Machining cast iron

Hi, I've been trying to machine a casting of cast iron and I'm having difficulty getting started. The tool bits are getting blunt and I'm getting sparks. It just seems the more I try the harder the cast iron gets. I've read somewhere that you've got to get under the casting muck with the first cut. This seems to be alright in theory, but in practice it's more difficult. I also don't have a lot of spare metal to machine off. Can anyone give me some advice please.

Garry

What are your tools made of? Carbide will stand more of a chance either the brazed on type of a tool that takes carbide inserts.

You can get chilled areas that are very hard and these usually form on corners or raised parts that cool faster than the rest of the casting which can be a pig to machine though heat treating can help.

Getting sparks suggests that the RPM may be too high. Put the lathe in back-gear and start from there; particularly while getting under the "skin". To avoid a lot of mess on your lathe, position a magnet inside a plastic bag under the tool, to collect the dust. When you are finished, simply turn the bag inside out, trapping the iron dust, and discard.

Great idea. Thanks for that.

Hi, I've tried both the brazed on tool bit and the indexable bits and both are giving problems. But I will try some heat and see what happens.

With machining cast iron it is important that the depth of cut is enough to get below the skin when machining castings.

Brian

Use back gear and make sure you have a good grip on the part.Turn the part slow and take a healthy cut.

You need more than "some heat", it needs to be held at around 900deg C for a good time depending on the thickness.

What is the actual casting?

FWIW... if you have a BBQ that you are not using, light it up & get the charcoal embers to the usual white ash stage, place your casting in the middle of the embers & leave overnight to cool off, that usually does the trick.

George.

It won't help Garry because he said 'I also don't have a lot of spare metal to machine off'.

Anyway I have a block of cast iron from a night storage heater that has an astonishingly hard thick skin - a couple of millimetres that HSS won't touch and carbide struggles with. Underneath the iron has good grain and no blowholes or other defects, Iit machines beautifully. I skim the surface with an angle-grinder before trying to turn it.

I don't know if the block was chilled accidentally or deliberately. Perhaps someone in the foundry hosed it down to get a non-critical casting off the floor quickly.

Dave

send the casting back

I think Garry has had a hard enough time getting the castings so may not want to send them back.

It must be one hard chunk of cast iron to be destroying carbide tooling , i have seen some horrible stuff before like sash weights and barbell weights but carbide got through it . I wonder if the tool is set too high and rubbing ?

Thanks for the BBQ comment. What I will do now is leave the casting in fire overnight. See how it is tomorrow.

The casting is the smoke box door, hence not a lot of metal can be removed.

Quite right JasonB, I will not be sending the casting back.