Attach two bodies using LCS and datum point (vertex-offset)

[quiret]

I want to attach this point...

to the following LCS...

but I have no idea how to do it directly, most-pleasantly. In the mathematical sense I want to set the positions of both the LCS origin and the datum-point equal, then transform the attached-body content by the LCS orientation.

I have tried using the body-attachment tool but the closest attachment-method I could find was "tangent" where the z-line is set to collide with the vertex. But this does not close the gap that is created by the z-distance of both the LCS origin and the datum-point vertex.

Please do not suggest that I should put constants "until it fits" or work with absolute coordinates because that would break the parametric, dynamic design workflow I want to abide by.

My workaround is to put in the vertex manually into the attachment translation. But imagine a change of the attached body, resulting in a change of the datum-point vertex. Manually readjusting these values is a pain.

I am using FreeCAD 0.19.4.

Please help!

[chrisb]

Hi and welcome to the forum!

You can attach the point to the whole LCS by switching to the Model tab where you can select it in the tree.

[quiret]

Hi and welcome to the forum!

You can attach the point to the whole LCS by switching to the Model tab where you can select it in the tree.

This makes the point jump to the LCS but the body of where it originally belonged to stays at the wrong spot. It does not solve my problem. I want to have the point stay attached to the body and then use it as attachment offset of the body.

[chrisb]

So you want to attach the point to a certain plane. Then create one.
It could also be helpful if you prepare a simplified file showing your issue so that people can play with it, and not every helper has to create it on his own.

[quiret]

So you want to attach the point to a certain plane. Then create one.
It could also be helpful if you prepare a simplified file showing your issue so that people can play with it, and not every helper has to create it on his own.

I am not sure whether you understand my problem 100% but here is the FreeCAD simplified sample file that you have requested:

https://green-candy.osdn.jp/external/fo ... oint.FCStd

Please attach Topper to Platform by setting the positions of both AttachmentSlot origin and datum-pt to equal, while keeping the offsets of the body origin to contained element the same.

You are not allowed to adjust the origin by magical constants.

[freedman]

Bodies don't have attachments and they don't have AttachmentOffset, all you can do is change their Placement. I can tell that you know Bodies can be moved but you want them attached.
To do this requires an additional program to keep them attached, this would be an assembly tool. FreeCAD has a few to choose from, do a search.

There are 2 typical approaches to building models; 1) Design in place so you set clearances as you model or 2) Design objects and then attach them with an assembler.

You can place objects and put them in a Part container and they will move together.

[edwilliams16]

Bodies don't have attachments and they don't have AttachmentOffset, all you can do is change their Placement.

You can attach them if you want using Part WB|Part|Attachment.

Screen Shot 2022-06-15 at 1.25.54 PM.png (41.9 KiB) Viewed 530 times

EDIT: Seems limited in what you can attach to, though.

[freedman]

edwilliams16, you recommended that to me once and I tried it, there were issues. I can't remember exactly what happened but I quit using it. I think when I moved one of the objects the attachment failed or maybe it was a parametric update that failed. Anyway, I didn't think it was reliable enough to recommend.

[drmacro]

edwilliams16, you recommended that to me once and I tried it, there were issues. I can't remember exactly what happened but I quit using it. I think when I moved one of the objects the attachment failed or maybe it was a parametric update that failed. Anyway, I didn't think it was reliable enough to recommend.

Hmm...works reliably for me.

[drmacro]

...

If you just want position them, then you may find the Manipulator workbench of interest.

If you want future movements of one to track the other then the Part workbench Attachment tool may suffice.

Otherwise, one of the assembly workbenches may be of interest.