What are square end lathe cutters for?

[ErichKeane]

I bought a set of NOS lathe tools on ebay, and got a couple of square end carbide tools, but I have no idea how to use them! See https://www.amazon.com/American-Carbide-Tool-Carbide-Tipped-Neutral/dp/B00365FESO for an example.

I generally understand left vs right hand tools, but this one throws me for a loop. Is this simply for plunge cutting?

On top of that, I picked up a set of insert holders locally, and found a kenmetal insert holder that uses a triangular insert, but presents the whole side at once. Presumably for the same purpose...

 

[benmychree]

The example, to my experience is generally used for regrinding to another shape, such as radius form tools. The other one could be used for facing into a narrow slot, possibly.

 

[pontiac428]

This tool can be used as a rougher and a facing tool, depending on how you set the lead angle in your tool holder.

 

[RJSakowski]

It is a C style tip, used for chamfering, turning or facing or for custom ground tools. If some relief is set for turning, the leading edge will cut on an angle and tool pressure will tend to force the tool away from the work, preventing digging in and chattering. I like to use my tool for turning and facing on the same setup so I grind the carbide to an acute angle to have relief for both turning and facing.

 

[shotgun choker]

They are made like that so you can grind whatever kind of tool you want.