Draft anaylsis accuracy question?

I have a molded part model that I've just finished. If I run a draft
anaylsis on it with default settings it passes the test for 1.5
degrees.

If I set it to show gradual transistion and then zoom in on a couple of
small faces it reports small draft that 1.5. If you run your mouse
pointer over top of these areas the mouse flag shows the actual draft
(from your neutral plane) in realtime. And I question these values as
the report numbers that seem to be off by over 2-3 degrees. Even
reporting negative draft where a drawing section view shows 0 or
greater draft.

Who do I trust?

 

Trust yourself. I haven't seen errors as big as you seem to be getting, but
I have seen what seem to be errors of around half a degree or so. I would
put some planes in the questionable areas that are parallel to your draft
direction and roughly perpendicular to the part surface and generate some
intersection curves, then check them visually.

Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

Without looking at your model I have to make some assumptions. The only
time I see this issue is when I have a surface that has a defined tangency
or normal to an end condition. (could be created with lofts, sweeps,
fillets, etc..)

This is a very tiny area that is normally ignored in CAM. However if the
area is large enough you can trim it out and fill it in (without the
optimize) option. This will eliminate the "bad" geometry. (I usually go
back and fix the geometry at the start)

Normaly I only see "errors" at the surface connection or very close to it.
If you crank your model accuracy up to the max tihs usually minimizes the
areas in question.

If you have an example model I could elaborate further.

Cadguru

 

One issue is that the draft anyalsis gives the green (or red) light to
a face even if only a small part of that face is drafted as much as
specificed. This is misleading and it should work the other way. ie.
If any part of a face needs draft it should shade it appropriately.

I had already done many section views in my check drawing of this area
but I was surprised at how much discrepency there was from what the
mouse-over value was when I ran the analysis with 'gradual transistion'
enabled. Areas that are in the neighborhood of ..5 to .6 positive
report -2 to -3 when I mouse over them.

Also, manually checking draft can be tricking when splines result from
plane intersection where sw wont dimension or even measure them.

Zander