The cheapest possible place to fix a design problem is in the model, while it is still just lines and surfaces on a screen. The most expensive place is after a whole batch has been made and shipped. The trouble is that many of the costliest errors are completely invisible on screen and only reveal themselves when the part arrives wrong, too late and too dear to simply ignore.
After years of fixing other people files in our CAD service, the same mistakes come up again and again, regardless of how the part was eventually going to be made. Knowing what they are and where they hide is genuinely half the battle, because once you are looking for them they become surprisingly easy to catch before any harm is done.
The faults we see most
A small handful of recurring errors account for the great majority of rework, scrapped parts and missed deadlines. None of them are difficult to avoid once you know to look, but every one of them survives happily in a model that otherwise appears finished and correct, which is exactly why they slip through to production so often.
- Walls too thin to print or machine reliably.
- No clearance designed in between mating parts.
- Non manifold geometry that confuses the slicer.
- Detail far finer than the process can reproduce.
- Wrong units, so the part arrives ten times too big or small.
Why they slip through
These mistakes survive because a model genuinely looks complete on screen long before it is actually manufacturable in the real world. A wall that is a fraction of a millimetre thick renders perfectly and looks solid, yet it cannot physically be built by the chosen process. A hole sized exactly to a pin looks completely correct but will never actually assemble.
The fundamental issue is that the model rewards appearance while manufacturing rewards intent, and the quiet gap between the two is precisely where money leaks away. The screen tells you the part looks right, but only a manufacturing minded check tells you whether it will actually behave and assemble the way you need it to once it is real.
Building habits that prevent them
Most of these faults come down to a few habits that are easy to learn and quick to apply. Setting your document units correctly before the first sketch is drawn removes the single most embarrassing error in one stroke, the part that arrives ten times too big or small. Modelling to the real requirement rather than to whatever looks neat on screen keeps walls, clearances and detail within what the process can actually achieve.
It also pays to design clearance deliberately rather than leaving features touching at their nominal size. A gap of around 0.2 to 0.4mm between printed parts that must fit is a sensible starting point, tightened or loosened to suit the process. Checking the mesh is watertight before export, and measuring the finished model against the brief one last time, turns a hopeful guess into a part you can trust. We bake these checks into every job so they are never left to memory or to chance.
How to avoid them
The fix is a short, disciplined check carried out before any part is made, looking specifically at wall thickness, designed clearances, mesh integrity and overall scale. Our team runs exactly this review on every single job as standard, which is the main reason files we prepare tend to print or machine correctly the very first time rather than after several costly attempts.
If you have a model you are unsure about, you do not have to gamble on it. Send it through to us for prototype development and we will flag anything risky and explain how to fix it before it ever costs you a wasted run. To get started, get a quote and tell us how the part will be used.