Rolling into mid-February, we thought we’d give a little advice on running a successful machining program! In order to run a successful program, it’s best to have a standard operating procedure (SOP). This ensures that there is a concrete plan laid out for all users to machine the parts correctly. Proper planning greatly decreases the possibility of errors since parts may be repeatedly used by a different machinist.
Our team at Leading Edge Industrial is a strong advocate of frequently using SOPs to increase efficiency and accuracy in the shop. We’d like to give you an insight on the requirements for a successful machining program so you can develop your own procedures.
CNC programs list instructions that are to be performed in the exact order in which they are written. These instructions are very straightforward, and they read like a book (left-right, top-down). Each sentence of the CNC program is written on a block, or a separate line. These blocks are arranged in a sequence that ensures safety, readability, and predictability. This is why it’s crucial to adhere to a standard program structure.
Blocks are generally arranged in this order:
1) Program start
2) Load tool
3) Spindle on
4) Coolant on
5) Rapid to position above part
6) Machining operation
7) Coolant off
8) Spindle off
9) Move to safe position
10) End program
These steps represent the simplest type of CNC program, where just one tool is used and one operation is performed. However, programs that use more than one tool repeat steps two through nine for each tool.
Outlined below are the procedures we use at Leading Edge Industrial when running parts:
- Header Line
The header line consists of the following points:
a. Program Name
A CNC program can be identified by both its number and its name. While program number can be used for identification, program name provides a brief description of the program. According to the CNC Textbook, “All programs must begin with the letter “O” (NOT the number zero). The program name must be an integer up to five digits long. No decimal point, letters, or special characters are allowed.” In order to track who programmed the file, you may also wish to add your initials to the end of the program’s name. See reference below.
O0001 (Programming DEMO [JMC])
b. Tools used
The next portion of a CNC program’s header lists all the tools that are used within the program. In this section, the tools being used within the program are displayed as comments, notated by surrounding parenthesis “( )” on each line, and contain critical information regarding the necessary tool dimensions, types, and order.
(T1 D=0.5 CR=0 – ZMIN=-0.1 – flat end mill)
(T2 D=0.25 CR=0 – ZMIN=-0.3 – flat end mill)
(T3 D=0.125 CR=0 – ZMIN=-0.3 – flat end mill)
(T4 D=0.5 CR=0 TAPER=30deg – ZMIN=-0.17 – chamfer mill)
Default/startup parameters for that program
These are the factors that establish the program’s foundation. Each program has a set of default/startup parameters. Common default/startup parameters for our milling programs include:
G90 – Defines machine movement in ‘absolute coordinate programming mode’
G94 – Defines feedrate as ‘per minute’
G17 – Defines ‘X-Y plane for arc machining’
G20 – Defines inch units
Example:
‘%
O1001 (LOGO JMC)
(T1 D=0.5 CR=0 – ZMIN=-0.1 – flat end mill)
(T2 D=0.25 CR=0 – ZMIN=-0.3 – flat end mill)
(T3 D=0.125 CR=0 – ZMIN=-0.3 – flat end mill)
(T4 D=0.5 CR=0 TAPER=30deg – ZMIN=-0.17 – chamfer mill)
G90
G94
G17
G20
…’
- Set-up sheet
Creating a set-up sheet is priceless for your operator because it paints a clear picture of the entire process. It is also necessary to make sure you have proper tool heights for clearances. We’ve provided an example of what a successful set-up sheet should look like. The more detail, the better.
- Proper Speeds and Feeds
Please see Lesson 3.6 of the Fundamentals of CNC Machining textbook (here) for formulas and tables on how to calculate proper speeds, feeds, and chip loads. Learn it – love it – live it!!
- Correct Tool Selection
Selecting and using the right size and diameter drills and end mills is essential to saving time and making great parts. When doing this, there are a few guidelines you should follow.
- Rough with the largest tool you can use, leaving just enough material for your finishing pass.
- Finish with the intended tool or one just under the internal radius size.
- Use 4 flute cutters for excellent mirror finishes on internal and external walls.
- Coolant/Lubrication
Using coolant/lubrication on your machine is recommended. Implementing a flood/mist coolant system or dabbing/squirting oil “old-school style” will make your tools last longer and your cuts/parts look nicer. This is a standard procedure for all machined parts and is used by manufacturing companies around the globe.
We made a list of 5 items required for a successful machining program, now here is a quick overview of two additional items crucial to proper inspection techniques.
Drawings
It’s imperative to have good drawings that, at a minimum, show critical dimensions. This allows the user to follow along easily and accurately in order to verify that the parts being machined are within the allowed tolerances.
Inspection Tools
A successful machining program needs inspection tools to accurately measure the dimensions and locations of features on a machined part. These tools may include a caliper – an instrument used for measuring internal and external dimensions, and micrometer – an instrument used to accurately measure small distances or thicknesses between its two faces, typically external diameters or rounded geometries. If you want to know what else to include in your CNC machining toolkit, please check out our blog going live in the last week of February!
Check out our G-Code basics videos on YouTube to learn how to write a basic program start to finish. Does writing machine programming by hand sound complicated and tedious? Fortunately, you’re in luck, as Autodesk’s Fusion 360 software will output all of this information for you, saving you hours of time! Click here to download and go to our YouTube channel to learn how to design parts and machine them using Fusion 360. This software is available to all students, educators, and small businesses/entrepreneurs for free!
With very little work you can create great CAD designs, dimensional drawings, and CAM your parts in one software system to be made on our HX Series CNC Machines.
Requests?
We hope you’re gaining a wealth of knowledge from our weekly educational blogs! Please don’t hesitate to contact us with ideas or suggestions on blog topics you’d like to see next. We’d love to hear from you!