[crumpets13]

Is it possible to set my cut levels off the spoil board rather than the top of stock. It doesn't seem to like negative values, if I use "cut geometry at bottom" option.

The desired approach is to avoid any variance in stock thickness.

thanks for any help you can pass on.

[bhurts]

I haven't used rhinocam but I have at times made the table top my 0 plane. To do this touch your tool to the table top then zero. Make the top of stock the thickness of the material. Then make the rapid plane the thickness of material plus the amount of clearance you want. For 1/4" material the top of stock would be .25 and if you want 1/4" clearance the clearance plane would be .5".

Ben

[fizzissist]

Regardless of where you set your stock Z0, your program and your machine will proceed without regard to variations in stock thickness.
It's a good idea to find your stocks max and min Z, and program accordingly.

One caveat, using the top of the spoil board, or table, as your Z0 means all of your Z moves will be positive. From a programming standpoint, the machine don't care, and neither should the post processor..... HOWEVER.... When you go in to proof/edit your program, it's a LOT easier to read the code when all the Z- moves are above the part.
That's one reason most guys set the Z0 to the top of the finished part. Sometimes there's a reason to set it elsewhere, but generally, it's just good practice.

[crumpets13]

Thanks for your replies.
In the case of a two sided part, I understood a good approach was to reference the top plane of your material and when you flip the part you reference the same plane in the negative. I take it that's not a common practice then?

[bhurts]

It is not standard practice for a machine shop. It is standard practice in some industries though. A lot of plants that produce sheet goods and granite shops use z0 as the cutting plane and all moves are positive. The biggest difference is that they usually make one pass with no z level roughing cuts. Its all the way with one pass. There is nothing wrong with either method. You just have to be aware of what is going to happen when you hit the start button. I like negative z moves for what I do but I would have no issue understanding the code from either approach. You can also take the middle ground. Sometimes I touch my tool to the table top and zero. Then ill move up the theoretical thickness of the material and zero again. That will allow you to program in negative z and also insure you know the true distance to the table top. When in your shop do what your comfortable with. If your working in someone else's shop do what they are comfortable with.

Ben

[FoxCNC1]

Good advice bhurts.