Beginner question: Locking Mates or Fully defined mates

I've started assembling my parts into assemblies. Is there a way to mate via 1 or 2 "attributes" then lock the piece in place?
I find that when I assemble sometimes I only need to mate a part in two places to get it in the right position, but then when I move the assembly the part slides out of position. What I am trying to avoid is mating in three different axes in order to get the part to stick. Sometimes it's easy for me to figure out how to get a part to stay with only 2 mates. But I also run into situations where parts need to be mated and there is no easy way to do it, because there are no "real" references to work from, like trying to mate two spheres that don't touch, to me it gets tricky since I am still learning.
Thanks,
Max
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Max wrote:

You could mate two spheres using the primary planes in each sphere and distance mates. Since there are three dimensions in our normal coordinate systems, you will need three mates. One of the mates can be a "parallel" mate to stop rotation of an object, eg, a screw or pin. If you have a (-) in front of the part name, it isn't fully constrained and will be able to "slide" around as you put it. To look at it in a slightly different way, could you locate a piece on the floor of a room with only one dimension or two? This isn't possible in 3-dimensional space. Don't be cheap with the constraints, they don't cost anything.
BB
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
On Sat, 08 Sep 2007 19:42:55 -0700, Bruce Bretschneider

Thank you for the response. Next question, what do you do if the references aren't obvious? :DOH: I guess I didn't realize that I could reference off other parts not just those that actually touch.
I think what I am trying to ask is if you mate once and the parts are in the correct orientation can you simply lock them there so that you don't have to mate in other directions as well.
Glad you said they don't cost anything, I was wondering if there was such a thing as too many mates.
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
There are six degrees of freedom for every component, three transitional along each axis and three rotational along each axis. For making a part fixed you need to fix all these movements and most of the time you need 3 mates to fix these freedoms so there is no escape from the mates. You have to put them.
Deepak

âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Engineer wrote:

Jeeeeeziz. Another blohard know-nothing!
You can use the "for position only" mate option, and then just fix the part.
Two situations where you can fully define a part with just two mates are a pair of edge to edge mates and a pair of concentric mates.
Remember that you can always mate to planes. You can use something as vague as a parallel mate just to align parts. Remember that the assembly also has planes.
There is definitely a thing as too many mates. Your tree will light up red and you will find out one day. If you start duplicating contraints, you will find out.
Daisy.

--
Posted via a free Usenet account from http://www.teranews.com

âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
On Mon, 10 Sep 2007 17:04:05 -0700, jon_banquer

Your changing the context Jon, I quoted the part where he was right. The OP didn't give enough information to trouble shoot his problem, you know where he was getting an error message but didn't state what the error message was. You jumped in parroting and plagiarizing one of your tutorials as if it was your original content without your understanding the subject.
Tom
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
On , snipped-for-privacy@aol.com wrote:

BUT....if you havnt read it...isnt that a good thing?
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
On , jon_banquer wrote:

As well as explaining wtf it actually is?

Makes a cool looking spring too!
Not that

âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
wrote:

Ha, ha. Until you get someone (god knows why) who makes a part that when it's in it's correct location and orientation it's planes are all jacked up parallel to nothing. Oh and it was a smooth organic shape with a few flat surfaces not parallel to anything when in the correct location. Ended up using points at surface intersections and distance mates to assembly planes. "Reference geometry? What's that?"
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

Though it does happen, I rarely find a mate that is not obvious, because the way my product assembles and works usually instructs me about how to make the mate.
You stated at the beginning of the thread:

This brings up the natural question: What keeps this component from sliding out of position in the real world? Because, er, that is probably how you should mate it.
If it is located in the real world with screws, use the concentricity of the screws to component A and component B to align those parts, and (if the screws are tightened in the real part) the screws bring the components coincident to each other. If friction locates a component on a plane (like a lamp sitting on a table) you can generally just mate to the table then position using the base planes of the components. If there are stops that allow some movement but prevent movement outside of a range, you can try limit mates (which are unstable if you have too many mates -in my experience, but see below about how to beat that). If it is something sliding in a slot with a tolerance on the slot, you can put a plane in the center of the component and another plane in the center of the slot component to simulate the 'nominal' motion of the part and use your GD&T analysis to be sure it works when manufactured.
There are some things that are a lot harder or perhaps impossible to truly mate - for instance, a length of chain that needs free motion like a real chain, or your shoulder joint (which is a ball and socket with restrictions on free motion in all directions due to the muscles, etc, connecting your torso and arm). These come up rarely, but they do come up, and not knowing your industry I don't know if they apply.
For the vast majority of manufactured articles, the true function of the parts (what-runs-into-what to keep parts from flying off) will tell you how to fully constrain components with mates.
When choosing what-to-mate-to-what, I look at the following 'laws' of mating to decide what to do:
1.    Mate functionally! How I mate in SW should match how the parts actually interact with each other in the real world when they eventually get made. 2.    To promote stability I will try to use mates with alignment direction- 0° angle instead of coincident to point, etc, -(and this is important) only when it doesn't violate the first law 3.    Finally, to promote stability, I will try to mate with things that cannot change due to additional features added to the model (Mate with planes, sketches, origins over faces, edges, and verteces) only if I can do it without violating the first or second laws. Mating to the base planes is a great thing, but it can't be done just for convenience - it has to relate to how the product works or you will run into issues, either with the model or when it comes to assembling first-articles.

Mates not 'costing anything' is not my experience - except on smaller assemblies.
When I get into products with over 100 or so mates (I do not know that actual number, but it is in that range) I have seen perfectly Kosher mates cause problems. Those additional mates do not actually over- define anything, but they cause errors to pop up anyway.
What I have found to be very reliable is, again, letting my product tell me how to arrange the assembly representing that product.
For a simple instance, if five components are screwed together before being added to other components in the assembly, I move those five components and their mates to a sub-assembly. This is how it works in real life, so this is how I make it in SolidWorks.
Sure, I take the hit on having multiple level assemblies (having more files to manage as I have subassemblies and sub-subassemblies, etc) but I gain stability, speed, and it makes the whole thing easier to check from a design standpoint because I can do interference detection on each subassembly, work those out, then only have to work out the top-level interferences in the final assembly. It also helps visualize how the thing really goes together to insure that there are clearances for tools (screwdrivers, spotwelders, etc) at each step of the real-world assembling of the product.
The fact that a previously ornery assemblies now works well (due to fewer top-level mates) is just gravy.
Do I do everything I just said all the time? No - it can seem like a lot of extra work, especially in the concept phase when I am throwing stuff out fast and loose just to see flesh out an idea.
But I can tell you for certain, that if I don't do the above, I can and usually do run into problems. And when I do the above (or re-work my assemblies so they follow the above) all my problems go away. Every time.
Ed
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
> 'What would > an average user of the rpoduct say is the front, the top, or the > right?'
They don't have a drug for eggheads to take that cures dyslexia, do they? Or a spell checker apparently.

What kind of parts are you designing that are aligned concentric by screws? These things made in China by any chance? Lead paint makes very good lubricant for when screw heads are not concentric, I've read. Screw heads used as bearing surface - now there's the name of a troll post. You don't really do this, do you? I had so much confidence in you because you can read magazines, and we all know the best info comes from magazines. Aligning by screws is a design no-no. In fact, modeling such that a screw is the concentric reference is a big time no-no.
Maybe you better get you some of those videos what make JB so smart.

Wow. 1701, you must be brilliant. Solve everyone's problems every time. Except people that drive locations of parts from concentric screws. You're as bad as JB posting about Multiple References and the Flex feature.
Daisy.
--
Posted via a free Usenet account from http://www.teranews.com

âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

Depends upon what you are designing. If your parts only need to be aligned within +/-.010", there's no reason to design in a more expensive location method. I've been designing plastic and metal parts for over 30 years and often rely on the screws to do the alignment. Works great!
Jerry Steiger Tripod Data Systems "take the garbage out, dear"
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
If the part slides out of position when you move the assembly then you do not have sufficient mates for anything other than visually correct. Mates should capture design intent. If your intent is for a part to stay put when moving the assembly then you don't have enough/correct mates.
TOP
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

As a general rule, I think about mates before drawing my first part to be used in an assembly.
Some things sit on "the floor", so my shop layout has the "Top" plane as the starting point for all tables and equipment, making it easy to do mates to move things around in doing a facility layout.
Other items are mirrored or concentric about a certain plane or axis.
I have found alignment with planes and axes (including those I define)have always been the most solid mates.
Bo
âœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

Site Timeline

• Share To

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.