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M-head spindle rebuild.

ole4

Plastic
Joined
Aug 27, 2020
I have a old (1943) bridgeport M-head I have owned since 1985. It has worked OK until I had a boring head stuck and tried hitting the drawbar top with a brass mallet to get it out and then a wedge between spindle bottom and the boring head to remove it. Ever since it would get a harmonic chatter when boring that was not there before as well as leaving a rough finish when flycutting. I always had slop between the pulley splines and the spindle but it did not seem to cause issues with the surface finish. After reading thru these forums it seems when the spindle bearings are worn issues like I am having will occur. I purchased all 6 bearings for the spindle and pulley assembly as well as a NOS MT@ spindle with the drive splines/pulley top with those retaining nuts and funny lockrings. I took apart the spindle today and all 4 spindle bearings were common 5205/c3 bearings. The new spindle bearings I bought were a NSK matched set of 7205 ctynsul p4 abec7 for the spindle bottom and upper bearings of 6205 C3. The angular 7205 bearings have a sidways v scribed on the outer race which i am guessing is the shape of the races. I have the folowing questions.

1) which way do I install the bearings or does it not matter the bearings also have a radius on the edge of the outer race on one side if that means anything. Both bearings came as a set in one box.
2) the original spacers appear to there is the preload set by them? Is one supposed to be a different width from the other?
3) when assembling the bearings on the spindle the 7205 I will press on by the inner race so as to put no side pressure on the bearings.
4) installing the top nut will squeeze the races in place between the spacers (upper bearings also have a inner and outer spacer. Is there a torque value for it or just tighten real good till a locking prong will fit in one of the 4 slots? DSC02217.jpg
 
The bearings also have a sideways v symbol on them maybe that has to face a certain way? DSC02213.jpg
 
These are the markings on the annular groove bearings not sure how to install them. If anyone could explain what they mean and which side faces up on the quill I would be very gratefull. DSC02218.jpg
 
The bearings should be in DB configuration Look up angular contact bearing installation...

The spacers need to be exactly the same length. BP cheated... used cheap bearings, and ground spacers to get proper preload. Your proper $$ Spindle bearings, require proper install..

Again spacers should be checked for length, if not same length, have them ground to exact same length on a surface grinder.. Tenths of a thou matter here...

Not having the slip of paper enclosed in your bearing packaging.. Go to NSK website, drill down to Precision bearings.. Their marking system should be explained..

I am pretty sure the Vees on OD of bearings, should be pointing this way for DB < > .

I would install inner race dot marks, with dots on race.. on spindle in line, same with outer race dot marks in quill bore..

"Optimum accuracy is achieved when bearing is mounted so the dots ( O ) are placed opposite of highest eccentricity of shaft and housing" Is going to be tough to measure in home shop.. And a M head will flex, far more than the minor spindle runout..

Spindle nut should be tight, Hard to describe a torque... No need to get super tight, just holds races against spacers.
 
The spacers need to be exactly the same length. BP cheated... used cheap bearings, and ground spacers to get proper preload. Your proper $$ Spindle bearings, require proper install..

Actually not true. B'port cheated, but the spacers will be the same length. To run the radial bearings in approximation of angular contact
mode, they actually ground the faces of the bearings - but had the ID and OD spacers be the exact same length. I know this because
I re-did an M head years ago. I still have the doctored radial bearings with parts of the outer race ground on each one.

Would not hurt to put the spacers on a surface grinder and touch them up so the are closer to flat and the same length.

Another critical issue with the M heads is DO NOT PUT ANY SEALED BEARINGS IN THERE. The wick feed oil cup sends oil to the
lower-most (critical) bearings through all the other bearings, including the pulley bearing pair. Any sealed bearing in the chain will prevent
the angular contact pair from getting lube.
 
Thank you both for the replies! It is making some sense now. I did get a paper with the bearings and it was so tiny I had a hard time reading it but I was able to scan it at a high resolution and blow it up. I will have to go look for the dots tomorrow, I did not notice them but did read about it but did not understand it till readind your notes. I did measure the inner and outer races and they were the same diameter but I used a dial caliper. Tomorrow I will get my good mic that reads in ten thousandths and check them. Here are the instructions I was able to scan. bearing 1.jpg bearings.jpg
 
Got the spindle/quill reassembled with the new bearings installed in the DB orientation. I am waiting on a quill return spring from H&K before installing the Quill. What is the best oil to use for oiling the spindle? I have been using automotive synthetic racing oil but see Mobil sells a spindle oil that is some kind of mineral oil. Was wondering if using the automotive oil is bad for the bearings.
 
Got the spindle/quill reassembled with the new bearings installed in the DB orientation. I am waiting on a quill return spring from H&K before installing the Quill. What is the best oil to use for oiling the spindle? I have been using automotive synthetic racing oil but see Mobil sells a spindle oil that is some kind of mineral oil. Was wondering if using the automotive oil is bad for the bearings.

The system is total loss. Any oil you put in the wick feed oil cup at the top, comes out the bottom of the spindle. I used mobil one full synthetic engine oil in my M head. 0W20 weight. Be sure you have the tin shield inside the housing when you button it up. The up-down sliding tin sheild keeps junk out of the lower bearings and makes sure all the oil dripping down inside the system goes where it is supposed to.
 
Mine did not have a tin shield but I will go look on the parts list H&W has for the M head. I just finished assembly and I could not get a indicator to reliably read the inside of the spindle taper so I used a 1/2" collet and carbide endmill and read of the round section of the mill bit right near the collet and got about 6 ten thousandths of runout. DSC02222.jpgDSC02221.jpg
 
I dont see a tin shield on the parts breakdown unless you mean the round split brass shim that sits inside the top of the housing under the pulley?
 
Yesterday I milled a couple of small single cylinder heads with a flycutter and the finish was very smooth and before the spindle bearings were changed it left a pretty rough finish so It looks like it fixed that issue. I have not done any boring yet but I will post back my results when I do.
 








 
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