topic Re: How to make predictable 3D sketches? in Inventor Forum

How to make predictable 3D sketches?

torbjorn_heglum1 — Wed, 06 Sep 2017 05:34:31 GMT

I use 3D sketches for some elements of our design, but struggle a bit to get them properly consistent. Several issues could be mentioned, but the most cumbersome is when sketch elements flips. The dimensions have no ‘direction vector’, so when the sketch is solved after a reference change you never know if a constrained line points up or down.

The Screencast shows a lifting set defined by the lifting height needed in the Assembly. This height controls a 3D sketch used to define slings, shackles and lifting head. This is a very simple 3D-sketch, but still the small 66.5mm line flips when the height is reduced.

Any proposals on how to lock the direction to upwards?

(Note, even if the line colors indicate that the sketch isn’t fully constrained, I don’t think any constraints are missing. But for a 3D-sketch you never know for sure, here you have no indication of remaining degrees of freedom)

Thanks,
Torbjørn

(Inventor 2017.3)

Re: How to make predictable 3D sketches?

torbjorn_heglum1 — Wed, 06 Sep 2017 06:21:14 GMT

The Screencast was missing....

Torbjørn

Re: How to make predictable 3D sketches?

-niels- — Wed, 06 Sep 2017 07:41:56 GMT

@torbjorn_heglum1 wrote:
...

(Note, even if the line colors indicate that the sketch isn’t fully constrained, I don’t think any constraints are missing. But for a 3D-sketch you never know for sure, here you have no indication of remaining degrees of freedom)

...

Light blue lines aren't fully constrained, that's about all the indication you get in a 3D sketch. (depending on colorscheme ofcourse)

What happens if you fully define every endpoint in relation to the origin planes?

If you remove every degree of freedom that way i'd suspect it would become a bit more robust...

If your lines have a certain length already, you won't need to define all 3 dimension from the origin.

Just add dimensions till every line is dark blue...

Re: How to make predictable 3D sketches?

torbjorn_heglum1 — Wed, 06 Sep 2017 11:19:31 GMT

Thanks Niels,

I learned something new today - dimensioning to planes. I see that you get some negative and positive dimensions, i.e directed dimensions. Just what I need.

In this specific case I cannot use the origin planes as reference for the dimensions, as the part adapts to the assembly, adjusting rope lengths according to to COG and lifting lugs. But I can define adaptive planes as references for dimensions, and the 3D sketch is back in control.

Torbjørn

Re: How to make predictable 3D sketches?

JDMather — Wed, 06 Sep 2017 13:11:17 GMT

Can you attach your 3D Sketch file here?

Virtually all of my 3D sketches (other than for Routed Systems) are controlled by 2D sketches - rock solid and robust.

Re: How to make predictable 3D sketches?

torbjorn_heglum1 — Thu, 07 Sep 2017 12:45:20 GMT

The 3D sketch alone doesn't tell the whole story, as it is controlled by adaptive work geometry from the assembly. Cannot share the assembly (IP + size), so I made this simplified version. The complete skid is replaced by the master part for the bottom frame, and I think that all required relationships are in place.

When applicable I use 2D sketches to control/guide the 3D sketches as well. It helps a lot, but I am not sure if I would call it rock solid. Also in 2D I miss 'directed dimensions', have seen flipping lines here as well for large changes. But experience build the number of workarounds in the toolbox, most stuff can be fixed.

Torbjørn

Re: How to make predictable 3D sketches?

torbjorn_heglum1 — Mon, 11 Sep 2017 08:24:50 GMT

JD,

did you find time to look at this model? If you have any other proposals about how this 3D sketch can be more stable, I am indeed interested to know.

(the 3D sketch is inside '1671303-001_00', an the top assembly is 'Lifting set')

Thanks,

Torbjørn