Thoughts on BIM

One of the difficulties we’ve been facing with BIM is the best way to approach it. There are some schools of thought that everything starts with the model. You begin by modeling the work, then you derive your shop drawings, fabrication drawings and everything else from the model. I think this type of “top down” modeling would work pretty well in a field where the parts being modeled are fairly consistent and how they are used varies. So, for instance, if you were an electrician or an HVAC or Plumbing guy, or even structural steel, you have a specific kit of parts. A library of sorts that you pull from. These parts then can be placed and modeled fairly easily and even though where they are might change, the parts themselves don’t.

The problem we face is that the kit of parts changes constantly. In addition, the parts interact with each other so if one part changes, it not only impacts that particular part but usually all the parts that intersect with it. In addition, the parts are a bit in flux when you start the job. You have to design them, get them approved by the architect, then get them built by the extruder before you “really” know what the parts will look like. So in our world, if we start with a model, we will have to modify the basis of the model, not just the geometry which is easy, but the logic and the parts which is hard.

The next problem is one of detail. Most models for Mechanical/Electrical/Plumbing or Structural have to detail that trade. In our world, we need to detail all the trades. The most important thing we are doing in our model or shop drawings after showing the aesthetics of what our system will look like, is to show how we will maintain water integrity with the rest of the skin. Now we have a level of detail problem. The standard Revit model doesn’t really model caulking. So now we are creating 2d details that represent the other trades materials, flashings, membranes and caulking. Not the end of the world, but another consideration. Most architectural drawings are 80 percent plans/elevations and sections and 20 percent details. Our shop drawings are 20 percent plans elevations and sections and 80 percent details. It is a big consideration.

The final issue is getting a model to shop floor solution. While it isn’t hard to create a model for the contractor or architect, it is quite another thing to create a model that will drive your fabrication tickets and CNC process. Another consideration in the mix. So let’s examine the different software choices and their strengths and weaknesses.

Revit. This is the tool of choice for Architects. Clean and simple interface, look good and will update your drawings as you modify the model. Keeps your drawing sets coordinated. Lots of good features. We see a number of curtain wall companies using Revit for creating shop drawings and models. It is a great tool for the plans/elevations/sections part of the drawings. It is not as good with detail. It is hard to get blown up elevation drawings with dimensions. It is not a great 2d detailing tool. Some of the things that we produce (metal panels for instance) are not as easy to create. Revit is not good for fabrication tickets and information.  Also, a curtain wall can have a ton of parts and if you try to create and represent everything, Revit can have a hard time handling that much detail.

Inventor (or any of the other solid modeling platforms out there). This tool is actually a pretty good way to model. Lots of detail. Details update when you update the model. It is a good tool for metal panels and other things. Good for fabrication tickets and downstream data also. Not the best at 2d details (caulking, waterproofing, other trades) but you can just do that in Autocad after the fact. If parts change on you, you have a lot of re-work though. A good solid middle ground.

Third party programs. Things like V6, Tekla, or other programs are also a good option. Usually with these types of programs you end up with some setup required for the systems. When systems are constantly changing, this is where you will find your issues. In addition, many of them are not good at shop drawings. They can create something basic but for a major curtain wall company, the drawings need to be world class and we found the outputs less than stellar. You can get there, but there is a lot of work and it won’t be as flexible as you want. You will also need another solution for your other products (aluminum or composite panels, etc…).

Plain old Autocad. Seems boring, right? So, here’s what we’ve found. It is completely flexible. You can model anything in it and fairly easily. No it doesn’t have bi-directional detail updating and families and all the other features of some of the other software, but I can draw details for a custom system in an hour or so, get them to the architect, share them with my vendor and be off and running with no setup, no families, etc… With a ton of customization, you can make it do anything.

So here is where we are today.  We have a custom Autocad solution that we use to get from the shop drawings to the shop floor.  It’s really a combination of a database and Autocad that drives the system.  Everything is in 3d.  But we start with 2d shop drawings and then create our model from them.  This gives us the best of both worlds.  A quick way to work through design and changes to create the shop drawings efficiently and when we know what the customer wants to build we model it for the rest of the process and then provide that model back to the customer for coordination.  The only issue we have found is that by modeling everything to that level of detail, the model is very heavy.

So I’m curious what other people are doing.  What BIM solution have you settled on?  Please leave a comment and let me know!