As a professional machinist I use around 95% carbide tooling and maybe 5% HSS. If you are using HSS by all means go with the the cobalt grades. They are much tougher and hold their edges longer. The minus part is that they are a bit tougher to grind. It is absolutely essential to have a properly dressed grinding wheel. A dressed wheel grinds easier and with far less heat buildup in the tool being ground. Use a medium to fine grit wheel on a quality grinder, such as a Baldor or other industrial grade grinder. The cheap imported grinders have flimsy tool rests and guards and typically won't have the power to keep the rpm of the wheel up and may have disappointing results. Cheap, lightweight tools won't hold up like a quality tool will.
As for the "junk" carbide cutters, it is probably more a problem of selecting the wrong grade. I use many imported inserts with excellent results. Here is an explanation of the grades.
C2- A bit softer grade with high abrasion resistance, used mainly on abrasive materials such as cast iron. This grade is also excellent for non-ferrous metals such as brass, bronze and aluminum, although aluminum tends to weld itself onto the carbide unless used with a cutting fluid. Kerosene works great and is much cheaper than store bought cutting fluids for aluminum.
C5- A general purpose grade that is useful in roughing and limited finish work. Its abrasion resistance is as its grade suggests, between C2 and C6. It will take a light interrupted cut but no carbide grade excels in this case. HSS is the way to go on interrupted cuts. C5 gives a reasonable good finish and is more forgiving of inexperience than the C6 and C7 grades.
C6 is a general purpose grade that gives a superior finish as compared to C5. As the grade numbers go up the carbide becomes less abrasion resistant and more brittle, but harder. This serves to hold the cutting edge longer and also allows the machining of harder metals with a slicker finish.
C7 is recommended for finish work. It generally doesn't hold up for roughing and will chip easier than the lower grades. This grade is commonly used in CNC work as a dedicated finishing tool for removing small amounts of metal at high speeds.
This is just a general recommendation and many jobs will require modification of the feeds, speeds, and depth of cut. This only comes with experience. I once had a sigh in my shop that someone had given me. It goes like this:
"We use good judgment in our work"
"That judgment came from experience"
"And that experience"
"Came from using bad judgment!!!"
Seriously though, there is a steep learning curve to contend with, and just having a lathe or a mill won't make you a competent machinist. You'll also need tooling, which in many cases will cost more than the machines themselves. You'll also need an analytical mind and a lot of patience. Math is as necessary a tool as a wrench or a cutter.
Many poor results of machine work are the result of improper speeds and feeds. To calculate any mill or lathe tool speed the following formula applies:
4 X SFM/diameter.
HSS tooling is most commonly used in the 40-80 surface feet per minute range. Carbide ranges from around 200 sfm to 600+, depending upon the material. I have just barely scratched the surface with these few hints, but these will help you get started with the results you need.
Have patience and above all, HAVE FUN!!
Mike Montieth
Rutherford Machine