Bridgeport clone spindle problem ??

[Bigbloke]

Hi

I have a 1990's vintage Taiwanese clone of a Bridgeport varispeed milling machine (Chen Ho).

Over the past few months I have noticed a number of things:

1. The spindle has been getting more and more noisy, particularly when using heavier cutters. Not so noticable on light cuts or plastics.
2. There is a lot of nose when changing direction in a cut, it will seem to settle in ok over time but then as it goes round a curve, or other change of direction it suddenly goes very loud and clattery and the finish goes completely.

I checked the runout today inside the taper section of the spindle (R8) and there appears to be about 2 thou of runout but this isnt even, there is a definite sharp movement somewhere in the rotation, every turn or so.

By the time I have a tool in a toolholder in the spindle, the runout is getting nearer to 3 thou than 2 even if I fiddle with locations on the toolholder to try to cancel out some of the runout.

My assumption here is that as a minimum, the spindle bearings are shot.

Does this sound like the case to others on the forum or am I missing something here ?

To get an idea of the racket, here is a link to a short video clip I took this afternoon. As the cutter gets toward the boss sticking out on the lower left side of the part, the noise goes way up, it sounds a bit like re-cutting chips in a slot but that isnt the case, the aur keeps the work area nicely clear. Once the cutter swings past the problem direction, it can be heard to be settling back into normal cutting.

Noisy spindle cutting pocket video by koiboi_2007 - Photobucket

This is a 22mm 3 tip Alphamill cutter low carbon steel plate, 1650RPM, 250MM/Min feed and 1mm depth of cut, 4mm width (<20% cutter engagement).

I'm pretty sure, the cut is not an unreasonable ask on a machine this size in fact the feed is backed off a long way (40%) from the manufaturers anticipated minimum for the tool to keep the noise down.

Is it worth attempting to put new bearings in myself or is this strictly for the professional spindle servicing companies out there ?

Any thoughts here would be appreciated.

Thanks

Paul

[machintek]

Usually when spindle bearings go, three things happen. Noise, loss of finish and heat.
Sounds like you have 2 out of the 3.
I have replaced Bridgeport spindle bearings. At customer request. But that is not the correct way to go.
My solution is sending the spindle to C and M precision spindles in Oregon. They will put new bearings in, preload them and then regrind the R-8 taper so you have no run out. The spindle is a unit with bearings, spacers and a shield that is removed and installed as a unit. For those with deeper pockets, they will replace the spacer between the 2 bottom precision bearings with 2 additional bearings. This gives a lot stiffer spindle. But I do not know the fit of your quill to its housing so I do not know if this will do you any good.
A few notes: Do NOT tighten the set screw t the back of the quill that keeps the nose piece from turning more than finger tight or you will "egg" the quill and will not want to go up all the way. Also you need a gap between the nose piece and the face of the quill when the nose piece is tight. You want it to press up on the outer bearing races to prevent up and down movement. If it bottoms out on the quill, it is not pressing on the bearings.

George