G71/G72 type I vs. type II cycles

[sinha_nsit]

Type I cycles require that there be monotonic increase or decrease in the part diameter, along its length ... Everybody knows that.

Type II cycles relax this requirement. Diameter can vary in any arbitrary manner.

The surface finish by type II cycles is better than that obtained through type I cycles, because type II cycles do not create steps during roughing operations, obviating the need for G70 (unless a finishing tool is desired to be used in the end).

Now the question:
Why use type I cycle at all, when type II also can be used for monotonic increase or decrease in diameter?
Is there any specific advantage in type I cycles which is not there in type II cycles?
Is there an example where only type I can be used?

Some expert machinist may have the answer.

Thanks in advance.

[stevo1]

Sinha,
There may be a reason out there but I don’t use type I cycles. I only use typeII. If I had to ass u me then I would think this is the same scenario as macroA and macroB. Even though most people use B instead of A, the A option is stilled offered. It could be that when typeII was developed they designed it using things with typeI so they needed to keep typeI.

Stevo

[derek68]

i have a fanuc 16t control and i would like to use a g71 to cut an internal profile with and undercut but the machine wants to do the undercut in 1 cut how can I get it to rough it first

[dcoupar]

i have a fanuc 16t control and i would like to use a g71 to cut an internal profile with and undercut but the machine wants to do the undercut in 1 cut how can I get it to rough it first

Why not post your program here, so maybe we can see what's wrong?

[sinha_nsit]

G71 Type I does not rough out undercuts. It would remove the entire material in the undercut portion in the final (step-removal) pass. You have to use G71 Type II. For this, just specify both X- and Z-word in the P-block.