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Making multiple "copies" of an assembly that have no ties to each other

Making multiple "copies" of an assembly that have no ties to each other

Making multiple "copies" of an assembly that have no ties to each other

Hello all,

I was unable to find any solutions when searching for this topic. I do a lot of work with large models of entire facilities. Some of these facility models take over a year to complete. What I am looking for is a way to make copies of a large assembly and be able to modify constraints, sub assemblies, .ipt parts, etc. without it blowing apart the other assemblies. I can copy design and rename each part, but the last time I tried a large facility, it took my 7 hours to get a little over half way through the list of files. I ended up having nothing but nightmares with unresolved files, and unable to save/check in, position reps were gone. I've tried to "save copy as" but modifications to parts happen across all assemblies, not just the one I want to change. There has got to be a quicker way to make variants of an assembly right? Just wondering if anyone has found a trick for this. If not, no worries. I'll quit crying on my way home.

RE: Making multiple "copies" of an assembly that have no ties to each other

This is not an uncommon problem, and not specific to Inventor, really. There are a variety of strategies that will help.

First, the means that individual parts are constrained within an assembly will determine their "tolerance" to being changed. Clearly, a part that has two hole-insert constraints that is mated to another part, whose holes later move, will end up with broken constraints. Did that part need to have two hole constraints, or could it have been completely constrained with one hole-insert and one angle-zero-degrees constraint, for instance? Later, when these parts are fastened together with bolts, screws, etc., it gets even more complicated. The bolt is constrained to the hole, a nut is constrained to the hole of the other part, and two parts may or may not have a mutual constraint at the same hole. Chasing broken constraints through a chain like this can be a nightmare.

Worse, changing the parts first, and then fixing the assemblies later is the wrong way to do it. Been there done that. Then it gets worse when fixing positional representations. You can inadvertently delete the constraint used by the position rep while fixing numerous other constraints. How can you really tell "Insert:37" from "Insert:36" anyway?

I work with a designer who, when opening an assembly that another designer started, prefers to delete all of the existing constraints, and then ground everything, before he starts to work on it. He knows that there is no way he can figure out all of the constraint combinations that the previous designer used, and he has already spent more time in the past fixing broken constraints than making new ones.

Now that the assembly is done and built, and you're not eager to go through and re-constrain everything all over again, then I would suggest something like my colleague's approach. Copy the assembly that will be changed, then open the assembly (before changing any parts) and ground all parts and assemblies that are inserted at this assembly level that you will be modifying, or that contain parts that will be later modified. Before opening up parts that will change, drill down through the assembly tree (if there are levels of sub-assembly before reaching the parts in question) and ground/delete constraints as you go. Don't bother copying or breaking assemblies you won't change, of course. Just focus on the branches of the tree that the changed parts will affect. Eventually you will work your way down to the parts that need to be changed, and further changes to them won't make the assembly model "blow up".


What you really want to capture is the "design intent" in the parts and assemblies as you make them. This isn't always obvious, but when you get assemblies with hundreds of parts or more, it becomes more difficult to stay on top of the constraints as the design changes, so it's worth understanding.

I am not so draconian in my approach as the other designer I mentioned. My preference is to locate complex assemblies and sub-assemblies in absolute co-ordinates. This means I define an origin and I stick to it for every sub-assembly or part brought in later. Since I usually work on aircraft, every aircraft already has 3 datums defined, so I use those. A building, a vehicle, a power drill, all can have a meaningful absolute origin, even if it isn't so conveniently selected in advance for you. Parts inserted into the assembly can be referenced to that origin in numerous ways that will be impervious to part design changes, yet still maintain their intended function and follow the design intent.

That also implies that the assemblies and parts themselves may be built in absolute co-ordinates too (not always possible however). The beauty of this is that the model browser entry for such an item will need only 3 constraints under the sub-assembly entry, all referenced to the origin planes of the top-level assembly. If the sub-assembly was already modeled at the absolute coordinates, then I only have to insert it with "Place grounded at origin". Done.


<another tangent>
There are a number of ways to model parts to be dependent on other parts. If the two parts always mate together anyway, then why not make the changes to one automatically force the other to update too? Consider derived components in these cases. There is more than one way to accomplish the derived component arrangement, too.
</end tangents>


RE: Making multiple "copies" of an assembly that have no ties to each other

Just use pack and go

RE: Making multiple "copies" of an assembly that have no ties to each other

All I can say is WOW! That has got to be the best response I've seen to any question in any forum. A lot of good tips there SparWeb. I will also try the pack n go mcgyvr. Thanks all.

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