What inserts do you like and why?

[DavidR8]

I didn't see this in the video. (Yes, I watched the whole video.) I did understand his point about splitting the cut. It's a good lesson. Something I never did before but fully understood. I might try it more in more detail another day.

I guess I am a "forum idiot who sneaks up on my dimensions". However, I have only blown a few in a few decades so I'm not accepting his criticism. In fact, unless I'm missing something I'd say that I use the same technique on sneakups as he does with bigger cuts. Basically that is to measure, set a cut, take a cut, measure again, take the same cut or very close, measure again, etc. The key being to take the same cut so spring back etc are accounted for and you are not chasing your tail.

I can't wait to try it with bigger cuts.

But I did not see anything in his video about this business of nose radius limiting the minimum cut.

I didn't learn the nose radius thing from Stefan. That I learned from folks over on Hobby Machinist when I asked why I missed dimensions. After explaing the setup, tooling and material someone said that the nose radius of that insert is xyz so any cut has to be at least that.
Then I was referred to that video as a primer on hitting dimensions.
Nothing more, nothing less and certainly not calling anyone an idiot. I'm just reflecting my learning about insert tooling...

 

[little ol' e]

After explaing the setup, tooling and material someone said that the nose radius of that insert is xyz so your last cut has to be at least that.

In theory that is what some think.
You do have wiggle room with speeds and feeds with DOC's in any condition thou. Carbide needs a good amount of material to bite on, no question, otherwise your essentially grinding the insert away with shallow DOC's .
When taking under .01 with any insert, you end up wanting to increase the speed due to the surface finish becoming worse and worse, that's when people give up on indexable tooling and reach for the HSS in my experiences over the years.

 

[Former Member]

Do you sneak up on dimensions with HSS tooling?

How you cut whether you sneak up and account from give (spring back) in material's or do you do a cut to dimension without worrying about it. No matter what you do all that matters is you do it consistently and you will get the results that you want. Bounce back and forth so will your results.

Some of you have done one method or the other for years, stick with it as it works for you.

 

[DavidR8]

Do you sneak up on dimensions with HSS tooling?

I used to because I was afraid of overshooting. It's also a bit of a holdover from wood working where hitting a really precise dimension involves taking smaller and smaller cuts, using increasingly precise tools. Chop saw, --> hand saw, --> hand plane for example.
It's a hard habit to break.

 

[Former Member]

In theory that is what some think.
You do have wiggle room with speeds and feeds with DOC's in any condition thou. Carbide needs a good amount of material to bite on, no question, otherwise your essentially grinding the insert away with shallow DOC's .
When taking under .01 with any insert, you end up wanting to increase the speed due to the surface finish becoming worse and worse, that's when people give up on indexable tooling and reach for the HSS in my experiences over the years.

I'm surprised at your view on this, I regularly do cuts of 0.001" and achieve the results required along with great finishes.

My suspicion is that you have not set up tooling correctly, either too high or too low with carbide does effect finish quality greatly as it smears or grabs when cutting. Correctly set up carbide cuts as it should.

 

[Susquatch]

Nothing more, nothing less and certainly not calling anyone an idiot.

Holy smokes. That was supposed to be a joke David! I never considered that you might think I took offense! Absolutely ZERO offense taken. My apologies for leading you or anyone else to think otherwise!

OK, gotcha on the source of the nose radius limitation. But just so you know, I don't think that's right. I have not analysed it yet, but my instincts say that you have been misled. I'll think on it some more before and after falling asleep. Maybe @PeterT can help using his guru cad talents (if he feels like it).

Perhaps a small insight into my thinking. While there is a little side pressure on the insert due to its right to left travel, this is minor compared to the cutting loads which are primarily down against the top of the insert as the part turns. Or looked at slightly differently, the insert cuts left only by the feed rate per revolution. However, the majority of the cut is the full circumference per feed unit left.

I'm still very pleased to finally understand where the folks who don't believe in sneaking up on dimensions are coming from. Can't wait to try their version of it. Heck, I might even change my process!

 

[Canadium]

I didn't see this in the video. (Yes, I watched the whole video.) I did understand his point about splitting the cut. It's a good lesson. Something I never did before but fully understood. I might try it more in more detail another day.

I guess I am a "forum idiot who sneaks up on my dimensions". However, I have only blown a few in a few decades so I'm not accepting his criticism. In fact, unless I'm missing something I'd say that I use the same technique on sneakups as he does with bigger cuts. Basically that is to measure, set a cut, take a cut, measure again, take the same cut or very close, measure again, etc. The key being to take the same cut so spring back etc are accounted for and you are not chasing your tail.

I can't wait to try it with bigger cuts.

But I did not see anything in his video about this business of nose radius limiting the minimum cut.

@DavidR8 has probably been reading the David Best book on insert tooling where this is spelled out more thoroughly.

 

[DPittman]

For sure, sometimes I will throw my morning coffee at it, then my lunch...

Yes coffee makes everything run smoother, it's an excellent lubricant, especially for the mind.

 

[DavidR8]

@DavidR8 has probably been reading the David Best book on insert tooling where this is spelled out more thoroughly.

I do own that book and it's an excellent reference.

 

[Susquatch]

I do own that book and it's an excellent reference.

Can either of you (@Canadium and @David_R8) explain it to me? I'm drifting off to sleep here. So far I don't get it. I don't think sleep is gunna change that.

 

[PeterT]

Carbide needs a good amount of material to bite on, no question, otherwise your essentially grinding the insert away with shallow DOC's .
When taking under .01 with any insert, you end up wanting to increase the speed due to the surface finish becoming worse and worse, that's when people give up on indexable tooling and reach for the HSS in my experiences over the years.

This gets repeated often, but I am still struggling to understand why or what the basis is. I mentioned this in post #142 where I scribbled on the little operating window chart provided by carbide insert manufacturer. Particularly where I randomly flagged a faceted style finishing insert with a very small DOC range, 0.002-0.032" if I understand the specs correctly (excerpts below). There may be other carbides optimized with even smaller DOC than this, I just grabbed this one as example. This (0.002") seems to completely contradict 'a good amount of material'. Yes, there are heavy hogger carbides & I think that DOC is reflected in their respective operating plots, no? Isn't that how FT machinists choose tools?

Looking at this a different way, say you matched a HSS grind to dimensionally identically equal a carbide - rake, relief, nose radius, edge sharpness, surface finish.... (for now disregard carbides chip control features & coating to keep thing simple). What are we left with? The 2 tools differ only in their basic material properties: hardness & modulus & ?? Now all of a sudden they have dramatically different DOC 'bite'? That makes no sense to me. Now running them both for 1000 parts in production mode is a different thing. I'm just asking why does carbide 'need' a big bite?

 

[PeterT]

I must admit I'm a bit confused by this particular graph because they kind of plop the various insert models over the operating range. Maybe more of a sales brochure format?
i.e. the X&Y axis is not a linear progression, it relates to the particular insert. But the way I interpret their operating range is the 2 corresponding shaded extensions. Maybe its 0.001-0.008"? I dunno
The other image is how Korloy & others display their graph, a little easier to digest

 

[Dabbler]

From my experience of using carbide, even ground and polished ones, the DOC is only a small part of the story. For a polished carbide insert to not 'skate' as I call it, or @little ol' e puts it 'grinds', you need pretty high RPMs and feed rates...

Maybe things have changed and newer specialized inserts may contradict this, I'm fine with being wrong.

But for an ali-express insert or even a mid range Kinnemetal insert (which is all I have direct experience with), My minimum DOC is about 6-16 thou depending on the profile. If I hone it to a sharp insert I can get away with .004-008 minimum DOC. So for my purposes I never take less than .010 with a carbide insert, just to be safe.

With HSS, I can easily get to .001 min DOC.

So apart from making a theoretical discussion out of this, where's 'the meat'? For a non-ground cheaper coated carbide insert, you need to take at least the radius, if not more, which for the insets I buy is still a hefty chunk, around .010-.018 [correction]

For a ground an polished insert I take about .010 - no less certainly. I just have to plan my turning accordingly and leave enough for filing and honing as required.

 

[PeterT]

From my experience of using carbide, even ground and polished ones, the DOC is only a small part of the story. For a polished carbide insert to not 'skate' as I call it, or @little ol' e puts it 'grinds', you need pretty high RPMs and feed rates...

But for an ali-express insert or even a mid range Kinnemetal insert (which is all I have direct experience with), My minimum DOC is about 6-16 thou depending on the profile. If I hone it to a sharp insert I can get away with .004-008 minimum DOC. So for my purposes I never take less than .010 with a carbide insert, just to be safe.

So apart from making a theoretical discussion out of this, where's 'the meat'? For a non-ground cheaper coated carbide insert, you need to take at least the radius, if not more, which for the insets I buy is still a hefty chunk, around .010-.018 [correction]

For a ground an polished insert I take about .010 - no less certainly. I just have to plan my turning accordingly and leave enough for filing and honing as required.

I will reference a different but well known manufacturer, Korloy. Their operating charts are a bit more straightforward to read. I'll do some metric to imperial conversions just for consistency (so check my math haha). These are off the shelf lathe inserts. I just pulled a few random ones that had the application 'finishing' in their description. I'm trying to direct attention to what the manufacturer recommends for feed (Fn) and depth of cut, DOC (ap) vs. the narrative discussion thus far, what people claim or have experienced as 'minimums'. Again, if I am out to lunch let me know. I'm just conveying what is in the specs.

First off, I recall my 14x40 lathe has a power feed range of 0.003 - 0.086 inch/rev. That works out to .076 - 2.184 mm/rev so on Korloy application chart, roughly the blue box. That seems to be in a useable range of many carbide choices, just perusing the offerings. Some are outside the range as would be expected, so don't run those.

So here are some random finishers. Behind the scenes they vary by other sub-criteria - material suitability, coating, nose radius, rake geometry, chip control, blah-blah
I picked the low Fn & ap values off the respective blue/green bars & converted to imperial cells on right cells.
So in this example Fn=0.002 in/rev, DOC=0.004"

Some more. I actually use the AK myself for aluminum. It says DOC=0.004" but I can tell you (or show you next visit) a thou comes off as a tiny continuous thread. If I change feed & take off the hilltops I'm pretty sure its half that, 0.0005". On that basis, and I am only guessing here, I don't think the operating bars are hard stop do-not-pass limits. Obviously its peeling off a thou, just like you know your HSS is peeling off a thou. The bars (or operating windows on other vendors) is probably for guidance, or maybe extended tool life, or other factors important for manufacturing, I dunno. The point is, these DOC examples are not 10,20,30 thou just because its carbide.
Note the 2nd pic KF, insert. Min DOC = 0.0004" I have seen that style in Ali / Ebay lurkings. So I don't think they are super exotic or even 'new'. Now one could argue that Fn is very fine, outside the range of hobby lathe. But again will it be 'pretty good' at my min feed? I would wager a coffee yes.

Example on the other end of the range, cited for heavy duty cutting. Minimum DOC of 0.275" That is a hefy bite. Very different cutting geometry as would be expected.
I hope you see where I'm going with this. On one end of the carbide spectrum are Finishers. On the other end are Roughers. In between is a bazillion other inserts. Which one do you have & what is the corresponding operating window?

 

[Canadium]

At one extreme too fast rpm results in too much heat which results in a poorer result. At the other extreme too slow rpm will fail to cut and just rub or cut intermittently. The "ideal" rpm can be estimated by a simple formula RPM=(SFM/D)X3.82
SFM=surface feet per minute
D=diameter of workpiece in inches
3.82 = a constant derived from more complex formula RPM=(SFMX12)/(DXpi)

This does not account for differences caused by differences in quality of the material machined which is typically given as a table of material vs ideal SFM to KISS

 

[Former Member]

At one extreme too fast rpm results in too much heat which results in a poorer result. At the other extreme too slow rpm will fail to cut and just rub or cut intermittently. The "ideal" rpm can be estimated by a simple formula RPM=(SFM/D)X3.82
SFM=surface feet per minute
D=diameter of workpiece in inches
3.82 = a constant derived from more complex formula RPM=(SFMX12)/(DXpi)

This does not account for differences caused by differences in quality of the material machined which is typically given as a table of material vs ideal SFM to KISS

Points to one thing I've mention all along, coolant/lubrication is important particularly for carbide cutting results vs wear prevention on HSS.

 

[Susquatch]

I hope you see where I'm going with this. On one end of the carbide spectrum are Finishers. On the other end are Roughers. In between is a bazillion other inserts. Which one do you have & what is the corresponding operating window?

I like your thinking Peter.

Ever since we came down out of the trees, humans have had a long history of challenging accepted facts, evolving our knowledge, and creating new knowledge. As you know, I love sayings. The one that comes to mind in this case is: Many an impossible thing has been done by someone who didn't know it was impossible.

I have always accepted the direction that says Carbide can't handle small cuts and learned to live with it. But my views are changing. The day that @Dabbler talked about honing carbide was an eye opener for me. In fact, just yesterday I tried sharpening a carbide threading insert. It was an eye opener. I got nowhere. I plan to try a diamond wheel or a diamond hone next.

In the process of deciding what grind I should be shooting for, I had a good look at the old edge with a 20x jewelers loop. It was unmistakably rounded vs what a sharp HSS threading tool looks like. So I plan to try to make it sharp and we will see how it works.

In the meantime I thought a little about the conventional sintering process used to make carbide inserts. A sharp edge would be difficult to make easily. Then the question of edge durability for sintered parts passed through my mind with a similar ending. Inherently difficult to maintain an edge.

So it's not hard to see why and how early carbide or cheap carbide might have developed a reputation for poor sharp performance.

The terminology that @little ol' e & @Dabbler use are also informative - or at least provide a bit of a window into how they visualize a carbide insert cutting steel at the margins of its capability. Rubbing in one case, skating in the other. Both are excellent ways to visualize a failure to "bite".

No matter what our knowledge levels, I think the majority of machinists can appreciate the differences in the way various solid materials cut. I'll arbitrarily put rubber at one end and diamond at the other. Additionally, we can all appreciate the way that different materials interact with each other in a cutting process.

I think you are probably onto something. The mere fact that you have found documented examples of Carbide inserts that are recommended by their manufacturer for use at low depths of cut is compelling to me.

It might be time to put that old knowledge which says that carbide cannot make tiny cuts away and accept that the world is round. Maybe the correct question isn't can carbide make shallow cuts, maybe the correct question is which carbide insert do I use to make shallow cuts?

All great musing.

I just want to know which quality holder and inserts to buy to expand my machining horizons and improve my carbide machining horizons.

 

[Canadium]

I just want to know which quality holder and inserts to buy to expand my machining horizons and improve my carbide machining horizons.

About half of the David Best book is recommendations.

 

[Susquatch]

About half of the David Best book is recommendations.

OK...... Now you have my undivided attention.

Just so you know, I really like books. I have a nice library that will heat the house for 5 years after they bury me.

How old is this book? Does it know what @PeterT has been talking about? Or does it still think the sun orbits the earth?

I know, I know, I know...... Does anyone know what Peter is talking about???

JKg Peter!

Gunna go find this book right now.....

Ps - I totally love that book you folks pointed me at - Beyond Measure by James Vincent. Fantastic read.

 

[Susquatch]

@Canadium - it is $75 Canadian. Is it really worth that much?