3

The benefit of true right-handed and left-handed turning lathe tools is obvious: You can get right up against the shoulder or face with them:

enter image description here enter image description here

The benefit of neutral-handed turning lathe tools is also obvious: You can cut in both directions or plunge cut:

enter image description here

So then what is the advantage of LH and RH turning tools that don't let you get up to the shoulder? enter image description here enter image description here

It would seem these would be niche tools for when you need a to be able to plunge cut and get closer to the shoulder with a single tool, but my understanding is that these tools are actually more commonly used than the true LH, RH, and neutral tools. They can't face or get as close to the shoulder as a true LH or RH tool but also can't be as strong as a neutral tool (which can get more material behind the cutting tip).

Are facing and 90 degree shoulders just a lot less important than I think they are?

Images from: https://www.mcmaster.com/lathe-tools/carbide-tipped-turning-lathe-tools/

DKNguyen
  • 4,625
  • 1
  • 9
  • 22
  • 2
    over my head, but you're talking about "negative" clearance angle on leading edge? quick search on this -> http://www.mitsubishicarbide.com/en/technical_information/tec_turning_tools/tec_hsk-t/tec_hsk-t_technical/tec_turning_cutting_edge – Pete W Feb 06 '22 at 20:14
  • 1
    @PeteW I think that is the answer. They're after lead angle (which I guess is what negative clearance really is because once it goes negative it's no longer clearance). Increased cutting area means you wear more than just the tip so you can cut faster with longer life, but with increased forces, more part deflection resulting in less precision. But that makes it a better roughing tool where those things don't matter. Due to symmetry, neutral tool with small lead angles so you can still get close to the shoulder would be narrow and weak, and if using large lead angles makes shoulder very far. – DKNguyen Feb 07 '22 at 01:46
  • There's a fixture that lets you angle such a tool and get right up to the shoulder. The geometry you pointed as neutral, I thought was mainly for 60 deg thread cutting. – Abel Feb 07 '22 at 12:39
  • @Abel Yes, I have those Swiss Multiquik toolposts. But that still doesn't help the strength issue on the neutral tool, and if you try that on the handed tool that can't get close to the shoulder the edge on the shank tip no longer has clearance. The neutral tools I have seen are 30, 80 and 90 degrees. The 60 degree ones are actually called threading tools. – DKNguyen Feb 07 '22 at 15:05

1 Answers1

0

So it turns out the tools that can cut a 90 degree shoulder have what is called "negative lead-angle" which results in just the tip cutting and also results in clearance. This allows the tool to face and also turn a 90 degree shoulder.

Conversely, the tools I was asking about in this question have "positive lead-angle". The reason these tools exist is to take advantage of this positive lead angle which cuts along a greater portion of the edge. This results in increased tool life since more of the edge is being utilized and distributes the cutting force along more area which helps reduce certain kinds of failures.

The disadvantage is increased cutting forces for the same depth of cut, increased radial forces, and greater potential for chatter. The increased radial forces result in more part deflection and less cut precision.

What this means is that tools with positive lead-angle tend to best for roughing where tool life and speed matter more than finish and precision.

The reason they are more common than neutral tools is that unless you have extremely large positive lead angles, the neutral tool ends up being too narrow and fragile due to symmetry. The LH and RH tools with positive lead angles don't have this problem since they only cut in one direction so the opposite side can be bulked up with lots of material to support and strengthen the tool.

DKNguyen
  • 4,625
  • 1
  • 9
  • 22