Thread: Cutting Speed Black Bar ?

Black bar is s##t.

I'm surprised you can even get a good finish on it.

Do youself a favour and get some bright machine grade steel to play with.

The HSS cutting speed depends upon the diameter. There is plenty of information on the net about speed v diameter.

Unfortunately a lot of small diameter steel rod etc is black steel, and it really is difficult to get a decent finish. Can be done, but it will never be as good as bright steel.

It's cheap and it's nasty.

Try out on some big old bolts if you can find some, these are usually a decent grade of steel.

If you are going to use black bar, try a round nose cutter on it at a medium feed rate. Anything too pointed will just tear it up.

Rob

Originally Posted by nearnexus

Black bar is s##t.

I'm surprised you can even get a good finish on it.

Do youself a favour and get some bright machine grade steel to play with.

The HSS cutting speed depends upon the diameter. There is plenty of information on the net about speed v diameter.

Unfortunately a lot of small diameter steel rod etc is black steel, and it really is difficult to get a decent finish. Can be done, but it will never be as good as bright steel.

It's cheap and it's nasty.

Try out on some big old bolts if you can find some, these are usually a decent grade of steel.

Rob

Thanks Rob. Will abandon attempts to practice on black bar, .................... however am still curious regarding exactly what it is, and where it fits in the spectrum of materials.

Am aware of relationship between surface speed vs diameter but was wondering what the relevant cutting speed for black bar is to plug into the equations.

Have found cutting speed recommendations for Brass, Aluminium, Low Carbon Steel, High Carbon Steel, Stainless Steel etc but nothing for black bar

Is black bar a uniquely australian slang term ? Should I have been searching on Hot Rolled Steel instead ?

I've discovered that the black is a scale formed on the outside as the hot steel is rolled out of the machine.

Will see if there is one of those useful little Workshop Practice Series books about material types.

Off to play with some bright steel now, as you have suggested

Bill

Originally Posted by steamingbill

Will abandon attempts to practice on black bar, .................... however am still curious regarding exactly what it is, and where it fits in the spectrum of materials.

Bill

It's a good question.

It's generally hard and scaley, feathers badly, and generally machines poorly. I think hot rolled is the correct term.

You would be tempted to say it has a low carbon content, but when you compare it to say mild steel water pipe, it machines much worse.

Maybe it's more crystalline given the way it's produced.

I hate the stuff.

Rob

About 30 m/min. I thought it was just hot rolled mild steel. Like maybe 1012? It's often described as gummy and machines poorly because of built up edge.

Balzers_CUT and Build Up Edge formation.MPG - YouTube

Next time you get a good finish, stop and write down all the parameters, including tool geometry and bar dia/stickout. 27 x 100mm could chatter if your lathe is less than ideal. Eg, ropey bearings, worn chuck, being a Hercus etc. <ducks> A sharp tool always helps.
When it goes bad, stop and feel the top of your tool with a fingernail. Betcha there's a ridge on top of the cutting edge.

You will probably find that "hot rolled bar" is just all types of scrap metal recycled into the mix, it could have HSS, cast metal, car bodies, high carbon steel also, which is why you get good cutting then crappy cuts.
I've had a hot rolled sheet of 1.6mm that was porous, made into a fuel tank that leaked nowhere near a weld.
Kryn

Hot rolled mild steel would most likely be 1045 in my experience and as most of the fellas above have said, its utter crap to machine. The manganese that is added into it improves its hot workability (and it helps reduce brittleness...something to do with sulfur, but I cant remember beyond that) and that comes at the cost of its machinability. The manganese also helps resist abrasion.

Something like 1018 mild steel would be somewhat better, but if I was in a major city or had a good metal supplier handy, id be looking at either 12L14 or some of the machine spec alu's. Anything in the 2xxx range of aluminium is generally quite nice to machine and very forgiving.

I don't think I ever have problems with hot rolled stuff Bill, could you post some photo's of your cutting tool, the problem might be there in the grind, centre height of the tool would cause problems also.
I use indexable tips and/or HSS, same with thread cutting it.

Also hot rolled is not too round, so you must turn it a bit to find the best pozzie before tightening it in the chuck, if you
haven't got the sweet spot you might have problems.

Black mild steel or ‘hot rolled mild steel’ is covered in a black/blue/gray scale, is not very accurate in sizing and may have surface flaws.

Bright mild steel or ‘cold rolled mild steel’ is black steel that has had the scale removed and has undergone a further process called ‘cold rolling’ to achieve accurate sizing and removal of surface flaws. Generally it is not supposed to have surface flaws as per black steel; however?

Hot rolled is generally used in general fabrication work, whilst the more expensive cold rolled, due to it’s more accurate sizing, lack of surface scale and surface imperfections is generally used for assemblies that require accurate sizing: Axles, etc. They are the same and will turn the same; the scale on hot rolled is easily removed and doesn’t cause problems.

In brief: bright steel is black steel that has been cold rolled.

For machining, bright is best simply because it requires less work, ie: if you buy 25mm bright steel, then it is 25 mm, concentric and uniformly sized throughout. Hot rolled is a different proposition, if you buy 25 mm hot rolled, generally it will be slightly under/over 25mm and not uniformly sized in either concentricity or along it’s length.

Round tipped tools give a better finish than sharp pointed tools; however they are limiting in terms of cutting to a nice sharp corner. Sharp pointed tools are the exact opposite. Look at rake angle when grinding bits and when cutting threads you may also need to include a helix angle. All are easily googled, as is information on black/bright steels and cutting feed rates.

Originally Posted by gngh

In brief: bright steel is black steel that has been cold rolled.

That is NOT true. It used to be the case that some bright bar would be hot rolled bar that had been pickled to remove the scale. With such bars, obviously the composition is the same and itll machine just as badly, without the crusty hard layer on the outside. The bar wouldnt be cold rolled afterwards if they were being particularly tight, and you could see the surface imperfections from the pickle and from the hot rolling process. This sort of bar still has a place in fabrication because the removal of the scale means that there are less impurities included into welds.

Cold rolled stock now has different alloying elements included to make it more suitable for cold rolling to the required profile. Its slightly better for machining as a result. Its not as good as the machining specific alloys though, but a little stronger as a result. The Interlloy website has plenty of datasheets for those with lots of time on their hands, but it makes for interesting reading. It shows the additives used in steels and describes how they behave in the usual metalworking processes.

Your 'googling' must differ from mine, but I'll stand by my original statement. As for black machining badly, I've never had a problem, I'd pretty much agree with Shedhappens.

if you google 'one steel martin bright' .. there is some good information

re: onesteel martin bright technical handbook, there is some good info on the differences between brt & black/hot rolled bar on pages 12-13 or so

mark

1045 Medium Tensile Carbon Steel Bar | Interlloy | Engineering Steels + Alloys

Thats your regular hot rolled stock. Sometimes other steels come in hot rolled, but if you dont specify, its likely youll be handed this.

1020 Bright Carbon Steel Bar | Interlloy | Engineering Steels + Alloys

or

http://www.eaglesteel.com/download/t...eel_Grades.pdf

Is typically what youll be handed if you ask for bright bar. Again, you might get something else if its cheap and on hand (included pickled, hot rolled 1045) but usually, this is the go to "bright mild steel". Note the differences in additives, theyre not drastic, but they are different metals.

Originally Posted by scottyd

1045 Medium Tensile Carbon Steel Bar | Interlloy | Engineering Steels + Alloys

Thats your regular hot rolled stock. Sometimes other steels come in hot rolled, but if you dont specify, its likely youll be handed this.

While 1045 may be available as hot rolled, it's not the default in my experience. I have 1045 and I have black 'mild' and they machine quite differently.

I believe what I know as the default black bar - and what the OP is probably referring to - is described in your third link:

A36 Mild Steel
ASTM A36 steel is the most commonly available of the hot rolled steels. It is generally available in round rod, square bar, rectangle bar, as well as steel shapes such as I Beams, H beams, angles, and channels. The hot roll process means that the surface on this steel will be somewhat rough. Note that its yield strength is also significantly less than 1018 this means that it will bend much more quickly than will 1018. Finally, machining this material is noticeably more difficult than 1018 steel, but the cost is usually significantly lower.