[rmdesignworks]

Hello all...I am Thomas and I am a designer and part time fabricator.

I need to explain to a machinist how to stop the cnc at intervals around a 2D design milled in plate material in order to create small webbing tabs to keep the milled piece attached to the blank stock....what should I relate to him?

[mfgbydesign]

simply put: leave tabs.
You could define the tabs in your CAD model, but this is usually left up to the programmer.
Sometimes the tabs are the same thickness as the material, but most times the tabs are on the order of .005-.010" thick so they are easily removed by hand finishing.

[rmdesignworks]

Thanks.........

What would be the best way for me to define the tabs? Break the entity line along the tool path or what?

I know I can simply draw in tabs to the outside of the piece/s but how do I define it so that the operation takes place as a lift out of the tooling path to move beyond the tab and restart the milling on the other side of the tab?

[mfgbydesign]

Using surface geometry it's easy; place a rectangle shaped surface over the tab and the CAM software skips this section.

Wireframe perhaps like you suggest. Seperate chains with a break, just make sure the cutter retracts and plunges in the right place. The cutter will probably drive until it's tangent to the break. Put the tab in the geometry and it'll stop at the right place regardless the size cutter used.

[rmdesignworks]

Ok..why does the cam skip at a rectangle...?

[rmdesignworks]

so...like this?

[mfgbydesign]

Might help if you tell us what CAM program you're using.
However, when surface machining I define the tabs with a rectangular shaped surface OVER the tab. Set the maximum Z at some distance below the rectangle.
Now from your sketch it appears you are contouring wireframe geometry. In that case I'd use what you have but take the rectangle off. Keep the chains seperate. When selecting the chains for the contour operation, pick them in the order you want to machine, from the end of the chain you want the cutter to enter.
I bit more explaination is in order: Your chain looks like this:
|______| |______|
Sorry for the use of text to explain, imagine that each of the two chains are connected at the corners, but not to each other.
When prompted for geometry selection pick the left chain at the upper left corner, then pick the right chain at the upper left corner as well.
The tabs need to be at least as long as the radius of the cutter plus any stock left on the first pass.
Now go play with it and see if you can make it work! That's how I figured it out, long before the internet!