Parting off blade shape.

[Parlo]

Parting blade cuts on the face in normal operations. When cutting straight in you have no side pressures. You swarf will be as thick as the infeed till it breaks off.
When looking at the parting blade what gets dull. The face top edge not the sides, and I e seen some carbide parting inserts with side relief no way for sides to touch.

Good point, the wear on the top of the blade is a true indication of where the the cutting is done. No visible wear is seen on relieved sides as they don't touch the sides of a wider groove.
Wear can be seen on the corners though, this is from the depth of cut which is the feed per rev. This indicates clearly that the cutting is also performed on the sides, but only on a small distance from the cutting face = to the feed per rev.

 

[mmcmdl]

Wear can be seen on the corners though, this is from the depth of cut which is the feed per rev. This indicates clearly that the cutting is also performed on the sides, but only on a small distance from the cutting face = to the feed per rev.

I'm not following you on your thinking here .

Good point, the wear on the top of the blade is a true indication of where the the cutting is done. No visible wear is seen on relieved sides as they don't touch the sides of a wider groove.

This is your answer , you said it yourself . Of course you'll see wear on the corners , they are part of the face which is doing the cutting !

 

[Parlo]

I'm not following you on your thinking here .


This is your answer , you said it yourself . Of course you'll see wear on the corners , they are part of the face which is doing the cutting !

Very true. A corner has two sides, one is the face and the other is the side.

 

[mmcmdl]

On ignore .

 

[Parlo]

Here is a link that describes how the formation of the spiral grooves either side of the groove are greated by the sides of a relieved tool.
The same pattern can be replicated by facing with the same relieved tool, a coarse feed will show the spiral better than a fine feed.
The section of the spiral will be the same as the shape of the tool corner giving a saw tooth finish.
I think this helps to describe how the side of the tool shears away the chip from the sides by leaving the tool corner shape on the part.
The advancing tool won't knock off the peaks formed by previous revolutions as it is smaller due to the relief angle.

parting tool.jpg

drive.google.com

 

[Parlo]

Thanks for all the posts.
It seems from this small straw poll that:
4 - posts say on the front only.
5- likes for front only.
Just one like for sides and face.

Unfortunately the diagram and my descriptions haven't convinced this small cohort.
Before I demonstrate my expectations on video, is there anyone who has seen the image willing debunk my conclusions.

Cutting material away from the parent stock with tools that generally need relief to cut, is at the heart of most of the posts on the forum. Please post why you agree the trapezoidal tool cuts on the sides, or if you disagree, the reasons why not.

 

[OCJohn]

 

[Parlo]

Thanks John for posting the video.

The demonstration only shows that a fine feed produces a fine finish. The initial plunge cutting of the groove was at such a very slow hand feedrate it could not show the saw tooth ( phonograph ) section grooves on the sides, as the overlaps were so close together.

When the face was cut under power feed it produced a much coarser finish and somehow actually managed to break the sharp corner and even remove the scratch where the tool was retracted, both off camera.

Apparently the video was produced to disprove the now deleted comments from Bill Shiff that categorically proved that a relieved parting tool will cut on 3 sides and produce a sawtooth finish on the walls of the groove. To disprove his conclusive comments the sides were " removed " actually just relieved to be precise in an attempt to prove cutting was only on the face.

Realizing the comments were too descriptive and overwhelmingly correct, all the supporting comments were deleted and then....

The video description was changed to infer that Bill's comments suggested that a dovetail tool could not produce a groove at all with a tool of this shape. Not, as Bill confirmed, that the tool would produce a groove but with a saw tooth spiral on each side, which it simply does. The video attempts to hide the sawtooth grooves by handfeeding the tool as slow as possible to make them less visible.

Thereby suggesting Bill's conclusions were wrong and the apparent victory assured. Which is all that matters?

 

[FOMOGO]

I've had great luck parting on the old Atlas 12" lately with a standard HSS blade. Sharp and straight seem to be the important components. That and a little practice. Lower rpm also seems to help on machines that aren't supper rigid. I touch it up on the grinder after every few operations. Mike

 

[jaek]

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.

What kind of nonsense is this? The parting tool cuts on the top, not the front or the sides.