ISO lathe toolholders and inserts

I've got a bit of an idea of how the ISO numbering system works for milling cutters but my understanding of turning tool numbering is sketchy to say the least. Might be a good time to brush up, as I am planning to buy some tooling for the Tree.

Numbering system:
Have a look at the Korloy cutting tools catalogue for a definitive reference. In the meantime, here's the toolholder system at a high level:

Thus, "DWLNL2020K08" is:

• D: clamp type ("top and hole clamp")
• W: insert shape (trigon - which has 80 degree tip angle)
• L: insert angle (95/95 degrees ie +/-5 degree clearance for trigon inserts)
• N: clearance angle (zero degrees - double sided insert!)
• L: LH or RH (left handed shank here)
• 20: shank height (20mm)
• 20: shank width (20mm)
• K: shank length (125mm from insert tip to rear of shank)
• 08: length of cutting edge (8mm)

NB: some turning inserts ("V" shape for instance) have long "cutting edges" relative to their size - this is a key difference between the numbering system for milling and turning inserts. Milling inserts seem to default to the "inscribed circle", which makes less sense for some turning inserts, given the wider variety of turning insert shapes.

NB: The Tree seems to be intended for 125mm length toolholders ("K" length according to the ISO convention). I may as well specify all toolholders to this length so that the tool length offset is pretty close and consistent for external tools.

The "N" (negative) inserts have zero clearance angle on the insert. The clearance is provided by the angle at which the insert is presented to the work. The upside of these inserts is that they are double sided, so a trigon insert thus has 6 edges (or corners depending how you look at it). They also require a more positive clamping solution than a screw to prevent the insert sliding off the toolholder into the workpiece.

Clamping types:

To date, most of my lathe tooling has used the screw ("S") system, using "positive" inserts where the front clearance angle in provided by the insert itself. Keeps things pretty simple but the alternative clamping methods look more secure and also come with the advantage that the negative inserts used are typically double sided. The tooling that came with the machine are the "clamp and pin" variety, while the Teknik branded trigon toolholder I bought from Cutwel recently had a "lever lock" clamp. I prefer the look of the "clamp and pin" flavour, not overlooking the availability of the various toolholders and inserts on the likes of AliExpress.

Turning Inserts:

For completeness, I need to be able to define / identify suitable inserts for any toolholders I have or obtain. Here's the ISO insert numbering system from the same catalogue. It's very similar to the milling insert system but clearly there are different insert shapes so it might be a mistake to assume they are the same:

As an example, a suitable insert for the toolholder example above might be "VNMG160404-MP":

• V: 35 degree diamond shape (definitely not a milling insert)
• N: zero front clearance ("negative" insert, where the clearance is provided by the toolholder)
• M: tolerance
• G: cross section type (suitable for a locating pin rather than a screw)
• 16: cutting edge length (16mm here)
• 04: height code for cutting edge (actually 4.76mm)
• 04: nose radius (0.4mm)
• VB: chip breaker shape (this will often be specific to the manufacturer I suspect)

"Handedness"(?) of the toolholders:

As noted previously, it's clear from the construction of the ATC turret that the Tree spindle needs to rotate "backwards" relative to a conventional manual lathe (ie clockwise) and present the toolholder with the insert facing up. Or in simple terms, external tooling needs to be "left handed". 

On the other hand, internal tooling should be presented upside down (boring bars) and the spindle needs to rotate conventionally (ie counterclockwise) for boring bars and drills. That's handy, as I'm not aware of having seen "left handed" boring bars. The only place I could imagine them being needed would be on a secondary spindle which sounds expensive.