is in the cutting of inconel and many of the really gummy stainless grades. When used at slower surface speeds, they will last longer and are not prone to crack shatter, like ceramics and carbides. Gummy materials will cause a hammering effect and destroy the harder cutting materials. Some have pointed out, and I agree, that gummy materials grab and cause suck in and a hammer effect. I have seen loose tailstocks sucked in and carriages pulled in when cutting with positive rake tools. I have also seen negative rake carbides totally screw cast nylon, aluminum, and 360 brass when the cross section gets thin. Instead of cutting, they like to push the material away. Suddenly a 0.005" cut becomes a twenty thousanths cut after the push gets big enough. If the edge is not perfect; they will wipe the finish.
High speed steel is far superior in applications where there are intrerrupted cuts. Just today I took a piece of square sugar maple and tried to make tool handles. On the first pass, while I attempted to round a three inch square chunk, in a Sharp eighteen inch gear head lathe, the Kennametal negative rake cutter bit broke off from the vibration. I was pissed because that was my last good cutter bit insert. I had to get an old piece of 3/8" M2 and grind a roundnose tool. I then put the cutter in the Aloris holder to finish the task. A seven dollar insert was shattered by wood and a castoff chunk of M2, that I brought from home, made a perfect job.
Carbide and ceramic suck at slower spindle speeds. I have to make parts on many underpowered and slow RPM machines. My employer's Bridgeport CNC will not go much over 4000 RPM without disaster. For today's machines, that is a snail's pace. The Jet lathes at work will not take carbide. The less than rigid toolposts, and slop, snap carbide like a sledgehammer. At home I use South Bend lathes and those old belt slappers are rigid enough for carbide. Unfortunately the spindles are turning at Model-T and 490 Chevy speeds. They do better with T-15 inserts or M2 ground bits. Negative rake eats horsepower and many machines, even new CNC machines, do not have the horses.
I use positive rake inserts in shell mills to get good finishes. Many times I just remove all but one insert. Guys laugh when I face aluminum in a CNC mill and use a fly cutter and a piece of T-15 for a bit. It is like the perfect meld of ancient artifact sticking on a quickchange #30 shank. That old tool sits in the tool lineup sandwiched in with all that new high tech stuff.
I bore deep holes with solid carbide bars, while there is a nib of old round M2 on the end. The positive rake M2 does not eat horsepower. That means less deflection with less passes.
Every farm boy knows that the old herd dogs are over the hill. They are blind, slow, and weak. A retriever, belgian, or any fighting dog comes head on. The old border collie will circle around and get you from behind. They turn a weakness into an asset. I have seen an old fawn collie whip a three year angus bull, in the bull's pen. After a few well placed nips to the balls and other tender parts; the bull was ready for a halter.
High speed steel and shaped W1 are old. Their time has passed. That does not mean they can not adapt and overcome. Most fellows today think of M1, M2, T-15, and W1 as crap. All they have ever seen is chinese mystery metal and the cutter bits that have the good stuff at the minimum of the grade spec. Take a walk on the wild side. Buy a few quality T-15 inserts for your tools. What can go wrong? They will cost a lot less than the latest exotic insert. If they last half as long, they still are the better buy. The bottom line is cost per cut. Who cares if the insert lasts all day? The purchase price eats into your profit. Just throw the high speed insert away every four hours. It is cheap. Adaptability is just a bonus for you.
