Top Down Versus Bottom Up Design Within Onshape...

larry_hawes

I am curious about the various design approaches and how they relate within the context of Onshape and its design features, studios, derived sketches, in context and assemblies. Are there good tutorials on same? Or is it more a philosophy that develops over time and overall design experience? Would like to understand both concepts better so I can apply them appropriately.

I am using derived parts from studio to studio successfully and really like the flexibility and iteration possibilities but am mostly faking it and eventually run into trouble. I've watched a couple of videos but wonder if there isn't something more Onshape specific?

john_mcclary

Anyone can be up and running drawing parts in a day.

What separates the newbies from the professionals is how intelligent the model is.

Having parts practically draw themselves is a double edge sword. Go too far and you will be chasing your tail fixing broken references. Don't go far enough, and you will need to manually modify every feature even for small changes.

It's all about balance larry-san

mahir

You can use bottom up with Onshape, but the part studio methodology is really better suited to top down design. You can relate geometries from one part to another without having to worry about getting tangled in in-context relationships. If parts are meant to fit together, then they should be designed together. Assembly contexts accomplish the same thing but with parts that can move relative to each other instead of remaining static in a part studio. Derived parts are a good way to reuse a base part and build off of it without modifying the original. In the end which techniques you should use depends on your end goal.

larry_hawes

mahir said:

You can use bottom up with Onshape, but the part studio methodology is really better suited to top down design. You can relate geometries from one part to another without having to worry about getting tangled in in-context relationships. If parts are meant to fit together, then they should be designed together. Assembly contexts accomplish the same thing but with parts that can move relative to each other instead of remaining static in a part studio. Derived parts are a good way to reuse a base part and build off of it without modifying the original. In the end which techniques you should use depends on your end goal.

Thanks Mahir,

Derive parts is the last method I embarked upon and was pretty happy with the results. Surprisingly flexible by deriving both sketches and parts. As is obvious any method that works to serve the design intent is the correct method and what that method is termed, top down or bottom up, is most likely not important but sometimes for the sake of discussion it matters that the methods be understood at least in a cursory fashion.

I think when first beginning both CAD drawing and design within Onshape mysteries abound and solving some of those mysteries seems to simply take experience with general CAD tools and Onshape specific tools. Perhaps with a little better understanding of design methods those methods will come closer to hand with each new design adventure.

billy2

This is a heavily contested style that's been talked about since the beginning of parametric CAD.

I was one of the guys that battled against the evil empire in 1987 stating that designing parts and adding to an assembly was backwards. PTC came up with "design in the assembly" in 1989 to address the issue. Solidworks calls this "incontext".

This argument will never go away until we all sit down with a couple of pitchers of beer and hash it out.


I'll win, I know it, been doing this for a long time.

larry_hawes

Certainly not intending to argue the benefits of systems I don't understand and was more curious about the definition and techniques involved with each discipline. I even looked up PTC to be able to discuss more things CAD. I think I have a little better understanding of how to achieve either/both in Onshape but still have much, much to learn.

john_mcclary

Anyone can be up and running drawing parts in a day.

What separates the newbies from the professionals is how intelligent the model is.

Having parts practically draw themselves is a double edge sword. Go too far and you will be chasing your tail fixing broken references. Don't go far enough, and you will need to manually modify every feature even for small changes.

It's all about balance larry-san

larry_hawes

CAD on, CAD off......

billy2

The only argument for bottom up is the ease of use and this is where it all begins. And, this is also my point.

For simple structures, keep it simple. For everything else let's move on, it's time.

I have a problem to solve. How do you get people to not design everything in a partstudio? 

john_mcclary

SW, i only do bottom up, for many reasons. Mostly file ref management garbage.

But with Onshape, i do waaay more top down. Because there is never a reference error (ever)
And it is nice, but to me it still comes down to edit input. Or how much study needs to happen to make a change. So that's where the balance comes in.

Layout sketches are good, but i tend to derive more than in-context just to keep the right-click -> update to a minimum

billy2

PTC, parametric technology corporation, pro/e or creo.

Current day CAD is patterned off of one guys ideas and at the root of these ideas was the argument, it's all backwards.

billy2

I was instrumental in proliferating solidworks throughout the State of California's education system and because of this I've suffered the consequences of business owners & managers asking me why college students can't design.

Well... they're just starting out and this is where it all begins?

billy2

A few years back I was working at company who hired a bunch of college interns. These kids like to show off their projects to anyone who'll listen and I like to listen to people and discuss how to put projects together.

His project looked fine, but that doesn't do well by me, I want more. I asked about his structure and why he did what he did. I was grilling him and he didn't like it. I needed to get these kids up to speed quickly and wasn't getting paid to stroke their egos. This is business. He called me an asshole and stomp'd off.

I felt badly and the next day I sat him down and showed him how I modified my layout from the previous design meeting notes. 20 updates in 20 minutes. Some where deep changing design intent.

He was silent making it easier for me to blast through the list of changes. At the end I looked at him, first time I really paid any attention to him. He was speechless, I told him this is what I want from you. 

We're best friends now, and he's now a really a good designer.

john_mcclary

You're a designer after my own heart. That's where I sit at my company, but the kids are older than me and still don't listen. Even when I show them a way they admit to liking. Next project it went right out the other ear

billy2

You're passionate about CAD and what you do. That's refreshing and it's fun hanging out with like minded people. To promote your structure, write it down, print it out and then hand it out. Companies have to coalesce on these topics, accept other ideas and try to reach common ground. I've worked at companies that work together and it's much more fun than those that are dysfunctional.

My advice to you is figure it out. There's more dysfunctional companies out there than those that work. If you figure it out, you'll do really well.

I'm a CAD junkie, have been for a long time, it's a good group of people and I've been enjoying it for a long time.

john_mcclary

   now you probably know why I spend so much time on the forum.. need to talk to open minded people who actually feed off one another for new and more efficient methods. I bet I've doubled my effectiveness (even in SW) since joining the Onshape community. This is stuff you can apply in other cad's. But some are a much less stable with it...

In fact I didn't even know you could multibody model in SW. Then I tried it. Then beat my head against the wall for that mistake... apples are not apples, save bodies is a bad joke!

billy2

yeap, I remember when multi-bodies were added to solidworks and the first question was: "What'a we do with assemblies?". The majority of SW users don't know about multi-bodies.

The other thing that gets me is when SW users call base part designing "master models". This is a pro/e term that filtered into the SW community. Part into part in SW is called a base part. Mahir got it right which is the correct terminology.

The whole master part concept started from injection molding and working the cavity & part. At least that's my first exposure to this pattern. It's interesting to see how it's morphed into the preferred design style by only exposing it.

I was wondering if solidworks had multi-body from the get go, would there be this hesitation to use assemblies like we have in onshape?

john_mcclary

Hesitation to use assemblies is a mystery to me...

john_doubleday

billy2 said:

I was instrumental in proliferating solidworks throughout the State of California's education system and because of this I've suffered the consequences of business owners & managers asking me why college students can't design.

Well... they're just starting out and this is where it all begins?

So what are you saying about the new web-based CAD system Onshape? I am interested as I am in the process of trying to change everyone onto Onshape down here in Australia.

billy2

Well- I think it's the right way to go. From a top down stand-point it's got everything. From an assembly stand-point it's better than any thing out there. From the stand-point of install & maintain it's far superior to the other guys.

You're doing the right thing,