I have had my 1980 Enco mill (Bridgeport clone) for about a year and a half now. I tore it down and changed most all of the bearings when I got it. I did not change the spindle bearings. All I did with them is clean and re-pack them. I was motivated to do that based upon the cost of high-grade spindle bearings. I have been happy with the results. Recently I was watching a youtube video about spindle runout on a mill. I checked mine and discovered about two and a half thousands!!! I was shocked. The R8 socket in the spindle was cut off center! A gunsmith friend told me that it did not make any difference in the accuracy of the mill as long as the spindle was secure and not moving side to side or front to back. The runout of the spindle socket just adds and subtracts from the diameter of the cutter as it rotates. I use a 3 inch diameter convex cutter to cut flutes in rifle barrels. Now that I knew the runout of the spindle I understood why the "wow, wow, wow, wow" noises were coming from when I cut flutes. That cutter was only cutting on the "wide side" of the runout. All of the Internet marketing sites have many listings for spindles complete with bearings. The prices listed for a complete spindle and bearings are about half the price of the bearings alone. I doubted that they were any good. I doubted that they would fit my machine. I doubted that it would be returnable without a hassle. A couple of weeks ago, I was on Jeff Bezos marketing site and discovered the same spindle/bearing combo for $175. I know that returns are easy on that site if you are not completely satisfied. I ordered a set. UPS had it at my door 4 days later. The packaging was poor. A single sheet of cardboard wrapped around the spindle. Many holes and tears along with a lot of tape. I was skeptical at best. I almost sent it back right then. Changing the spindle is a simple operation. One set screw, One threaded cap for the quill needs a spanner and a hammer to get loose and then a Leather mallet to drive the spindle out. 15 minutes. Inspected the new spindle closely. Beautiful ground finish on the r8 socket inside and out. Perfectly deburred everywhere. (I really didn't expect that). Even the collet alignment pin was perfectly set up. I installed the spindle and when I I tightened up the quill cap there was a .003" clearance between the quill cap and the quill. Perfect. The cap is pushing on the bearing, not the face of the quill so no up and down movement of the spindle inside the quill. I ran the spindle at about a thousand rpm's for about 30 minutes in each direction. No perceptible temperature rise detected with my calibrated finger. 
I got out the Noga and Interapid 312-b. (half thou indicator). The needle didn't move when I rotated the spindle!??? I played with the indicator and then realized that it was working ok. I got my Mitutoyo tenth indicator out and finally got some needle movement. As best as I can measure, I have about a tenth of runout! I was in disbelief. I know the proper way to measure runout is with a collet and ground pin. In my case, I don't have a collet without 2 or 3 tenths of runout. I guess some good collets are in order. It will be interesting to see what the runout is in a month or so. I am also interested if the "wow,wow,wow" goes away when cutting flutes. This product was not the typical "Chinese machined" product. I believe that it was an overrun from a manufacturer that makes high quality mills. I did keep my old spindle and bearings. If this one fails down the road, I will get the original one out and attempt to regrind the R8 socket like Stan of BarZ did on his youtube channel. The bottom line here is that I was impressed with the quality of the product and I would not hesitate to recommend that if you need bearings for your spindle of your hobby machine, this seller (with their satisfaction guarantee) is worth looking at.
I got out the Noga and Interapid 312-b. (half thou indicator). The needle didn't move when I rotated the spindle!??? I played with the indicator and then realized that it was working ok. I got my Mitutoyo tenth indicator out and finally got some needle movement. As best as I can measure, I have about a tenth of runout! I was in disbelief. I know the proper way to measure runout is with a collet and ground pin. In my case, I don't have a collet without 2 or 3 tenths of runout. I guess some good collets are in order. It will be interesting to see what the runout is in a month or so. I am also interested if the "wow,wow,wow" goes away when cutting flutes. This product was not the typical "Chinese machined" product. I believe that it was an overrun from a manufacturer that makes high quality mills. I did keep my old spindle and bearings. If this one fails down the road, I will get the original one out and attempt to regrind the R8 socket like Stan of BarZ did on his youtube channel. The bottom line here is that I was impressed with the quality of the product and I would not hesitate to recommend that if you need bearings for your spindle of your hobby machine, this seller (with their satisfaction guarantee) is worth looking at.
