G74 Drilling Cycle With G96

G74 Drilling Cycle With G96

G74 Drilling Cycle with G96.

On a CNC lathe G96 is used for most machining. It was amazing in the old days when we suddenly discovered G96.

Because you are using a constant surface speed the metal cutting is consistent so you get a great finish.

The Black Art Of CNC Programming

CNC Programming was a bit of a black art back in the old days and generally speaking we used G96 for everything except for screw cutting and drilling holes on centreline (G74 Drilling Cycle).

When CNC Programming a drilled hole you would always use G97, (this means the speed is in RPM).

If you were to program for example G96 S50 M3 and then rapid to X0 and Z3. ready to drill a hole the machine would just go to its maximum RPM. This would be the speed you set in your G50. (The G code used to restrict the speed.)

Oh by the way that 50 meters per minute is for a B & Q drill.

Don’t get me wrong I love B & Q products but HSS drills are not for grown up engineers they are great for metal work classes at school and making a coffee table for the misses but it’s time to join the big boys and spend some money.

I Digress

Anyway the machine would calculate the speed at its current diameter. So at zero the spindle would always be flat out.

So you could say G96 is pretty useless for a drill.

But you would be wrong!!!!!!

Take a look at this bit of code.

The idea is to send the machine to the drill diameter. Because the machine is in G96 it calculates the correct speed. When you then issue G97 it fixes the speed. Now when you move to X0 it has the correct speed.

Let The Machine Do What It’s Good At

Mmmmmmm… So all you need to do is send the drill to its diameter and the machine does the arithmetic.

Let the machine do what it’s good at and you do what you’re good at.

What are you good at by the way?

Threading is the same if you were machining an M20 thread at 100m/min calculate the surface speed.

(This is the quickest way I have seen)

20/314.2 =.06365

100/.06365 = 1571 RPM

You could do the same thing let the machine do it’s shit.

Rapid to the diameter of the thread then program G96

G0 X20. Z5.;
G96 S100 M3 (Start Spindle at 100 metres per min);
;
G97 (This will swap to RPM and clamp the speed at the correct RPM);
X21.;
;
G76 P010060 Q20 R.02;
G76 X16.93 Z-25. P1534 Q485 F2.5;
;

ETC

So with this bit of code you can get the machine to calculate your speed.

Thanks for watching and reading

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