Not really enough information to make a sensible choice. Are you talking about the overhead ram or the outer arbor support that hangs on the ram? And what rough size?

If we assume that the steel lump is going to be fairly chunky it'll depend on what you can get rather than what you want. For an overhead ram I'd use hot rolled steel. It'll be cheaper than cold drawn and won't resemble a banana when you try and machine it. For an arbor support again I'd use hot rolled steel for the same reason. Or you could use continuously extruded cast iron as, again, it won't distort much when machined. Most original arbor supports would have been iron castings as were rams, unless round supports were used.

Andrew

I think I would go with Andrews suggestion of cast Iron bar as it is easy to machine and unlikely to move though to be safe I would rough out then let it rest for a couple of weeks before finish machining.

You can easily get hold of Grade 250 (old GR17) cast iron bar in square or rectangular section cut to length.

Hi Adam. Machining cast iron is if anything easier to get a nice sliding finish on that sort of item as that is what was used on the majority of that sort of item, but you would be using a solid piece of material, unless you commissioned a casting. The drawback to cast iron is it is a dirty material to machine and produces a lot of graphite dust but that is why it makes a nice sliding item and it is fairly stable when roughed out and left to stand for a few weeks outside in the weather. What sort of size mill is it for and have you got any sizes as that would make all the difference to the type of material you would use as a heavy solid piece of steel may sag or bow the original machine.

David

If you are are talking of an arbor support bracket, then I would go with a flamecut blank. Steel specification is not critical but you may find 080M40 (EN8) and 080A52 (EN43) as being most common. Cast iron Grade 250 can be expensive in big sizes.

Centec style arm makes more sense unless you have the casting

Might be a small affair for you Adam, but a billet that size will weigh about 90kg (200lbs). Too much for me to lift even when I was young and fit. (As for lifting it today, youth, beauty and physical fitness all deserted me back when we still had £sd.)

Do you know what load the bracket is expected to take? Might indicate something high-tensile is needed. Also, if the load puts the finished bracket in tension it might not be a good idea to use cast iron, though I confess I don't know what that part of a horizontal mill is normally made of and could be talking rubbish.

How much wear and tear expected on the dovetails? Mild steel may be a bit soft, although it could be case hardened.

Tasty project – good luck with it.

Dave

Edit: apologies, I see others have made the same point about weight.  I must learn to type faster.

Edited By SillyOldDuffer on 04/10/2018 17:35:25

The original would have almost certainly been cast iron, not steel.

Andrew

Material Cast Iron, my guess is the original will have been hollow, in order to make to manageable.

Shaun