Need Help!- Radius compensation in lathe cycles

[Zudo]

Hi,

Can anyone tell me if it is possible to use radius compensation in cycles like G71 or G72

Thanks

[dcoupar]

From the Fanuc 21iT-B Operator's Manual:

11. Tool nose radius compensation cannot be applied to G71, G72, G73,
G74, G75, G76, or G78.

[sinha_nsit]

But can be applied to G70.
So, if you are finishing with G70, you finally get the correct dimensions.

[Zudo]

Originally Posted by sinha_nsit But can be applied to G70. So, if you are finishing with G70, you finally get the correct dimensions.

I know that, but there is some situations that we need compensation on roughing cycle, consider a U shaped box you cant use G70 direct you need to rough first... you use g72 cycle cause its to deep to use g70 direct but the compensation will not work so the perfil will be wrong.

[Geof]

When you need to use compensation on the G70 cycle you have to put a finish allowance a bit larger than the nose radius in the G72 using U and W.

[Zudo]

Originally Posted by Geof When you need to use compensation on the G70 cycle you have to put a finish allowance a bit larger than the nose radius in the G72 using U and W.

In a box wont work. W will give you sub-metal only in one side... one direction. If you use for example an 10mm round insert the error is massive.

[Geof]

Originally Posted by Zudo In a box wont work. W will give you sub-metal only in one side... one direction...

Right, you have to do it the hard way; write code that leaves a finishing allowance all round for the G72 cycle then use the correct code for the G70 with tool comp.

[sinha_nsit]

Machining a U-type groove is a tricky problem which has bothered me since long. One such example is a tensile specimen the drawing of which is attached. The simplest way would be to use a sharp angle diamond insert (which may avoid interference problem at the left and right edges of the groove) with G73, followed by G70. However, in most cases, round insert would have to be used (because of interference problem). This would cause excessive error without radius compensation. I thought of the following method:
Create an offset profile (offset amount = radius of the round insert) in AutoCAD (or some other drawing software).
Make the center of the round insert the reference point.
Machine along the offset profile with G73 (finishing allowance U = <some positive value>, W = 0), followed by G70, without using radius compensation.

Any better idea?

[Zudo]

Originally Posted by sinha_nsit Machining a U-type groove is a tricky problem which has bothered me since long. One such example is a tensile specimen the drawing of which is attached. The simplest way would be to use a sharp angle diamond insert (which may avoid interference problem at the left and right edges of the groove) with G73, followed by G70. However, in most cases, round insert would have to be used (because of interference problem). This would cause excessive error without radius compensation. I thought of the following method: Create an offset profile (offset amount = radius of the round insert) in AutoCAD (or some other drawing software). Make the center of the round insert the reference point. Machine along the offset profile with G73 (finishing allowance U = <some positive value>, W = 0), followed by G70, without using radius compensation. Any better idea?

I do it with an CAM program its the easy way, but i would like to know a way of doing that with direct programing without "tricks" and hard work lol but maybe there is no way...

[Geof]

Adapting to the machines limitations is not really trickery it is good practise.

I realised that what could be an easy solution both in CAM and direct coding is to simply draw or write the groove as a leading section and a trailing section that overlap slightly in the middle. The leading section would have a minus W value in the roughing cycle and the trailing section a positive W.

One thing you would have to watch would be the approach and retract moves for the trailing section.

[sinha_nsit]

Oh!
I forgot to upload the drawing with my previous reply. It is attached here.

This particular shape does not have serious interference problem. But, if the leading and trailing edges are, say, quarter circles, then round insert would have to be used. And, it is not a good idea to machine the left edge with a RH tool and the right edge with a LH tool, because there would always be a step on diameter, no matter how small, where the two tools meet. This would cause stress concentration in tensile test at that location, and the specimen would break at that location only.

[dcoupar]

You're right, Zudo. There is no way. RADIUS COMP DOES NOT WORK in G71, G72, or G73et al. Period. Exclamation point.