Parts 1mm too large?

I ran a square and circle test in aluminum on my HDM, the square is 20x20mm and the circle has a diameter of 10mm. The results were pretty much exactly 1mm oversized. I used two 2d adaptive tool paths in fusion 360.

I read a possible factor was tool deflection. My speeds and feeds were:
1/4 Zrn Carbide 3d endmill
22k rpm
333mm/min ramp/plunge
0.5mm optimal load
2.5mm max step down (high?)

Is it likely tool deflection or a mistake in my CAM? I did a similar test in mdf and had no issues.

Have to ask. Did you have any “stock to leave” set in your settings?


I agree with Neil. this looks like Fusion360 stock to leave… as it’s set to 0.5mm by default and on by default … 0.5mm x2 sides = 1mm oversize (or 1mm undersize if it’s a bore … ask me how I know … )


Yep, that was the issue, 0.5mm stock to leave. I’m pretty new to metal milling in fusion, I probably had this on the entire time cutting wood because I never bothered to measure. Thanks!

I assume this setting is to leave stock for a finishing pass, would that be done by creating a new toolpath or is there a separate option to incorporate it in to the same toolpath.

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Just for future reference digital calipers can be unreliable when the battery gets low. If you measure the same thing multiple times and get different results change the battery before jumping through hoops. FYI


You’d create a separate toolpath for finishing.
In your case a simple contour path would probably do it. Adaptive toolpaths aren’t a great finishing strategy, and leaving some stock intentionally allows you to come back and finish without the same cutting forces for deflection to be minimized.


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