Going from CAD to build instructions?

My team has separate build and design teams, but we don’t always have a design student to show build what to build. Build people make mistakes (building things in the wrong order, forgetting parts, etc.) when we just give them the CAD. How do y’all tell build how to make things?

I’ve thought about just making a step-by-step list and using Onshape’s drawings feature to show visual part-by-part assembly, but that sounds like a lot of work and leaves a lot of room for design to make mistakes. Do y’all have easier ways?


Cross-train, build people should be able to open, navigate and measure in CAD at a minimum, and CAD people should have build experience so they can design parts for manufacturing/assembly and more easily assist the build team when problems arise.

Make sure the people building an assembly know and can consult the designer. It should be a priority to assist the build team when needed.

Design mechanisms that are easy to build right and hard to build wrong. This can be hard to do or train, but if a reasonable person can’t assemble something properly with the CAD open in front of them its probably too complex. Avoid parts that look almost the same but aren’t. Avoid parts that can be put on backwards, this can be done by making mounting holes irregular so the hole only line up when installed properly or by making parts reversable so it doesn’t matter.

If a part can be easily left out but not easily identified as missing after assembly, is in necessary or did build just improve the design? Assuming it is necessary, BOMs are very easy to export from CAD so print one out check off every part before you get started and make sure everything gets used.

Expect assemblies to be misassembled. I have written assembly instructions for products in my job, and the way we did it was to build the product from CAD while making notes, repeatedly if necessary to figure out how to do it efficiently, then write the instructions and take pictures of the assembly process. You can encourage the designers to think through assembly as they design mechanisms (this comes back to cross-training) and write down assembly tips but in general you just have to expect to have some assembly errors and plan in time to fix them.


We have build and design as one combined team which helps. We did have to recut all our arm pieces because our tolerances weren’t close enough and what helped a lot was creating technical drawings of every part for the arm and then changing the manufacturing approach to get better tolerances.

My recommendation would be to make technical drawings that specify tolerances and manufacturing methods as a stop gap, but really I think you need your designers and builders to talk to each other more. I recommend that at minimum every time you hand a builder a part you talk to them about what the critical dimensions are and how precise you need to be and then talking again before they assemble the cut parts to make sure that they understand what they need to do.

As far as missing parts, I’d recommend that you give them a bill of materials for each assembly so that they can check they have each part as they go along. One thing we did this year that I liked was printing out one technical drawing for every part (including duplicates) and then keeping that technical drawing with the part through fabrication.

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The easiest way is to have overlap between design and build. Not every person needs to be doing both, but having some that do both is helpful. If designers don’t build, they may create designs that are difficult or impossible to build. If build does not design, practical ideas and problem solutions may never make it to the design. If design and build work together, a lot of things that would otherwise need to be documented with drawings can be handled more quickly with communication.

Documenting with drawings is the most common way to formally transfer information between teams. Drawings are often used to show details for individual part fabrication. However, Onshape also makes it pretty easy to create exploded views to aid in assembly. These exploded views can be put in drawings. Here is one video out of many that can be found that concisely shows how to create drawings with an exploded view and a bill of materials.

Design can help build by creating logical subassemblies with complete bills of materials. Build can reduce issues with missing parts if they kit all the parts they need (custom fabricated and COTS) for each subassembly before they start working on it.

If your designers and builders aren’t talking, that’s the first problem.

One thing I tend to do if I think there’s something funny with the build order is to do a partial assembly drawing that shows that specific section, then write out instructions on the drawing. That way I remember, and the next person is instructed.


Great suggestions from paulonis, Eric and Brendan.

I want to add some notes about drawings and documentaion. Your designers should know how any part they are designing is going to be manufactured, and based on that they should be able to pretty easily create the necessary documentation. For CNC parts you’ll probably want some system to track part fabrication, but this a weak point of my team so I’m not going to try to suggest anything. With manual milled parts, teach your designers to make basic drawings (pictured), don’t worry about getting everything perfect just good enough to manufacture. I recommend having standard tolerances for different operations, manual milling for us is ± .005" unless otherwise noted. For many things you might not need a drawing, For shafts and tubes we just have cut lists. For shafts we list stock, length, and thread size if tapped, with the expectation that everything will be square off the lathe and withing .005" preferably .001". For tubes we usually only care about the number of holes, so a nominal length is all we need with the expectation that all tube cuts align with a hole and the tolerance is +0.0", -0.1" or so.

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Thanks for all of the suggestions. I’ll make sure there’s always a design student ready to help build if they need help. I’ll also make sure our BOMs are simple and look into technical drawings with Onshape for when one would be useful. Design’s been helping with build recently, but I’ll make sure they’re spread out and aren’t all doing the same thing.

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Great topic!

We use a combination of techniques. Our design and build teams are also separate. Since design and build happen fast we don’t always do a perfect job of creating drawings from the OnShape models. It depends on the complexity of the assembly. Here are a few suggestions:

  • We review the design progress and current model on a classroom monitor to the full team at the beginning of our meetings. Early on, it’s just 2d and 3d doodles before the design gets detailed for build. Build is constantly providing feedback during the life cycle of the design.
  • We will usually print assembly and parts drawings with key dimensions and text notes pointing out the critical items.
  • An exploded view would be used assemblies that are more difficult to understand.
  • In all cases, we just go over the drawings or CAD as a hand-off step. Build would never be given content without a discussion.

Good luck with your process!


We have combined design and build trams. Typically the upperclassmen are driving the design and the underclassmen are doing the assembly. The designers make drawings of the parts and this year we started making assembly drawings with exploded views.
Typically we skip part drawings for sheet parts we run on the router (gussets and plates) but will make them for tubes, shafts, and gearbox plates (calling out critical dimensions). I’ve made a few drawings with manufacturing steps on some of our parts too.
The exploded views go a long way to help assembly. As does a bill of materials table so whoever is assembling can find everything hey need before they start. This year I want us to get better at written assembly instructions in her notes.
I’ll try to dig up an example this evening.

For us, there is a CAD PC in the assembly area of the shop. Since we use Fusion 360, we can access the robot’s CAD models from this single PC. The shop mentors and assembly kids can refer to this PC to build the robot and open sub-assemblies on the screen.

I work in automation machine building. This is the same thing that happens in the real world. Assemblers on the floor have a PC they can use to open the design files up from the floor digitally.

They use the measure tool in CAD if they question anything. So far that has worked for us.

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Everybody here has such great ideas so far! We are a big team, so we have separate design, fabrication, and assembly teams. To get from design to fabrication, we use basic engineering drawings, like the ones show above. To get from design to assembly, we have each main designer for a feature create an assembly workflow which is just a set of really detailed steps with step by step screenshots of cad showing “at this point this is what you should have”. It also specifies what nuts, bolts, and even tools you should need for each step. Then, even if the build people have no design knowledge (which most of them do), they can follow the instructions to build the feature correctly (the first time).

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The only solution I found, after several years of struggle, was to merge the design and build team into one mechanical engineering team. Most students don’t spend equal time doing both CAD and building, but at least the leader of each mechanism team is deeply immersed in both and can oversee the builders. At this level, it would take more time to write/draw/animate build instructions, than it would to just supervise the build in real time.

As a designer, I had some spare time and created some assembly guides that makes it as if its a Lego building set.

We have BOM and stuff like that for actually making sure that things have been manufactured:

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