Does a modern lathe tool need clearance?

[Shotgun]

This Old Tony has a video I think you'd like. (Don't let that dissuade you from trying it yourself... As long as nothing gets broken, that's the best way to learn.) He's gonna make an ugly tool, one grind at a time, starting with literally, a square blank, reacting to one problem at a time.

Unfortunately, the first grind Tony made was to relieve the front face
Oh well, I've got material to play with.

 

[Tozguy]

Cause I wanna understand why? Not going to change the world. . . but hopefully I'll be smarter.

Valid attitude.
I had the same question a while back.
The need for a relief angle on the face of a tool is explained by the deformation of the metal being cut. When a tool is cutting it is deforming the metal until it shears. This diagram shows the areas of deformation.


The area immediately after the cutting edge is 'bouncing' back against the face of the tool. This area is obviously very small but significant enough to cause rubbing and heat build up in the tool. The relief angle in the face makes room for the metal to 'bounce ' back with less rubbing and heat build up on the face of the tool.

 

[Shotgun]

Thank you, @Tozguy . That reminds me of the video below. Watching it again with this in mind. . . yep. Gotta get the back end of the tool out of the way.

 

[Jimsehr]

The side clearance, I understand. The tool has just cut a "shelf" and will rub on the side without clearance.
The front clearance seems like a carry-over, though. With a lantern tool post, you gotta have that front clearance cause the tool is generally coming up from below at an angle. But, if the tool in coming in flat, the work is providing the clearance at the front.

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?

If you want to see a tool with NO clearance cutting a ball.
go to you tube and look for ( ball turner) by Jim Sehr.
You can turn an od but you can not face with the tool.
The cutter is a 1/4 round held straight UP. Cutter should be on dead center to work well.