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Vertical shear lathe tool

John Conroy said:
Experimenting with angles I've tried between10 degrees and 20 degrees from vertical. 10 seems to give a better finish and the edge needs to be razor sharp.
Click to expand...

I got around to measuring one of my shear tools. As I expected, it looks like they are all 10 degrees plus/minus a degree and they all have a mild 5 degree back/end relief. I've tried lower back reliefs but they seem to catch swarf once in a while with a mild effect on finish. Too much and the edge seems to dull faster. I ended up at around 5.

Here is one to show what my typical grind looks like. Please ignore what looks like a chip breaker - it's actually an artifact of a previous grind. No point in chip breakers on a shear tool.

20230414_193441.jpg


20230414_193615.jpg
 
johnnielsen said:
As an aside.

What you call a shear tool, I have called a skiving tool. I know that some cutting tool manufacturers make custom tooling incorporating the concept.
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Makes sense in a way. I always thought of "skiving" as peeling off a layer of something, usually keeping the layer intact (a skive), but not necessarily. So that works for me too.

The word "Shear" works cuz the cutter acts like a scissor edge (also called shears) shearing the metal sideways (in shear).

Seems like the forum is into words lately! Elsewhere, endmill lead was asked about. My dad spoke many different languages. One of his interests was Etymology - the derivation and evolution of words. I inherited a very limited version of his interest. I think @Dabbler dabbles in Etymology sometimes too!

Nice piece of info John. Next time I see "Skive tool" I'll know what is meant!

Murphy (or Google) will make sure it comes up shortly! LOL!
 
johnnielsen said:
Here is a link to an article about it.
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If I knew you better I'd think you are playing a great joke on me! But likely not.

Every once in a while I read some article that makes me feel as dumb as a two toed sloth. This was one of them. I had to read the whole thing three times before it finally dawned on me that they are NOT describing the same thing as what I normally call a shear tool.

I'd love to hear what you and @Dabbler and @PeterT understand from reading this, but here is my take:

What they are describing might be better called a "phased form tool" (my words simply thrown out there to help discern the difference). Think of it like a wide shear tool where the width contains the desired form but cut on a steep angle so the form only cuts where the edge is tangent to the part. You raise the tool from top to bottom (bottom to top on the part) so that the entire form is not cut at once but instead only cuts that portion of the form dependent on the height of the tool.

They do describe the actual cutting as a shear process. And they also claim the finish benefits of shearing, but I think the main advantage has little to do with shearing and much to do with using a very wide form tool without the heavy cutting forces that would normally result from such a wide edge being plunged into the part all at once.

Why would I like to know what you and others think? Well, simply put, I'm still not sure...... I wish the form they chose to describe wasn't so linear. Some of the examples are great but they don't show a corresponding form edge. So I was left to speculate about the meaning and intent. That's a very dangerous instigation. Left unguided, my brain can turn an eyeball inside out. Maybe I've made a mountain out of a mole hill.

Anyway, at least I can point out that I don't think they are describing the shear tool I normally think of. At least that way you guys don't get dragged down a maneating rabbit hole like I was. Or maybe they are but I just don't see it!

Finally, if they are describing what I think they are describing, I wanna watch someone sharpen that form tool! :oops::eek:o_O
 
Yes, to my eye, it looks to be a different geometry setup than what was being discussed as a shear tool, which always has its (longitudinal) cutting edge at the 3:00 stock position viewing from HS to TS.
I have seen some different parting/deep grooving tools & also ball turning cutters possibly like the article.
Interesting that the rake angle goes from neg to pos based on tool setting significantly below center. Maybe the sketch angles are exaggerated, or? Show us some of your setups & maybe that will clarify.
 

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I think the skiving principle is what is used during a “cut knurling“ operation as well.

There seems to be a speed, tolerance and superior finish advantage in using the skiving (shearing) process of material removal.

Very cool stuff. Thanks for sharing @johnnielsen.
 
Thanks @johnnielsen, @Dabbler, @PeterT, @RobinHood.

I can relax a bit. There is still at least a few more weeks before SWMBO drags me off to the looney bin....

@RobinHood - Excellent observation regarding cut knurling. It took me ages to get my head around that too, but like @Dabbler says, once YOU finally do see it, you can't unsee it! LMAO! Pretty sure this skiving thing will soon be like that too! Now that I know I'm not miles off base, I can take another look at it.

@johnneilson - thanks for teaching me something new! I'd pay the temporary confusion price for things like that 1000's of times over again.... all year long! THANK YOU!
 
johnnielsen said:
Here is a link to the right technique but not the descriptor I am used to. I will call it the Vertical Shear method from now on.

Click to expand...

A rose by any other name smells the same John.

Yes, this technique exactly covers my understanding of a shear tool and how it is used. The only place it differs is in the aggressiveness of the angles. It seems I am at the bottom limit of what the article suggests. But it works for me that way, so I'm not about to change my practice.

I found the discussion about using a shear tool for facing rather interesting. I may or may not create a new thread on that aspect of using a shear tool later on. But for sure not right now. If I do, I'll reference this thread to connect you in.

Also odd to call it "whispy" swarf when almost everyone can recognize steel wool... LMAO!
 
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