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Florinel10-Marble
10-Marble
September 14, 2021
Question

Use a plane as a middle point?

Something is strange with this part. The sketch of the extrude has only one reference, a plane, that was used with a middle constraint to a line. It doesn't make any sense. That constraint is supposed to be between a point and a curve.

Does anybody understand how it is possible that the sketch to be fully constrained?

The part was made with Creo 6.

14 replies

MartinHanak24-Ruby III
24-Ruby III
September 15, 2021
@Florinel wrote:

Something is strange with this part. The sketch of the extrude has only one reference, a plane, that was used with a middle constraint to a line. It doesn't make any sense. That constraint is supposed to be between a point and a curve.

Does anybody understand how it is possible that the sketch to be fully constrained?

The part was made with Creo 6.

Hi,

1.] section of Extrude feature is placed on TOP datum plane

2.] section of Extrude feature is extruded to both sides of TOP datum plane symmetrically

I do not understand what is wrong.

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Florinel10-MarbleAuthor
10-Marble
September 15, 2021

Hi Martin,

The sketch is constrained only horizontally. There are no vertical constraints. That constraint should have been required.

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kdirth
kdirth21-Topaz I
21-Topaz I
September 15, 2021

Cannot look at sketch as I am still on 4.0 for a couple more months.  A screenshot would be great for those of us that are still in the "dark ages" of Creo.

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Florinel10-MarbleAuthor
10-Marble
September 15, 2021

Here is a screenshot

The sketch should have been constrained vertically to the FRONT plane or to the coordinate system. But you can delete the FRONT plane, and the coordinate system has only the RIGHT and TOP plane as dependencies.

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tbraxton
tbraxton22-Sapphire II
22-Sapphire II
September 15, 2021

The sketch is not fully constrained. You can see this by inspection of the sketch references where it is shown that the section is only partially placed. The rectangle is defined but its location on the vertical (z axis) is not explicitly constrained. The intent manager is making an assumption to create the extrusion. This is concerning that the feature is created without a warning of the constraint deficiency.

 

Partially placed sketchPartially placed sketch

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Florinel10-MarbleAuthor
10-Marble
September 15, 2021

I agree with you: the sketch is not fully constrained. If you add the FRONT plane as a reference to the drawing, then do an Edit Definition again and delete it, you cannot exit the sketch. Therefore I agree with you that the sketch is underconstrained. This is what I said in the initial email.

My question was, how come it is possible to have an accepted sketch that is not fully constrained. Up to now, I wasn't able to have an accepted underconstrained sketch. Can you duplicate this behavior?

If you have no datums, you can make the first feature with no references, but this is not the case.

I know that there are some implicit constraints. For example, the right vertical line doesn't need a vertical constraint because the dimension ensures that the line is parallel with the other vertical line. Is there another hidden or assumed constraint?

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kdirth
kdirth21-Topaz I
21-Topaz I
September 15, 2021

Does Creo 6 allow Under-Constrained Mode in sketches?

In Creo 4, Under-Constrained Mode is only allowed in cosmetic sketches.  You can complete a cosmetic sketch without any constraints.  But, if you go back and start adding constraints, it won't let you complete without fully constraining.

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