12-02-2005, 05:43 PM
Anyone know the correct size for spindle bearings in a bridgeport J series mill? I was looking for a set of class 7 bearings from fafnir.

12-02-2005, 06:38 PM
I would suggest ordering by the original Bridgeport part number. Or send them the information and ask for specifications on their corresponding part number.


12-02-2005, 10:01 PM
Along the same lines are the spindle bearings adjustable? I noticed some chatter the other day using an insert 2" face mill taking a light cut, seems my bearings are either bad or loose.

-Christian D. Sokolowski

12-03-2005, 09:23 AM
Hi Christian,

(EDIT) OOPS... disregard... wrong machine http://bbs.homeshopmachinist.net//eek.gif


[This message has been edited by Leigh (edited 12-04-2005).]

12-03-2005, 09:34 AM
SChristian the bearings are a angular contact design and can be preloaded with shim. This will tighten them up a bit. If badly worn though a replacement set are required,. Non matched sets are cheaper just shim them tight and just as good as the matchebd sets but WAY CHEAPER.

12-03-2005, 10:09 AM
I have the same chatter on my J head but I think it is the coupling on the main shaft. If you look at a breakdown drawing there is a coupling that has like 6 square teeth on it that mates to another part. I think this gets worn and then there is play between the drive and the spindle. My Mill is a step pully and if I grab the pully and turn it there is a about 20 degrees of rotation before the spindle turns. I am living with it for now put plan to pull it apart and make a new coupling. They list at around $300 US to buy.

12-03-2005, 11:21 AM
The part that I am talking about above is called the Splined Gear Hub.

12-03-2005, 12:02 PM
hey guys ,
Is there any grease like substance that could be applied to this spined shaft to take up the play.
all the best.mark

12-03-2005, 01:34 PM
Thanks guys, I'll try rotating the nose piece. I doubt it's the other since the chatter marks where indicative of wobble in the shaft but we'll have to see.

-Christian D. Sokolowski

Peter S
12-03-2005, 08:27 PM
Come on guys, these aren't wheel bearings! http://bbs.homeshopmachinist.net//smile.gif They are not adjustable. The nose cap won't change a thing. Forget shims.

I am sure this has been dealt with many times on the Practical Machinist Bridgeport forum, and on the Yahoo Group for BP.

Sorry, I don't have the Fafnir numbers, but my UK built machine uses RHP 7202 TADU EP7.

These are angular contact bearings, basic dimensions ID 35mm, OD 72mm, individual bearing width 17mm.
T = laminated fabric cage material
A = Cage located on outer ring
DU = Paired unit (they come together in a single package). They are intended to be fitted back-to-back.
EP7 = Precision grade is ABEC 7 or ISO 4.

It is fairly straight forward, but requires care and cleanliness. If you are not used to working with surgical cleanliness, don't even start.
You will probably need to heat the bearings before fitting them onto the spindle, this can be done by placing the bearings in new oil in a spotless container, warmed over a gas cooker. The bearings should not sit on the bottom of the container (they may overheat), but be suspended.
As you can imagine, you need to be well prepared, have clean areas ready, parts and tools washed and ready, hands clean...etc etc

Search for other postings on this subject.

Just looking again - you just wanted the bearing numbers, not a lesson - sorry! http://bbs.homeshopmachinist.net//redface.gif

I had a Holke mill (BP-type) which was giving a bad finish. The spindle was floating up and down a little. I ordered new bearings, but I found the actual problem was the main nut that held all the bearings onto the spindle had come a little loose. Actually, it seemed like the long spacer tube had been given too large a champher, and the end of the tube had deformed slightly, allowing everything to come loose.

Rich Carlstedt
12-03-2005, 09:59 PM
Right on Peter !

The first thing to check if you sense play in the spindle, is the nut at the bottom of the quill. You may need a spanner to tightnen it. I have run into this before on BP's

Another way to warm bearings safely ( means no contamination !) is to turn a drop light upward . carefully set the bearing on top of the clean bulb, and turn it on.
In about 4 minites the bearing will be hotenough for slipping onto the spindle. Use a clean pair of gloves to remove.

A old fashion way to stop a BP spindle from clanging with backlash, is to mount a snubber made of cork. (drink the wine first !) use it to put a very ( ! ) light drag on the spindle...worked in the old days

Charles Ping
12-04-2005, 02:29 AM
Quite Peter.
The only adjustment is by grinding the spacers and that shouldn't be necessary (and wasn't with mine).
My book says Fafnir MM207 LU35T at the bottom
and Fafnir M206K 132J30 at the top.

There's also a school of thought that says you'll never notice the difference between ABEC 5 and ABEC 7 in normal use since the ABEC 7's in a used machine will have been worn for most of it's life anyway.This however has been debated by more qualified people than me but I can safely say that ABEC 5's haven't caused me any trouble but it's a personal choice that depends on what you want to use it for. I have a deep mistrust of unnecessary precision in the home workshop.


[This message has been edited by Charles Ping (edited 12-04-2005).]

[This message has been edited by Charles Ping (edited 12-04-2005).]

Charles Ping
12-04-2005, 02:30 AM

[This message has been edited by Charles Ping (edited 12-04-2005).]

Forrest Addy
12-04-2005, 06:37 AM
Pay close attention to Peter's, Rich's, and Charles' remarks. I've rebuilt a few spindles, I've talked to experts when I wrote the bearing class content, and I've worked with bearing experts my full career. The remarks I've indicated distill the general knowledge for servicing spindle bearing down to the essentials.

Flash's emarks about gear hub rattle (actually the face clutch between the hub and the spindle) addresses a well known J head fault.

A few of the remarks I see in this thread while well intended show their authors harbor misinformation. There are hazards and difficulties associated with a naife soliciting expert advice from an internet message board. The hasard is plausible seeming bogus information can be mixed with awkwardly written sound advice. The difficulty is distinguishing the sound from the bogus.

The solution as I see it is for people offering high consequence technical advice (electrical advice, spindle bearings, scraping for wear and alignment correction etc) is to publish with the information some remarks addressing their expertise as I did in my lead paragraph above. It's tedious but if it gives pause to someone with more enthusiasm than knowledge then it's all for the better for all.

There are far more likely sources for "chatter" than faulty spindle bearings. It's unlikely for bearing wear sufficient to relieve the prelod and open further to clearance enough to cause end and side play in the spindle. It's sufficient to suggest that one should first conduct some simple test with a dial indicator and if there is indeed play then and only then verify that the bearing retaining nuts and rings are tight. After this is done try the spindle again making no other changes.

Rolling element bearings do not fail through loss of dimension as do journal bearings. Normal rolling element bearing failure is race fatigue where race material flakes away or spalls off leaving a rough track for the equally fatigued balls to roll over. Actual dimensional wear suffuicient to relieve the preload is end-stage wear whose roughness will be apparent to the ear when the machine is started.

A well used and thoroughly cleaned bearing will show a diminishing of the normal gloss on the ball path and the balls or rollers will show many tiny indentations from rolling over race debris. A bearing showing such a marked rolling path may be good for another ten thousand hours or it may die in twenty. The simplest solution is to replace it.

When bearings get up to $300 a pair (spindle bearings can get up to $50,000 a pair) then one has to wrestle with his deamons.

[This message has been edited by Forrest Addy (edited 12-04-2005).]

Spin Doctor
12-04-2005, 06:45 AM
<font face="Verdana, Arial" size="2">Originally posted by HENLINEAJ:
Anyone know the correct size for spindle bearings in a bridgeport J series mill? I was looking for a set of class 7 bearings from fafnir.</font>

2MM206WICRDUL or 207's IIRC (or possibly 106/107's. And in my opinion the idea of shimming spindle bearings is stupid. The preload on the bearings is set by the two spacers between them. If the spacers are the same height then the preload is the factory set. If the inner is shorter then the preolad is set tighter. In this application I can't see more than .0005" preload being added. But these spacers have to be flat on both ends and the the ends have to be parallel to within .0001". Preferably less. One trick we used to do is to make new spacers that allowed us to use a set of three bearings to increase rigidity.

John Stevenson
12-04-2005, 07:14 AM
Take a read of this :-


Sir John.

12-04-2005, 09:23 AM
Hey spin doctor angular contact bearings are designed to operate in a preloaded condition,. DDUHH. Glad youre not working on my mill haha. Anyhow on the upper splined clutch drive assmbly mine was badly worn. I tig welded up the edges ground the top face flat and remachined the dogs on both halves. Worked perfect was done twelve years ago and i use mill al lot. Cheap repair teqnique.

12-04-2005, 11:17 AM
We replaced the spindle bearings on my buddy's newly-purchased B'Port because they were noisy. Had been run with inadaquet/no lubrication, or so it seems.

He did some shopping for the bearings, as we were replacing both the lower bearings and the upper one. Found a better price for one from Detroit Ball Bearing (or whatever they call themselves now), with the other coming from High Quality Tool, a vendor of B'Port parts. The difference was significant, something like $200.00 vs. $300.00; this was a couple or 3 years ago, so my memory might not be 100%.

Spin Doctor
12-05-2005, 11:35 AM
Madman, I really do not want to get into a flame war here but before I retired I rebuilt precision spindles* for a living. I do have a very good idea what I am talking about. The use of ground spacers with precision angular contact bearings as opposed to the generic angular contact bearings is to increase the preload to a specific design amount. But more preload means more heat also. If the bearing spacers are not flat and parallel then the bearing will be constantly unloading and loading each revolution leading to a very premature failure

*The spindle types included every thing from drilling and milling spindles to grinding spindles along with work holding spindles in lathes and grinders and centering units