Are CNMG inserts actually negative rake?

**GT inserts are intended for cutting aluminum. They work very well cutting steel especially on low HP machines.
 
G is the tolerance and T is the hole/chipbreaker, correct? What does that have to do w/cutting aluminum?
 
They have a high positive rake and are polished. I admit there is nothing in the insert designation that spells out the rake and the polish. When I order CCGT I get polished inserts.
 
ddickey said:
G is the tolerance and T is the hole/chipbreaker, correct? What does that have to do w/cutting aluminum?
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There are lots of ccmt aluminum inserts but the ccgt seem to be coated and work killer on steel that tears instead of cutting nice.
 
A CNMG-style toolholder mounts the insert at a 5 or 6° negative rake. This is to provide clearance under the cutting edge of a CNMG insert. The majority of CNMG inserts are double-sided and thus have have a 90-degree front face below the cutting edge (zero relief). A CCMT or CCGT insert is single sided, and has a built in -7° clearance under the cutting edge, so the toolholder for that insert has a zero rake angle (horizontal). You can put a CCMT or CCGT insert in a CNMG holder, but you can't do the reverse because there would be no clearance/relief under the cutting edge.
 
ddickey said:
G is the tolerance and T is the hole/chipbreaker, correct? What does that have to do w/cutting aluminum?
Click to expand...
The "G" tolerance is tight enough that the insert has to be ground or honed sharp after it's out of the mold to meet the tolerance specification. A "M" tolerance is sufficiently sloppy that the inserts coming out of the mold will meet that spec without any further tuning and generally have a more blunt cutting edge. The degree to which the chip breaker alters the geometry to present a positive cutting edge is a function of the manufacturer's grading specification. Some CCGT inserts will have a pronounced spoon-shape behind the cutting edge, others will not - it all depends on the chip breaker spec and grade.
 
davidpbest said:
The "G" tolerance is tight enough that the insert has to be ground or honed sharp after it's out of the mold to meet the tolerance specification. A "M" tolerance is sufficiently sloppy that the inserts coming out of the mold will meet that spec without any further tuning and generally have a more blunt cutting edge. The degree to which the chip breaker alters the geometry to present a positive cutting edge is a function of the manufacturer's grading specification. Some CCGT inserts will have a pronounced spoon-shape behind the cutting edge, others will not - it all depends on the chip breaker spec and grade.
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I wish there was more visibility as to amount of positive rake the inserts have. It's tough to determine exactly what you'll be getting other than CCMT=positive rake.

Does anyone have experience with CNMG inserts on a smaller (~10" 1hp) lathe? I'm thinking I'll end up going CCMT 21.5X for OD holders and boring bar. But am still curious how the CNMG does being negative but having a positively ground insert.

Anyone know of a quality 1/2" SCLCR holder that takes the 21.51 size insert? I see kennemetal makes one for about $75. Any other options I should look at?

Also, are the ISO inserts a direct replacement for the ANSI inserts? It seems like kennemetal makes whole different holders for CCMT0602 inserts and CCMT21.5X although the shank dimensions are actually 12mm instead of 1/2", so that may be the real difference. Are CCMT 21.5X and CCMT0602 completely interchangeable?
 
When I first got my Heavy 10 I ordered some cnmg inserts and holders, including a boring bar. They work, but it's hard to get a decent finish and the machine works hard (and may stall) with anything approaching a reasonable depth of cut. I have since bought a bunch of ccmt tooling, it is much better suited to the capabilities of the machine. I also got some scmt inserts and holders because the inserts have 4 useable corners. I use this one a lot for rough turning, facing and chamfering.

WP_20200404_12_37_49_Pro.jpg

All of my tooling has come from China, mostly Aliexpress and eBay. It is all of good quality. I would never have been able to afford the assortment of tooling that I have otherwise. The inserts are acceptable, if not comparable to the name brands, but at a buck apiece I have no complaints. If you haven't already, I recommend upgrading to a serpentine belt.

The cnmg tooling is rarely used now. Here's a cnmg at work, boring out a 6 in. pipe coupling. 250 rpm, .025 doc, .0042 ipr feed rate.

 
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Lucas E said:
I wish there was more visibility as to amount of positive rake the inserts have. It's tough to determine exactly what you'll be getting other than CCMT=positive rake.

Does anyone have experience with CNMG inserts on a smaller (~10" 1hp) lathe? I'm thinking I'll end up going CCMT 21.5X for OD holders and boring bar. But am still curious how the CNMG does being negative but having a positively ground insert.

Anyone know of a quality 1/2" SCLCR holder that takes the 21.51 size insert? I see kennemetal makes one for about $75. Any other options I should look at?

Also, are the ISO inserts a direct replacement for the ANSI inserts? It seems like kennemetal makes whole different holders for CCMT0602 inserts and CCMT21.5X although the shank dimensions are actually 12mm instead of 1/2", so that may be the real difference. Are CCMT 21.5X and CCMT0602 completely interchangeable?
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You are correct. Those two sizes are the same.
 
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