Machining Black Steel Bar

[electrosteam]

I have acquired several samples of 50 mm hot rolled black steel bar from the TAFE machining course scrap bin that I attend.
This bar is used for test pieces within the subject modules for assessment and marking purposes.
Heavy cuts with carbide tools at moderately high speeds gives a good finish - not the finest, but OK.

Under no circumstances can I get anywhere near the same finish at home with HSS.
I have tried on a Sheraton 9A, and more recently a Colchester Bantam.
On both these lathes, free-machining steel like 1214 is no problem.

I have seen several threads, on this forum and on others, where experienced senior members recommend that, for hobby use, there is no need to use carbide.

Is there a case for the use of carbide on this very low grade steel, or should the hobbyist not attempt to use such nondescript material ?

If carbide is justified for 'some' materials, what can the senior members recommend as suitable tool acquisitions ?

Note that the Sheraton certainly, and possibly the Colchester, would not provide the stiffness needed for typical industrial tooling to work efficiently.
What we hobbyists need is a a carbide material, shape, orientation and toolholder useful for handling problem materials.

I do appreciate that the problem could be one of cut depth, if you cannot achieve a deep enough cut the material will always slip/tear instead of peeling.
The necessary cut depth could simply be beyond the machine.
If that is the case, then I will only use the black bar for non-critical applications.

Happy machining,
John.

[Dave J]

Hi John,
A nice sharp tool with a radius should leave a decent finish on hot roll. I have not had any problems taking small cuts, so there shouldn't be a problem there
Dave

[matthew_g]

Just wondering why you have been told that the hobbiest should not use carbide?
All my tooling is carbide, Although I do have 2 HSS holders in 1/4" that I have never used.
I always get a good finnish off carbide, Why would I want to change to HSS ?
Just a query....
Regards Matt

[electrosteam]

Matt,
Thanks for the comments on carbide.
What information can you provide describing your setup ?
Example: machine type, tool holders, inserts, material, speed, cut, feed.

Dave,
I will try the HSS, yet again.

Happy machining,
John.

[Grahame Collins]

I believe some newby hobbyists are getting to a stage where they the are readily convinced those that don't really know, that all tooling has to be TC insert tooling.

Perhaps what they do not realise that not all their machines are in fact suited to use the TC insert tool.

I am told by some fitters & turners that TC needs horsepower and rpms to utilise to its full extent.

Not all machines have the horsepower or rpm.HSS is cost effective and takes a bit of skill and experience to grind.

just my 2c

From my research on it when prior to buying my lathe I found lots of variation among lathe tooling sizes because of power requirements given that and the reasons for positive and negative rake.Perhaps some fitters and turner types would like to jump in about here.




Grahame

[graemet]

When I bought my lathe, it came as a package with a set of carbide inset tools included.
I also bought some HSS to play with, to learn to grind my own tooling etc. I also bought a Diamond tool from Eccentric Engineering. I find that the carbide works well on most steels for general work, and lasts a long time, but for a fine finish, HSS is better. The Diamond tool was a surprise, as it is a breeze to sharpen and works well on almost any metal, but it has to be tightened up well or the HSS insert will slip.
If I find that a particular job is not cutting as I want, I change the tooling, but I still haven't worked out which works best on what! (Cringe!)
Cheers
Graeme

[bollie7]

I believe some newby hobbyists are getting to a stage where they the are readily convinced those that don't really know, that all tooling has to be TC insert tooling.

Grahame

This might be a case of a seller promoting carbide as well. Why sell a couble of bits of HSS when you can keep selling carbide inserts?

Your are right Grahame. A lot of smaller older machines don't have the grunt to run carbide successfully. I have a lot of carbide tooling which has been sitting in a box for years as the lathe I have can't run it. (I've kept the tooling in the hope that one day I could afford a decent machine)
I can understand why blokes like to use carbide if they have a machine capable of doing so. I'd love to be able to use it at home, Its easy with no grinding, but I reckon for a home shop HSS is the best option if you have to watch the money. A stick of HSS lasts a long time.
For the original poster, You should be able to get a reasonable finish with the blackbar & HSS, even if you have to resort to a water finish which is achieved with a real slow speed and real slow feed and coolant. Lead angle tool with a small flat on the end. Takes a while this way but you should be able to get a mirror finish on black bar if you want that.
You say you are at TAFE doing machining. Take a sample of of the bar to TAFE and show your teacher the finish you are getting. Take your tool as well, also he'll probably ask what speed and feed you are using. Ask him to show you the best HSS grind for that material.

bollie7

[electrosteam]

bollie 7 and all,
The blackbar came from the TAFE and we did have a demonstration with a small flat on the tool and slow speed and feed with coolant, the finish was quite good.
Thanks for the reminder, I will go back to the shop and try that.

I guess I was just reluctant to think of using water based coolant on my lathe.

Happy machining,
John.