Thread: black bar experiment

I use black bar when there is nothing else to use.

I seem unable to get it to finish well . Even to turn it reasonably well to size, I find I have to some down the say .030" over size and try to turn it off in one hit.
The HSS seems to cut the black bar better when it is loaded up. I find there is a poor finish if just taking a skim. The radius tip works better than a point.

Another thing I have noticed is that the black bar seems to vary batch to batch.Sometimes it is like turning a lump of plasticene and tears more than it cuts and other times its a bit better..It rust more and I do not like turning rusty stuff, I wire brush it first

Maybe I am doing it wrong and if I am, I do hope some will come along shortly and point both of us straight.

I save old grd 8 bolts and turn them for a lot of jobs .They finish much better than black bar.

Grahame

Hi Grahame,

I agree with your comments about black bar ! It does seem very variable in quality. Like you I tend to pick up large bolts to provide steel stock. I also grab brake disks, the solid ones for cast iron stock.

I did see some very large roller races this morning whilst nosing about. Unfortunately I didn't have my camera with me. These things were huge ! One in particular was about 3 foot across and about a foot thick. Ruddy great rollers. Pity they would be so hard as to be unusable for anything other than skates.

Originally Posted by Grahame Collins

The HSS seems to cut the black bar better when it is loaded up. I find there is a poor finish if just taking a skim.

Grahame, try a shear tool. They've been discussed here.

Originally Posted by Grahame Collins

I seem unable to get it to finish well .

I find there is a poor finish if just taking a skim.

Another thing I have noticed is that the black bar seems to vary batch to batch.Sometimes it is like turning a lump of plasticene and tears more than it cuts and other times its a bit better..It rust more and I do not like turning rusty stuff, I wire brush it first

I have noticed that when turning it the finish seems to get better the closer you get to the centre...but only for small dia stuff...say 0.186 - 0.25"

Originally Posted by Bryan

Grahame, try a shear tool. They've been discussed here.

here we go again...now I have to go look for it....

Originally Posted by Grahame Collins

I use black bar when there is nothing else to use.

I seem unable to get it to finish well . Even to turn it reasonably well to size, I find I have to some down the say .030" over size and try to turn it off in one hit.
The HSS seems to cut the black bar better when it is loaded up. I find there is a poor finish if just taking a skim. The radius tip works better than a point.

Another thing I have noticed is that the black bar seems to vary batch to batch.Sometimes it is like turning a lump of plasticene and tears more than it cuts and other times its a bit better..It rust more and I do not like turning rusty stuff, I wire brush it first

Maybe I am doing it wrong and if I am, I do hope some will come along shortly and point both of us straight.

I'm afraid that here, HP and rigidity is working against you with small machines. I can get a decent finish on black bar, but only by using TCT tooling, as high a spindle speed and as aggressive a cut as the machine & tool will handle. If you're not getting a shower of tight blue curly chips, you're not going fast/aggressive enough.

Generic black bar is crap to machine, no doubt about that. Hot rolled steels of known quality are better - I had a fair bit of 1080 hot rolled and it machined well.

PDW

Minimum nose radius on your HSS tool will help produce a better finish at light feed rates.
Usual 30m/min surface speed. Feed at .1/rev. Then trial and error.

If anyone is interested in more info about the vertical shear cutter, have a look here
http://www.chaski.org/homemachinist/...ic.php?t=84313

Sorry for pointing to another forum but it is such a good thread it seems pointless in trying to replicate it

It works very well but has to be used at low speed which can be a disadvantage. I hadn't used it for while because using carbide at high speed with a decent doc gives quite a good finish on black bar too. However, I just couldn't get a good finish on copper the other day, not using carbide or normal HSS so tried the shear tool and it worked great.

It makes getting the right diameter easy for a beginner because it really only works for 1 or 2 thou cuts so you can sneak up on it easily.

If you have never tried it, it is worth checking out because it makes getting a nice finish so consistent and easy (if a bit slow)