Parting off blade shape.

Parlo said:
leading face of the tool ) will never shear the sides of a groove,
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You don't suppose the ends of the leading edge cut to the ends, do you. Well, they do, whether you call it cutting on the side or the face.
 
T Bredehoft said:
You don't suppose the ends of the leading edge cut to the ends, do you. Well, they do, whether you call it cutting on the side or the face.
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Don't forget, the chip has a thickness equal to the feed per rev. This creates a 3 sided shear requirement which is the blade width plus the feed per rev per side. So yes, the blade shears at the front and also has to shear at the sides.
Are you saying that there must be cutting around the corners of the leading face to detach the swarf from the sides?
 
Parlo said:
Does anyone believe that a parting tool only cuts on the leading face.
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If the parting tool is normal (90º) to the work, then only the face cuts--the sides are present to hold the face from vibrating.

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.
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If the tool is properly setup in the tool holder, only the face cuts.
If the tool is not set normal, all sorts of strange effects may be encountered.
 
Mitch Alsup said:
If the parting tool is normal (90º) to the work, then only the face cuts--the sides are present to hold the face from vibrating.



If the tool is properly setup in the tool holder, only the face cuts.
If the tool is not set normal, all sorts of strange effects may be encountered.
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Just to clarify. The parting tool is a dovetail shape. Square at the face and relieved sides.
The chip cutting perimeter, looking down on the tool is the same shape as the tool. It stays the same throughout the plunge.
The face cuts the bottom of the groove and the sides of the tool cut the swarf from the sides of the groove .
The swarf thickness is the feedrate per rev, which is the same as the depth of cut per rev, which is also the same amount the sides need to cut per rev.
What part of the tool detaches the chip from the sides of the groove if only the front cuts?
 
How much top rake does the tool have?
If you're only feeding a couple thou per rev, then the leading edge could be slicing under the material and pulling it off the sides instead of cutting. That'll leave a nasty finish, but isn't that what we see from most parting operations.
 
No top rake, completely flat to keep thing simple and not introduce any more variables..

I agree; if the sides of the tool are not cutting & the material is 'pulled off ' in parting and grooving operations, a poor finish is probable.
If a good finish is acheived on the walls of the groove, would you agree that the sides of the tool are cutting?
'
 
Parlo said:
No top rake, completely flat to keep thing simple and not introduce any more variables..

I agree; if the sides of the tool are not cutting & the material is 'pulled off ' in parting and grooving operations, a poor finish is probable.
If a good finish is acheived on the walls of the groove, would you agree that the sides of the tool are cutting?
'
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I'll agree, as long as the beer holds out. But this very much reminds me of a serious debate about the number of angels that will fit on the head of a pin. :)
 
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.
 
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