Carbide insert positioning for turning and facing

C

Clunker1

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I've begun using carbide inserts recently. I am a little confused as to the positioning of the leading edge on the insert. According to some YouTube videos, the leading edge is positioned raked away from the cutting direction rather than toward the cutting direction as a hss toolbit is ground.

Am I over thinking this and should just position the holder perpendicular to the part? What about when facing?

Thanks
 
I suspect you are referring to type C or W inserts. The normal presentation of these inserts gives 5* clearance for both turning and facing. Some boring bars using triangle inserts have a negative angle on the end so they can face the bottom of the hole.
 
The holder should be perpendicular to the part, i.e. the holder is parallel to the face of the chuck. Inserts that are used for facing have a relief behind the insert cutting tip. It all depends on the insert type and the cutting angle.
 
Inserts like feed, speed and cutting depth. The results depend on the rigidity of your lathe, tool setup and material you are turning. Rigidity is important so let the tool stick out as less as possible. Keep the tool above the tool post and use the power feed.
Experiment using higher RPM (results most of the time in better finish), deeper cuts and faster feeding. You can probably hear when you are reaching the limits and see the finish degrading. The settings on the insert box are optimal for a rigid lathe. Most of the time I use the advised speed (Vc) but can't come close to the advised cutting depth (Ap) and Feed rate (Fz). The result is that I can't use the full cutting edge of the insert. So it doesn't make any sense to buy the large inserts. I go for the smallest and cheapest ones (CCMT060204, dcmt070704, TCMT110204). On my bigger lathe, I use the same type inserts but with a 0.8 mm nose radius (CCMT060208, dcmt070708, TCMT110208).
Inserts tend to break. Buy the cheap ones until you don't break them anymore but wear them down.
 
I bought some turning holders that use double sided inserts that have negative rake in holder for clearance. Don't seem to be very forgiving with mixed results. Like you said maybe not using enough feed and speed as I got started with hss. I do find that my boring bar using one sided tcmt is easier for me to use. I'll look into some of the inserts you mentioned.
 
Clunker, There are double-sided (negative rake) inserts available with positive rake molded in chipbreakers.
 
Clunker1 said:
I'll look into some of the inserts you mentioned.
Click to expand...
If you don't cut deeper than the tool nose radius, only the tool nose radius cuts the material and the insert geometry (First letter is the geometry, last 2 digits the nose radius DCMT060208,TCMT,CCMT,WNMG) doesn't matter. On my 2 Chinese bench top lathes, most of the time, i don't cut deeper than the tool nose radius.
I will make a video showing the cutting performance of some inserts I use next week. Even on a mini lathe you can do some "serious" cutting:
 
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