spindle assembly

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.

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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 a watch.

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:

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Does that answer your question? --Glenn Lyford

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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? --Glenn Lyford

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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?

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Ron Bean

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

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Paul D

Thanks for the replies, your information helps a lot. - Lucas

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