Speed Secondary Spindle
I kept coming across articles
about folks that were attaching small high speed spindles to their mill
head for various reasons, so I finally decided to create a page whose
focus is this phenomenon. The reasons for doing it make sense. Most mills
in home shops are doing good to hit 4000 rpm. Mine tops out at 3200 rpm
if I change out the motor and 1600 rpm otherwise. The combination of cutting
aluminum, which has very high surface speeds, using carbide cutters, which
takes the speeds up further, and trying to use small cutters for accurate
3D profiling of fine detail or engraving all add up. I define a small
cutter, BTW, as anything 1/4" or less, which is what I've seen on
the web as the crossover point for HSM (high speed machining).
spindle attached to mill head...
Using my copy of ME
Consultant Pro to look at feeds and speeds, I came up with some interesting
scenarios that reinforce my thoughts below that a high speed spindle would
be helpful. ME Pro suggests a spindle rpm of 20,390 (!) and a feedrate
of 17 ipm when cutting aluminum with a 1/8" cutter. No way your average
HSM can touch those numbers! Except, ME Pro will also say the horsepower
needed is only about 1/10 HP. That combination of high rpms and low horsepower
required sounds like something a small high speed spindle could do.
There are a variety
of alternate spindles you could strap on your quill. The Bosch Roto-Zip-like
tools, the Proxxon high-end Dremel tool, as well as high end die grinders
from outfits like Makita will get you anywhere from 15,000 to 30,000 rpms.
I've seen folks using air powered spindles, there are expensive commercial
spindles available (watch for them on eBay), and there are also devices
called spindle speeders/increasers/multipliers that are just gearboxes
that attach to your existing spindle and give more speed for smaller cutters.
Here is a
typical thread on this subject from CNCZone.
Pictures of Other's Slave Spindles
an air grinder as a spindle for engraving...
rpm air spindle by MacroTechnologies...
This fellow made a router holder for
his CNC knee mill that uses a #40 taper shell mill holder on one side
and a shaft with a linear bearing on the other to support the router.
The linear bearing is necessary because the router goes up and down in
Z as the quill moves:
You can see it works pretty good!
I like the idea that you can quickly detach
this rig from the mill by popping out the shell mill holder and undoing
the clamp for the linear bearing. For my mill, I wouldn't be using the
quill, so the shaft would just clamp to the mill head directly for support.
This is the first time I've seen
on a manual mill:
He's using a small 1.5mm endmill
to cut a hex shaped hole in the workpiece rather than broaching.
Install the high speed spindle inside
the main spindle with a flexshaft
Here is one of the cleverest ideas yet. This
fellow built his high speed spindle so it can be installed inside the
It seems to me there has to be
enough room in an R8 spindle to do something similar. Tres clever!
I hear good things about those Bosch Colts...
Proxon on a Tormach. I'd be worried about
the air cooling holes that close to flood coolant!