Various HSS tool size needs?

On my AXA, I mostly use 5/16 or 3/8 tools, as they can be tightened flush with the side of the holder, allowing one to come right up to the chuck jaws with a cut; the setscrews have difficulty doing this with 1/4" or smaller tools. I'd just use 3/16 or smaller bits for boring bar bits. As was pointed out above, the bigger the tool section, the more grinding you have to do.
 
I just wanted to say that in my experience, a 3/16" bit is bit small but a 1/4" bit is definitely rigid enough to cut well on a 10" lathe, especially if it is ground well. I use 3/8" bits almost exclusively on my 11" lathe because it allows me to stick the tool out however far I need to get the job done and it fits the AXA tool holders better. 1/2" is too big and doesn't confer any advantage to me. Bottom line is a 1/4" or 3/8" bit will be far more rigid than your lathe is, and either will allow you to get them on center height.

The parting tool is shop ground and will work fine for smaller diameter work if it is sharp. A P-type blade will be better, especially if you go with a P-1N or P-1.

The tool blanks you got are good ones - Morse, Mo-Max cobalt - both top of the line. The brazed bit will be okay but needs to be sharpened well to work if you can get it on center.

You are going to find that the lighter the lathe, the more important it becomes to grind good tools and get them dead on center height. Bigger, more rigid lathes have more latitude but small ones need every advantage they can get.
 
Makes sense, Mikey. I'm going to continue focusing on getting my 3/8 ground well and using them first, but look forward to trying 1/4s. The others for fun at some point when I get to the "fun at some point" point.

Tim
 
I bought a selection of used shop ground lathe bits from a local that was selling for friends who'd had a machine shop for decades. Not only was the grade of tool very good the selection of sizes and grinds was very interesting. In trying in them out on my 9x20 I've got some new favorites that are not conventional grinds but work really well on my lathe. They probably wouldn't appeal to others. But I was using 1/4" before and this one 5/16" and a 3/8" have become the go to's.
 
A lot of smaller bits were ground for use in the tool holders for lantern toolposts. Most of those tool holders had about 15* back rake built in. When used in a QCTP the back rake will be highly negative and will not cut well. Those tools need to be re-ground to get proper cutting angles.

A few years ago I made a pair of tangential tool holders for use on my South Bend 10K. I also wanted a toolholder for my 17" lathe that would hold a HSS bit with proper back rake. I made a holder for the BXA toolpost that holds the tool with 12* back rake. I ground 8* relief along the entire left side of the bit, then I ground a groove in the top of the tool that gives me 15* side rake and acts as a chipbreaker. When the bit wears all I need to do is grind back the end of the tool.
 
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