Design for Manufacturability (DFM) isn't about compromising your design — it's about achieving the same function with less machining time, fewer setups, and lower risk. Engineers who understand DFM get better parts, faster delivery, and lower costs. Here are seven principles that make the biggest difference.
1. Use Standard Hole Sizes
Every non-standard hole size requires a special drill or reamer. A 0.251" hole needs custom tooling. A 1/4" hole uses a standard drill that every shop has on the shelf. Stick to standard fractional, letter, or number drill sizes whenever possible. Your shop will thank you — and your quote will reflect it.
2. Avoid Deep, Narrow Pockets
A pocket that's 4x deeper than it is wide is a nightmare. The tool deflects, chatter increases, and the shop has to take tiny passes at slow speeds. If you need a deep pocket, make it wider. A good rule of thumb: keep pocket depth under 4x the width. If you need deeper, consider a through-slot or a multi-piece assembly.
3. Add Radii to Inside Corners
Sharp inside corners are impossible to mill — the tool is round, so there's always a radius. If your design requires a sharp corner for a mating part, add a relief (a small undercut) instead of forcing the shop to use a tiny end mill that takes forever. Specify inside radii of at least 1/3 the pocket depth.
4. Minimize the Number of Setups
Every time the part gets flipped or re-fixtured, it adds time and introduces alignment error. Design parts so that as many features as possible can be machined from one direction. If a part needs 6 setups, ask yourself: can I redesign it to need 3? Can I split it into two simpler parts that bolt together?
5. Specify Tolerances Only Where Needed
This comes up in every article because it's that important. Over-tolerancing is the #1 cost driver we see. A part with 50 dimensions at ±0.001" costs dramatically more than the same part with 5 critical dimensions at ±0.001" and everything else at ±0.005". Be surgical with your tolerances.
6. Use Standard Thread Sizes
Like holes, standard threads are faster and cheaper. UNC and UNF threads in common sizes (1/4-20, 3/8-16, 10-32, etc.) use taps that every shop stocks. Metric threads are fine too — M6, M8, M10 are all standard. Avoid exotic thread forms unless the application truly requires them.
7. Consider the Raw Material
Design your part to fit efficiently into standard stock sizes. A part that's 2.050" wide requires 2.5" bar stock — wasting almost 20% of the material before the first cut. If you can make it 1.950", it fits in 2.0" stock with minimal waste. Check standard bar, plate, and tube sizes before finalizing dimensions.
The Best DFM Tool: Talk to Your Shop
Send your design to the shop before it's finalized. A 15-minute DFM review can save thousands of dollars in production. Good shops will point out features that are expensive to machine and suggest alternatives that achieve the same function for less. At Reliable Manufacturing, we do this on every new project — it's part of the quoting process.