Parting off blade shape.

[Parlo]

Does anyone believe that a parting tool only cuts on the leading face.
There is a lot of discussion on this subject at the moment.
One opinion believes that only the face of the tool cuts when plunging in.
The other opinion is that the face and edges cut, even if relieved.

 

[rabler]

Joe Pie (youtube) did a short video where he made a HSS trapezoidal grooving tool, essentially a wide parting blade, wider at the front and narrowing significantly, and plunged it into a piece of brass. I believe it was in answer to this discussion.

 

[mmcmdl]

Wouldn't see how the relieved sides would cut ? If they cut , they aren't relieved ! You could part with a form tool of course such as a pulley groove tool in which the sides would cut . If you're talking about a regular parting groove tool , be it HSS or carbide insert type , the face cuts .

 

[Cadillac]

I think it’s easy to see where it’s cutting look at the chip. The face and top are what make the cutting surface. Reliefing the top I find helps the cut.

 

[SLK001]

You should cut only on the face. If you're cutting with the edge, then your tool isn't perfectly perpendicular with the work and you are going to break your tool.

 

[Winegrower]

The other opinion is that the face and edges cut, even if relieved.

Perhaps some advocate of this theory would explain why he/she holds this opinion?

 

[Parlo]

Perhaps some advocate of this theory would explain why he/she holds this opinion?

One opinion is that the sides of the chip do not need to be sheared and are detached from the part by tearing. So only the face cuts.

The other theory is that looking down on the top of the blade, the chip has a shear area which is the width of the blade x the feed per rev. This gives the chip a u shaped perimeter of 3 sides that are all need to be cut, even with a trapezoidal ( dovetail ) shaped tool.

 

[cathead]

Sometimes I will add a small groove down the middle of the top of the cutter to force the chips to cave in some resulting in
better chip removal. Another thing that is handy is to sharpen the cutter at a slight angle on the face to produce a nice clean
cut on the part being cut off.

 

[Winegrower]

I saw the Joe Pie video before I started this thread, so of course I will just leave this question for the machining philosophers.

 

[Parlo]

I saw the Joe Pie video before I started this thread, so of course I will just leave this question for the machining philosophers.

I understand:
There is a palpable reluctance to stand up and be counted on this one. It really is lesson 101 in cutting tools.
For example:
Is it possible to cut a slice of pizza with one cut? - No.. - two sides of the triangle need to be cut to remove the slice from the disc.
Is it possible to cut a triangular thread with one side of the tool? No.. once again the perimeter needs to be gradually cut to remove the chips.

A proposed theoretical one dimensional line ( leading face of the tool ) will never shear the sides of a groove, how are they cut?