Machining Cast Iron

Machining cast iron can be quite easy with the right tools, but you do have to be careful with cast iron that might have sand still in the surface and so I thought a page giving hints and tips would be useful.

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 Tools

Lathe tool angles for turning cast iron:

Material Side clearance ° Front clearance ° Side rake ° Back rake °
Cast Iron 10 8 12 5


Glanze Tungsten Carbide Lathe Tools

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.

Thread Cutting

WD40 is an excellent lubrication for threading cast iron. It prevents tearing of the material as the thread is produced.

About Nigel 338 Articles
I've been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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