Merged Frame Generator members equal wrong total length.

[BLHDrafting]

I have a feeling this goes way back to the first release of INV we had (release 14?). Basically the merged FG member length seems to be calculated using the member centre line instead of real lengths. See the attached Pack-N-Go.

The view on the left is a Merged FG member. The view in the middle is individual FG members based on a line of symmetry in the same sketch. Both are placed using the mid point option in the FG dialogue. The views on the right are the 3 separate members used for the middle view.

The Merged length shows 722 mm whereas adding the 3 member lengths (RH view) equals 740 mm. 18 mm short, or 2 sets of 9 mm (shown in the middle view) which represents the end cuts to the middle member in the RH view.

I would have thought this error would be fixed by now. Any comments/suggestions?

[blair]

It's really not an error but more of a material cut length. If you started with a full length of material and placed it is a saw and cut your three pieces prior to doing either a Miter or Notch, added up the three cut lengths it would equal the merged length as you have noted.

And yes it's been like this since F-G was added to Inventor.

Insert a steel shape from CC, then shorten the length using the Extrude/Cut. The CC length displayed will still be the CC length when the item was placed in the IAM. The length is written in at the time the item is placed and not recalculated each time a feature is placed.

[BLHDrafting]

Thanks Blair, but it can't be called anything but an error. Inventor is touted as manufacturing software in that you model as if you were making it. This functionallity is clearly faulty when using Merged option.

If you had perpendicular 2 sketch lines that overlapped and applied FG memebrs to these they would be at the sketch line length. But if you then mitre these 2 members their length shortens to suit the mitre. This is normal and expected.

What I have posted is not normal or expected. It should report the overall length of the member normal to the members midplane, but instead it is using the member length along the midplane which is incorrect. There is clearly something wrong with the MERGE option. I have submitted it as a Support Request through the Subscription portal.

Below is a subsequent FG assembly where I can show how Inventor calculates the Merged length incorrectly. The LH vies is separate members. The outer dimensions are the longest length of the member and are reported corectly in the part lIst (see items 3 and 4). The inner dimensions (highlighted) are the member lengths through the member midplane. The RH view is the same sketch and same mebers and same offset, just the Merged option is used. Again the overall dimensions are correct but the reported overall length of the Merged member is 900 mm (item 2) which is WRONG!

So a warning to all Frame Generator users who choose the Merge option, CHECK THE LENGTHS BEFORE PUBLISHING YOUR DRAWINGS. You may be surprised!

[blair]

When you place the items, if you use the outer edge rather than the center-line placement, do your mitre and merge will the length be correct.?

I suspect the Merge is looking at the line segment length

[BLHDrafting]

Hi Blair.

The previous graphic of the 2 elbows used the outer edge orientation. I've tried several variants and it always calculates the length based on the member mid plane length. Below is the same assy/sketch/FG members using the centre orientation. Again both views are identical except that the RH view is Merged FG members and the LH view is separate FG members. Note the length of Item 2 (871 mm) and then add up the 3 highlighted midpoint (midplane) lengths in the LH view (293+286+293=872 (allowing for rounding)).

Note the 7 mm distance (yellow highlight) from a mitred end midpoint and the longest length of the member. Note that there would be 4 of these distances (4 mitred ends), so 4*7=28. Note that the Merged member is reported to be 28 mm shorter than expected. Coincidence, I think not.

[LT.Rusty]

I'm not sure what's happening with your assemblies, but merging by part number is giving me the right overall cut length, regardless of whether I align the parts on inside / center / outside of the skeleton sketch.

[BLHDrafting]

Thanks Rusty. but wrong Merge. Not BOM merge on Part Number, rather the Merge option in the Frame Generator dialogue.

[LT.Rusty]

Ah, okay.  Gotcha.

Hm.  That's ... interesting, to say the least.

[BLHDrafting]

After a bit more thinking I reckon I've figured out what the Merge option is doing, but I still think it's wrong (for my needs anyway).

See the below graphic. In the top part of the graphic is what I think Inventor FG Merge oprion is doing to calculate the 'overall' length of the member by using the members midline lengths as the calculation. This is correct and probably as designed, but who manufactures like this? We don't. Instead we would make the 3 items as can be seen in the bottom part of the graphic. And it is this difference that becomes the length difference of the Merged member.

If the Developers were interested into change this (to what is in the lower part of the graphic) then a feature of further benefit would be to allow for the cutting width as this could be added to the overall Merged member length. Maybe a set of configurations so that the individual company and cutting processors could be catered for.

And as a further enhancement what is seen in the lower part is basically how we manufacture these types of items. Out of 1 piece of steel we cut wedges and then bend the steel member to create the mitred join.We don't actually cut the member all the way through. This would be of great benefit to me and I suspect to many others also.