Tuesday, 23 February 2016

Redefining middle plane of Content Centre parts.

While writing this post I realised that it's practically 1 year to the day since my last post! Seems like only last month. Time sure flies.

Anyway, onto the topic of this post. The title is really referring to Structural Steel members placed from the Content Centre (CC). Each family, even those supplied by Autodesk, appears to be an extrusion from the Start Plane out 1 direction, therefore making a midpoint Flush/Flush constraint difficult because you need to do some calculations (1/2 the member length) to get it constrained mid-plane into your assembly. For reasons I won't go deeply into now, I place all CC members as Custom. I do this is mainly because the file becomes somewhat editable and I can change the extrusion to get the mid-plane where I want it, in the middle.

In the above picture it can be seen that a normally placed CC member has all the usual planes as well as a Start Plane and and End Plane. It's these 2 that control the length of the member and where the G_L parameter (which is the member length) comes from.

In the assembly shown I want to constrain the mid-plane (half way length) of this member to the Origin plane of the assembly so that the EA member is evenly placed both sides of the assembly Origin plane.

I could edit the CC part and manually place a plane, or use the newer Plane features like Mid-plane Between Two Planes, but both of these have drawbacks if I change the placed member length.

My answer to this problem is to edit the part and change the Body (a.k.a. Extrusion) used to make the part. By default the Extrusion Extents are Between and the Start Plane and End Planes are used to determine the length of the extrusion. I change the Extents to Distance with the length of G_L and then make the Extrusion Symmetric. This then makes the Origin Plane that the CC Family was originally authored on the mid-plane. See the below picture. The new mid-plane can't be seen directly but the sketch of the member can be seen around the middle of the part.

The result is that now I can change the length of this placed CC member as I wish and the extrusion (Body) is always going to be made each side of the mid-plane, and it makes it much easier for me to constrain this in my assembly. See the next picture.

A keen observer will see that this plays around with the Start and End planes as they are now floating. This doesn't cause me a problem in this workflow as I am not using them for anything and changing the members length also alters these to generate the correct G_L and the planes still float. Bah humbug!

Note that if the member is replaced with a different Family member or Family that this procedure needs to be repeated. I find doing this much easier and predictable than remembering or measuring the lengths of members and entering the half the member length into the Constraint box.

There are other ways to get this functionality, I just think this works the best for me.

Cheers all :)

P.S. I promise the next post won't be so far away as this one.

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