Which method is best, Top-Down or Bottom-Up

If you're using models of existing parts, it would seem that bottom up is the way to go.

The assumption here is that you don't have pre-existing SW parts, but do have many parts in some other system. Not knowing specifics as to what it is you are really talking about makes it a bit hard to generalize, but generalize we will.

Do you have an existing PDM system? That might play into the answer.

How many parts in the typical assembly? High range and low range please. Do the assemblies have many sub assemblies? Of the parts in an assembly how many are those that contain slight differences?

There would be two approachs to implementing SW in the scenario you have presented. Neither really has much to do with top down or bottom up design.

1. For the parts with slight differences use Design Tables. This will generate many configurations and this might impact performance and the ability of your PDM to handle those parts. Ditto for assemblies, they can also be made with design tables.

1. For the parts with slight differences use a database to create each part from a generic part. This requires use of the API and is similar to how the Toolbox works for fasteners. Each part will have one configuration. Most PDM systems will be able to deal with the subsequent parts.

and of course you could just model each part separately which is the third and most basic method.

In general you use top down to control the geometry of parts related by geometry through an assembly or inserted part. Since your parts are already defined this would not be appropriate unless the pre-existing parts in some way drive the sizing of parts in a top level assembly. Then you would have to create a new configuration or a copy of the assembly for each variation.

Using parts and assemblies that are configured assures that things that are supposed to be common remain common. Using copies gives the best performance and is easiest to manage files.

In addition to what other experienced users of SolidWorks in a company environment have noted, I wonder whether you have considered hiring a SolidWorks consultant to go over your specific company's needs so you can get to bottom line "must avoid" and "must have" and then the grey area decisions.

A number of people here on this board are consultants and their websites list their type of work. Your VAR ought to know who is available in your region.

These guys hired for 2 days might save you man months of wasted time in the next year, and a large amount of frustration. Their fees may be high, but they earn it by keeping you from avoiding the worst of the known mistakes.

Bo

The quick way to know which route to go:

Is the part specific to that assembly? That piece should be created top-down. Example: some edging

Is the part used in multiple assemblies? Best to use bottom-up. Example: A screw

Even if it just has slight variations, it's best to use top-down instead of configs. However, it is possible to tie those two together and have a really fancy top-down assembly. How? Make an assembly that is driven by a sketch, then tie the sketch to the top assembly. Sound complicated a little I guess, but that will keep you from having to make new drawings everytime and you can work configs into that assembly.

Gromit,

I just worked a project that was entirely top down and will add a few observations here on the subject that I haven't heard mentioned before.

The model I built is for all practical purposes a simple open topped box. The design intent is for the box's internal volume to meet certain criteria. The criteria are contained in a spreadsheet from the customer in the form of length, width and depth.

Step 1. Build a part with a design table driving this simple "box". Cut and paste the customer's criteria into the design table spreadsheet.

Step 2. Insert the "box" model into an assembly as an envelope.

Step 3. Model all the components off the envelope using in-context references for all the features that might be driven by the "box" geometry. This means the sides and bottom.

Step 4. Create a design table in the assembly and cut and paste the customer's information into that table as well using the DT in the assembly to drive which configuration of the "box" envelope part is being used.

The assembly will now cause all the parts to change depending on which configuration of the "box" envelope is being used. Note that the parts in the assembly have only one configuration except for the envelope part which has multiple configurations. This means that it would not be possible to make a standalone drawing of the in-context parts without also having the assembly also in the drawing to drive which configuration is being used. For this project that is OK because the customer only want's drawings of the entire assembly.

This excercise also demonstrates why having in-context features in general can be very dangerous. When there is an in-context feature driven by a configuration of another part through an assembly that feature's dimensions will require the assembly to be open to update and will not be controlled by anything in that part. The part with the in-context reference will therefore have multiple configurations without having them explicitly managed by the configuration manager in that part. Instead they may be managed by configurations in either the referenced part or the assembly. In fact the parts with in-context references will only show one configuration and "Find External References" will only show the currently referenced configuration for that part.

TOP

Gromit,

As Top's example shows, there's no hard and fast rule that everything must be one way or the other. Each situation has to be judged based on the requirements of what is being created in SolidWorks. Also, Top- Down is a tool for design of an assembly, but it can be dismantled once the assembly is complete (e.g., remove all in-context requirements after assembly desgin is complete). If you do have common assemblies slighted edited to suit each customer, perhaps consider an even more robust approach by controlling design with a macro that gets minimal input from the user and automatically generates the expected results. Just some ideas.

Matt