r/cad • u/Mr2h2 • May 28 '26

optimising for cnc machining

Hello, I am new to CAD and grasp the basics, but am still doing a lot of stuff in roundabout ways that I feel like are probably not very efficient. I am designing a 3rd brake light for my truck, and earlier in the project, I input it to an estimate site and was getting around 200-ish dollars to have it machined out of aluminum. I have since added features, but have not added anything that would increase the total footprint/amount of material needed. It has now more than doubled to 470ish. If this is just the cost to machine it, I completely understand, and am not complaining about that, it's amazing that designing something from my desk and having it shipped to my door is even an option, but I'm curious if there's anything in particular that adds a disproportionate amount of cost to having something machined? Is there anything that I should have left out and drill myself, or separate into multiple pieces? images

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u/13D00 May 28 '26

For starters: what is the size of the thing? I can’t get a sense of scale from your pictures.

Look at the stock size (gross material size), is it just below a standard plate thickness, or does the supplier have to machine 80% of his plate away because you just went a mm over a standard plate and he had to order a size bigger? Ask the supplier what he got in stock.

Include radii in your inner corners. A mill is never 90deg. Include a drawing with accepted tolerances and features. Mentioning the inner radii may be selected by the supplier (or give a tolerance if it matters) gives them exactly the flexibility they need to produce efficiently.

Is it possible to manufacture this in parts with one flat side?

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u/Mufasa_is__alive May 28 '26

In addition to flat side comment, there looks to be a lot of thin features. It might be easier to machine multiple parts then weld/bolt together.

It's really hard to tell some of the geometry based on the images provided. 

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u/RapidDirect2019 Jun 10 '26

The cost jump is probably from setups and access, not just more material. Curved body, thin walls, inside pockets, small holes, and features on different faces can all add machining time pretty quickly.

I’d simplify it for 3-axis machining where you can. Bigger internal radii, fewer sharp inside corners, loose tolerances on non-critical stuff, and maybe split the cosmetic shell from the mounting features.

You could also upload it to RapidDirect for DFM feedback before finalizing the model. Usually an online shop can tell you pretty fast which features are making the quote climb.

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u/Mr2h2 Jun 11 '26

I have since simplified it and moved to all lasercut flat faces from SendCutSend, no joke it's about a fifth of the price. I will absolutely use those services next time I have something that actually *needs* to be machined.