When I started using SW in 1999 you couldn't locate one part to another with two concentric mates between screw holes and matching clearance holes. some where along the way that changed. Most of my co-workers mate the majority of there parts this way and I personally don't think its a good idea. What are the pro's and con's of this mating scheme?
What way did you use in 1999? And what is your preferred way?
SW then would not accept two concentric mates, so if you used on concentric mate you would need to use a parallel or coincident mate with it generally. I was taught back then to mate parts using planes and/or faces. over time I mostly started using planes or axis created from the primary planes since those are absolute and aren't affected by dimensional changes to geometry.
Richard Lundy wrote:
I was taught back then to mate parts using planes and/or faces. over time I mostly started using planes or axis created from the primary planes since those are absolute and aren't affected by dimensional changes to geometry.
I still vouch for using default planes or created reference geometries from these than faces, edges etc.
The con of using two concentric mates is that any imperfection, no matter how minor, will break your assembly.
The pro is that you have a built-in check to show you any imperfection in your hole locations.
Your pro only applies to a pair of holes, if that hole pattern has more than two holes you could still have unfound error.
Ok, now I understand. You mean that, if you had, say, 4 mounting holes to mount part 1 to part 2, then you would create a concentric constraint from hole 1 in part 1 to hole 1 in part 2 and then another concentric constraint from hole 4 in part 1 to hole 4 in part 2. Then all you would need it a coincident constraint between the two surfaces.
I get it now.
Right now, with the skeleton part method that I am using, the main way that any part lines up in the assembly is through origin and parallel constraints.
Then the holes for each part is driven by a master part that also drives the basic profile of each part.
However, when I am not using skeleton part method, then since most of our parts are doweled to each other, I would generally make the dowel holes concentric and then coincident the two faces to each other.
If Dan's explanation is correct, then I use that often. They should work fine as long as the distances are correct, and if they aren't I want to know about it anyway.
Personally for me if there is a need to position a lot of fasteners, basic things to look for - Can I do patterns - are there any L - Shaped sketch lines that I can use, (you can eliminate a lot of mates if you can use two mates instead of three). If I need to position hardware in a SSP assembly then I will definitely use a Sketch within the SSP and mate with a Coincident mate, circle to circle and a parallel mate to lock the spin (if I can) if not I'll use the Concentric mate with a Lock Rotation Mate and a coincident for the linear lock...
Yes, Dan described the condition I meant to present correctly. I just don't think this type of mate scheme is very stable or robust. I also wonder if a large model is mated in this manner if it has any effect on rebuild times. Anyone have any thoughts or info on that?
Dan, you mentioned the skeleton part method of design. I have read through at least one explanation of this but I still can't exactly understand this concept. Can you give me a link to any info on it?
John,
Just curious, but why do you need to "lock" the rotation? I usually get my fasteners concentric and mate to the face (or sketch component using SSP), but allow it to free rotate to keep the number of mates down.
I completely agree that Pattern Driven Component Pattern is a game changer for fasteners.
"Curiosity Killed The Cat" - dead yet..
Only a personal crusade - just can't stand the ( - ) sign anywhere - even in mating, we need a positive connection
John, fasteners are the one type of component that I do use concentric mates for. We have our own fastener library (not SW Toolbox) with mate references set up that allow us drag and drop most fasteners into position and then lock all the concentric mates. on larger hole patterns we pattern them from the first position in the pattern we mated a fastener to.
Richard Lundy wrote:
Yes, Dan described the condition I meant to present correctly. I just don't think this type of mate scheme is very stable or robust. I also wonder if a large model is mated in this manner if it has any effect on rebuild times. Anyone have any thoughts or info on that?
Dan, you mentioned the skeleton part method of design. I have read through at least one explanation of this but I still can't exactly understand this concept. Can you give me a link to any info on it?
Here is probably the best explanation that I have seen so far:
Skeleton Sketch Part Method for Large Assemblies
Also see the PDF attachment that is in the beginning post of the link.
Aside from not wanting any ( - ) signs in my tree. I was also told by one of our re-seller tech people that leaving things not completely constrained increases rebuild times. Now that we have the "lock concentric rotation" command there is no reason to leave then unconstrained.
Very very rarely would I ever have a part that's not a fastener that I would mate. My parts are designed to not be forced in a position and locked down like a inmate they just stand there, willingly, all calm and reserved, always wanting to be right where there at...
I find that if you only use concentric mates for hardware aside from coincident faces, it can play havoc on rebuild later especially if you have hundreds of fasteners in your assembly. I try to lock them all down, concentric, coincident faces, and a plane to stop rotation. It rebuilds much safer and reacts faster when you open it the next time.
Also, like John Stoltzfus said, Use patterns as much as possible. It reduces the amount of hardware you have to mate and the data associated with each set of mates. I like to use the hole pattern mates along with linear.
I use both methods. However the skeleton one gets pretty intense for large assemblies. I will sometimes use two concentric if I know for sure that the hole patterns will never change on an assembly but in truth, how often is that. If say you used two concentric mates and the hole pattern diameter changed on one component, you just broke your model. You'd have to know how many assemblies that component is used in and change or replace the mating component in each.
Richard,
I have heard similar statements however in reading Alin Vargatu 's threads on large assembly management I am beginning to question that thought process.
This is why Pattern Component Pattern is usefull for fasteners. If you move a hole, or delete a hole, it should update correctly. But you are absolutely correct, if done incorrectly things can break on you horribly.
I heard the exact opposite from my VAR. The more mates you have the longer the rebuild time. So, the thought process was to use as few mates as possible to have rebuild times as quick as possible. I wonder what Alin Vargatu has to say about this? Alin, is it better to fully constrain fasteners? And what impact does lock rotation have versus another mate?
But as Tripp says below, using patterns for fasteners is a wonderful idea and really cuts down on those mates.
How many mates would I have here if I hadn't used patterning?
That assembly has 62 mates for 2000 bolts and 2000 nuts. If I had been smarter about how I laid that assembly out, I could have reduced the number of mates probably by half.
Jim Steinmeyer wrote:
Richard,
I have heard similar statements however in reading Alin Vargatu 's threads on large assembly management I am beginning to question that thought process.
Let's just consider what happens when an assembly opens:
1. Component data is loaded (body data for both resolved and lightweight, and feature data for resolved). There is a difference on what gets updated between clean and dirty assemblies, but let's not get there.
2. Components are located based on:
a) Last known position if there are no mates whatsoever, or fixed conditions.
b) By solving the mate matrix for components with mates attached.
3. In-context operations are performed. If any of thes operations affect mated entities, the mate matrix gets solved again.
4. The graphics-triangles get computed by the CPU and handed over to the GPU, so you can see, move, zoom, select, etc.
So, less mates = shorter rebuild time. Assemblies with no mates are the best, from this point of view. Anyone here using the master-model workflow?
Mind you, lately I have never seen an assembly where the mates take more than 5 seconds to rebuild. If one of you has an assembly where the mates solving is the biggest contributor to the rebuild time, please show it to me.
Usually mates get you in trouble only in conjunction with bad in-context operations, or circular references. And, please, solve any mate errors before releasing your assemblies!
Lock rotation is using a hidden parallel mate between 2 internal planes. So, by locking a rotation, you introduce an extra mate.
Teoretically you should experience a slow down during rebuilding, but most likely you would not notice it.
Alin Vargatu wrote:
Usually mates get you in trouble only in conjunction with bad in-context operations, or circular references. And, please, solve any mate errors before releasing your assemblies!
A couple of weeks ago I did some editing on an Assembly that hadn't been worked on in a while, so I'd forgotten what I'd done. I edited a sketch for a virtual part, creating some relations between it and some other components, and all kind of ugly things happened in the tree. It turns out that those components I'd set relations to had been mated to the line when inserted. There's a prize-winning circular relation.
One big con is that the default is coincident. For each of these mates you manually have to choose concentric. But, I do use this functionality all the time. Right now I am thinking of this ladder system that has slots everywhere. I just added sketch points at the center of the slots to mate the bolts to as concentric. Could I have done it differently? Surely! But, that's what I chose.
I'll be interested to see some other's answers to this as well.