We love helping our customers create physical products from their concepts, ideas, and visions. Sometimes all you’ve got is a drawing on the back of a napkin and no time to learn a complex 3D CAD system – no problem! We can take anything from your sketch to a full 3D CAD model and turn it into reality with our machining, 3D printing, and laser cutting services. In this post we want to share five secrets to help improve your drawings to save you time and money when you send in your design for review and quoting.


1. Too many or not enough significant digits

Your part is 5mm wide – so do you write 5, 5.0, 5.00, or 5.000 mm on the drawing? Well it depends. For a napkin sketch, 5 mm is probably fine. If you’re producing a drawing with a CAD system, we recommend you set this number to reflect the tolerance of that dimension. It’s always best to avoid un-necessary precision as you may calculate a dimension of 4.87596542 mm, but that is clearly going to be impossible or very expensive to produce. For critical dimensions it’s best to specify a tolerance such as +0.01/-0 for parts that can be oversized, but not under or a symmetric tolerance such as +/-0.005. Don’t know what tolerances are appropriate? We’re happy to go over classes of fit with you and determine the most economical option for your job.

2. Dimension based on what matters

Depending on the application of your part, some dimensions are likely to be more critical than others. For example, on a part with a series of holes, is the spacing between the holes most important or their distance from one end of the part? Specifying a spacing keeps the holes a fixed distance apart, but tolerances can stack-up and be unacceptable if the distance from a mating surface is what really matters. If you’re unsure of your drawing, don’t fear! We’ll talk over the application of your parts with you to ensure the best fit is achieved.

3. Diameter, radius, and wall thickness

One of the most common mistakes we see on sketches is miscalculation of diameters or wall thicknesses. “Well, I’ve got a 2 inch diameter bit of stock and I want 0.1 inch thick walls, so the inner diameter will be 1.9 inches.” Wrong! Don’t forget that you’re dealing with a diameter, so the wall thickness applies to both sides of the part – or work in terms of radius.

4. Missing dimensions

Another common mistake we see are missing (or even conflicting) dimensions on hand sketches. Before you send your sketch in, take a look for anywhere you haven’t dimensioned. We never guess and will ask for clarification, but ensuring you send in a fully dimensioned sketch will speed up the process!

5. Use callouts

Callouts are handy ways for you to tell us more detail about a feature. Need threads? Call it out! What about special surface finishes, masking for anodizing, or just specifying a fit class? Call it out! These are great ways to remember/communicate things that are not simple dimensions and don’t require us to trace the requirements down in a long email chain. It saves our CAD operator time and saves you money!

Let’s talk shop

What’s your next idea? Using the tips above we can turn your sketch into parts faster than ever. Quotes are fast, friendly, and free – so send us your idea today!

John Leeman
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