Bridgeport spindle bearings

[ronm]

This question laid a big fat goose egg on the "other" board, so here goes: A while back, my son was using the BP (J head, step pulley) for a project & he happened to insert a collet w/the keyway not lined up...no biggie, I had done the same thing a couple years ago & found out, I think from somebody on the Chaski board, I could remove the nosepiece from the quill, giving access to the special setscrew that forms the key, reworked the end which was slightly buggered, & everything was OK. This time, it seems like I overtightened the nose cap, as the spindle seemed tight...not seized, but not free either...I fiddled w/it, & found a spot where the spindle runs free, but not loose. According to the manual I have, the bearings are ball bearings, not tapered roller. Is the nosepiece supposed to preload the bearings just enough to remove end play, or??? My manual (from ebay) is pretty sketchy in most areas except parts breakdown. The thing seems to run fine, but it has bugged me ever since I messed w/it. Any ideas? One other question that has always been in the back of my mind-are the 2 oil cups really all it takes to lube the whole head, feed gears & everything? That's all my manual gives as lube points for the head..
PS-this head was "supposed" to be rebuilt, new bearings, one owner back, the PO didn't really run it much. I see no reason to doubt it, it runs smooth as silk.
Thanks-Ron in CO...

[Jim Caudill]

The spindle bearing preload is set by the bearing assembly on the spindle by means of special inner and outer spacers. There is no adjustment to preload except by altering the height of these spacers. The nose piece you are referring to only secures the spindle in the quill and cannot change the preload. What it can do however, is distort the shape of the quill and cause binding such as you experienced. It is desired that the nosepiece be snug and still have just a little space between the quill and the nosepiece; this is simply to insure that the spindle is in fact pressed in securely within the quill. Original spindle bearings were open and oil from the cup could drip into them. Many replacement bearings (such as those sold by High Quality Tools) are sealed for life and oil that is dripped in from the cup, never will get inside the bearings. Without knowing whether you have sealed or open spindle bearings, it is best to keep feeding the oil cups. You do visit the yahoo group for Bridgeport mills, don't you? They have most manuals available for download and they love to discuss the care and feeding of these mills.

[ronm]

Thanks, Jim, I'll check out that group. I hadn't known of them before. I had a feeling the quill had distorted a little, hopefully it wasn't permanent...

[Spin Doctor]

One thing to check for is any high spots on the end cap mating surfaces or on the mating surface that holds the bearing stack in the quill. In actuality the surface that contacts the bearing stack should place a load on the outer races to retain them in place with the surface that comes close to the quill body having a .005" gap between the two surfaces. This is pretty standard practice with precision spindles. Often with precision spindles there is a torque setting for the screws holding the end cap on that can not be exceeded because it may cause ditortion in the spindle housing. IIRC the preload on a BP spindle is all in the bearing set them selves with the spacers being equal length. One trick I used to do on BP heads when rebuilding them was to make a new set of spacers that were shortened to allow the use of a triple set of bearings in the spindle with the bottm two set in a tandem mount so that they are both back to back with the third bearing. This greatly stiffened the spindle leading to better finishes with the additional benefit of not getting beat to death when the idiots would run fly cutters. For anybody interested in doing this the new spacers have to be dead nuts flat. They can't just be faced in the lathe they need to be ground properly on a surface grinder while being held on a set of ground at set-up magnetic parellels. Grinding the parallels at set-up ensures the surface you are working off of is as flat as the grinder can produce

[madman]

Theyre angular contact bearings in em, I used non matched (way cheaper) and a can of coke cut it into a bearing shim. Perfect. If i run super high speed i would back of the bottom bearing retainer a notch .Usually i just leave it alone. I cut .100 at a time with my old bridgeport mill and a three flute chipper cutter. Takes low horsepower to run and also cheap inserts. My toolbox was full of those inserts when i got layed off/. Lucky me eh>?