3D printing is a great technology – in fact, when I talk with children, they don’t realize that not everything is 3D printed, in fact, little in the average person’s life is. Subtractive manufacturing and injection molding are still the dominant players in mass produced consumer goods and even in some prototypes, but that does not mean they are the right fit for whatever you’re working on.

In this post, I want to provide some tips on deciding if your part(s) are best produced with 3D printing or with another, more traditional, manufacturing process. There isn’t a one-size fits all bit of advice here – we’re always happy to look at your parts and help you decide, but here are some things to consider:

What are the structural requirements of the part?

What is the part doing? If it’s supporting a safety critical piece of gear or holding up the front end of a 787, 3D printing may not be the right fit. Yes, metal 3D printing does exist and is VERY good, but it is also very expensive and generally beyond the budgets of most prototype projects. If the part needs to be very strong in multiple directions, 3D printing might struggle as the layers give the parts strong and weak directions. Inclining the layers can help, but it won’t be the same as a solid piece of plastic that was machined. For parts that are not under incredible loads, 3D printing may be a good alternative though!

Does the part design eliminate machining or printing?

There’s an old saying that “machinist” isn’t spelled “magician” – I’ve had prints of parts come to me with holes that turn 45 degrees mid part, parts that have a large internal bore with no access to the outside save one little hole, or parts that simply cannot be made for a number of reasons. Things like this are a show stopper for traditional machining, but may be able to be accomplished with 3D printing. Likewise – large unsupported overhangs, steep angles, and tiny features may be relatively easily accomplished on a milled or molded part, but be very difficult for a 3D printer. Consider the part design and how it could be modified to make either of these techniques more viable.

How many, how fast, and how precise?

A big consideration is how many parts you need to produce. 1 part? Consider 3D printing if we haven’t already ruled it out. 50 parts? Maybe consider it still. More? Time to invest in a print farm or just setup a molding or milling approach that can turn parts out in much less time than 3D printing. The setup time and cost for these traditional methods is certainly higher, but in quantity it quickly becomes worthwhile. Speaking of speed – that’s our next factor. How fast do you need the parts? If you need a prototype tomorrow for an experiment or demo – 3D printing might be the way to go. If you need 5 tomorrow – maybe. If you need 50 tomorrow – you probably are going to be in a tight spot. Consider the duration of your need as well – 1/week or 10/week makes a difference in terms of machine run time and payback! Finally, consider how precise you need the parts to be. 3D printing has gotten much better here, but traditional plastic printing can’t touch what our CNC mills and lathes can do in a fraction of the time. In many cases this may not be a big deal though!

How finalized is the design?

The most common mistake I see made is by far investing in tooling too early. Molds can become very costly, custom cutters can add up, or odd geometries can result in high setup charges. If your design is still in flux – don’t invest in a scale-able solution yet. Even if the part must be metal, 3D print the designs first to help find any user issues or clearance problems, then invest in the machining or molding of the project. Maybe your final part is going to be plastic – great! Then you can 3D print the first production pieces and get them into the lab or field before you invest in tooling and can easily catch and correct any issues. The moral here is prototype cheaply and quickly, then settle into the final design. This is especially true if you are not using a 3D CAD system to catch mechanical issues, but no CAD can replace holding the device and saying “does this feel right?”

What is your future plan?

This question drives more of the design process than anything. Do you want to prototype this, then plan on selling 100k units/year to a retailer or do you really just need a couple for your lab or shop? These numbers should guide how much effort is put into the “design for manufacturability” (DFM) of your design. Each process has different DFM tips that we can help you with, but if you just need one or two, it’s likely not worth the time to save the additional manufacturing hassle. If you need fifty, we can probably help save you a significant amount by optimizing the design for manufacture and assembly.

Case Study – Fiber Optic Adapter


Original part (left) and 3D printed replica (right). These parts both serve the same function identically, but have drastically different costs in quantities of 1, 10, or 100 based upon the production method.

Recently we had a project come though the shop that needed some duplicate parts made for an older instrument design. The original parts were machined from a plastic bar on a lathe, but the tolerances were not that critical, just a loose slip fit. Molding was immediately out as we only needed to make a couple of parts and the per unit cost would have been too high. Machining is still a viable option here, but each part would have ended up costing the customer around $175 after about an hour’s labor in CAD/CAM. Not ideal for such a simple part that as it turns out is not a structural part, just a simple adapter for a fiber optic assembly. 3D printing ended up making a part for about 1/10 the cost of machining and it worked beautifully! If our customer needs more (say 10 or more) we already have the CAD model and can transition to machining the part as with quantity the cost will become more comparable (and the 3D print time becomes too high). If the customer then needed 10000, we can transition to molding. Knowing your part, application, and needs determines the method of manufacturing you need to pursue. We’re here for you the entire way, with all three processes in-house and ready to scale with your project!

John Leeman
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