Use top assembly dimensions/parameters in a sub-assembly/part

Question

I have a top assembly of a set of steel or aluminum stairs that has a parameter for the stair tread depth (from front to back, when ascending the stairs). I have a sub-assembly of each step that has a piece of steel angle in the front, one in the back, and a stair tread resting between the two. I would like to be able to change the tread_depth parameter in the top assembly and have it change the distance between steel angles and coincidentally, the stair tread depth in the sub-assembly.

Is there a way to reference a top assembly parameter in the sub-assembly? I am familiar with relations, but I'm not sure if there's a different format for referencing a d-value (dimension) in a sub-assembly.

Thanks in advance

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BrianMartin · Accepted Answer

Hi Chris...Sorry - I thought I saw on a tag that you were on Creo 2. Ah well.Simple answer... set the relations in your parts and subassemblies from the top level assembly relations window. Pro/E will automatically add the correct Component ID to the dimension. Get to your top assembly. Name your dimensions however you wish. Edit the dimensions of your parts and subassemblies using relations... but do it at the top assembly. Go to the relations window and select the arrow icon (shown below)... next pick the part or subassembly containing the dimension you wish to change.Once you've selected the appropriate part or subassembly, pick a feature or component and you'll see the dimensions pop up. You'll notice they no longer appear as simply "d1", "d4", "d18", etc... but they have a colon and a number appended as a suffix.Click any dimension to add it to your relations window.For example, instead of "d14", you'll see "d14:5" (the number after the colon will vary). This is the Component Id of the model. If you want to look further, you can turn on Feature ID in the Model Tree and at the assembly level you should see the Component Id is the same number that Pro/E is appending to your dimensions.So in your case, if the dimension you're trying to vary is deep down in a part:open your relations editor, pick the arrowheadselect the part you wish to grab a dimension frompick the feature to show the various dimensionsselect the desired dimension - the dimension appears (complete with component id) in the relations editorComplete the relations as desired...If the width of your tread is driven by "TREAD_WIDTH" minus 1/2" for clearance, then your relation might be: d14:5 = TREAD_WIDTH - .50When you exit the relations editor and regenerate, the model wil update.Although I should reiterate ... this is not the best way to accomplish this goal. You should really try using top level design techniques or, at the very minimum, a master model to handle this. There's documentation on the web for both techniques... or I can demonstrate (although I am getting a bit busy today and I may not get back to it in time).Thanks!-Brian

BrianMartin · Answer

Hi Chris...I created a sample set of parts with a sample step subassembly. I then assembled each step and used a pattern to make a repeating set. Here's a picture...To modify the stair pattern, open the top level assembly (called step_assy.asm). Modify the PATTERN and you'll see both the height and width dimensions. When you modify the width dimension, that number ripples down into the subassembly and parts. The stair tread will adjust accordingly... and so will the dimension between the front and back angles supporting the tread. This is what you asked for... so this is what I modeled.However... this is a really poor way to go about modeling this staircase. Having assembly dimensions that drive part dimensions is a bad way to go. A better way would be to leverage a top-down design process with a skeleton model. The skeleton would hold all pertinent information about your staircase including tread height, depth, etc. This data would then be referenced in the tread part and in the subassemblies. There are several ways to go about achieving what you've asked for. All of them are better than what I've modeled here. If you're interested, I can remodel this using a top down design scheme with a skeleton. I think you'll see the difference immediately.Take a look at the attached models and see if they make sense to you. There are relations driving the tread width and the subassembly width between the angles. Look at the relations in those models and you'll see how I did it.Thanks!-Brian

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