Building a Plastic Injection Mold - Lesson 2: Selecting Cutter Speeds and Feeds - Fusion360

Introduction: Building a Plastic Injection Mold - Lesson 2: Selecting Cutter Speeds and Feeds - Fusion360

Starting with understanding your cutters, helps you understand your part design better. Using known feeds and speeds for various materials helps insure that you do not break cutters. This lesson will help you understand how to select cutters and how to use them properly. Here is a ball end mill in action.

Step 1: 2 of 10 Mold Making - Selecting Cutters and Speeds and Feeds Fusion360

We can start with designing molds and even going back to the original 3D part design for manufacturability, yet lets start this session with cutters. Cutters are the shapes that spin in a machine to take metal out by forcing the work piece into the cutter. To make a mold you run the biggest cutter you have in the shop first, then the nest one smaller and so forth until you can get into all features.

For the most part cutting metal or aluminum molds is all about not breaking your cutters. As you start to program CNC Mills to shape aluminum or steel, you will begin to snap cutters. It will become very frustrating. The best place to help a mold making project move along fast is to "start with the part design." Always remember, big radius help us move metal faster. The best advice I can give is to talk to your cutter tech support and have them help you set up feeds and speeds for the material you are cutting. But lets talk about how you can get close to the machining parameters.

We all want to go fast while trying to get the best quality. Our cutters are made of a hard tool steel called tool steel, yet we can get harder ones like carbide. Cutters can even be coated with diamonds to cut ceramics. The cutter tend to break when we don't follow rules for your tooling strategy. We need to calculate how deep the cutter must go into a piece of steel, and how fast our CNC pushes the cutter thru the material. There are a few formulas that can help find the perfect formula.

Here is a screencast that will show you how to calculate these numbers. Attached are the the tools for your CAM toolbox of tricks. Just crunch the numbers and you will rarely break cutters. Here is an online calculator.

Tech Support to help set feeds and speeds is 330-688-6667 Have the cutter number you are using.

Step 2: Cutter Programming for CNC Equipment

Programming the cutter is next in this 10 part Lesson. Here is a CNC making an injection mold.

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    6 years ago

    very nicely presented basics. don't forget about chip load, as opposed to feed per tooth. because the feed per tooth is calculated by the chip thickness at approximately 30% of the cutters diameter engagement or a fraction of the circumference (I don't remember the exact test standards offhand) basically the chip load can go well into excess of the calculated feed per tooth in corners and slots (the loading on the emill can be a few 100s percent higher then max) snapping the emill. I usually just run my numbers twice, once for side milling and once for corners, using kenmetals feed rate calculator as it take into account chip thickness and run my corners at a separate feed rate. Of course plunge milling will usually take care of that as well, and speed up cycle times on lower hp mills, although I have no experience plunge milling in a cnc, it's a charm on manual machines. (I use both types often)


    Reply 5 years ago

    Interesting. But will you make it up to making of the press itself?