Diamond files will shift anything and are quite cheap, so they're what I would use.

Martin.

Never had this scenario but in general cast iron is easy to file but there is likely to be some crud left in the hole from the casting core so I would start with an old file. Don't assume that there is a skin–might be but there again maybe not.

I agree with Martin diamond files will cut almost anything but they are slow to use, one other type of "file" you may hav seen at the ME exhibitions is the ones with carbide bonded onto a piece of sheet metal and they are considerably courser than diamond files–can't recall the trade name though.

Cheers John

Hi

More than likely there will be a "skin" but this is usually very thin once this is removed cast iron is a dream to file compared to some other metals. Built a 7.25g loco which had lots of casting some years ago and did not use anything special in the line of files. As my old dad used to say elbow grease my lad… Good luck with the burrell and keep all of us posted as to progress.

Bob

Take the skin off as much as possible with a carbide burr or small grinding bit in a Dremel or die grinder then file out the corners and tidy the faces with a file.

You say the part cannot be machined but why can't you mill out to the 7/8 square and then just file the corners if you don't want an internal radius. You could also knock up a tool like a slotting head and plane the corners out. I think filing alone will not give a good sliding face unless you are very good at filing or use a rest.

To help people see what you want to do, this is the part in question

J

Edited By JasonB on 25/03/2012 08:16:43

Martin just get a 6" second cut Vallorbe flat file, easy. Many places do them.

If you go for the square files they have rounded or radiused edges so cant get a sharp edge.

What i would have said if seen this thread is centre existing square hole and drill out just under 7/8", plain sailing then.

Square holes relatively easy, just keep an eye on what your doing.