Problems machining a cast iron sash weight

[RupertTheBear]

Hi,

Apologies if I am posting this in the wrong forum but following an interesting suggestion in the plans for Bogstandards piston valve engine I went to my local dump and bought an old cast iron sash window weight. It has now blunted several cutters and I haven't ecen scratched the surface  .

Can anyone tell me what I'm doing wrong?

Thanks in advance

Rupert

[kvom]

Might not be cast iron, or may have hardened inclusions.  Either way it's no good.

[steamboatmodel]

With cast iron you have to get in under the surface skin with a very aggressive first cut. Sash weights are notorious for being poor quality material and will usually have lots of air/sand pockets in them. Its better to but cast iron sticks at a metal supply for serious work. I generally use HSS bits as sharp as I can get them on sash weights.
Regards,
Gerald.

[potty]

kvom and steamboat are spot on.

Good heavy first cut to get under the hard skin, some of the later sash weights were made from cast steel, 
I've been on the look out for some down the scrappy for ages all the cast iron ones seem to have gone, so you may have a steel one, grind a groove around the it and give it a whack with a sledge hammer it should break around the groove and show a gray cristeline structure, you'll struggle to break it if its steel:- if at all. 

Also all the dross from the casting gathers at the top end of the weight:- the eye end, a good couple of inches at this end should be thrown away, don't try using it it will have holes and all sorts of hard rubbish to break and dull your tools.

Stew

[RupertTheBear]

Thanks for your advice guys, last night I ground the rusty exterior off a section and tried to drill it - no luck. I think it will be visiting the bin soon!

Rupert