Spindle bearings. Every machine with a rotating cutter (such as a CNC router) has them. While they are not nearly as impressive from a technology standpoint as something like a microprocessor or an FPGA, one still has to stand in awe of the manufacturing process used to make these things. The steel has to be utterly, totally pure, and the surfaces are ground to a mirror finish, and to a roundness of a few microns. After doing this, the manufacturer then picks through them, looking for pairs that are exactly that same couple of microns off, and matches them up in pairs. Here’s a picture of the ones I just installed:

Because they were old stock in a scruffy looking box I was able to buy them on ebay for slightly under $200. If you bought new stock in shiny pretty boxes they would set you back about $350. They are the hardest working bearing on the machine. When they are in top condition miracles are possible, kind of like a prima-donna ballerina or a tenor in Italian opera.

As you can see from the picture above, they live in a bad neighborhood. The red circle is around the “bit” (it slightly resembles a drill bit) which gets shoved through the material at speeds up to 10 inches per second while spinning at 15,000 rpm. My finger is pointing to the housing where the bearings live. Hour after hour, day after day, year after year that spinning bit rudely transmits vibrations, sideways loads, and belches out clouds of chips and dust, a microscopic fraction of which finds it’s way into the bearings despite the best efforts to keep it out.

As these miraculous bearings go into decline, however, they are the exact opposite of an operatic singer. They make more and more noise. Everybody who owns a CNC router lives in dread of a dying spindle. You cope. You slow down the speeds a little, and look for those particular speeds where the resonance works in your favor and try to do your cutting at those speeds. But you can only cope for so long, and eventually you just have to bite the bullet.

You can either pay in time or money to get them installed. Hiring the job done costs an amount in the low four figures, so I opted to run the gauntlet of finding the exactly right $30 an ounce grease, building the special tools necessary, and learning how to carefully run the new bearings in while monitoring temperature. A plastic bag can become a temporary clean room.

Now I get to enjoy the quiet “whir” of my new bearings! It’s a beautiful sound.