25mm seems to be the smallest diameter stocked by most suppliers

I seem to remember having that stuff at School, experiment to show how steel expands and contracts on cooling. A bar was heated between a couple of fixed points, a test piece of cast iron was slipped into an eye of the bar at one end and as the bar contracted on cooling, it would snap the test piece.

I've never seen 3/16" sash weights and not seen CI bar sold in smaller than 25mm

Circlip,

What a heap of cast iron turnings that would create bringing a sash weight down from about 35 mm diameter to a little under 5mm while at the same time hoping it isn't full of inclusions and holds together while you are working on it.

It is a curious requirement anyway and even in sound material it will be about as fragile as egg shell in that size.

I doubt you could machine it successfully over a length beyond an inch or so. Maybe Nick's scientific supplier is quite right to charge properly for such material!

Brian

does it have to be round – I have a couple of feet of 6″ by 1″ cast iron which was easy to get though relatively expensive as compared to steel – saw off 5mm or so then slice on a mill or saw into square section ?

Cast iron welding rods are available in 6mm; the problem will be getting a small quantity, unless you need a box full!

Brian

Cast iron can be welded with either a nickle filler of an S.G. iron one.

SIF seem to do S.G. iron rods in either 6 or 10mm

Hope that helps

Brian

another source of cast iron is brake pads – just looked at a set of 4 I bought for a ?1 at auction in case I could use them looks about 10mm slab bonded to the steel carrier – maybe local garage can supply some worn pads

I have a large amount of cast iron welding rod (R-CI). It is about 3/16" dia. The finish is sand cast and the halve are slightly offset (mold mismatch). I don't see how they could be used for anything but welding. If you need a smooth cast iron rod I suggest you find a larger diameter and set up a hollow mill on the lathe to reduce the diameter.

Sash weights may be a cheap source of CI but they are normally made from cheap material and contain lots of cavities and impurities. The outer surface is often very hard and difficult to machine.

Paul.

Depending on how many rods are needed, it might be worth talking to a foundry that makes large iron castings. When they vent large sand castings with vent wires to allow trapped air steam and gases to escape, the iron often fills the vent cavities in the sand to make "wires" of cast iron projecting off the castings. Usually not such large dia as 3/16 but if you ask they may be able to oblige and make you some "wires".

Not sure how machinable such wire would be, could be chilled, could have a lot of sand inclusions picked up from the vent openings in the sand. Just food for thought.

Some time ago I saw a TV program showing such a foundry in I think Cornwall UK making Royal Mail post boxes and parts for Aga cookers among other things. This may help track a foundry down, I hope.