5 Tips to Design Machine Parts for CNC Machining

You’re designing a new part for CNC machining.  Design parts for CNC machining with cost savings in mind from the beginning. There are a few details you can address that can cut the cost of your CNC machined parts and speed up production.

Know Your Materials

Find out the standard size your raw materials come in and make your design fit well within those dimensions.  For example, if you’re going to have sheet metal parts CNC machined and you design them 3’6” long, only to find your raw stock comes in 10-foot lengths, you’re going to be buying a lot of waste material.  Get those stock dimensions and design your part to fit that with minimal waste to save money.

Cutting Recesses

If your part has recesses, consider the depth as a ratio to the diameter.  The rules aren’t hard and fast, but generally, the machining will go faster and easier if the hole’s depth is no more than three or four times the diameter.  You can certainly increase that, but just understand the deeper and narrower the pocket, the more care has to be taken when cutting it.

Also, design those recesses to have corner radii.  CNC machined parts manufacturers can certainly produce pockets with sharp corners, but that does call for extra work.  If your design can accommodate them, round those inside corners for quick cost savings.

Know Your Tools

On a related note, you’ll do well to know standard tool sizes.  For example, if you need a set of holes in a piece, designing them to be 0.625” will be notably cheaper than if they’re cut to 0.628” because 5/8” (0.625”) is a standard bit size.  Those holes can be drilled in one quick operation.  The very slightly larger holes are no problem to cut, but they do require a standard mill bit to cut a hole, then migrate around to ream it to the finished size.  It takes more time, so it costs more money.  Likewise, those inside radii mentioned above?  If your recess is 5” deep, designing a 1/8” inside radius won’t do you much good because 1/8” end mills don’t come that long.  Know your tools.

Watch the Details

It’s not difficult to get swept up in tiny details.  Remember those details can get expensive.  Design the critical features first -what the part needs to do the job.  Then you can come back and add the features you’d like to have.  That way you know you’re coming out with a functional part, and if it comes in over budget, you know which details you can scale back to bring costs back in line.

One detail that can get out of hand quickly is surface tolerances.  Of course, you’d like every feature to be accurate to a thousandth of an inch and shiny enough to see yourself.  But that’s almost certainly not what you need.  Reserve the critical tolerances for the critical points and use lower tolerances in other areas.  That speeds up machining.

Know Your CNC Machined Parts Manufacturer

That said, don’t be afraid to reach beyond what you think is doable. Work with your CNC Manufacturer.  They know a lot more about what’s doable than you do.  For instance, if you’re working with an experienced CNC machine shop like Macfab, they specialize in thin wall milling.  They can likely provide a thinner wall than you expect for the price.  That’s good information to have while you’re designing the part rather than after you’ve completed the first iteration of the design.

CNC Machined Parts Manufacturers are constantly adding new capabilities, new techniques, and new tools.  They have engineers on staff that are up to date on all of the latest material developments -both metals and plastics.  They know what can be done with today’s best equipment, and if you’re dealing with Macfab, they have all those resources ready for your project.  Let them be your primary design resource.


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