CNC Rapid Prototyping Vs. 3D Printing

Posted By: Zach Schantz
Jul, 2020

When you have a great product idea, it’s natural to want a part in your hand as quickly as possible. This allows you to look at the product, test it, and see if it will fit where it’s meant to be. Of course, most designs require some degree of tweaking; you’ll probably go through a few iterations before getting exactly what you need. The faster you receive your prototypes, the quicker you can get to market. Unfortunately, there’s a belief in some quarters that rapid prototyping is just another term for 3D printing. We’d like to compare CNC machining and rapid prototyping with 3D printing and explain why CNC machining is the faster prototyping process.

Understanding the 3D Printing Process -
3D Printing for Prototyping

A 3D printer may be many things, but if you’ve ever watched them work, you’ll know that “rapid” isn’t one of them. Building a 3D part layer by layer can take hours, and it doesn’t stop with the actual printing. A CAD model isn’t enough to get started; you have to add support structures so the part doesn’t collapse. Then, once it’s printed and you’re happy with the part, additional cutting is required. Most printing processes leave layers visible on the surface, so you can plan on grinding or sanding them off, too. All in all, 3D printing is suitable for some prototypes, but also faces a number of limitations.

Material Limitations of
3D Printing

Metal printing is evolving quickly, but these processes are limited by the need to deposit and fuse a powder. This means you may not be able to have a part 3D printed in the exact material you want. That can have implications for testing and appearance.

Size Limitations of
3D Printing

Most 3D printers on the market today have a working envelope no bigger than a shoebox. Yes, there are some larger machines, but unfortunately, they carry large price tags, too! Comparatively, most CNC lathes and mills offer much larger envelopes.

CNC Machining is More Accurate than 3D Printing

CNC machining is extremely accurate. We can hold tolerances as tight as +/- 0.05mm (0.002″). Fused deposition modeling, (FDM – the plastic extrusion process), achieves about +/- 0.5mm. Selective laser sintering (SLS) is around +/- 0.35mm.