Parting off blade shape.

[Parlo]

Your drawing shows the dark rectangular cutting surface on the top of the tool perfectly.

Too bad there is no way on here to show a live 3D video of the cutting stresses in the tool and in the part as the tool cuts the part. That is what is missing in this whole discussion.

Does anyone on here have access to an engineering workstation powerful enough to run CAE software that can simulate parting off and create a short video?

Ideally, the video would show several cross sections of the part and the tool at various places and demonstrate the stress gradients of the parting process.

I am going to film a trapezoidal section tool facing off a part at a high feed to show the saw tooth steps formed. This should confirm that the tool cuts on the minor edges and leaves it's form as a spiral groove.

 

[Susquatch]

Would an IR camera would show the heating of the cutting edges? Might be useful to confirm the simulation?

I was thinking something like that earlier near the beginning of this post. My thoughts at the time were that it's entirely possible that part heating and tooling heating might expand the sides of the parting groove enough to precipitate some side cutting. Then it hit me that the whole premise of the discussion was wrong. It isn't the front or the sides, it's the top rectangle and it's edges that does the cutting.

@jaek 's comment about nonsense crystallized it all for me. It's funny how we get locked into nonsense so easily when we ignore the obvious.

 

[Susquatch]

I am going to film a trapezoidal section tool facing off a part at a high feed to show the saw tooth steps formed. This should confirm that the tool cuts on the minor edges and leaves it's form as a spiral groove.

Keep in mind that these spiral marks only show the end result, not the process itself. It could well lead to a misleading conclusion about what is really happening. I think high-speed video that can be slowed down might be more telling because it might show the compression of the material as it buckles and fails ahead of the tool.

 

[Parlo]

I'll make sure I have a rigid setup and hope to feed at least 0.2"/rev. The stock will probably be Delrin or pvc about 4" diameter. If the large relief angle on the tool is reproduced on the face of the part, I will be convinced that the sides of a dovetail shape tool cut & not just the face.
I expect to see a sawtooth profile on the spiral which would be replicated both sides if machining a groove.

 

[Parlo]

Here are some images of a tool & how its profile is transferred to the workpiece despite being acutely relieved.
And a short video of cutting the groove.

 

[jaek]

It is indeed possible to create a very large surface finish with a high secondary cutting angle, tiny nose radius, and a high feed rate.

Is there some larger point being made here?

 

[Parlo]

It is indeed possible to create a very large surface finish with a high secondary cutting angle, tiny nose radius, and a high feed rate.

Is there some larger point being made here?

Several YouTube comments from retired engineer of 55 years, Bill Shiff were deleted because he proved that a trapezoidal ( triangular ) parting tool cut around its perimeter and not, as stated just on the primary edge. With respect for Bill, this is the best evidence I could supply to dispel the myth and to respect his wisdom.

 

[jaek]

Every trapezoidal cutoff tool I've seen has a top cutting face with parallel side edges. This page has some drawings.

Someone could hypothetically grind one like you did, which would result in less rubbing but a worse surface finish. Doesn't seem like a common choice.

Why should people care which edges a cutoff tool cuts on?

 

[Parlo]

Every trapezoidal cutoff tool I've seen has a top cutting face with parallel side edges. This page has some drawings.

Someone could hypothetically grind one like you did, which would result in less rubbing but a worse surface finish. Doesn't seem like a common choice.

Why should people care which edges a cutoff tool cuts on?

The trapezoidal shape in my demonstration is looking from above, your link refers to the shape from the front of the tool.

Parting inserts are relieved to reduce rubbing and improve surface finish.

What's wrong with demonstrating how the perimeter of a tool cuts, it's fundamental in all machining.
The video shows a simulated magnified view of the process for the benefit of those who haven't had the opportunity to have seen a demonstration before.
Lots of the previous posts believed that only the front of the tool did the cutting, so it has helped to dispel that belief.

 

[jaek]

If parting inserts are relieved and they cut on the sides why doesn’t that make the surface finish worse? How can they cut a square groove without square sides?