Product TechMet Turning inserts samples

[Susquatch]

I've read that the insert material, cutting edge, relief angles, chip breaker, and coatings are all different. But I'd bet a coffee that it's mostly the cutting edge that makes this performance difference possible. I'm thinking it's a lot like carefully grinding a sharp cutting tool out of Carbide instead of HSS.

@Dabbler @RobinHood ???

 

[RobinHood]

I believe it is mostly the geometry that is different. If you look at a designated Aluminum (or other non-ferrous material) insert, one will note the high rake angle and the relatively small top radius (ie, the insert feels sharp).

My dedicated steel inserts seem much more blunt with almost no rake (other than the tool holder induced one). This requires much more DoC in a steel insert for it to work properly - thus no “sneaking up by thousands” to a dimension. The tool “calibration” has to happen before the last 10-25 one thousands as the min DoC may be 10-20 one thousands (or more).

This takes trust in your machine/tooling.

With “sharp” inserts (like the ones for aluminum and SS), much smaller DoC can still make the insert work properly, leaving the option to sneak up and have good surface finishes. (The kind of things hobby machinists like/want.)

HSS tooling is more forgiving (because it is usually sharp) than carbide inserts. Carbide does not like being razor sharp - it has a tendency to chip. Polishing the edge helps reduce that.

 

[Dabbler]

Just caught this thread again...

I think it is the grind that makes it possible. The edge *will* wear down much quicker than a traditional insert. But then it will perform like any normal carbide insert. That's my experience. They are more fragile, so the tip will break off if you hog the cut in steel.

I use regular inserts to get close, then use a ground insert for aluminum to make the nice finish and get the dimension.

 

[DavidR8]

I recently watched two videos on making balanced cuts so that a person doesn't sneak up on the finish dimension.
One was by Stefan G, the other was by Jon's Workshop (great channel btw)

 

[Susquatch]

making balanced cuts so that a person doesn't sneak up on the finish dimension.

I use balanced cuts for large balances and for small balances. I don't count on being able to take spring passes to hit my dimension. Too often, that approach takes too much and you can't put it back.

By that, I mean that you can take large cuts (10 - 20 thou) to determine how much actually comes off for a given setting so you can get there by balancing the cut (this is what I would call the normal method), but you can also get there with a very sharp HSS tool and very small balanced cuts (1 to 3 thou with tenths) to hit a tighter sub thou dimension. I cannot personally reliably hit sub thou dimensions with large balanced cuts, but I can with HSS & small balanced cuts. It's really just scale. Large balanced cuts to get within a thou and small balanced cuts to hit sub thou.

What is new to me here, thanks to @Dabbler & @RobinHood, is the use of an insert for aluminium instead of sharp HSS. In my ignorance, I had always assumed incorrectly that aluminium inserts were not as strong as inserts for steel and would fall apart on the first cut in steel. Using an insert for aluminium to shave a grade 8 bolt put that old belief in its grave forever. I have lots more to learn about it in the months to come.

I'm hoping Santa brings me a top notch carbide threading tool with threading inserts for aluminium for Christmas. THAT should be INTERESTING!