I've been working with a mini-mill for years and finally bought a full size knee mill.
Now that I have the ability to use larger cutters I'm moving toward the type that use carbide inserts.
How can I maximize interchangeability?
My first thought is to limit the number of shapes, pick a common insert for each shape then buy cutters that use my chosen insert.
I would appreciate any thoughts on this strategy and recommendations on which cutters/inserts to choose.

Thanks! Sounds like me, home shop use. Look on the bay to get price ideas on the tooling. Then price the inserts. Go with tooling that uses common, cheap size inserts. It is easy to get a cheap tool where the inserts cost 5 times as much.
I would settle on just a few common size inserts and tooling to hold them.
In theory a round insert has infinite new cutting edges. but it will not cut into a corner.
Much stuff sold from China has metric shanks but they call it inch size. Make sure your collets will hold that shank.
Bill D I've tried to build my collection of tooling around common inserts. Having a low HP lathe, I went with the CCMT inserts. Tooling for them is quite common and cheap, and the positive rake is helpful with low HP. I then got holders for those same inserts for my fly-cutters, including ones to utilize the "free" corner. When it came to an actual inserted milling cutter, after being disappointed with the AFTN insert performance, I got one that uses the SEKN inserts. It is quite impressive, cuts steel with no drama or difficulty and the included "Lamina" inserts give excellent life.

HTH It's a lot easier to get multiple holders that use a common insert size/shape on the lathe than on the mill. The common inserts (especially TPx) suck as milling inserts, and many, many milling inserts are proprietary. For a modest sized mill, your best bet for most sources of least expensive yet decent performing inserts is to choose one of APKTxx PDxR or APKTxx PDxR, where the two xx's are the radius and the single x is usually either E or T. There is an intermediate size, 11T3xxx, but my impression is it's less widely available. There is also an size, but I'm not sure it is compatible with 11T3 bodies, and it's definitely less widely available.
Now, you may look at Sandvik R390 bodies, of which there is a wide variety to choose from, and say to yourself "Those inserts look just like APKT inserts". Well, they don't fit well. R390 is proprietary and just a little different from the industry standard.
If your mill could use an 6" diameter cutting body, I'd have a different recommendation (such as SEKN already mentioned above), but if it doesn't have a NMTB50 taper (or something comparable) there's no point in talking about that. The first thing to address is are you doing facing only or do you need 90 degree walls.
, Hard D2, or Aluminum? I have never seen any one milling cutter that can do all of these well.

2 to 3 inch is the most a B-port style knee mill will like in a 90. Up to 4 inch in a 45 but you will stall it easily.
Tooth density (insert spacing) also counts.

While I do have and use some I'd recommend staying far, far away from TPG-322 milling cutters.
Yes they are cheap, yes the inserts are cheap. The most common designs are 0-0 and pound away like a sledge hammer.

SEKN-43 or the ilk the most popular in 45 mill. APKTs in the 90's but insert interchangeability between makers can be a problem.
https://www.maritool.com/Indexable-Tooling
https://www.latheinserts.com/FACE-MILLS_c177.htm
Both are members here and I would rate A+ as reliable and trusted suppliers.
Bob
(me thinks this all of little help as it is all so confusing)

It's a lot easier to get multiple holders that use a common insert size/shape on the lathe than on the mill. The common inserts (especially TPx) suck as milling inserts, and many, many milling inserts are proprietary. For a modest sized mill, your best bet for most sources of least expensive yet decent performing inserts is to choose one of APKTxx PDxR or APKTxx PDxR, where the two xx's are the radius and the single x is usually either E or T. There is an intermediate size, 11T3xxx, but my impression is it's less widely available. There is also an size, but I'm not sure it is compatible with 11T3 bodies, and it's definitely less widely available.
Now, you may look at Sandvik R390 bodies, of which there is a wide variety to choose from, and say to yourself "Those inserts look just like APKT inserts". Well, they don't fit well. R390 is proprietary and just a little different from the industry standard.
If your mill could use an 6" diameter cutting body, I'd have a different recommendation (such as SEKN already mentioned above), but if it doesn't have a NMTB50 taper (or something comparable) there's no point in talking about that.

I was hoping to avoid the learning curve I went through with lathe inserts but this looks much the same. I found a reference for the APKT inserts. They look good - cheap and available. Any recommends on a source for reasonably priced cutters?

The first thing to address is are you doing facing only or do you need 90 degree walls.
, Hard D2, or Aluminum? I have never seen any one milling cutter that can do all of these well.
2 to 3 inch is the most a B-port style knee mill will like in a 90. Up to 4 inch in a 45 but you will stall it easily.
Tooth density (insert spacing) also counts.

While I do have and use some I'd recommend staying far, far away from TPG-322 milling cutters.
Yes they are cheap, yes the inserts are cheap. The most common designs are 0-0 and pound away like a sledge hammer.

SEKN-43 or the ilk the most popular in 45 mill. APKTs in the 90's but insert interchangeability between makers can be a problem.
https://www.maritool.com/Indexable-Tooling
https://www.latheinserts.com/FACE-MILLS_c177.htm
Both are members here and I would rate A+ as reliable suppliers.

I honestly don't know the difference between the 45s and the 90s. Is it that the 90 is stronger and will cut deeper? Most of what I do is mild steel or stainless
I appreciate the links, I've been roving ebay but would like to develop more reliable suppliers.

I honestly don't know the difference between the 45s and the 90s. Is it that the 90 is stronger and will cut deeper?

Other way around, in general. The 45, 90 (and often 75) degrees mentioned here is the angle of the shoulder the milling body cuts relative to the flat face. 90 degrees are obviously vertical shoulders. 45 degree and 75 degree shoulder milling cutters are also common, but you can't use them to cut a vertical wall. They tend to be stronger, taking advantage of chip thinning for a given material removal rate. It is very common (but certainly not universal) for these angled shoulder cutter bodies to take square inserts, and very often the square inserts have an angled flat that wipes the flat face while holding the majority of the cutting surface at the specified shoulder angle. So you probably cannot reuse exactly the same inserts in milling bodies with different shoulder angles, unless it's a not-very-well-performing insert in a lots-of-compromises body.
So CarbideBob was asking if you just need to face off flat surfaces (any shoulder angle will do, since you won't be leaving any shoulders) or if you care about the shoulder angle.

Other way around, in general. The 45, 90 (and often 75) degrees mentioned here is the angle of the shoulder the milling body cuts relative to the flat face. 90 degrees are obviously vertical shoulders. 45 degree and 75 degree shoulder milling cutters are also common, but you can't use them to cut a vertical wall. They tend to be stronger, taking advantage of chip thinning for a given material removal rate. It is very common (but certainly not universal) for these angled shoulder cutter bodies to take square inserts, and very often the square inserts have an angled flat that wipes the flat face while holding the majority of the cutting surface at the specified shoulder angle. So you probably cannot reuse exactly the same inserts in milling bodies with different shoulder angles, unless it's a not-very-well-performing insert in a lots-of-compromises body.
So CarbideBob was asking if you just need to face off flat surfaces (any shoulder angle will do, since you won't be leaving any shoulders) or if you care about the shoulder angle.

Ahhhh...thanks! For now I'm looking to face off flat surfaces. So a 45 degree cutter that uses the APKT style inserts? I'm starting to see that there are a lot of different APKT inserts so like you said, I may not get the interchangeability even within that style.

How to Select the Proper Milling Grade

Selecting the appropriate indexable milling insert for your application does not have to be a complicated process. Despite a variety of grade and geometry combinations and any number of application scenarios, optimized milling operations can be obtained for all material groups to improve removal rates, tool life and surface finishes.

Guangzhou Ruiyi Technology Co., Ltd. are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.

Common Milling Insert Grades and Types

The “grade” of a milling insert is the combination of its base material (usually tungsten carbide), coating and any other post- and pre-treatments. To enhance performance, Seco uses either a chemical vapor deposition (CVD) or physical vapor deposition (PVD) process to coat the carbide substrate of its milling inserts.

CVD bonds a coating to a tool by injecting a combination of volatile gas and metal or ceramic vapor into a heated vacuum chamber. CVD produces a layer that is 7 µm or thicker and provides an effective heat barrier for increased cutting speeds. CVD’s thick coating capacity will not allow it to be applied to extremely sharp cutting edges, and it is prone to cracking and breaking in comparison to PVD coatings.

PVD layers coatings by using an electrical charge to vaporize solid metal in a vacuum. PVD coatings can be up to 4 or 5 µm thick and can be applied to all geometries but are most beneficial for sharp geometries.. PVD coatings are tougher due to process-related compression stresses with smooth surfaces that generate less friction for operation at lower cutting speeds.

As an alternative to coated tools, uncoated milling inserts are well suited to machining non-ferrous materials such as aluminum alloys.

Grades tend toward “toughness” or “hardness.” Tougher grades are more resistant to impact and can withstand the heavier mechanical loads of interrupted cuts, vibrations and processing heterogeneous materials without chipping. Hard grades show less abrasive wear, and in combination with CVD coating provide high heat resistance for high-speed uninterrupted cutting. Hard grades are more brittle, however, with a higher tendency toward a wear mode of chipping or thermal cracks.

Why Insert Grade is important to your Machining Process

Choosing and using the appropriate grade for an application is essential to balance tool life, performance and productivity. For sustainable, cost-effective manufacturing, tool life must be maximized and the machining process must be as efficient as possible. Undue tool wear, scrapped parts, downtime and excess machining all increase costs and reduce profitability. In terms of insert grades, shops should optimize to the most wear-resistant grade that provides the least amount of chipping while providing predictable wear pattern and development.

What to Consider when Selecting Insert Grade

Workpiece material is always the first element to consider in grade selection. Non-ferrous metals, super alloys, steel and other materials will directly influence grade choice. Workpiece size and shape are also considerations. For example, larger workpieces, in many cases, require bigger cutters and longer in-cut time. The combination of increased cutter size and in-cut time can lead to higher temperatures in the cutting zone. Those conditions would suggest a tendency to use CVD grades as opposed to PVD on large components.

Are you interested in learning more about Milling Inserts? Contact us today to secure an expert consultation!

Machining conditions are the next factors to consider and involve answering some key questions. Are the conditions stable or unstable? Is the milling continuous or interrupted? And, has the surface been pre-machined or is it rough skin?

A shop’s overall tooling strategy also plays a role. Some grades are suited to machining the wide variety of materials and applications found in high-mix/low-volume production; however, their versatility comes at the expense of high performance for a particular process encountered in low-mix/high-volume manufacturing. As a result, shops must decide whether a more universal, all-round performance grade will cost-effectively meet their requirements, such as F40M, or whether they will need a number of more specific grades to perform well in specific recurring situations, such as MP and MP.

Insert Grade and Tooling Geometry

An insert’s grade should not be considered apart from its geometry. The combination of grade and geometry can play a significant role on grade wear and performance.  For example, a hard grade combined with a sharp, positive or unprotected geometry will easily chip and fracture during uninterrupted cuts or when encountering inclusions.

Seco provides five geometry categories ranging from E for easy cutting through M for medium and D indicating difficult machining conditions. Two intermediate ranges – ME and MD -- on the easy and difficult side of M, respectively, allow fine tuning of the operation after analyzing wear patterns and performance. Fully optimizing tool life and performance with your machining objective depends upon properly balancing insert grade and geometry.

Seco’s General Insert Milling Grade Chart helps shops find a general starting point for their applications with the appropriate combination of insert grade and geometry. Grades are arranged on the chart over workpiece material and ordered top to bottom by increasing toughness.

The harder, more wear-resistant grades are shown at the top of the chart. The chart also indicates a general starting point for geometries, progressing left to right from the most unprotected, positive geometry to heavily protected geometries for difficult cutting conditions. By analyzing results and wear patterns, processes can be optimized and fine-tuned by selecting a grade above or below the initial choice.

Conclusion

Selecting the proper insert grade will refine your milling operation for the proper balance of cost effectiveness, productivity and performance. Analyzing workpiece material, size and shape along with machining and surface conditions will present a solid starting point in grade selection. Fully optimizing the process with a more appropriate grade to the application and conditions can be accomplished by observing initial results and wear patterns and then adjusting accordingly.

Refer to our extensive overview of suitable milling grades

The company is the world’s best CNC Turning Tools supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.