Thread: Cutting Speed Black Bar ?

Originally Posted by Bryan

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.

Maybe its location? I buy metals for my school pretty regularly and ive worked in coastal and riverina NSW. Every time Ive bought, ive been told im receiving one of those three metals. Ive got one example of a pickled bar and it still had some paint on the end, which a local engineering firm reckons was a pickled hot rolled 1045 bar. I keep it for showing the kids the differences, particularly with regards to dimension (the pickled bar is wonky as). At Taree, I had to take what range was in town, which wasnt much at all. Griffith is a significantly more industrious town, a hell of a lot more metals to pick from.

I'm afraid you've lost me, I never have a problem getting a good finish on black, nonsensical argument to me!

Well i have always found it far far easier to get a good finish on bright bar then on black. There is no way they are the same steel (locally anyway*). Bright bar feels "buttery" to cut, where as the black bar sort of feels brittle-ish i guess. Its not impossible to get a good finish on the black bar. Just not as easy as with bright bar.

*The biggest problem with the whole discussion is we are not comparing apples with apples. Depending on where the steel comes from it could be very different stuff, even if different members are calling it by the same names. Best thing to do is ask for a data sheet the next time you buy some stock.

Ew

*The biggest problem with the whole discussion is we are not comparing apples with apples. Depending on where the steel comes from it could be very different stuff, even if different members are calling it by the same names. Best thing to do is ask for a data sheet the next time you buy some stock.

My sentiments exactly.

My black bar always feels quite nice after I've finished with it - smooth even, albeit a tad smaller!

Thanks for all of the suggestions.

will get a data sheet from the shop next time I am down there.

Given the range of opinions regarding whether or not its difficult to achieve a good finish, it's probable that "black bar" might mean different things to different suppliers and users.

Bill

I machined some small dia bolts for my model cannon using 1/2 or was that 12mm..?..black bar

My notes:
when cutting the finish my be good in a certain spot along the rod but at another area its awful..it varies as your moving along....the sound of cutting also varies...eg when a rough finish was produced the sound it made when cutting was as though you were using course emery tape

However when getting close to the centre of the black bar at 0.165dia the finish is good and even all along the entire length...I have know idea if this means anything..as cutting speeds were same as when started at 12mm

Originally Posted by markaus

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

Thanks for the tip about the book and spending so much time explaining things to me today Mark.

Have googled and downloaded the book and will educate myself a bit better about metal specifications.

Bill

Initially I also had problems with getting a good finish on hot rolled steel. The steel just seems to start tearing for sections as you cut. There's no doubt that getting your HSS as sharp as possible makes a big difference, and radiusing it correctly. It should be able to take a shaving off your thumb nail with ease. An arkansas oil stone helps to get it really sharp for final cuts. However, since no-one else has mentioned it, you can get a really good finish using a vertical shear cutter. For me, this gave results I just couldn't get with normal HSS cutters. There is a good thread about this here The Home Machinist! • View topic - Vertical shear bit
This gives a finish almost like a ground finish. It takes ages though, because you need such a low speed and it is only useful for very fine cuts, once you have the piece to size. If I am after a fine finsh, I find using Carbide at about 1mm cut at high speed gives as good as the vertical shear cutter, maybe better. I find less depth of cut with Carbide gives a patchy finish on hot rolled steel. The advantage of carbide is you run it at high speed, so it doesn't take long at all.