Parting, HSS vs Carbide insert

I have an EMCO Compact 8 bench lathe so just hobby grade, neither rigid nor powerful but I use carbide inserts only because I don't like doing tool grinding. My experience is that for light machines of this kind the insert need be quite sharp or it wont cut into tough materials such as 304 stainless. I have two boxes of not-so-sharp parting carbide inserts which I bought some 20 years ago and they are still sitting in the box.
 
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compact8 said:
I have two boxes of not-so-sharp parting carbide inserts which I bought some 20 years ago and they are still sitting in the box.
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They are not difficult to sharpen, you just need a cutter with a harder material than the carbide. Diamond works very well, and is not that expensive, especially given the increased cost of the carbide over HSS. Save those dull tools from being wasted!
 
Bob Korves said:
They are not difficult to sharpen, you just need a cutter with a harder material than the carbide. Diamond works very well, and is not that expensive, especially given the increased cost of the carbide over HSS. Save those dull tools from being wasted!
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In addition to that, there's a perfect video for that from a great machinist who likes to share his tips with us :
 
OP what does your cutter geometry look like? I use a cheap Chinese HSS one too but it's not a problem.
 
Unlike turning tools with which you can control the depth of cut, you have limited freedom for parting tool because the width of blade cannot be arbitarily small or it will not be rigid enough. 1.5mm is the narrowest tool I can get and it works OK on my bench lathe ( Emco Compact 8 ). For soft materials such as brass, aluminium or 12L14 steel, it's OK but for 304 stainless steel, it just barely works. I have not tried it but parting other harder materials is probably not possible with my lathe.
 
Going back to your concern. This chart shows that the machinability of 4130 steel ( annealed ) is 75% ( bigger number = easier to machine ) compared with 45% for 304 stainless and 170% for 12L14. The use of HSS parting tool should not be a big problem but again, it will depend on the blade width, rigidity and power of your lathe.

Machinability Comparison Chart - provides percentage scale of machinability of various metals indexed on 1212 carbon steel: carbon steels, alloy steels, stainless steels and super alloys, tool steels, gray cast iron, nodular cast iron, alumunum all

Machinability Comparison Chart
www.carbidedepot.com
 
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