Working with cast iron, what is different?

WobblyHand

WobblyHand

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I know about the mess, and covering things up. Have seen the pictures of the paintbrush trick. I've never machined it so I don't know if somethings are bad to do.

Are there any major gotchas? Heard about hard spots.

I made a design that has 1/4-40 threads tapped in cast iron. Is this a bad idea? I've tapped an M5 hole in cast iron and it was ok.

Actually have two different projects, a diamond dresser for my carbide grinder, and a back plate for my lathe.

First one to tackle will be the diamond dresser. That's a milling project. Due to the possibility of hard spots, should I go with carbide end mills? Can I use a carbide fly cutter on cast iron? What about drilling? HSS ok?

Grateful for any tips.
 
Minor suggestion... if your design allows it, take a grinder to the cast Iron you are about to machine. The most outer layer of cast iron is what eats tools and throws off the worst of the black dust.
 
cast iron is abrasive. even if you take off the outer layer, you will wear tools down. Carbide for cast iron is less about hardness and more about toughness.
 
addertooth said:
Minor suggestion... if your design allows it, take a grinder to the cast Iron you are about to machine. The most outer layer of cast iron is what eats tools and throws off the worst of the black dust.
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Good to know. I'll find out soon enough how much oversize the iron is. Think it was -0 to +0.125", each side. I bought 2.25 square stock to finish to 2" square.
 
Good quality cast iron is no problem for HSS tools, I actually like to work with it, never had a problem with hard spots; the trick is to take a deep enough roughing cut to get under any possible chill/hard spots. A good foundry will not give you hard spots continous cast iron will have a somewhat harder shell, so allow a generous oversize to get to sound soft metal.
 
All good comments.
Woodchucker mentioned the fine abrasive nature of cast iron.
I really messed up a chuck when I didn't disassemble the jaws and screws after the job.
Also watch under the carriage, etc.
I never used forced air! Because it pushes swarf and dust into tiny places.. But a vacuum would have been really nice....

Even high quality castings will occasionally have an inclusion (hard spot). But with "good stuff" it is rare.

Daryl
MN
 
benmychree said:
Good quality cast iron is no problem for HSS tools, I actually like to work with it, never had a problem with hard spots; the trick is to take a deep enough roughing cut to get under any possible chill/hard spots. A good foundry will not give you hard spots continous cast iron will have a somewhat harder shell, so allow a generous oversize to get to sound soft metal.
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Years ago, I made the MLA-21 5C collet chuck from a kit offered by Andrew Lofquist. The casting was good quality and cut easily with HSS. More recently I ordered a semi-finished 10" chuck backplate on eBay. There was a world of difference between the castings. The backplate was nearly impossible to cut with HSS and was full of hard spots. I switched to an old, cemented C2 carbide tool purchased many moons ago from Enco. It cut the casting like butter. If you know the material is from a good source, I wouldn't hesitate to use HSS tooling. However, if you suspect the material was from an offshore source, I wouldn't attempt HSS, but rather go straight to C2 carbide.
 
benmychree said:
I, personally would allow more than that for finish.
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Good to know. Next time I will size the cast iron a little larger. Fortunately, I have some wiggle room in the design for all the dimensions. I'll check that in my CAD model, however.
 
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