I was given some old cast iron sash weights that had a hard surface like yours.

I cut anend off with an angle grinder and then tested the core with a centre punch to determine the

depth of hard ness, some went to the scrap man!

I then used a carbide tool to get through the surfaces of the ones I felt usable.

Hope this helps

Steve

Try annealing it. Find a friend with a coke boil er or stove. Put the cast iron into the centre of the fire. Bring to red heat, then cover with fuel and let it "cook" for a few hours, then let the fire go out. Leave the casting in there till it has all cooled down. It worked for me on a set of Clarkson casting that I had, which were un-machineable.

Maurice

When faced with chilled castings I put em in the woodstove for an evening and fish them out next morning.

I have some cut offs from sash window weights as well, was going to light up the BBQ & soak them until the BBQ went cold so far the BBQ has remained stored away since we've only had 3 days of summer this year hence I miss the opportunity… ah well there's always next summer…

​I did have a chilled casting on my S10V standard flange, managed to get it to size with brazed carbide tip tool but supported with live centre for safety & low revs… the top face was machined using 2" 4 tip carbide face mill as this was the only way I could get a decent finish on it…you can see the uniform chilled area on the OD.

​Using carbide tip tool to get OD to size… bloody hard!

George.

Many years ago the corners on the valve face of my 10V were chilled, first time I encountered this.

If you have a chilled sash weight, the best thing to do is drop it on your foot as this will hurt less than trying to machine it.

Neil

I can confirm that the woodstove treatment works. I often pick up lumps of metal that have been left lying around at work: when we replace, for instance, small track components on the railway, the old ones usually just get thrown down the bank as nobody can be bothered to take them to a scrap bin. I have quite a few large (30mm-ish) nuts and bolts that are still usable but, more importantly, after 'normalising' in the woodstove, will machine beautifully. I assume they are high-tensile, as before normalising, they can't be sawn or filed easily.

One caveat, however, is that if you are normalising something like a flywheel, make sure you support it adequately, or you may end up with something Salvador Dali would have been proud of!

Regards,

John.

Skin around the edge was pot hard, dremel fixed it. Pic won’t seem to respond to repositioning though, right way when taken.