Insert clearance angles. Uses?

I have two sets of turning tool holders, one with 7* and the other with 11* clearance (or relief) angles.

Searched around but couldn't find what the practical difference was other than tip strength, so lower angles better for roughing obviously.

Anything else?

Wall clearance for profiling, I make control valve parts so I turn a lot of contours and radi in stainless and nickle alloys. The shavings are stringy, especially on light finish passes, and have to go somewhere. I find they evacuate the cutting zone better if there is less insert in the way, even more so when boring to a shoulder. I don't know if this gospel but these considerations inform my choices when thinking about tool selection.

And bigger clearance angles create less heat - especially on plastics.

I am confused and am asking, not saying anything.

As I understand it, inserts have the clearance angle built in to them. At least every one that I have seen does. They are designed to mount at a horizontal angle (0 deg) in the holder and have the clearance and rake angles set for that mounting angle. So, just what are these holders actually doing? Adding more clearance? Are these holders a way to decrease the rake angle or even make it negative? Or what? I am curious.

A photo might be nice.

If you push the tool tip in against the diameter of the work, and then look at it from directly above, the clearance angle is the angle that the front edge of the tool makes with respect to the work or to the spindle center line.

This has nothing to do with the rake or relief angles that I think EPAIII is thinking of.

Though, to answer EPAIII's question, any insert that has a 0 degree relief built in will need to be tilted forward in the holder, to get front and side relief from the work. CNMG insert, for example.

awander said:

If you push the tool tip in against the diameter of the work, and then look at it from directly above, the clearance angle is the angle that the front edge of the tool makes with respect to the work or to the spindle center line.

This has nothing to do with the rake or relief angles that I think EPAIII is thinking of.

Though, to answer EPAIII's question, any insert that has a 0 degree relief built in will need to be tilted forward in the holder, to get front and side relief from the work. CNMG insert, for example.

Click to expand...

Ya, it's not rake I'm asking about, it's the clearance angle below the insert.

For instance, TPXX inserts have 11* clearance and TCXX have 7*.

I use some high rake 11* Iscar inserts a lot for finish turning and boring but they're not great for roughing, plus they only come with an .008" nose radius:

https://www.iscar.com/eCatalog/item.aspx?cat=5505423&fnum=1682&mapp=IS&app=28&GFSTYP=M&isoD=1

For roughing I've been using the holder for 7* but the selection is limited with the SB-2 (80-90* 2-56) screw.

Sooo, I was thinking of just getting some inserts more suited to roughing for the 11* holder but was wondering if it will work as well?

To some extent, it works the opposite way, EPAIII. The inserts with larger clearance angles usually go with holders that give a positive top rake. Negative rake inserts usually have zero clearance angles, so their holders have to tilt them to a negative top rake to provide effective clearance.

Terry Keeley said:

Ya, it's not rake I'm asking about, it's the clearance angle below the insert. For instance, TPXX inserts have 11* clearance and TCXX have 7*.

Click to expand...

As a very rough rule of thumb, you need more clearance on softer materials and on work-hardening materials, less clearance on hard materials.

However, I think buying inserts with 7 degree clearance to use in holder designed for inserts with 11 degree clearance will not make you happy. The issue is the insert pocket shape. It's quite possible that the insert with lower clearance angle won't fit in the higher clearance angle pocket, and won't be supported if you shim it up high enough to fit. If you get lucky with a particular 11 degree holder, be very happy and make smug noises at me.

awander said:

If you push the tool tip in against the diameter of the work, and then look at it from directly above, the clearance angle is the angle that the front edge of the tool makes with respect to the work or to the spindle center line.

Click to expand...

Actually this top view on the front is the tool lead angle.
Clearance angle is the side or flanks of the cutting tool so in a zero by zero rake holder a 11 has 4 more degrees than a 7. Often called heel clearance.
What counts here is "effective clearance". A 11 degree insert in a 4x4 positive pocket is the same as a 7 in 0x0.
Also feed per rev decreases the front effective clearance which is why threaders need more rake on the leading side. The cut material is "coming at you" decreasing the clearance.
The same is true in milling. Effective clearance is clearance not just as mounted in the holder but in the cut.

Differing materials (and diameters) need different heel clearance angles.
Very generally speaking softer materials need more angle.
This is due to the compression that takes during shearing. The material "springs back" after shearing trying to rub on the flank of the tool as it relaxes. "Softer" stock tends to compress and release more.
For this reason aluminum cutting needs more (another 2 to 4 degrees) and plastics even much more angle here. This is one thing in aluminum cutting that can't be fixed with high rake chipbreakers in a steel cutting designed holder or milling cutter.
Larger dias also need more as the part does not "fall away" from the cutting tool as fast.

In the same material a higher side rake inserts allows you to tip the insert in the holder (or go above center) making the top more positive cutting.
Certainly higher is weaker in breakage strength so you don't want more clear than needed to prevent flank contact or wear.

Before others jump on me with real world experience I should add that high positive top rakes do remove some (or a lot of) compression force allowing you to get away with less heel clear as the spring back is reduced.
Do not confuse flank wear here, this is flank contact in the first cuts of a tool while the top cutting edge is in perfect condition and not worn.

Too little effective is bad and rubs, too much effective is bad and leads to early breakdown of the edge which then looks like flank wear.
It is all so .
Try it and run with what works for you. The proof is in the pudding.
Bob

What you're calling "clearance angle" is properly termed "relief angle"

Terry Keeley said:

Ya, it's not rake I'm asking about, it's the clearance angle below the insert.

For instance, TPXX inserts have 11* clearance and TCXX have 7*.

I use some high rake 11* Iscar inserts a lot for finish turning and boring but they're not great for roughing, plus they only come with an .008" nose radius:

https://www.iscar.com/eCatalog/item.aspx?cat=5505423&fnum=1682&mapp=IS&app=28&GFSTYP=M&isoD=1

For roughing I've been using the holder for 7* but the selection is limited with the SB-2 (80-90* 2-56) screw.

Sooo, I was thinking of just getting some inserts more suited to roughing for the 11* holder but was wondering if it will work as well?

Click to expand...

I will not argue terms with you. Call it what you will.
I think myself still a rookie after some long time invested but I'm learning more everyday.
Willing to surrender that you know cutting tools, geometries and cutting actions better than I can ever understand.
Bob

Bob, I should have specified, I was calling the trailing edge of the tool's angle to the work, the Clearance Angle

CarbideBob said:

Actually this top view on the front is the tool lead angle.....

Click to expand...

awander said:

What you're calling "clearance angle" is properly termed "relief angle"

Click to expand...

I've seen it called both, Iscar calls it "clearance angle":

https://www.iscar.com/eCatalog/MoreInfo.aspx?mapp=IS&fnum=1682&app=28&isoD=-1


Thanks all for the input, it looks like I probably won't see much difference just using my "TPXX" holders and 11* inserts. I use mostly aluminum and plastics and for the times I want to hog some 4140 or whatever I can't take 1/4" cuts on my Super 11 anyway, lol.

And no I wasn't thinking about trying to use the 7* inserts in the 11* holders or vice versa.

Thanks guys, I do get it. I just have not had any experience with that kind of insert. Perhaps I should try some.

There's more things under the sun than anyone has time to imagine.

Thanks for the clarification.

holders with a positive rake? how common are they nowadays? i have some ancient ones for inserts that are flat on top. but with the current inserts i see no sense behind them.

Terry: Several years ago, I had a customer that needed some pockets for profiling type inserts milled into some high dollar wood lathe tools. The inserts were as you describe, more clearance than normally used in metal turning. These were hand tools with exotic, beautiful custom wood handles.

JH

EPAIII said:

Thanks guys, I do get it. I just have not had any experience with that kind of insert. Perhaps I should try some.

There's more things under the sun than anyone has time to imagine.

Thanks for the clarification.

Click to expand...

This is a really good thing and it is best to find out by educated descisions what works best for you.

A good process and access to knowledgeable salesmen will give you much more savvy in the use / best use of inserts.

Iscar and of course the many mainline insert makers can teach you a lot.

If you ask for help on here you will get good assistance. You do not have to wait because your decision to investigate will give you many first hand opportunities to better your skill using these.

There used to be days when these inserts were so new and so expensive that the reps would come out and hand out books on their inserts. They included extensive information that when applied one could do well on their own using what was learned. They also showed up in person with the booklets. They answered questions and everything on how to maximize good use. In later years they were not doing that as much. They sold a lot more inserts.

We treated the individual inserts like gold. The machines we used were manual and the full use of the insert strength and the righty of the machine was a very fun combination.

Good luck.

Terry Keeley said:

Ya, it's not rake I'm asking about, it's the clearance angle below the insert.

For instance, TPXX inserts have 11* clearance and TCXX have 7*.

I use some high rake 11* Iscar inserts a lot for finish turning and boring but they're not great for roughing, plus they only come with an .008" nose radius:

https://www.iscar.com/eCatalog/item.aspx?cat=5505423&fnum=1682&mapp=IS&app=28&GFSTYP=M&isoD=1

For roughing I've been using the holder for 7* but the selection is limited with the SB-2 (80-90* 2-56) screw.

Sooo, I was thinking of just getting some inserts more suited to roughing for the 11* holder but was wondering if it will work as well?

Click to expand...

If you talking external turning i would think main difference is strength.

ID turning the smaller the bore the more clearance you need.

Inserts with full-area smooth surfaces are still available. They[FONT=&quot]’re not the most expensive ones and can be useful in some circumstances. For these you need the right angled holders. Am thinking of hard turning, skiving soft materials, milling of nickel alloys at slower speeds.[/FONT]

Thanks guys.

I'm going to "standardize" on the TP(M/G)T 11* inserts, same as the Iscar I've been using. That way it'll fit my turning and boring holders.

Found a good deal on some Kennametal TPGT2152HP that should do well for turning steel.