Datum and Multitransform

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ChemicalCoal
Posts: 5
Joined: Sun May 09, 2021 3:38 am

Datum and Multitransform

Postby ChemicalCoal » Sun May 09, 2021 4:17 am

I created the following part, It uses pad to create a square, pocket to cutout a plus, and MultiTransform+PolarPattern on the pocket feature using DatumLine as a reference.

If I add a second datumLine (DatumLine001) after the Multitransform I can't use DatumLine001 as a reference for MultiTransform. When i change the Axis selection box to "select refrence..." I can't select DatumLine001. I think this is expected since DatumLine001 was created after the MultiTransform feature.

My question is if I use the "move object after other object" to move DatumLine001 before MultiTransform, I still can't use DatumLine001 as a reference. I would expect this to work since DatumLine001 is now before MultiTransform in the tree, so I would expect to be able to refrence it. Why does this happen?

If I delete MultiTransform and add it back in, both DatumLine and DatumLine001 work properly. The tree looks identical to when it didn't work.

Here is a photo, the top is the prior "move object after other object", the bottom is after. The figure in both have a MultiTransform+PolarPattern applied on the pocket feature with DatumLine as a reference.
Image

This is the object before the MultiTransform and DatumLine001:
Image
chrisb
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Re: Datum and Multitransform

Postby chrisb » Sun May 09, 2021 4:30 am

You probably have attached the DatumLine to some generated geometry of the MultiTransform (which isn't a good idea anyway, see this page, especially the paragraph about creating stable models). If you would select it in the MultiTransformm you would create a cyclic dependency. If you attach the DatumLine to one of the main plains or axes, it should work.
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Bance
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Location: London

Re: Datum and Multitransform

Postby Bance » Sun May 09, 2021 8:31 am

chrisb wrote: Sun May 09, 2021 4:30 am attached the DatumLine
The screens show an unattached datum.

The line is in fact able to be used, but it must be selected from the treeview.

I think there are some bugs in multitransform, I know for instance that converting a Std (pattern)transform to a multi does not work.
chrisb
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Re: Datum and Multitransform

Postby chrisb » Sun May 09, 2021 8:43 am

Bance wrote: Sun May 09, 2021 8:31 am The screens show an unattached datum.
I should have seen that from the overlay :oops: .
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Willem
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Re: Datum and Multitransform

Postby Willem » Sun May 09, 2021 11:19 am

I think Chemicalcoal has something wrong in his model. Without any problem I can make this model with multitransform
Attachments
Multipattern.FCStd
(75.68 KiB) Downloaded 6 times
Bance
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Re: Datum and Multitransform

Postby Bance » Sun May 09, 2021 5:32 pm

I didn't look at Willem's solution, but a better way to model would be to pad symmetric then use Std axes for multi-trans forms, from a single rectangular pocket.
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Willem
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Re: Datum and Multitransform

Postby Willem » Sun May 09, 2021 5:54 pm

I agree with you Bance that using the standard axis is the most simple solution, but I wanted to check or there is a bug as you insulted on your previous post
ChemicalCoal
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Re: Datum and Multitransform

Postby ChemicalCoal » Thu May 13, 2021 7:41 pm

chrisb wrote: Sun May 09, 2021 4:30 am You probably have attached the DatumLine to some generated geometry of the MultiTransform
This originally was the case, it was attached to a piece of geometry generated by MultiTransform, but I would have expected to get an error when moved it earlier in the tree than the geometry that it references. Is this the expected behavior? Is the tree really a tree, or is it more of a suggestion?

I recreated the issue and took photos when it happened instead of afterward, this is a picture of the tree and DatumLine001.
Image
Image
Bance wrote: Sun May 09, 2021 8:31 am
chrisb wrote: Sun May 09, 2021 4:30 am attached the DatumLine
The screens show an unattached datum.
I assume this is the purple thing, this is a byproduct of me messing around before taking the photos.

The datum line was attached to the multi-transform body after the first Multitransform + PolarPattern + Pocket has been applied but before the second. Referencing the datum001 at this point would have been a cyclic relationship, which is why I assume that it didn't work.

After thinking about it my question is really about the behavior of datum001 referencing geometry after it in the tree, and not about the model itself.
Bance
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Location: London

Re: Datum and Multitransform

Postby Bance » Thu May 13, 2021 8:08 pm

Unfortunately without the actual model, it's very difficult to know exactly what has happened here.

In reality the model might've been padded symmetrically, then all axes for patterns would've been available as std. without effort.

That does not solve the conundrum, but might serve as advice for further models..... :lol:
chrisb
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Re: Datum and Multitransform

Postby chrisb » Thu May 13, 2021 8:51 pm

So it is indeed as I had guessed. In the image of the attachment dialog you see that the Multitransform is selected.

The tree is not showing all dependencies. For that, use the DpendencyGraph. The graph is directed and acyclic.
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