Posted by: davidhayden | September 25, 2010

Proven Tips, Tools and Tactics: Understanding G82


The Problem with Counter Boring

When creating a counter bore, if the tool retracts too quickly, it may leave a step or uneven finish at the bottom of the counter bore. The CNC programming G code to address this issue is G82. This simple CNC canned cycle bores the hole to depth at the desired feedrate and allows you to specify a dwell time for the tool pause at the bottom. This insures a good clean face at the bottom.

 

CNC Code Data

Code: G82
Modal: Yes
Group: 01
Action: Boring / Counter Boring
ANSI Std: Yes
Requirements: Point to move to(X,Y), Feed Rate at which to move (F), Dwell Time (P), Final Depth (Z)
Options: R (rapid return plane, Feed rate, G98 / G99 Rapid plane selection, G17/G18/G19, P time in milliseconds to dwell
Conflicting G Codes G00, G02, G03, G04, G80 All Canned Cycles, Any other G code in Groups 00, 01 or 09 

Description and How to Use G82

The G82 is the NC command that tells the machine to: 

  • Move to an X,Y location
  • Rapid to a clearance Plane (R Plane)
  • Feed into the bottom of a hole or counter bore at feedrate specified by the F parameter
  • Dwell at the bottom of the hole for the amount of time specified by the P parameter
  • After dwelling at the final depth, retract to the reference plane above the part
  • Move to the next hole and start the process all over again.

Here is a side by side comparison to counter bore 2 holes 1″ deep, with a dwell at the bottom for 1 second ( hole to be drilled at X0, Y0) at 2 IPM 

With G82…………………………………………Without G82
G00 G90 X0 Y0 …………………………………………G00 G90 X0 Y0
Z.1 ………………………………………………………………….Z.1
G82 Z-1.0 P1000 F2.0……………………………G01 Z-1.0 F2.0
X1.0 Y0.0 (drill new hole)………………………..G04 X1 (or G04 P1000)
…………………………………………………………………………X1. Y0 (move to new location to start this all over again) 

Calculating Dwell Time

The P parameter in the G82 command is time in milliseconds so P1000 = 1 second, P500 = 1/2 second and so on. To calculate the correct amount of dwell time use this formula:
P = Dwell Time
DR= Desired revolutions of tool at bottom of hole
RPM = Revolutions per minute of tool 

P = DR / (RPM/60) * 1000 

For Example: You want your tool to dwell for 2 revolutions. With spindle speed is 500 RPM you would program P240 as shown below: 

P = 2 / (500 / 60) * 1000
P = 2 / (8.3333) *1000
P = .24000 * 1000
P = 240 

REMEMBER: Only dwell the tool for the minimum amount of time necessary to insure a good clean counter bore face. Dwelling too long will only dull your tool and possibly work harden the piece. Not to mention that long dwell times increase production times. 

Benefit – simplicity and time-saving
While this canned cycle doesn’t save as much programming time or NC code as other canned cycles, it is still very simple to use and edit. Like all CNC programming canned cycles any of the parameters can be changed in the middle of the cycle to adjust feedrates, depths, dwell time, clearance planes and so on. 

There are many canned drilling cycles you can use to save time. Look for future articles to learn more about these labor-saving commands. 


For a complete introduction to the fundamentals of CNC programming, take a look at 7 Easy Steps to CNC Programming . . . A Beginner’s Guide or 7 Easy Steps to CNC Programming . . . A Beginner’s Guide, the Ebook
   

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Responses

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