Need Help!- Change diameter of a circle

[sansbury]

I bought V22 last summer but am only now starting to really try using it. I've used a variety of other CAD programs and one thing that I find confusing is changing the size of a piece of geometry. I can redraw stuff, but half the reason I bought BCC is so that I don't have to redo the CAM every time I want to tweak the part a little.

In this case, I have a circle (arc) which has a radius of .647" which I would like to increase to .650". The only way I can see to do this is to use the Translate>Scale function, but this causes the center of the circle to shift. Is there a setting I'm missing, or better way to do this?

[Journey_Man]

Can you just redraw the arc using Arc Coordinate and snap it to the center or the one you want to change???

[BurrMan]

Right click the arc and choose "Entity Modify". Select a new value.

[sansbury]

BurrMan, that's the recipe. Thanks!

[sansbury]

OK, found an interesting wrinkle.

If I change the circle diameter, then the toolpath for the pocket does not seem to update automatically. In other words:

1. Draw circle .500" radius
2. Create a pocket operation on the circle
3. Compute toolpath
4. Modify the circle to have a radius of .750"
5. Recompute toolpath
6. Toolpath doesn't change

What I've found is that after modifying the circle, I need to re-select the geometry for the pocket, or else the toolpath doesn't update to fit the changed radius. Is that right?

[BurrMan]

I would say this is right as per the software as it stands now. Maybe with future enhancments the "history" of features should improve, but for now if you change geometry you must re-select and treat it as "new".

In it's simplist form, the geometry is "new". But as the software gets more powerful and robust, we can look forwar to having it work as you expect. A history based mechanism.

I wonder if its in the cards? It would be a huge area of work.

[sansbury]

OK, well, at least now I know it's the software and not me. It isn't the worst thing in the world. At least all the parameters of the machining operation don't need to be redone. But it does still seem "wrong" to me. Software is my day job and if I were designing a system from scratch that's how I'd want it to work. I suppose there is a reason deeper down the stack that explains the difference.

[BurrMan]

Yeah, a history mechanism like that is a very complicated thing to implement. It would tend to come later.

An announcement could look like this:

BobCad hires 5 more fulltime programmers to work on quality history mechanism to be released in 2012. Raises its price to $5000.00 +!

[sansbury]

BurrMan, do you have software development experience? I'm curious because it's non-obvious to me why maintaining the entity relationships would be so hard. If I change the radius of the circle by modifying the entity, is that actually erasing the old entity and creating a new one? Just wondering.

FWIW I know that history can be a tricky thing--I've had customers asking me for years for an "Undo" function and have explained many times why it's probably the single most costly feature they could ask for. But this seems a bit simpler than needing to maintain a full history.

[BurrMan]

Hi Sansbury,
I have a bit. It would seem simple on a single arc, but it can become convoluted, especially in a Cad/Cam app where precision is required. For instance, what if you had added a dimension to the arc? A connected Tangent line? What happens to the rest of the model? Then moving into 3d.

Whether its creating a "new entity" or just modifying the existing geometry, Implementing it would be an involved process. You really couldnt do it "Partially", it could get confusing to the user. So in its simplist form, changing geometry has to be re-dealt with.

I think in V23 they are starting to implement this as when you go to re-select geometry, the original entities are preselected! I'll test and post back if this works as you expect in the newest version.

Burr

[BurrMan]

Sansbury,
I just tested this in V23 and it seems to work well, with one exception to how you would expect it.

If I modify entity, I still need to reselect it to generate a new toolpath from the modified geometry, but BobCad remembers the original selected geometry, so I only need to right click for reselect and choose OK, instead of actually re-select the entities.

There is a reason for this.

I can create multiple features and use things like a 4th axis output for indexing. When I create a feature pocket at 0 degrees for instance, then rotate to 45 degrees for a profile and so on, When I generate toolpath, my original pocket generates from the correct, originally selected geometry, even though I may have rotated my model around in the ucs to select another face or edge for another feature. This would be as I expect. So the feature "remembers" where the original selected geometry was performed and wont change unless I "re=select".

This could be the same for the modification of the entity. You could create a pocket for the .5 circle you originally made, generate toolpath, then modify the entity to .489 and create another pocket and toolpath, then post the code for "both" toolpaths. the original .5 circle would still toopath even though it was no longer there.

Anyway, good luck.

[BurrMan]

By the way, it works this way in V22 also, the only difference is V23 will highlight the original geometry when you go to "reselect it" and V22 doesnt do this yet.

I would say what we are seeing is "Camming History" and not "modeling history". Make sense?