Autodesk Inventor surfacing. An introduction to G1 Surface continuity

Thanks very much to David Harrington, John Evans and the team at AUGIworld for allowing me to re-publish this article. To read it in full, check out the May 2014 Issue of AUGIworld.

Hard Surface modelling is possibly the most challenging discipline within 3D CAD  – and the most rewarding, once you’ve got the way of it…

With a bit of surfacing theory you too can relish meeting the challenge with Autodesk Inventor!

Batcar collageImages from ‘Internet Movie Car Database’

Previously in this series, we learned about G0 surface continuity.

G1 = Continuity + Tangency

In Tim Burton’s 1989 movie ‘Batman’, Michael Keaton playing the part of Batman fires a side mounted grappling hook from the Batmobile, snagging a nearby lamp post and allowing the Batcar to execute an almost perfect 90 degree turn.

This is a great example of Tangency. The Batcar is travelling along a set vector, then it turns through a fixed point, before heading off in a new direction. In surfacing this is the second order of continuity  which we call ‘G1’ = Continuity + Tangency.


You’ve probably created G1 surfaces before without even knowing it. Any surface you created with Autodesk Inventor’s fillet tool has G1 continuity built in.

G1G1 curves are sometimes referred to as ‘Engineering Fillets’, implying that they are best used for practical reasons (knocking  sharp edge off a manufactured part) rather than aesthetic ones (smoooooth transitions).

Next up read all about G2 surface continuity

or read this article in full in the May 2014 Issue of AUGIworld.

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