Design for Manufacturability

This is the most common DFM mistake on milled parts, by a wide margin. Every pocket and slot machined with an end mill will leave a radius at internal corners equal to the radius of the tool used. A perfectly sharp 90-degree internal corner in your CAD model gives the machinist two options: use a corner-relief tool or tell you the part can't be made as drawn.

The fix is to design all internal corners with a radius. How big that radius needs to be depends on pocket depth and tool diameter. As a starting point:

In SolidWorks or Fusion 360, use a fillet on the sketch profile, not just on the 3D body. Filleting only the body can create hidden sharp edges in the toolpath that CAM software won't catch until setup.

Thin walls flex and chatter during machining. Past a certain threshold they can fracture. The minimum workable wall thickness depends on the material, the height of the wall, and whether it's a through-wall or a floor-supported rib.

The height-to-thickness ratio matters as much as the absolute number. A 1mm wall that's 3mm tall is fine. A 1mm wall that's 30mm tall is a manufacturing problem. Anything above an 8:1 ratio should be flagged for shop review before you finalize the design.

The depth-to-width ratio of a pocket determines how hard it is to machine. As a pocket gets deeper relative to its width, the cutting tool needs to be longer. Longer tools deflect more, need slower feeds, require more passes, and cost more to run.

If a functional requirement forces a deep narrow pocket, like a coolant channel or a precision bore, put it on the drawing explicitly and flag it in your submission notes. Most shops have a solution, but they need to know it's coming before they set up the job.

Every tolerance that's tighter than the functional requirement actually demands costs money. It shows up as slower feeds, more inspection steps, potential scrapped parts, and sometimes specialized finishing like grinding or EDM.

Before you finalize any drawing, go through every tolerance callout and ask yourself what it actually enables functionally. If you can't answer that question, default to plus/minus 0.127mm and move on. Reserve tight tolerances for bearing seats, shaft fits, and surfaces that must seal or transmit force.

A feature a cutting tool can't physically reach can't be machined. This sounds obvious but it shows up constantly in parts designed without visualizing the toolpath.

The fix: mentally simulate fixturing and tool access for every operation before you finalize the model. For complex multi-sided parts, sketch out the operation sequence and make sure every setup has a usable datum and enough tool clearance.

Specifying a thread that requires a custom tap or die is a quiet cost multiplier. Standard thread families available off the shelf at virtually every Canadian machine shop are metric coarse, metric fine, UNC, and UNF in common sizes.

Anything outside these families means a tooling surcharge, longer lead time, and sometimes a phone call to ask if you really meant that thread.

Machine to finish means different things to different people. Without an explicit surface finish specification on the drawing, you get whatever the machinist considers standard, which may or may not match what you actually need.

Best practice is to specify Ra in micrometers on every surface that matters, using the ISO 1302 surface finish symbol. This is especially important for surfaces that will be anodized, plated, or bonded.

In any assembly with multiple machined parts, tolerances add up. When every mating surface is at nominal everything fits perfectly, but in reality every dimension sits somewhere in its tolerance range.

For critical assemblies, run a 1D tolerance stack-up before you lock your drawings. Identify the closing loop and decide which dimension carries the closing gap. That's where your tightest tolerance belongs.