Posted by: davidhayden | June 24, 2010

Proven Tips, Tools and Tactics: Understanding G73


What a waste of time you say. Peck drilling with a full retract whan all you want to do is break the chip is a waste of time. And, in some materials can work harden the piece because if the temperature changes from drilling and then flushing with coolant.

The G73 is a great answer to this problem, because it only retracts enough to break the chip. That’s it. You don’t lose all the time required to fully retract and you maintain good chip control.

 

Code Data

Code: G73
Modal: Yes
Group: 01
Action: Drilling
ANSI Std: Yes
Requirements: Point to move to(X,Y), Feed Rate at which to move (F), Peck Depth (Q), Final Depth (Z)
Options: R (rapid return plane, Feed rate, G98 / G99 Rapid plane selection, G17/G18/G19, Q depth of peck
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 G83

The G73 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 hole the amount specified by the Q paramater at the feedrate specified by the F paramater
  • Completely retract the drill out of the hole to clear the chips
  • Rapid back into the hole a short distance from the bottom
  • Continue feeding down into the hole by the amount specified by the Q paramater
  • Retract as before
  • And continue this pecking cycle until the final depth specified by the Z paramater is reached
  • After reaching 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 drill 1 hole 1″ deep, with a minor retract every .25″ ( hole to be drilled at X0, Y0) at 2 IPM

With G73…………………………………………Without G83
G00 G90 X0 Y0 ……………………………………G00 G90 X0 Y0
Z.1 ……………………………………………………………Z.1
G73 Z-1.0 Q.25 F2.0………………………….G01 Z-.25 F2.0
X1.0 Y0.0 (drill new hole)…………………..G00 Z.-.249
……………………………………………………………………G01 Z-.5
……………………………………………………………………G00 Z.-.499
……………………………………………………………………G01 Z-.75
……………………………………………………………………G00 Z-.749
…………………………………………………………………..G01 Z-1.0
…………………………………………………………………..G00 Z.1
…………………………………………………………………..X1. Y0 (move to new location to start this all over again

Like the G83, you can you see the time savings in using canned cycles?
Now imagine having to drill 15, 20, or more holes. With the G73, all you have to do is enter the new XY location and the rest is done for you. When CNC machines had very limited memory, you could easily use up all of the available memory drilling a few holes.

Also imagine, having to edit the depth of the pecks. With the canned cycle, all you have to do is change the Q value one time and all holes following the change will have the new peck depth. Without canned cycles, you would have to edit every single drill cycle and update every single peck.

The beauty of all canned cycles, this one included is that you can change the parameters as often as necessary. For example, if you wanted to take shallow pecks for some holes and deeper pecks for other holes, all you have to do is specify a new Q where you want to use the different peck depth.

The Q parameter is modal, so once you set it, it will not change until you set it to something different.

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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