maching Aluminium with sub 4mm bits

**kell** · 26-11-2019

I am looking at uprating my spindle so i have at least 60000rpm available as all the feeds and speeds are saying i require more speed.
I want to 3d mill molds in aluminium, and up to press have only used corian and the machine is fine for that. I have added a hench fog buster so chip clearance and cooling should be no problem.
I wondered if anyone machines anything similar that could give me some pointers.

**Chaz** · 26-11-2019

You can certainly find spindles like this but they are pricey. For precision, you can also look at air bearing spindles but lots of money. What size bits are you cutting with that need this RPM? I run a 24000 rpm spindle on my main concrete mill and this works for alu without an issue.

Sub 4mm in the title, OK, but still, unless you are doing sub 1mm, just run at 24K RPM and adjust the feeds accordingly. Is saving 50% of the machining time (lets assume your machine can run high speed accurately) worth a couple of K on a new spindle?

**kell** · 27-11-2019

yes will be going down to at least 0.50mm

**JAZZCNC** · 27-11-2019

There's more to using sub 1mm cutters than just spindle speed.? While the speed n feed calculators spit out Rpm n feeds suggestions they don't and cannot take into account the machine your using.
When you get into miniature cutters then vibration is your biggest enemy rather than lack of RPM. If the machine isn't stiff enough then you won't achieve the feeds and therefore Rpm will need to be lowered to match what machine will allow.

I pretty much exclusively cut aluminum and have used cutters ranging from 0.1mm up to 16mm with 24K Chinese water-cooled spindle without any issues.
60K spindles come in various types but direct drive high-frequency motor types are very expensive, as are the air bearing types. So you may be better looking at the type which use a separate motor like found on engraving machines. 60k and 100k isn't uncommon in engraving.