HSS cutters vs Cutters with inserts

Certainly you can choose between them, but your machinery should be the dictating factor. Carbide doesn't perform well on small (light weight, under powered and slow speed) machinery, nor is there much of an advantage in using it unless you use it as it's intended to be used. When operating a mill, there may be certain advantages to using carbide in lieu of HSS, but, in general, unless you have a fairly rigid machine and run the cutter appropriately, you may find it performs poorly. Carbide is much improved as compared to years ago, when I broke into the trade, so it is far more forgiving than it used to be. In either case, HSS, or carbide, on milling cutters, you can't do much in the way of sharpening unless you own a cutter grinder, so in that case it makes little difference.

Lathe tools? That's a different story. Do yourself a favor and don't use carbide exclusively. You'll deprive yourself of the learning process of grinding cutting tools, which, in the long run, will be to your detriment. Until you understand cutter theory, you'll suffer with machining. You'll not learn it by using inserts. If you have a small lathe with slow spindle speed, I'd suggest you don't use carbide at all.

Harold

In general:

HSS tools can be ground sharper that carbide inserts. A properly ground HSS tool can produce a smoother finish than a carbide insert. Carbide inserts can remove more metal faster than HSS tools. Carbide inserts tend to chip on interrupted cuts, HSS tools don't. Carbide inserts wear better than HSS tools, espcially on hard or abrasive metals.

Ed

What Harold said, plus this advice: get a GOOD grinder to shape & sharpen your HSS tools. I finally got one and suddenly I suck much less at tool grinding than ever before!

My good grinder is a used Rockwell that was surplussed from a local business. All my previous cheapies are relegated to spinning polishing wheels after I know what a real grinder acts like.

Fred, what was different between cheap grinders and the good onethat you have now?

I have one 1" "little hogger" style carbide insert endmill. It cost more than a regular 1" endmill, but it can be fitted with new cutting edges for about 60 cents (it has 2 triangular inserts, so you get 3 sets of edges for about $2.00 on sale.) For rapidly removing a lot of material, planing off the top of some piece, etc. there is nothing that will beat it.

I use almost NO real HSS anymore. I use some Cobalt-HSS end mills in the larger sizes, such as M-42 and M-57 in 3/8 to 3/4" diameter. For 1/8 - 1/4", I have moved almost completely to solid carbide end mills. They can be had for ~ $3.00 each in small quantity on eBay, and the quality is very good. (There are also some plain HSS cutters from China that are execrable! They look like they were free-hand sharpened by an 80-year old blind man, and that is doing a disservice to the blind and elderly! These things come in blue 2-piece plastic tubes with a paper label, with the size rubber-stamped on the label. If you see those, run!)

I find the M-42 and M-57 cutters last 3-5 times longer than plain HSS. Stellite is also very good, if you run across some of them.

I also use some Mo-Max cobalt lathe cutter blanks in my fly cutter, and it does a VERY nice job, and needs to be sharpened every few months! The chips come off blue and smoking. I could probably run it even harder, but I can't stand the burns from the chips.

On lathes, carbide with negative rake inserts are great on machines with the power and rigidity to use them, but there is little negative rake machining done on mills, I think. Pretty much all standard milling cutters are set up for some positive rake. So, there shouldn't be any concern for rigidity and power when making the decision between the cutting tool materials. On the other hand, Carbide works best at much higher cutting surface speeds, so a higher spindle speed will be a great help when using carbide. A 1/8" cutter in aluminum comes into its own at

Jon

I use some carbide and some HSS. I use carbide indexed end mills when planing or to mill torch-cut steel. You can go a lot faster. I tend to use HSS end mills a lot too. On the lathe, I sometimes used brazed carbide tooling for interrupted cuts, seems to hold up a lot better than indexable. I do use indexable carbide lathe tooling a little, even on my little 9" South Bend. But mostly I just use HSS. I bought a carbide cutoff blade, uses GTN-3 inserts, and a nice block to hold the blade. It doesn't work nearly as well as a rear-mount toolpost holding a regular Armstrong toolholder with a .095" cutoff blade, HSS. That sucker flat works, even on a small lathe.

If you have a mill with an R8 spindle, you might look into one indexable endmill, say about a two-incher, holds 3 or 4 3/8" negative rake inserts. The import versions of those really work, and they don't cost much.

GWE

It was hard for me to understand that when you said:

"Pretty much all standard milling cutters are set up for some positive rake. So, there shouldn't be any concern for rigidity and power when making the decision between the cutting tool materials."

The negative rake insert shell mills I spoke of are included in the group of cutting tools that are considered *standard*. A general statement that insert cutters are positive in nature simply isn't true. That was, and is, my point. You are wise to not try them on light duty machines, and, I agree, the home shop is highly unlikely to have machines that can handle such cutters, but some do.

Harold

Thanks for all your answers posted or going to be They bring me some lignths in my darkness ;-)

Yup, I was just trying to simplify what can get quite complex, and went overboard. I suspect you could use a cutter with 2 negative rake inserts on a Bridgeport, but probably anything lighter than that would have a problem with even two inserts on the cutter. The original poster didn't describe his machine, so that makes it harder to recommend anything. I know some Bridgeport owners have gotten a steal on a big multi-insert shell mill, and ended up taking most of the inserts out to keep the machine within its power and rigidity limits.

Jon

For 18 months, just prior to starting my own shop back in '67, I was employed by a real nice job shop in Salt Lake City, United Precision. They had a few Bridgeports on which they ran a small insert carbide cutter, but I'll be damned if I can recall if they were positive or negative. I seem to recall positive, though. I spent my entire tenure there on lathes, so I didn't use them. At any rate, I think they had three inserts, and were relatively small, maybe 1-1/2" diameter. It was about all a Bridgeport could handle at that time, but remember they had only 1-1/2 horse motors. The 2 horse models with vari-drive came along much later, something like early '77 if I recall.

Your comment about great buys on large shell mills for light machines really brings a smile to my face. In truth, what they really bought was a large, expensive fly cutter. Before some of these things make sense, often a guy must see how they are put to use properly. Only then will the novice come to understand the huge differences in machines, and understand their advantages and limitations. Large multi-toothed cutters require a huge amount of power and rigidity in order to function anywhere near their capacity. Anything less is a waste---particularly in tool life. Cutting tools don't like to idle--it's tougher on tool life than making a cut.

Harold

Much better rigidity and balance.

There could also be an effect from the previous owner having dressed and trued the wheels better than I have.