Fasten Mate option to maintain offset between two parts/mate connectes (vs snap to 0 offset)

Malcolm_Daniel

I would really like the option to create a Fastened mate that automatically enters the X/Y/Z offsets to maintain existing spatial relationships between two mate connectors.
This is similar to choosing an offset mate in Solidworks before selecting the references...it automatically plugs in the offset value for you.

Alternative is allowing Group between part and origin.

I'm requesting this because unless there's something I'm missing....

• You can't group parts to the origin
• Fixed constraints don't carry to higher assembly levels
• So...to achieve sub-assemblies that remain fixed relative to their origin in higher assemblies, you have to create a Fastened mate between one part and the sub-assembly origin
• And...if you want the parts to all maintain there relationship to the assembly origin, that Fastened mate has to include offsets (unless it coincides with a mate connector on a part)...which you have to measure before-hand, and manually enter into the Fastened mate.

Is there an existing workflow I don't know about?  Offset Fastened mate seems like the right functionality...and having the offset values populate when you check the "Offset" option would be fabulous.

john_mcclary

first, you need to forget about origin it assembly. They don't carry over to highur level assemblies either. So you group two parts, then mate the base part in higher level assembles.

Also, you can create offset mate connectors in the part studio also. 

Question is, how will it know what the offset values should be?
You are just floating the part in positon, then hit fasten, check an auto offset box, then pick 2 connectors, then edit to nominal values? Or do you have something else in mind?

Malcolm_Daniel

Basic workflow I don't have a great solution for:

• Import assembly
• Re-arrange assembly structure as necessary
• Establish mates in lower levels that represent motion & limits (actuators, mechanisms, etc.)
• Establish combo of mates, fixed, and group at lower and upper levels to keep everything positioned in space as-imported but allow dragged motion for desired degrees of freedom

The problem I often encounter is that Fixed doesn't carry to upper levels, and if you don't fix/mate relative to origins at each level, things can get accidentally moved around, so they're no longer in the right position at upper levels.  So, it becomes a cumbersome exercise to get everything positioned properly so things stay where you want them, but you can drag degrees of freedom.  Things fixed at lower levels have to be fixed again at upper levels or grouped with something to keep them from moving unintentionally.  Being able to create an offset mate at a lower level between say your actuator body and the origin, then mating that origin to the upper level origin (maybe another offset mate if they don't align) would take some of the additional clicks/redundant constraints away and allow for more clear design intent.

Maybe there's another workflow I haven't thought of though?

owen_sparks

Just a quick question, forgive me if it seems daft...

Are you aware that when importing into an assembly parts automatically come in relative to their own origin unless you click on the screen as to where to put them?  That is to say if you pick the item from the list and then immediately click the green check button they'll be where you want them.

Many users seem not to realise this.  They'll assume they have to click somewhere on the screen to place them and then move it afterwards. (Calling Onshape UX Discoverability Team for this point.)

What we can't do, as far as I'm aware if move it and then send it back to its default insertion location.

Cheers,

Owen S.

john_mcclary

Can you create a simplified assembly structure, showing how you mated everything?

I've yet to come across a time where fixing things in multiple levels was required. In fact, I am more likely to persuade you against such habits.

Maybe there is something I'm missing, or a new way for you to mate your assemblies.

Malcolm_Daniel

@owen_sparks ... yep, i'm aware of how to get it to snap to default positioning.

@john_mcclary ... i'll work on a generic example when i get time.

thanks for the responses.  i'm probably missing something obvious that will result in a forehead smack when i finally realize it.

philip_thomas

All of the above are true - this is just another piece of information that may be useful.

If you add a mate connector to a Part Studio on the origin (owned by any part), then when inserted into the assembly, you now have something that does migrate to upper level assemblies. The workflow then becomes, group all the parts together, insert the sub assembly into the next higher level, fasten-mate the mate-connector to (presumably) a mate connector in the next level up (try to always mate to the mate-connector the was created at the highest level assembly). 
This workflow works, and reflects the process that some companies use when every part is built offset from the origin so as to define its position in the assembly - sometimes referred to as 'aircraft coordinate system' - but is not the recommended one. 
The recommended is;

• For each Sub Assembly, group/mate the parts.
• Insert each Sub Assembly  into the next higher assembly.
• Mate or fix any one part relative to something already in the upper level.

I hope this helps you.
Philip

john_mcclary

yea, @philip_thomas has a work around that would satisfy your current mating methods.

Malcolm_Daniel

I appreciate the ideas and dialogue.  I'll take another look, and if still struggling, I'll build the demo model.

Malcolm_Daniel

Here's another example of my perceived the use/need for offset fastened mate.  I made it a public document (link below).

Have a multi-axis actuator/mechanism I imported.  Trying to set up all of the mates to give it realistic motion.  In the cases where two components aren't aligned with default mate connector locations, you have to create an offset somewhere.  Only way I know to do that is take measurements and put them in as an offset to a mate.  My requested functionality would eliminate the measurement and manual entry of offset values.

https://cad.onshape.com/documents/60ae9cf99b6ed982260fee2b/w/0c4a04d70d08be7baf72bf06/e/5bf3bcd7f139f5a6646dfad8

john_mcclary

I see what you're getting at. What I would typically do in that case is add the necessary holes and use those to locate the part.

It serves two functions. one is to locate the part. the other is to check hole patterns. In this case your top hole overhangs the bracket. Which means your bracket is probably too narrow.
Also, we try any make details symmetrical whenever possible. By having a centered hole pattern on the part ensures design intent, while also acting as a replacement for in-context. Which should be used as little as possible.


There are two schools of thought here. My co-worker was taught to mate planes and faces and never holes. I was self taught and always mate holes. We strongly disagree with eachother.

But, guess who has fewer hole missalignments at assembly...  o/

philip_thomas

There is a lot going on here.

1) Lets not forget about 'Group' Mate. This is the #1 mate you will be using if importing assemblies. Look at my public document and you will see that every sub assembly has one Group mate and one fix.

https://cad.onshape.com/documents/32de233a6441c7e2332a27d4/w/488c34f00817dadb4206d6c8/e/5247e71333872dee44fd94ab


2) Other than allowances for motion, Group works everywhere and if the imported parts are in the correct spatial location, that is a good solution here.



3) As an academic exercise in mating these parts - yes, there is no default mate-connector location that will give you the correct location. That said, we have many fall-backs available to us. The two pieces of information that we have are (a) the axis of the spindle lies directly about the slide screw and (b) the top of the motor is coplanar with the bracket. And as much as I love sticking to my rule of '1 mate per part', I found myself expressing the two knowns as two mates.

Step 1 - create a Mate C.onnector on the center of the bracket face and align the primary axis vertically.



Step 2 - Create a Mate Connector at the center of the motor spindle and align it's primary axis vertically





Step 3 - Apply a Slider Mate between the two Mate Connectors




Step 4 - Apply a Planar Mate between the two outermost faces



I am not saying that this is the only way (the holes method that John McClary described is perfectly valid), this is just A solution and might represent ideas and techniques that prove useful to you here and in other situations.

Also - it's fun (that's why I work here )

Malcolm_Daniel

Thanks guys.

• On creating holes, agreed...but for concept modeling phase, importing and using models quickly, etc. it's too cumbersome
• On mating holes vs datum features, agreed...it's a religious debate with zealous arguments on both sides.  Either way you have to be diligent about checking that things are positioned properly and holes and other critical features align.
• On grouping...understood
• On using multiple mates to capture design intent, agreed, and I've done that before in Onshape

Edited to better reflect tone:
I still think it would be much easier if I could start a Fastened mate, check the offset button, click two references, then OK and my parts would magically be glued together with no change in relative positions   

owen_sparks

Malcolm_Daniel said:

BUT....don't you think it would be much freaking easier if I could start a Fastened mate, click two references, check the offset button, then OK and my parts would magically be glued together with no change in relative positions?    

Nope, that's exactly what the group mate already does, just with less clicks, no fasten mate required, and with as many parts as you wish in one mate

Malcolm_Daniel

Improvement request submitted:  https://forum.onshape.com/discussion/12229/fasten-mate-option-to-maintain-offset-between-two-parts-mate-connectors-vs-snap-to-0-offset

Malcolm_Daniel

If it wasn't obvious, I understand you guys were responding to the "am I missing some workflows" portion of my original post, and not trying to convince me the offset mate isn't useful.  I appreciate the dialog, and hope you see the value in the improvement request (if so, vote!) .

Malcolm_Daniel

owen_sparks said:

Nope, that's exactly what the group mate already does, just with less clicks, no fasten mate required, and with as many parts as you wish in one mate

@owen_sparks ... but the group mate only works at entire top level parts/sub-assemblies...you can't group the carriage on an actuator sub-assembly to the bracket/sub-assembly at the upper level.

But...maybe that's an alternative to the Fasten with offsets is allowing Group to work on parts/sub-assemblies within sub-assemblies (vs only at top level).

philip_thomas

@Malcolm_Daniel - As Owen and I are now pointing out, you are describing a Group Mate. Select any (two or more) parts and apply a Group Mate - they are now locked together. Your request is the exact behaviour that is already present in Onshape.

john_mcclary

To be clear, I never said your method was not valid. Nor will it upset users if this function existed. 

Just showing alternate work flows for the mean time.

Malcolm_Daniel

@john_mcclary ... yeah, i realized my comment sounded snipey after posting, which is why i wrote:

Malcolm_Daniel said:

If it wasn't obvious, I understand you guys were responding to the "am I missing some workflows" portion of my original post, and not trying to convince me the offset mate isn't useful.  I appreciate the dialog, and hope you see the value in the improvement request (if so, vote!) .

Malcolm_Daniel

@philip_thomas ... in my example assembly, if I try to group the bracket to the carriage of the actuator, it selects the entire actuator...not just the carriage.  what am i missing?

john_mcclary

@philip_thomas
Sort-of

You never want to add a sub assembly (that may change) into a group mate on a higher level assembly. That's when all hell breaks loose and you spend 20 min wondering why your weldment exploded..

With this fasten offset trick, you can apply the fasten to a part in your sub assembly. Without the extra step of measuring offsets.

Otherwise, yes. It is just like a group mate.

Or, mabybe we finially fix the group mate dilema with sub assemblies

Malcolm_Daniel

@philip_thomas ... also, when i group the rotary actuator to the bracket, the motion within the rotary actuator is now locked (rotary carriage to body).  all of these reasons seem to force me to use one or more mates vs grouping so that the mechanism operates as intended.

philip_thomas

@Malcolm_Daniel

Ok - I have done the rounds of our Assembly Development team and the weight of popular opinion has swung to you
All the methodologies described above are valid, but the team does feel that there may be room for an option to create a mate type such as you describe. Please submit the enhancement request.

Malcolm_Daniel

@philip_thomas ... thanks for the legwork and feedback ... here's the improvement request:
https://forum.onshape.com/discussion/12229/fasten-mate-option-to-maintain-offset-between-two-parts-mate-connectors-vs-snap-to-0-offset