Surface Area Drive - Best Practices 1

[DaSalo]

I have been using Surface Area drive method a lot recently for 3 axis contour milling that requires undercutting with a barrel-type cutter. As far as I can tell this and streamline are the only drive methods that will calculate this type of path correctly. I seem to get the best results from "Normal to Drive" but in some cases "Tool Axis" will give almost the same results, in other cases it won't work at all.

Can someone elaborate on generally what the different Projection Vectors are used for? The documentation gives several examples of "Normal to Drive". I believe there is also a "Towards Drive" when would one be used instead of the other?

Also, I have been using the drive surface alone for programming these parts. I am not defining a part or a cut area. I just create the operation, go right in to the drive method window, define the drive surface, and done.

I use the tolerance settings and offset settings in the drive method window to control tolerance and stock, not the settings in the cutting moves window like I would for other types of operations.

This calculates the toolpath WAY faster than if I define the part and cut area and seems to give just as good results.

Any reason not to do this? Is there a best practice here?

NX 7.5.4.4, NX 8.0(Evaluating)
Tecnomatix Quality 8.0.1.3

 

[markrief]

The Projection Vector is the direction the drive path is projected on to the geometry.

Normal to Drive comes from infinity along the vector toward the drive. Towards Drive starts at the drive and backs away opposite the vector, and projects back toward the drive. In an open area there is no difference in the result. To illustrate where they produce different reults, imagine cutting inside a large cylinder. Normal to drive would project on to the outside of the opposite side of the cylinder. Toward drive would project on to the inside.

If you are not using part geometry, then the drive path is built, but not projected on the the part. This is why it is so fast. If the part is relatively smooth, this may be OK, but there is a risk of gouging - use at your own risk.

Mark Rief
Product Manager
Siemens PLM

 

[DaSalo]

Thanks Mark. Very helpful information. Just to make sure I understand correctly:

In many instances drive geometry will not necessarily be the same as the part geometry and in these cases it would be necessary to specify part geometry so that the drive path is projected to the part and the resulting toolpath is used. If, however, you use the exact surface to be cut as the drive geometry AND that surface is relatively smooth then there may be little or no difference if part geometry is defined. But, to be safe, it is best practice to specify part geometry and wait the extra few minutes to be sure you have an accurate path.

NX 7.5.4.4, NX 8.0(Evaluating)
Tecnomatix Quality 8.0.1.3

 

[Jaydenn]

I work exactly the same way as you do i.e. drive surfaces only, no part.

I wouldn't say you get a more accurate path with part geometry selected. What you get is an automatic gouge free tool path. The software will consider the rest of the part so you don't have to.

Also, the idea that the drive need be "relatively smooth" is not really true. Any shaped drive surface should work fine.

As a matter of fact, for reasons beyond my understanding, my experiences show me that including part geometry often times ruins the toolpath. I end up getting undesired engages/retracts and transfers all over the place.

Either way I believe the best practice is the one that gets you a safe toolpath with the least amount of headache!

J

NX 6.0.5.3

 

[DaSalo]

It makes sense to me that you would need the part defined in Streamline because it is building a drive surface on-the-fly and that surface isn't going to be of a high enough quality to carry the whole load. I did some testing in surface area to day and was not able to detect any difference at all in my situation with and without the part geometry defined. The only noticeable difference was the path generation speed, which was much slower with the part geometry defined. These parts are heavily contoured but the shape is smooth: no sharp corners or interruptions.

NX 7.5.4.4, NX 8.0(Evaluating)
Tecnomatix Quality 8.0.1.3