View Full Version : 21.51 vs 32.52 Inserts

gordsgarage

10-16-2011, 11:14 PM

Being the self taught "machinist" I am I often struggle to trying to figure out concepts that are probably fairly elementary to most.

With my home lathe I work with tooling that accepts CCGT inserts. The inserts that I am running are CCGT-21.51 and work great for the work I do. My confunsion comes from trying to determine when to use a 21.51 vs a 32.52. I somewhat understand the differences based purely from the specs however I fail to understand what application is best suited for each.

Is anyone able to dumb this down for me?

Thanks!

Gord

beanbag

10-16-2011, 11:18 PM

I'm assuming you mean 32.51, which has the same nose radius. The only reason is if you want to take deeper or bigger cuts.

JoeFin

10-16-2011, 11:37 PM

You'll need to keep at it with the insert types.

Different manufactures differ slightly in thier normenclature of insert geometries but the numerical size standards hold quite true. I stopped trying to cross manufactures of insert holders vs: inserts some time ago as they didn't fit correctly more often then not. If its a Kennemetal Tool, I'll buy Kennemetal inserts for it.

As for lathe tooling I build my own tool holders and look up the manufacture's literature on the inserts. I usually look for decent quantities of 30 inserts or more on Eboner for a good price and then cross-reference the manufacture's literature to see if they are a good fit for the application. I have probably 5 - 600 inserts in the drawr and 10 or so tools I've made and can always find what I need to make the right cut.

danlb

10-16-2011, 11:51 PM

Being the slef taught "machinist" I am I often struggle to trying to figure out concepts that are probably fairly elementary to most.

With my home lathe I work with tooling that accepts CCGT inserts. The inserts that I am running are CCGT-21.51 and work great for the work I do. My confunsion comes from trying to determine when to use a 21.51 vs a 32.52. I somewhat understand the differences based purely from the specs however I fail to understand what application is best suited for each.

Is anyone able to dumb this down for me?

Thanks!

Gord

The first number is the size. The bigger the number the bigger from side to side. The 1.5 or 2.5 is the thickness. The bigger the number the thicker it is. The 1 or 2 on the end is how sharp the point is. A 0 is no radius, a 3 is a pretty broad radius.

I found the charts at http://www.carbidedepot.com/formulas-insert-d.htm pretty easy to understand.

BTW, you want the insert size and thickness that the tool is designed for.

Dan

macona

10-16-2011, 11:54 PM

32.52 inserts will not fit in your holder. First number is inscribed circle in eight's, 3 = 3/8", second number is thickness in sixteenths, 2.5 = 5/32 thick, last number is nose radius in thousandths. 2 = 2 thou.

Bigger inserts are for more powerful machines. Simple as that. Bigger machines can take a larger DOC, so you can use more of the side. No since using more expensive, bigger, inserts on a machine that can only use the tip and a touch of the side,

danlb

10-17-2011, 12:17 AM

32.52 inserts will not fit in your holder. First number is inscribed circle in eight's, 3 = 3/8", second number is thickness in sixteenths, 2.5 = 5/32 thick, last number is nose radius in thousandths. 2 = 2 thou.

100% correct.

The part I had problem initially was that I did not know what an inscribed circle is. I finally found it was a math term for "the smallest that the shape can be and still 100% contain the circle. So a lathe insert that starts with a 3 will fit a circle that is 3/8 in diameter. It does not matter if the shape is square, diamond or triangle, the same idea is used.

Edited once I read beanbag's post.

Daniel

beanbag

10-17-2011, 12:54 AM

100% correct.

The part I had problem initially was that I did not know what an inscribed circle is. I finally found it was a math term for "the biggest that the shape can be and still be 100% within the circle. So a lathe insert that starts with a 3 will fit in a circle that is 3/8 in diameter. It does not matter if the shape is square, diamond or triangle, the same idea is used.

Daniel

U got that backwards. a 32.51 insert is the smallest shape that completely swallows the 3/8" circle, i.e. the insert is always bigger than the circle.

danlb

10-17-2011, 01:14 AM

Thanks Beanbag. I always get things like that backwards. I updated my post just to avoid confusion for future readers. :)

What drove me crazy was trying to figure out what inserts my cheap HF turning tools needed since it was not listed on the page. I could not figure out what dimension of my triangular insert should match 1/4 inch :) Eventually I found that a 1/4 inch dot will just kiss all three sides of the triangle on a 21.51 insert.

Dan

PixMan

10-17-2011, 06:56 AM

32.52 inserts will not fit in your holder. First number is inscribed circle in eight's, 3 = 3/8", second number is thickness in sixteenths, 2.5 = 5/32 thick, last number is nose radius in thousandths. 2 = 2 thou.

Bigger inserts are for more powerful machines. Simple as that. Bigger machines can take a larger DOC, so you can use more of the side. No since using more expensive, bigger, inserts on a machine that can only use the tip and a touch of the side,

You were doing well up until that last digit.

The last digit is nose radius, that's true, but it is represented in 1/64" increments NOT direct thousandths of the inch.

0 = .004"

0.5 = .008"

1 = 1/64"

2 = 1/32"

3 = 3/64"

4 = 1/16"

....and so on.

Then there's the conversion if given in ISO designation.

A CCMT32.51 becomes a CCMT09T304. Confused yet? ;)

gordsgarage

10-17-2011, 01:11 PM

The information you guys layed out is fantastic. It has cleared up many of my questions and even answered some that I didn't think I had.

I think I have a grasp of the numbers and how they apply to the dimensions of an insert. Therefore I have 2 follow up questions;

1. How does one determine what nose radius should be used. I machine with 21.51 inserts and have success however should I switch it up to a 21.52 if I want to hog something out in a hurry? Should I be running a 21.50 for a final pass on pieces I want a good finish on?

2. Inscribed circle. I didn't have a clear picture of this till you guys helped out. So the follow up question is "who cares?" Why should we be concerned with inscribed circle. Is it just a way to classify insert sizes? Does the dimension factor into machining operations depending on what cuts need to be made and therefore impact insert selection/choice?

I'm all giggles with my new found knowledge.:D

Gord

Arthur.Marks

10-17-2011, 02:05 PM

No matter how many times I look this up, I always need to reference it again. Here is my favorite chart: http://www.arwarnerco.com/warner_products_inserts_chart.html

danlb

10-17-2011, 02:13 PM

2. Inscribed circle. I didn't have a clear picture of this till you guys helped out. So the follow up question is "who cares?"

Gord

The only reason we care is that it is a way to specify a 'size' for different shaped object. Your TCMT21.51 insert will only work in a tool holder that is designed for a T---2---- insert.

And that's all that really matters to most of us.

Dan