Computational Design + Fabrication: CNC

Jonathan Bachrach

EECS UC Berkeley

September 4, 2015

CNC 1

ComputerizedNumericControl

Benefits 2

AutomationPrecisionRepeatabilityFlexibility

Examples 3

CuttersMills3D PrintersLathesKnitting

stoll cnc knitting machine

CNC History 4

John T Parsons + MIT 1949

Categories 5

AdditiveSubtractive

additive subtractive

Axes 6

How Many?1D2D2.5D3D5Dlinear

What Kind?rotarylinear

Workspace 7

how bigshapeconstraints

by xiyang yeh @ stanford

Feedrate 8

how fast to do cutup to speed of breaking end millmore but slower cuts

Feedback 9

open loopcrash

closed looplimit switchrotary encodercamera

Kerf 10

width of saw bladecut radiusmust compensate in code

by parts express

Undercut 11

extra cut to compensate for mill radius

by wizard191

Lead-ins + Lead-outs 12

extra cut during start or finish of cutusually need to plan for this

by big blue saw

Coordinate 13

RectangularPrecision – incrementsOrigin – ZeroingAbsolute and Relative

Tool Changing 14

different cuttersthicker mill cuts faster but less preciseswitch between them under program control

GCode 15

word addressed format for programmingsentence like commands: letter followed by numeric argumentcommand is made up of words often one letter with intuitiveinterpretationsstep by step commandsread interpret execute each command

X10

Y20

Example Commands 16

O Program number (Used for program identification)N Sequence number (Used for line identification)G Preparatory function (See below)X X-axis designationY Y-axis designationZ Z-axis designationR Radius designationF Feedrate designationS Spindle speed designationH Tool length offset designationD Tool radius offset designationT Tool DesignationM Miscellaneous function

Example GCode Program 17

G1 X5 Y-5 Z6 F3300.0 (Move to postion <x,y,z>=<5,-5,6> at speed 3300.0)

G21 (set units to mm)

G90 (set positioning to absolute)

G92 X0 Y0 Z0 (set current position to <x,y,z>=<0,0,0>)

Manufacturer Specific Commands 18

G90, G91spindle speedcoolanttool changing

Programming 19

like turtle graphicsmovepen up/down

no loopsno subroutines

GCode Processing 20

send gcode to CNC machinemachine interprets one command at a timeusually microcontroller which is interpreting and executing

tinyg microcontroller board

Path Planning 21

organize cuts efficientlyplan motions according to dynamicschange speedsbang-bang control

Ordering of Cuts 22

need to plan cuts so parts are cut correctlycut holes out firstmuch more involved for 5 axis machines

by customlasercutters

Traveling Saleman Problem 23

salesman has to visit n city in minimum time

GLPK solution by xypron

Simulation 24

show planned out motionsactually interpret gcodevalidate that plan works

by modern machine shop

Visualization 25

show feedback during executioncommunicate to user for manual interventionWYSIWYG

by othermachine co

Input Formats 26

DXF,SVG,PDF – polylinesSTL,OBJ – meshesAMF – materials, frep

solid name

facet normal ni nj nk

outer loop

vertex v1x v1y v1z

vertex v2x v2y v2z

vertex v3x v3y v3z

endloop

endfacet

endsolide name

References 27

AMF – http://www.astm.org/Standards/ISOASTM52915.htm