High Speed engraving spindles

I though I might share this with the list.
I often have to do some engraving work and my big Beaver has a top spindle
limit of 4,500 rpm and at that speed it isn't happy. There's a lot of iron
wizzing around in the clutches and the rest of the transmission. For
engraving 4,500 isn't any near fast enough. I tried running a die grinder
clamped to the quill but I found it hard to regulate the speed and it was
bloody noisy.
So I then built an add on attachment for the quill. I can't post any
photo's as I've lent it out at the moment but I've posted a drawing in the
file section called High speed spindle.

It consists of a split oblong 'U' shaped plate that bolts round the quill.
I made mine with a split sleeve so it will fit two machines with different
sized quills. One leg of the 'U' is a lot shorter and in between these
there is carried an idler shaft with a double pulley supported on two
sealed bearings.
The hight speed spindle was actually one of these revolving centres where
you can change the centre pieces. Since then I have made up two new purpose
heads to replace the original.
I think the drawing shows the layout quite well. The outside of the spindle
drives the idler shaft with a step up ratio of about 2.5:1 by a small poly
vee belt. From the idler shaft the drive is taken back to the freely
revolving cutter holder at the same ratio by the same type belt.
So we finish up with a 5:1 step up ratio.
By running the spindle at an acceptable 3,000 rpm I then finish up with
15,000 rpm at the cutter.
As most engraving is done with small cutters, in my case usually about
0.020" the amount of power needed is small. In practice I have found that I
can run 1/4 cutters without loosing power.
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Regards,
John Stevenson
Nottingham, England