Milling Oak

Looks great! Nice finish. this really is the top end of what the proxxon/dremel can achieve.

the HF spindle (or other) with larger cutters can allow you to go deeper - but be careful - larger diameter cutters remove more material - the over all material removal rate increases - which has a knock on effect on the cutting force.

Equivalent depth in a 6mm cutter requires more force from the machine frame than a 3mm cutter.

A little follow up to this, confirming Rory's comment.

I was cutting with HF350, 5mm 2-flute bit, 2mm pass depth, in Meranti (Phillipines Mahogany) profiling through 12mm thick material. No problems. (Also cut lots of 12mm Birch Ply like this, never had a problem).
When I did the same cut (same toolpath, bits, speeds & feeds) in 12mm Oak it got to about 8mm deep then BAM! - crashed and gouged a big pit. You really need to take account of material density/hardness - one "hardwood" is not the same as another!

The profile was after 30 minutes of V-carving - job wasted. Did it again (in Oak) and did the profile cut out with 4mm straight bit, 1.5mm passes. I'm partially deaf (can't hear the top 2/3 of human speech range at normal volumes) but I could hear this screaming through the Oak (900mm/min feed rate) - it made the cut OK but sounded a bit stressed! I had the Steppi vacuum attachment running, with the brush enclosure - when the job was finished I found it was packed solid with chips/dust; I suspect this was the source of the noise rather than the wood cut.
As well as the Steppi dust extractor, I find I need to follow the spindle with a shop vac when using these larger bits - first time with the 4mm straight bit and it doesn't clear chips at all well!

Like Heustec I was needing longer bits, but opted for larger diameter to try to avoid "wobble" as the bit goes deeper.

I think next time I will go back to the 5mm 2-flute, but reduce to 1mm pass depth for cuts beyond about 5mm.

Follow up: cutting 12mm with 5mm bit, 1.5mm pass, 900mm/min feed - crashed twice (at about 9.5mm deep), once at 20,000 rpm (HF350) and then again at 16,000rpm (tried to get more power with reduced speed). Second crash damaged the workpiece too badly to be worth continuing - I'm going to try one of those Dremel 561 bits. I think 5mm diameter in Oak is too much for any sort of depth.

I have been cutting some 22mm Oak recently without an issue, I use a 8mm ball nose to cove the edges 4mm which allows me to cut the Oak as if it was 18mm (required for cutter length -3mm 3 flute). Working a treat!

Pushing the stepcraft hard though but new Kress is an absolutely brilliant upgrade.