Uh-oh...Nightmare Metal! 5 tips for machining Cast Iron.

[Xnke]

So you're trying to mount that EDIS trigger wheel, but the best method you can think of seems to always involve machining the damper metal. What's the damper for the Venerable L-series made from? How about that 3rd row add-on pulley from that aftermarket A/C unit? Or most any flywheel?

 

Some kind of cast iron or steel, but often hard as a rock! What do you do now?

 

Here's some helpful hints for machining cast iron:

 

1. LOW SURFACE SPEED! This will save you more frustration with burned up tool bits than any other single thing. Even the soft, free cutting varieties of cast iron or cast steel will not tolerate a high surface speed. Get the lathe's RPM down!

 

2. Take a heavy initial cut. Take at least .020 on the first pass, at a low cutter advance rate. Almost all cast metals have a hard skin that is difficult to cut, and very abrasive. Once you get through, though, it's pretty smooth sailing.

 

3. Keep aware of your tool's cutting edge. Keep the tool sharp, every few passes or minutes of cutting, touch up the edge with a hone or check the edge of the milling cutter. A dull cutter will harden up the skin of the workpiece, and really frustrate the machinist that doesn't understand why he just can't get the tool to cut.

 

4. Use carbide tooling. For all but the finish pass, carbide will go a long way to achiveing your goal of a nice finished part, in minimum time. For your finish pass, usually a razor sharp HSS tool will give a better cut. For those with access to a tool-and-cutter grinder though, diamond hone a carbide tool's facets to nearly polished level. This will also give a nice finish on that last pass.

 

5. Keep a good chip feed going. Once you get the tool cutting, keep it in the zone. Don't get too agressive, but don't be shy. burnishing the cut edge will only dull your tool and cause you to have to stop and sharpen that tool again. Too deep a cut will break the workpiece, stall your machine, or worse! Also, watch out for hard spots in the metal. These can be detrimental to tooling life.

 

Even when just drilling in a press, these tips apply. Slow the drill down, apply moderate to high pressure to break the skin, and keep up a good chip feed. Sharp drills are a must!

 

Keep these tips in mind, and machining that cast iron part will be a breeze.