Thread: Free machining cast iron?

I dunno Ken, but why not check out a scrap yard for some chunks that would be the right size, or a little too big, you can usually get it by the pound, then start from there?

I would think that a chunk of cast iron, while fairly work-able might be too soft for a vice...?

Most vices are built in a certain way, with ribs and such to give them a lot of strength, cast iron, by itself, is not that strong, it is fairly brittle.

What kind of vice are you making, if you give the details of what you want to do, maybe more help can be given.

Cheers!

The whole idea behind cast iron is to cast it in the shape you want, without having to machine too much off of it.

I guess you could buy a block of it somewhere, and machine it to shape, but that kinda defeats the purpose, and you will end up with a thing notably weaker than if it were cast in the desired shape to start with, and machined where necessary. Something to do with how the casting sets into shape I believe, I can't describe it exactly, sorry.

Steel, that's a whole other ballgame, machine that to whatever shape and it will be much stronger, but forging is even stronger.

Grahame had a link the other day to somewhere, and the fella there made a milling vise out of steel. Looked really good, and might be a better option.

Or you could find someone that casts iron, and get them to cast up a vise-shaped object.


Machinability? So long as the iron is not white, it should machine like butter. If it's white or heat treated, forget it. No real swarf, but pretty dusty and the dust isn't all that nice to machines. But it does machine very easily.

www.globalmetals.com.au

They sell all lengths all sizes and all steels, aluminium and cast iron.
They also have a very handy explanation of the different metal grade properties.
The site is worth it just for a reference point.

Ken,

Cast Iron is quite easy to machine. It does however make a very big mess, due to the insane carbon content. (Prepare for black arms and face.)
'Tis a very good idea to wear a dust mask when you machine it.

For a vice, it's an excellent material to use, because it doesn't move like steel does. Ever wondered why the base of a lathe is cast iron? It's not just to make a heavy base so the lathe doesn't rattle. It also doesn't move and warp like steel does over time.

If it were me, I'd machine the cast iron to shape and then grind up some steel jaws for it and send them off to heat treat.

Nuf said.

I'm gunna use mild steel. The mini machine vice I want to make is 50mm wide, 45mm high including jaws, and 100mm long. It's the type of vice that does not have the conventional screw, but a cap screw to tighten the jaws with a movable cross pin through the base.

The type of vice can be found here http://homepage3.nifty.com/amigos/index-e.html

No. 29 Vice.

The maker is Makoto Ishimura, he is a very clever man, I admire his work greatly.

Have a butchers.

Thanks to all,

Ken

Originally Posted by Article99

For a vice, it's an excellent material to use, because it doesn't move like steel does. Ever wondered why the base of a lathe is cast iron? It's not just to make a heavy base so the lathe doesn't rattle. It also doesn't move and warp like steel does over time.

Um, you might want to check up on that statement re: cast iron not moving. It sure as shoot moves, enough so that the most precise cast iron items go through extensive processes to stress relieve them before they get rough machined, and again before they are finish machined.

Once it's settled down it doesn't move, but until then it's a nightmare. Ever wondered why all them hand planes are often out of flat/square? Probably because Stanley et al, couldn't spare the time for seasoning, since stress relief was unheard of at that time.

Now we know about it, LN and LV stress relieve the iron, no more wiggling


Ken, great link. Thanks

- All you have to do is rough it out on the mill, put it in the furnace at 590deg odd to relieve the stress and then finish grind....

Yes, super accurate lathe beds are left out for years to weather, however for a vice, stress relieving in the furnace should be fine. I've made a couple of toolmaker vices this way and they hold things square to three or four micron over 120mm.

Ahh...

I bet generic blocks of cast iron are not stress relived though.


I heard that Rolls-Royce used to throw all their engine blocks from the foundry into a paddock for a few years before they did anything to them. Most of the owners wouldn't believe it, but when the guy telling you that is carefully hand rolling a new quarter panel for a roller, and he was flown from the factory to do it, then I think he might be right.

That was, of course when they still built them by hand rather than some faceless robot doing it.

Originally Posted by Article99

Ken,



For a vice, it's an excellent material to use, because it doesn't move like steel does. Ever wondered why the base of a lathe is cast iron? It's not just to make a heavy base so the lathe doesn't rattle. It also doesn't move and warp like steel does over time.

MMmm that is incorrect. I know this because I have studied materials science. Cast on is good for machine bases because of its dampening quality, not because it moves less then carbon steel. Steel only moves due to creep and this will only happen at elevated temperatures or if the material is subjected to a stress at or above its elastic limit.

Ken, Mild steel is also not the best as it is too sticky to machine smoothly and will build up on your tooling cutting edge. Also its soft and will distort under pressure more than better steels. You have gone from one end of the steel spectrum to the other . In the middle is some good machining tool steels that will be tough enough for a small vice and easy to machine. 4140 , EN19 or say Bohler K245 which is very tough , reasonable wear resistance and very easy to machine and is heat treatable.

I wanted a chunk of cast iron to make up a new cross slide for my lathe. I found that I could only purchase the material in round stock form. 125mm dia round stock would have cost me $33kg. With all the wastage involved, it would have cost me a fortune for the 350mm I was after, so I let it go.

I take it that you want to make the vise as an exercise, rather than out of necessity as those are a pretty standard machinist's vise, readily available from people like Hare & Forbes.

As for 'free machining' alloys - you will find a lot of different ones, some with high sulphur, lead or copper added, or 'maleablized'(sp) with magnesium (or was that manganese).