Hello all, I am a little confused on how the spindle assembly works on
my drill press. I've been googling it for a while now and can't find
any discriptive pictures at all. Some terms I have seen are quill,
drawbar, taper... Inside my drill press pully housing I see (typical)
pully stack attached to the motor shaft connected to (via belt) the
pully stack connected to the spindle assembly. How does this all work?
just a question, Lucas.
Usually, the pulleys drive a shaft running in bearings that has a
hollow spline. This shaft stays stationary. The spindle shaft
itself fits inside this spline and is free to slide in and out but the
teeth of the spline keep it rotating at the same speed as the
pulley shaft. Sort of like a keyway only better. The spindle is
in turn mounted in bearings in the quill, which is a piece that
usually has a rack gear either milled into the side or attached
to it, and is kept from rotating, either by a key that slides in a
slot in the head casting of the drill press, or by the depth gage
mechanism. The shaft that the handle mounts on also has the
pinion gear which engages the rack gear. On the far end from
the handle is the return spring, which is a coil like you'd find in
So in a nutshell, the spindle rides in its own bearings in the quill
which goes up and down, and is driven by the pulley shaft which
spins on the same axis but in its own bearings, and the spline
keeps them turning at the same speed. If the spline is well
made, there is just enough play to move in and out easily but
next to no slop when you try to turn the pulleys at the top and
the chuck at the bottom back and forth in different directions.
If it is poorly made or worn out, there will be a lot of slop which
can make a difference in how well the drill press does its job.
As far as tapers go, some drill presses are intended to be used
with morse taper drills inserted directly into the end of the spindle.
Usually this is only really needed for larger drill bit, so a morse
taper adapter is used to mount a chuck into the spindle's taper.
Often for smaller or less expensive drill presses, the chuck is
instead mounted directly on the end of the spindle. The chuck
can either be threaded on like that of an electric hand drill, or
more often, it is on a short taper known as a Jacobs taper (
JT for short).
Of course, a picture being worth a whole bunch of words, you
might find this of use:
I almost forgot: The drawbar.
Most drill presses don't have one. Most milling machines do.
Its job is to hold onto the back end of the tool inserted in the
spindle taper to keep it in place under sideways forces. Since
drill presses aren't meant to be used sideways, they don't
bother, and rely on the tang on the end of the morse taper
to keep it from spinning under load.
A milling machine can have any of a number of different tapers
to mount its tools. Some common ones are Morse, R8,
Brown and Sharpe (B&S), and NT. Some of these have
variations, especially the NT family of tapers which differ more
in the retaining system than the taper itself (there are a number
of systems that use this taper to automatically switch tools on
CNC milling machines).
In addition to a much more massive head assembly, larger
bearings, and larger, sturdier quill, the drawbar also helps keep
everything pulled tightly together.
It's one of the many reasons that people are frequently told not
to attempt to mill with a drill press. Either the morse taper or
the drill chuck taper can come unstuck without the added
pressure of the drawbar, and most drill press spindles aren't
even hollow to allow you to add one later. Also, a drill chuck
has a very poor grip on an end mill compared to an end mill
holder or collet.
Is this where this thought was headed?
And why exactly is it better than a keyway?
I ask this because I've noticed that really old drillpresses have a keyway
instead of a spline. This includes the old "camelback" drills that look
like they could develop some serious torque. Dave Gingery used a keyway on
his drillpress design.
All new drillpresses, including the dirt-cheap chinese ones, have splines.
Wouldn't a keyway be cheaper, and work just as well?
Lets think about it ....
Quill - really just a number of keyways around shaft
- ususlly 6 or 8
- that means 6 -> 8 times the driving surface area
- 6 -> 8 times less wear on quill ... very important with the soft
metals used in modern machinery