There are a number of different grades of cast iron and within these there are a number of different qualities depending a lot on the casting method. Sand castings that are found a lot in model engine kits can have holes, variable grade and often a very rough surface. The initial machining of these sand castings can rapidly chip and damage fine tungsten carbide tipped tools.
Lathe tool angles for turning cast iron:
|Material||Side clearance °||Front clearance °||Side rake °||Back rake °|
I always use Tungsten Carbide Tipped (TCT) lathe tools when turning cast iron.
These tools have a steel body with separate TCT bits that are pre-machined to the correct angles. When the bit wears out or gets chipped then you just replace it.
Note that when machining rough castings it is very easy to chip the tools, so take that into account and use small cuts at first or use an old TCT tool for the initial cuts.
The image on the right shows a piece of continuous-cast cast iron in the 3 jaw lathe chuck being machined down to a rough size with a large brazed TCT lathe tool – these tools are quite cheap and very robust for this type of work.
WD40 is an excellent lubrication for threading cast iron. It prevents tearing of the material as the thread is produced.