Solid Edge guru needed

[duncan webster 1Participant @duncanwebster1]

As a bit of brain stretching I'm trying to work out the position of the centre of area and the second moment of area of a bit of bent copper (crown stay). I've modelled it in Solid Edge, but can't make sense of the readout. The height of the cg looks about right (9.36mm). A hand calc assuming a square corner gets

ht of cg 9.6 mm,
Ixx = 7664 mm^4,
area = 67.5 mm^2,
radius of gyration about X = 10.6mm.

I can't get it to display the second moment of area

 

some time later… I've realised that axes 1, 2, 3 are not X, Y, Z as shown on the pictures. I think they pass through the cg. Is the radius of gyration relative to the cg? What does orientation of principle axes mean? I drew the L shape on the XZ plane then extruded it along Y, so Id expect axis 1 to be parallel to X and so on, but on the picture axis 2 does look parallel to Z (sorry I'd pasted the pictures in before I found how to display 1, 2 3)

Edited By duncan webster on 26/09/2023 15:57:41

[duncan webster 1Participant @duncanwebster1]

[duncan webster 1Participant @duncanwebster1]

I think I've realised what I'm doing wrong, the CAD is giving me the radius of gyration of a 3D thing which will vary as I make the length longer, whereas what I want is the RoG of the 2D L shape. How do I do it?

[JasonBModerator @jasonb]

It's the same, just ignor the third dimension. 9.3mm up in Z and 3.68 in X.

Alibre puts it in the same position and if I extrued equally either side of the sketch it just gives the Y position as zero

[SillyOldDufferModerator @sillyoldduffer]

Posted by duncan webster on 26/09/2023 16:36:18:

I think I've realised what I'm doing wrong, the CAD is giving me the radius of gyration of a 3D thing which will vary as I make the length longer, whereas what I want is the RoG of the 2D L shape. How do I do it?

How about extruding the 2D L by only a nanometre. Then the answer will be only slightly wrong…

Dave

[duncan webster 1Participant @duncanwebster1]

Posted by JasonB on 26/09/2023 16:53:46:

It's the same, just ignore the third dimension. 9.3mm up in Z and 3.68 in X.

Alibre puts it in the same position and if I extruded equally either side of the sketch it just gives the Y position as zero

The position of the cg isn't the issue, I'm trying to get second moment of area

Just to add complication, I've found out how to display axes 1, 2, 3 on the part end view, and they are not parallel to X & Z, I think axis 3 is parallel to Y. This means that radius of gyration around 1 or 2 doesn't help

Edited By duncan webster on 26/09/2023 22:23:11

Edited By duncan webster on 26/09/2023 22:25:43

Edited By duncan webster on 26/09/2023 22:27:12

[Michael GilliganParticipant @michaelgilligan61133]

This is probably no help, Duncan … but I remembered that SketchUp [which I abandoned years ago] has a plug-in which does this very easily.

Here’s a link to a good explanatory page: **LINK**

Face Centroid and Area Properties Extension for SketchUp

which may contain some relevant morsel

MichaelG.

[duncan webster 1Participant @duncanwebster1]

In the absence of a Guru I've done it the old fashioned way. Thank the Lord for spreadsheets! Got the same answer for c of g as SE got, so it's promising

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