Modern Machine Shop

JUL 2018

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CNC TECH TALK MMS JULY 2018 40 Processes and Programming DEBURR ANY CROSSHOLE divided by two (0.5) and then added to a value of 0.1 (the clearance amount), the result is 0.6. The result of this formula (with cell J7 currently set to 1.0) is: G00 X-0.6000 This should seem familiar if you have experi- ence with custom macros. Indeed, just about any- thing you can do with a custom macro program can be done with spreadsheet software. One advantage of using a spreadsheet instead of a custom-macro program is that the control will not have to perform calculations or make decisions during the program's execution. Another benefit is that the CNC machine tool need not be equipped with custom macros or any version of parametric programming. The illustration on the previous page shows a more elaborate example to demonstrate what is possible. The drawing shows the contour to be milled, along with the variable names for input data. The list of input data is to the right, and to the right of that are the resulting G-code motion commands. The created tool path, which is not interactive, is shown as well. As you change an input-data value, the related motion commands immediately change. Once all input data are appropriately set, you can copy the motion commands from the spreadsheet and paste them into your CNC program. Let's look at the formula for one of the motion commands. This is for the first G03 circular-mo- tion command: ="G03 X" & FIXED(J2-J4+J7/2,4) & " Y" & FIXED(J4+J5,4) & " R" & FIXED(J5+J7/2,4) This renders (for the current input data set- tings): G03 X4.300 Y0.4500 R0.7500 Again, each ampersand will add to previous data. And as with a custom-macro program, each CNC word will be the result of a calculation that involves input data. The X-word begins with the overall length (4.0), subtracts the step amount (0.2) and then adds the cutter radius (0.5). With the "fixed" function specifying four decimal places, the result is X4.300. Similar techniques are used for other CNC words in this formula as well as for other CNC words in the other formulae. AUTHOR | Mike Lynch Founder and President, CNC Concepts Inc.

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