- Dec 10, 2014
- Reaction score
- A hilltop in SE Ohio
No offence taken about my turning skills as this is the first time I have attempted to turn a piece of bar.
Everyone starts somewhere!
I started with the carbide tool because this happened to be mounted in the tool holder when I purchased the lathe, I tried a light cut to start but I believe that carbide tools prefer a more aggressive cut to give a better finish
This (carbide needs deeper cuts) is partially an old-wives tale. It's closer to the truth to say that the vast majority of carbide tooling, and especially replaceable-insert tooling, is designed for machines that can take a deeper cut, and therefore the geometry is optimized to produce a better finish with a deeper cut. Brazed-carbide tooling does not have exactly the same problem, and there are actual sharp carbide inserts - look for inserts designed for aluminum cutting if you want sharp - they last just fine in steel for hobby use.
That being said, your surface finish doesn't look like "not a deep enough cut". It looks like bad tip geometry for the material.
An insert that's designed for a vastly deeper cut is one source of bad tip geometry, but your lathe is not designed for taking "carbide deep" cuts, so if the carbide tool you're using came with the lathe, I'm going to bet against it being intended for super-deep cuts.
Incorrect tool height turns good tip geometry into bad tip geometry, so I'd say that stays on the list of possibilities, but, if you describe how you're setting the tool height, that would help us rule that out.
Tip damage also does exactly what you see in that section where you've got short little bright lines followed by tearouts going around and around your part. It also does that "mush metal over the edge" like you see at the shoulder between your different turning depths.
I bought a set of ready ground HSS tools but had no joy with these either they do seem to have a very sharp pointed cutting edge and I believe a very slightly rounded cutting edge can give a better finish.
It's definitely true that a more broad cutting edge can make for better surface finish, but unless you bought pre-ground tools from someone who's just being an ass, the problem is more likely that you're either choosing the wrong tool, or presenting it to the work incorrectly. (Or, the steel your turning is inappropriate for HSS) Many ground HSS tools have a rather sharp corner, but except for the threading tool, and sometimes roughing, few are presented to the work "sharp corner facing in". It might help for you to track down something like South Bend's "How to Run a Lathe"
And look at their section on tool geometry.
... it's also entirely possible that you've just chosen to try to start your turning journey with a piece of completely snotty scrap steel. I've a couple chunks of mystery metal lying around that just won't cut nicely for love nor money. They're out there. If you want to dial in your turning approach using a known quantity, buy a chunk of 12L14. Machines like a dream, and it'll let you focus on learning to do your end of the job of turning, and not spend time getting confused by mystery-metal weirdness.