Does a modern lathe tool need clearance?

Shotgun

Shotgun

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Every reference I've personally seen for lathe tools have shown a clearance angle ground under the cutting edge.
That make all the sense in the world when using a lantern post type holder that comes up at an angle.
But, does it make any sense for a modern QCTP, that presents the tool perfectly horizontal? When presented to the work on centerline, the material will always be moving away from the tool after the cutting edge. I don't see how it would do anything more that increase the grinding time and slightly weaken the cutting edge by removing support under it.
Do any of you guys grind the face of your lathe tools at a 90 degree angle?
 
I think Joe Pie or This Old Tony, or both have shown what a tool without all the recommended clearances will do. Joes machine is modern I suppose.
But you should do it too. It’s not gonna hurt anything to try it.
I try my best to approximate the clearances commonly accepted in books.
 
Shotgun said:
Every reference I've personally seen for lathe tools have shown a clearance angle ground under the cutting edge.
That make all the sense in the world when using a lantern post type holder that comes up at an angle.
But, does it make any sense for a modern QCTP, that presents the tool perfectly horizontal? When presented to the work on centerline, the material will always be moving away from the tool after the cutting edge. I don't see how it would do anything more that increase the grinding time and slightly weaken the cutting edge by removing support under it.
Do any of you guys grind the face of your lathe tools at a 90 degree angle?
Click to expand...
I think your dilemma assumes that both the cutting tool and workpiece are infinitely stiff. That is not the case. The cutter/workpiece interface includes some amount of elastic deformation and that's the rub (pun intended).
 
Shotgun said:
Every reference I've personally seen for lathe tools have shown a clearance angle ground under the cutting edge.
That make all the sense in the world when using a lantern post type holder that comes up at an angle.
But, does it make any sense for a modern QCTP, that presents the tool perfectly horizontal? When presented to the work on centerline, the material will always be moving away from the tool after the cutting edge. I don't see how it would do anything more that increase the grinding time and slightly weaken the cutting edge by removing support under it.
Do any of you guys grind the face of your lathe tools at a 90 degree angle?
Click to expand...
I find that if I fail to grind the proper relief, the tool does not function as well. I mostly use carbide, which will have built in relief either in the insert or the tool holder. But when I do use HSS tools, I grind the relief angle. It's sharper, cuts better, and gives a better finish. The time it takes me to hone that edge back to sharp is insignificant compared to the frustration of a lousy surface finish.
 
I guess I should have been clearer and called the front relief out specifically. Any side edge needs the clearance, as the work is not moving away from the tool.
 
I think optimal cutting is going to require a particular included angle, so what you save by not grinding clearance you would have to make up by grinding additional rake. i.e. no real savings. I'm sure it would cut though. Where I used to work (not a machine shop) we inherited a mill and lathe with a new building, and the local ME had some success turning with an unground tool blank - because he didn't know you needed to grind them! Anything will cut, with enough power, but the usual geometries exist to optimize accuracy, finish, tool life, etc.

GsT
 
I really think you need to try it. Lol. No need hypothesizing. Go out and try it and you’ll have the answer.
 
I'd say that all cutting tools need clearance to cut effectively, except perhaps EDM and lasers and suchlike. Lathe tools need front and side clearance at a minimum, most work better with side and back rake as well, depending on the material and the function of the tool.
 
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