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[Joel Hampshire]

I’m about to place a CNC machining order for a small ABS housing with some detailed features, but I’m unsure if the internal recess can be manufactured as designed. The model includes sharp internal edges and small chamfered corners. The outer chamfer is around 0.2 mm at 45°, and internal corners are close to 90° with minimal fillets. Has anyone machined similar features in ABS before? I’d like to avoid redesigning if this is doable within typical machining constraints.

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[Mattias]

Yes, I’ve machined similar parts in ABS before. I recommend reconsidering some of your internal geometry. ABS is easy, it’s got low cutting resistance and it holds detail well, but sharp internal corners are essentially impossible. You can’t get a perfectly sharp 90° internal corner with a standard tool because of the cutter’s corner radius. Even with 0.5 mm diameter cutters, there’s still going to be rounding in the corner.

Chamfers as small as 0.2 mm can be very challenging. The variation in a typical chamfer tends to be more than 0.2 mm! If the tooling isn’t dialed in precisely, small chamfers can either be skipped or deliver inconsistent finishes, especially in a softer material like ABS. You’re more likely to get better results with a larger chamfer, or a fillet that shows the variation less.

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[ekural]

If your design can tolerate slight fillets in those internal corners – say 0.5 mm radius – you’ll improve machinability and process times. That said, a good CNC shop can advise based on their tooling and precision level. I’d suggest sending them the STEP file and asking for feedback before locking in the order. It’s better to tweak the design slightly now than to get a part back that doesn’t meet expectations.

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