Boring Holes in Aluminum

When using the bore option in Fusion 360, what is the recommended endmill size to hole size?

Specifically, for a 3.3mm diameter hole, is a 3.175mm diameter endmill small enough? It seems Fusion lets me generate the toolpath, but is there enough of a difference in the diameters?

Cutting aluminum with the carbide3d 102-Z (it is 2 flute)

In addition, that last topic I saw when searching the internet was that, for boring holes, conventional cut with only 1 pass gave the best holes. Is that recommendation still applicable today with a Shapeoko 3 and HDZ?

Edit: So it figures, just after posting this, I found a Winston Moy video where he recommends a 10% difference. I’m not sure if that is material independent as in the video he was working with wood

I’d also recommend the 1 flute for chip evacucation as well. In general it’s a pretty awesome endmill

I’ve found (through the school of dumb luck and broken end mills) that using a endmill 60-80% of the hole diameter works really well and is quite forgiving.

You can make a tighter fit work - but it just increases the chance of it not working out quite right (typically skipping steps on the Z, snapping the bit, or having to use a very slow feed rate).

I drill and tap M3 holes quite often (both operations on the Shapeoko) - so I mill the 2.5mm hole with a 1.5mm or 2mm single flute.

Hope that helps.


Yup. Careful when going just under the size. Haas has a good video on the speeds and feeds in this situation.

You could also try a peck drilling op and then bore it.


It’s also different between Carbide Create and other tools, like Fusion. If the tool isn’t small enough (I think it was 10-15% smaller?) CC won’t attempt to use the tool for the hole and it can a bit confusing as to why.

A very interesting video, talking about the feed rate. Do you know if the “bore” operation in Fusion 360 does the automatic feed compensation?

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