Once the magic smoke comes out, things don't work any more.

John Kasunich
jmkasunich@fastmail.fm
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Mon, 01 Sep 2008

Spindle Project - Part 1 - The Spindles

The "Spindle Project" is my attempt to make something usefull (and perhaps somewhat profitable) out of some surplus machine tool spindles that I bought in late 2007. In the process I hope explore some areas of machining that I haven't done before, including hard turning, grinding, and extreme precision work.

I have sixteen spindles, all more-or-less identical (details later). I initially bought two, just for the bearings. When I figured out what they were I went back and bought the rest. A picture is worth a thousand words, so here are side and end views of an assembled spindle (click to enlarge):

After examining the business end for a while, and doing a lot of googling, I figured out that the spindle taper is HSK32. HSK tapers are relatively new and at least for the home-shop world, very exotic. Toolholders start at $200 and go up - way up. The premise behind HSK tooling is that it doesn't just make contact on the taper. It is designed to contact on both the taper and the flange at the same time, for increased repeatability and rigidity. The HSK design is also suitable for very high speeds.

The somewhat exotic and high-speed nature of HSK was my main clue that these were probaby some very high-class spindles, with correspondingly high-class bearings. Although most of the spindles had tags on them indicating that they needed repair, none were tagged for bearing problems. Most were things like damaged retention mechanisms, drawbar sticking, etc. So I decided to take a chance, and bought the whole batch.

The first step after I got them home was to remove the retention mechanism. That consists of a tapered piece that is screwed onto the drawbar, six fingers that expand inside the toolholder, and a crown-shaped piece that sits in the back of the taper and hold the backs of the fingers. Several spindles were missing one or more of these pieces, and some had broken or bent fingers, etc. The tapered center part unscrews, and the fingers and "crown" come out with a pair of needlenose pliers, leaving this:

Some more carefull fiddling around and I figured out how to get the rest of the spindle apart. Since HSK spindles are pretty much always used with automatic toolchangers, the drawbar is spring loaded. Some have a long stack of Bellville spring washers, others have helical springs that are sort of like a stack of Bellvilles where each layer is twisted and connects to the next. The helical versionis a lot nicer to handle - two spring sections instead of 132 individual washers stacked in a precise series-parallel pattern. I had to make a simple tool to allow me to compress the drawbar and retain it in that position while I loosened a setscrew and removed a cross pin - then I could release the spring pressure and the drawbar came out the back. The two photos below show the results of the second stage of disassembly:

In the first photo, the retention "stuff" is assembled as it goes into the spindle - in the second, the fingers, crown, and tapered part are separated. The drawbar in the photo has the helical springs (of my 16 spindles, 10 have helical springs, and 6 have Bellville washers).

I'm about 99% sure I'm not going to be using the retention stuff or the keys, so those pieces are bagged and tucked away. The drawbars, drawbar springs and various other bits and pieces will probably be reused, so they've been carefully cleaned, sorted, and stored.

The only thing left is to remove the bearings themselves from the spindle. So far I've only done that to two spindles. I figure if I don't mess with them, I won't mess them up. I might be able to do whatever work I need without removing them. If not, I'll remove them when it becomes neccessary, not before. The picture below shows one of the two that I did carefully take apart:

From the left, the pieces are: front ring (part of a non-contact labyrinth seal), front bearings, outer race support ring, inner race spacer (long tube), back bearings, and inner race nut. The bearings are two pairs of matched 25 degree angular contact ball bearings, each pair arrainged in "back-to-back" configuration. The clamping nut loads up the entire stack, with the clamp force going through the first back inner race, both back outer races, second back inner, the long spacer tube, first front inner, both front outers, second front inner, and into a shoulder on the spindle shaft.

The two spindles I've taken apart so far have bearings from two different makers, but they are basically the same thing. The front pair are trade size 7008, 40mm ID, 68mm OD, and 15mm thick. One vendor's datasheet for the front bearings is here. The back bearings are size 71908, 40mm ID, 62mm OD, and 12mm thick. Vendor data is here. A general page for that vendor's spindle bearings is here, and from there I was able to download their 11-megabyte spindle bearing catalog with lots of good engineering info about the care and feeding of high-end bearings. The other vendor doesn't have the same detailed data, but a magic decoder ring for their part numbers is here - the number on the front bearings is VEX40/NS 7CE3 DD/3. Both sets of bearings have ceramic balls in steel races, and are ABEC-7 grade, or the European equivalent. While googling for data on these bearings, I found a 2006 price sheet that listed the back bearings at 276 Euros each. At today's conversion rates, that is about $400 per bearing!

After much measuring and investigating, I made a to-scale EasyCad drawing that shows all the important spindle parts, along with several partial sections to show all the various holes and details near the front of the spindle. Click on the thumbnail image below to get a scalable PDF version.

The drawing does not show the retention pieces, or the key. Section B-B does show the slot that the key fits into, and the long hole for the spring loaded push-rod. The holes in section A-A are for coolant - apparently HSK tooling can accept high pressure coolant either through the center of the drawbar, or through the toolholder flange.

In my next posting, I'll describe my plans for these spindles.

(posted: 01 Sep 2008 00:45) (permalink)