# Thread: G98 and G99 differences?

1. ## G98 and G99 differences?

I know this may sound like a bit of a basic question to some people on here but i only completed my apprenticeship 2years ago so am still in the early stages of my career and trying to get my head round programming.
Can somebody please explain to me the difference between G98 and G99 drilling cycles with reference to a fanuc control?
An example of a cycle for each code with an explanation of the differences would be nice. Thanks

2. G98 is initial plane return and G99 is referance plane return.

M6 T1
G0 G90 X1 Y-1. M3 S2500
G43 Z2. H1 M8
G81 G98 Z-.25 R.1 F10.
X2.
X3.
X4.
G80

In G98 the tool will rapid to Z.1("R" plane), drill the hole rapid back to Z2.("Initial" plane) move to next position, rapid to Z.1 drill Rapid back to Z2. etc In G99 mode at 1st hole Z would rapid to Z.1("R" plane) ,drill hole, rapid back to Z.1("R" plane) move to next hole, drill etc.
I use G98 as a safety to clear clamps and fixtures
Hope this is clear
Pete

3. Thanks, that makes sense.
I also understand that if i change the G81 to G83 and add a 'Q' value (for example Q0.200) into the cycle then the drill will then take 0.200" cuts until it reaches the programmed Z depth, what confuses me is that some machines/programmes i have operated will rapid the drill to the R plane, take the 0.200" cut, rapid back to the R plane, rapid back down to the finish point of the last cut, take another 0.200" cut, rapid back to the R plane and continue like that until the full depth is achieved whereas other machines/programmes i have operated will use feed movements instead of rapid movements when moving back up to the R plane and back down to cut the next Q value.
Is this controlled by what is entered into the drilling cycle by the programmer, or is it just a case of different machines achieving the same outcome but in slightly different ways?

4. G83 is a deep hole drilling cycle so it will rapid out of the hole to remove swarf and then rapid to a position above the next cut depth and then feed to the next peck and so on until the final depth has been achieved.

Perhaps a parameter was changed to enable feed rather than rapid or perhaps the rapid was turned down.

5. It is called Peck drilling cycles. This is not going to be the style of machine that determines this. It will be the programmer. This is used for chip removal. The peck drilling cycles are G73 and G83. Using the G83 is what you are typically seeing.

As CNC-Hammer has stated G83 is normally used in deep hole drilling. This will bring the tool back to the R-plane after every pick amount set by your Q value. This is bacause due to the depth of the hole a lot of times the chips can't be flushed out or broke off at that depth.

The G73 cycle it is called high speed peck drilling. This will drill the depth of your pick and back off an amount. I believe that it is typically .1". I can't remember I think this value is set by a parameter. This is used when all that is needed to break and clear the chip is a small movement off of contact. This cycle is faster then the G73.

Hope this helps.
Stevo

6. Stevo1, correct me if I'm wrong but isn't G73 the high speed cycle?

7. cossiegaz!

Try the following link mate

http://www.cncezpro.com/gcodes.cfm

8. Originally Posted by CNC-Hammer
Stevo1, correct me if I'm wrong but isn't G73 the high speed cycle?
My apologize You are correct. I explained G83 then when It came to G73 I typed G83 again. I have edited my post. Thank you for the correction.

Stevo

9. Thanks for your help guys.

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