Blackening mild steel

So all quick change toolposts tend to have this sort of blackened finish to them and I was wondering if there was a hobbyist friendly way of doing it. I think I remember a video of putting hot steel into dirty motor oil in order to blacken it but I can't think where I saw it now.

The oil doesn't need to be dirty (contaminated motor oil causes several nasties, notably testicular cancer), I use rapeseed oil. Heat to a good black heat and drop in. Cover to prevent flames. Repeat.

Neil

There have been some cold blackening treatments on sale from ME suppliers in the past. Not sure about now.

Blackgates do a cold chemical blacking kit that works quite well, but I think when I have used up the chemicals I have I will go back to heating to black heat and oil quench. To me it seems to be longer lasting.

Michael

The Caswell kit seems to work ok, I've done hundreds of parts with it.

One advantage of getting old is that you reduce the chance of this disease (probably because of the increasing chances of developing something else).

It's a good idea to do it outside and be prepared for significant flames. It is also then much easier to avoid inhaling most of the nasties.

I was taught to use old engine oil at school

Edited By jaCK Hobson on 08/09/2015 08:26:24

I blacked a number of items with the motor oil method, heat and dip (about 20 items) 30 years ago although in a box they have been stored in a very damp garage and only one item shows signs of rust.

brian

I seem to recall reading somewhere that most modern motor oils contain additives which supress blacking. I've had good results with cheap supermarket own-brand margarine, but it does make the workshop smell like a fire in a chip shop...

I've tried a number of different oils in the past for blacking and all work pretty well. Like Neil I now use rapeseed oil (just the cheapest type from the supermarket ) and get consistently good results.

I tend to heat to dull red which may be a higher temperature than is needed, I must experiment at lower temperatures to see if it works just as well.

Doug

I use old engine oil, diesel is better as more black in it. Just keep all your working bits well away. Also does help with rust prevention.

"Black-it" from Pixel Plus also works well.

I've never done it but saw a demo of oil blackening to prevent rusting at school when I was around 12 years old.

The item was heated with a torch and oil squirted on with an oil can - oil ? what ever was in the oil can. The result was a pretty thick coating.

John

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As I remember, testicular cancer was caused not by inhalation, but by oily hands when going for a pee, or rags in overalls pockets.

I use linseed oil; heat item to be blackened to dull red and plunge into oil...outdoors of course. Very good results so far.

Mostly due to mist and splash onto overalls as I understand it, possible wiping hands on overalls too, oily rags in pocket etc.

John

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Many of the health risks in the past were down to poor hygiene. Not surprising really when you think about, not many even had a proper bath, washing machines very rare. The same clothes worn all week, etc.

Would it be best doing this before tapping? Wondering how it would affect the tapped holes of the toolpost

Rapeseed or sunflower oil from the supermarket is cheap enough not to bother with old engine oil.

Once done, rub the item all over with black shoe polish - allow to dry & polish off. It will help to delay any subsequent rusting and looks good.

You can also get a pretty good black appearance on an item you might not want to heat by purchasing some "Gun Blue". Follow the instructions carefully with regard to degreasing and certainly use the shoe polish afterwards as the black is only a "few molecules" thick.

If you use Black-It and similar selenium based products, which include commercial gun barrel blacking products, it changes the surface and does not merely add a layer of burnt oil (aka oily carbon) to the surface. This oily layer can be quite thick. This way threads are largely unaffected.