One of the issues with bearing replacement is, as already noted, the resulting TIR of the taper. The following business that specializes in re-grinding spindle taper seats in-place on the machine explains this in their advertising.
http://web.triton.net/r/rlgunn/
Other businesses request that the quill be removed with the spindle, and that those together be sent in for the re-grinding and, if necessary, bearing replacement.
I find the latter interesting since the Bridgeport service manual discourages removing the quill from its matched housing.
Logically one should expect a re-grinding to be necessary, after bearing replacement, if Bridgeport bought generic bearings, matched them, etc. and then ground the spindle seat in-place as a manufacturing process. As I read it one reply in this thread says this or the equivalent is the case.
In principle, it should be possible to install highly precise bearings, re-grind in-place or at least in the quill, and from then on replace those same bearings, if necessary, without the re-grind.
I recently purchased a Boss 5 Bridgeport on E-Bay. To my surprise I found the TIR of the spindle taper seat to be excessive. The center of the taper is .00075" off from the center of rotation. This shows a total movement of twice that on the indicator, or .0015", which I take to be excessive. However, the bearings are quiet and tight, and the taper seat undistorted. This combination has been a mystery to me (I am new to this and a hobbyist). From the contents of this thread I suspect a previous owner replaced the spindle bearings, apparently with good ones, without re-grinding the taper.
There are companies that sell bearing kits for these machines, as well as head rebuild kits. One of those is the following company that advertises its spindle rebuild kit on E-Bay:
http://cgi.ebay.com/Spindle-Rebuild-...QQcmdZViewItem
I have not decided what to do with my spindle yet, but I will do something. I have even considered getting the stuff to regrind it in place on my own machine. For one thing, I am not clear as to whether I should replace the bearings and re-grind the taper.
The statement that ice and heat should judiciously be used rather than a press, earlier, I found quite interesting.
I am new to this, as is the original poster. I read the service manual and am not clear exactly what the procedure in the manual means when it gives spindle removal instructions. I found the set screw in the quill, but I am not clear where the hammer blows are suppsed to be applied to remove the spindle with bearings (provided I decide to replace the bearings before the re-grind, and don't get someone to do it for me, etc.).
My inclination is to leave quiet and tight bearings well enough alone and just have the taper re-ground, even though I am not sure of the quality of the bearings in there.
Thanks,
Karl