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Home Xometry Community Industrial Design Design adjustments for workholding in CNC machining

Design adjustments for workholding in CNC machining

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Hi! I need advice on optimizing the design of a part that will be CNC machined for workholding. The part is an aluminum bracket with several cutouts, about 150 mm long and 50 mm wide, with tight tolerances on critical faces. The main challenge is securely clamping it without distorting the part or risking movement during machining. Currently, I’m considering adding clamping tabs or temporary holes for fixturing, but I’m not sure about the best placement to minimize post-machining cleanup while keeping everything stable. The cutouts are spread out, leaving the edges mostly linear and intact. I was thinking of adding tabs on the sides, but I’m worried they might introduce some bending when I clamp down.

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Solved by Anthony

Put them on the tabs, away from the required part edges. The final cuts remove the tabs. If you’re making only one, you can simply clamp on the tabs, of course. But a screw-clamped fixture would be better if you’ve several to do. If you’re doing this on a 3-axis machine, it’ll need a few setups. If you can get it onto a 4-axis machine and you have the volume to justify the option to make a fixture to mount it to, one setup is feasible.

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      Hi! I need advice on optimizing the design of a part that will be CNC machined for workholding. The part is an aluminum bracket with several cutouts, about 150 mm long and 50 mm wide, with tight tolerances on critical faces. The main challenge is securely clamping it without distorting the part or risking movement during machining. Currently, I’m considering adding clamping tabs or temporary holes for fixturing, but I’m not sure about the best placement to minimize post-machining cleanup while keeping everything stable. The cutouts are spread out, leaving the edges mostly linear and intact. I was thinking of adding tabs on the sides, but I’m worried they might introduce some bending when I clamp down.

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    • A

      Keep away from the big hole, there’s a serious lack of stability around there for clamping. Tabs on the sides or ends are generally a good choice, but you need to keep them thick enough to resist flexing during clamping – and clamp down to a flat surface. In this case, I suggest tabs like this:

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        Anthony

        That makes sense. If I add fixturing holes, how can I ensure they don’t interfere with the cutting paths or create additional machining challenges?

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        Theodore

        Put them on the tabs, away from the required part edges. The final cuts remove the tabs. If you’re making only one, you can simply clamp on the tabs, of course. But a screw-clamped fixture would be better if you’ve several to do. If you’re doing this on a 3-axis machine, it’ll need a few setups. If you can get it onto a 4-axis machine and you have the volume to justify the option to make a fixture to mount it to, one setup is feasible.

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        Anthony

        OK, that sounds good. Putting this onto a custom support with sacrificial areas at the tab cutoffs seems sensible, to allow the tabs to be machined fully off at the last. My volumes should justify the 4-axis with a custom mount type of setup.

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        Theodore

        Absolutely. Machine the fixture plate with mount holes, maybe even some location dowels at the periphery—better than relying on clamping screws for precise position. That ensures good re-alignment if it’s a 2 stage setup. Use the soft jaws for roughing, then transition to internal clamps or vacuum fixtures for finishing. That way, you maintain the tolerances without adding much cleanup.

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Design adjustments for workholding in CNC machining
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