# Need help understanding different inserts ie CCMT/CCGT etc



## Firstgear (Feb 21, 2019)

When I bought my lathe I also bought the turning and boring boxed set for BXA.  It takes the CCMT/CCGT 300 style according to the description on the web site.  I was looking at a carbide boring rod but it takes CCMT 21.5.

Can someone give me some guidance on what will work with what?  What is the difference?  Help!


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## SamI (Feb 21, 2019)

The M and G letters tell you the tolerance class of the insert.  M is general tolerance and G is ground.  Ground inserts generally work better for aluminium which has a habit of building up on the tip of the insert so a ground insert which is highly polished resists this binding.

So you could use either a CCMT or a CCGT insert in your tool holder. I am not entirely sure what the 21.5 refers to though so maybe someone else could help with that?


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## warrjon (Feb 21, 2019)

Hopefully this might help


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## Firstgear (Feb 21, 2019)

Awesome!


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## Firstgear (Feb 21, 2019)

What does the 300 mean?  I didn’t see that in the charts.....


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## darkzero (Feb 21, 2019)

Firstgear said:


> What does the 300 mean?  I didn’t see that in the charts.....



It's the size of the insert.

This page will pretty much explain everything.






						Insert Designation Chart - provides ANSI and ISO designation code definitions for carbide insert shapes, relief angles, tolerances, chipbreaker codes, hole types, size values, thickness values, radius values, wiper lead angle, wiper clearance angle, 
					

Carbide Insert Designation Chart



					www.carbidedepot.com


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## mksj (Feb 21, 2019)

I have attached another insert information sheet which may help, in the US we use ANSI sizing (inch), in most of the rest of world they use ISO (metric). So the lettering/numbering may be in either or both of these formats.

The identification system for inserts basically outline the shape and size characteristics of the inserts. You then have the additional information as to the type of carbide, coatings and chip breaker profile. Insert holders are specific for the type of insert that may be used in it.

1 Shape: So C is an 80 degree diamond or rhombic.

2. Relief Angle: is the relief angle of the edge, so a negative holder tilts the insert down so the relief angle is 0, this is a "N" insert. This allows the insert to be two sided, neutral angle is usually "C" so uses a 7 degree relief angle on the edge. A "P" insert sits positive in the holder, so the relief angle is 11 degrees. The more positive the tilt, the less horsepower is needed, but also the more fragile the insert edge.

3. Tolerance: is the insert tolerances/design, typically you will see "M" for molded which the edges are not as sharp but more robust. You see a "G" for ground edge which is sharper, but more fragile. The latter is typically used for softer materials and/or lighter cuts.

4. Type: Is the insert design which is specific to the holder being used. "T" is a single hole in the center which is countersunk which is used for screw down inserts. There are many different types of clamping systems.

5. Insert Size: s the size of the insert, in inch the increment is by 1/8" increments so a "2 or 200 series" is 1/4", a "3 or 300 series" is 3/8" and a "4 or 400 series" is 1/2". There is also a corresponding  ISO sizing, but it differs based on the shape of the insert.

6. Thickness: width of the insert in thickness, usually the same for the same size insert. So a  32.51 would be 1/8" thick, a 21.51 would be 1/16". So the increment is 1/16".

7. Corner Radius:  is the roundness of the edge tip, so a "1" is 1/64", "2" 1/32, and so forth. The increment being 1/64" for each integer increment. Typically you will use 0.5, 1 and 2. The smaller the tip the finer the cut at the tip and the shallower the cut you can take, but at the expensive of being more fragile.

There are a host of profiles and coatings, that are also specific to the materials and speeds/feeds the insert is designed for. Also the type of cutting be it deep interrupted cutting to finish cutting. This will dictate the shape and properties of the insert.

Also, what may be a good insert for turning, may not be a good insert for a boring bar. Most of my boring bars are  neutral rake "CC", although my 3/4" carbide uses a positive rake inset "CP" .  I also tend to use a bigger nose radius for boring, so something like a CPMT or CPGT 32.52 for the boring bar and for turning I use a CCMT or CCGT 32.51. I find that a ground edge for boring gives a better cut and less chatter as opposed to the molded, but also assumes you are not hogging a lot of material. Negative rake boring bars need more Hp and rigidity. Carbide is a very good material for boring bars because of it's rigidity, but they also snap very easily and unexpectedly.  The rule of thumb is for steel a boring a maximum depth of 3-4X the shank diameter, for carbide it is around 8 times the shank diameter. The other critical factor is to have the least amount of hangout from the holder as needed for you depth of cut.

Typically for boring bars I use the same "size" insert so 32.5x for boring bars in the 1/2" to 1" diameter size, below that you would need a 21.51 size. Mikey did a very nice review on boring bars and in much more detail, worth reading.








						A Boring Primer
					

Boring on the Lathe for (New) Hobby Guys  A Primer     Being able to bore an accurate hole on the lathe is an important skill every hobby guy should have. We may not need to bore a precision hole all that often but when we need to, we should be able to.  As we all know, that is easier said than...




					www.hobby-machinist.com


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