Bridgeport Spindle Preload

[Forrest Addy]

What's un-productive is anything that doesn't get JCD's spindle working. Apparently JCD was sold in all innocence the wrong bearings. They are unsuited for a Bridgeport spindle and there is no way the situation can be respolve by parsing messages.

There are two issues here, (1) a successful resloution leading to a matched pair of angular contact DU ABEC Grade 7 beaings in JCD's spindle at (2) no additional cost to JCD.

A few words about my qualifications. I've rebuilt machine tool spindles and conducted the preliminary housing and spindle inspections, conducted correction machining chrome plate and grind etc, inspected and installed the bearings (some of them go for tens of thousands of dollars a set) and assembled the spindle and bearings into their housings, set preload where they were adjustable.

I've spent hours in the spindle shops of Giddings and Lewis and C. O. Hoffacker, I've taken the precision bearing classroom courses taught by Fafnir, Toyo, and MRC, I consulted with the gyro shops of several defence suppliers, I researched, wrote, and taught the bearing class for Puget Sound Naval Shipyard. I've run bearings under Anderometer analysis and worked with the noise engineers and the Dabob Bay Accoustic Range trying to make quiet submarine machinery even quieter. I've even built 24 channel line amps having a -127 DB noise signature used to conduct accoustic range noise surveys. I've dismantled matched sets of bearings, determined that their ball paths were skewed, and reground them to correct the error back to factory specs.

Even then I'n not an expert but I do have experience in depth and breadth in the application and installation of angular contact bearings. This is not an idle parade of curruculum vitae intended to intimidate other into concession but an appeal to others having knowledge and experience to make only concrete contributions to the solution. I ask you at this point not to not weigh in with mere opinion or try to save face by technical posturing.

Regardless of how this thread started I submit the next thing to do here is wait for JCD to report back with his latest observations and an account of his dealings with his bearing supplier. He's in a real fix and we need to support him.

[This message has been edited by Forrest Addy (edited 02-04-2006).]

[Spin Doctor]

This is one topic that I was going to stay away from but alas I am tempted to stick my $.02 in. IIRC the bearings in a BP spindle are 2MM207WICRDUL Fafnirs or their equivilant from another manufacturer. If the head was built in Britian then the poosibility of their being RHPs is quite high. One thing about RHP bearings is that while the manufacturer was quite concerned about concentricity, runout etc they were much less concerned about overall width. The bearing races would have flat and parallel faces but the width from one bearing to another could vary up to 5 to 6 thou. This sounds incredible but it is true. Believe me, I had to deal with this quite often when our bearing supplier would ship in RHPs instead of SKFs, Fafnirs or NSK. When NSK bought RHP and began to oversee operations this problem went away. The reason this is important is a great many precision spindles have critical diminsions from the front face or a gage line in the spindle taper that has to be held to either a mounting shoulder or a keyway. Usually this is made up with a fitting spacer that goes in back of the bearing stack. Now on a BP head what if it has a long set of RHPs and they are being replaced with a short set. One thing that has to be checked is that the bearing stack is longer than the bore depth to ensure capture. If they are not then the bearings along with the shaft will float axially. Another thing with BP spindles is the spacer condition. While I admit I have not done a lot of BPs (just the ones we had in house, the majority of the spindles I worked on were far more complex than a BPs) one thing I did notice was the spacers often would be coined on their faces due to the pounding they were subjected to. This required either the manufacture of new spacers or regringing and fitting a spacer in back of the bearing stack. The last is not IMO a viable option on a BP. But one trick we did try a couple of BP spindles was to fit the spindle with a set of three bearings with the spacer machined to fit. The best method for grinding bearing spacers IMO is to place a magnetic parallel on the surface grinder and grind it in place. Without removing the parallel place the spacers on the parallel and grind (wet grind if possible). This method allowed me to consistently grind spacer to less than ".00005 out of flat.

[JCD]

Forrest,

Please send me your phone number again, one of the didgets must not be correct in the number I received, or this day is going to be very bad, as I can't dial. I get a recording from "Big Brother".

[pcarpenter]

I am a long time lurker and started following this post in search of information since I will be re-assembling mine in the near future. I have a Series 1 2J head from the late 70's that I have completely disassembled right now, and after some looking at the complete set of spindle parts, I am hoping I can contribute something useful. I will say, up front, that my spindle bearings have been replaced at some point as they are sealed and the whole mill was supposedly professionally rebuilt some years back in its previous life. It is therefore possible that the assembly has been modified somehow, although it does not appear that way when comparing to the many Bridgeport manual cut-away diagrams I have.

First, I would offer that it is important to be careful with "Bridgeport says". There is no one named Bridgeport. Some employee who may or may not be qualified to give correct information on bearing types at Bridgeport gave out information...that now looks to include completely incorrect information on the more general bearing type info (they *are* supposed to be angular contact bearings). I hope that JCD can get the right bearings from his supplier given that they gave him incorrect advice.

The notion that Bridgeport spindles are not adjustable for preload may also not to agree with what I can see in looking at my disassembled spindle. It is true that this adjustment *does not* occur from the "quill cap" nut. I wasn't sure of that since other sets of instructions on spindle work have recommended marking the location of the cap before disassembly, but it turns out that is likely just to get the set screw back into the relief that was designed for it. On the other end of the spindle, however, is another nut, a castle nut in fact, with a tab washer designed to lock it into its adjusted position. Under that nut is another bearing, and a long spacer that touches only the inner race of the two main spindle bearings.

The bearings in my spindle, do, in fact, have an inner ring (race)whose width is slightly (about .006") narrower than the outer race. If you take a look at a Bridgeport manual, it looks as though the nut on the top of the spindle assembly is to provide preload adjustment by applying force to the inner race of the two spindle bearings. The inner spacer is also almost .008 shorter than the outer one.

The bearings I have are Fafnir and carry the following number on the outer race: M207PP PRB DB C4 FA52730. Further around the same face, they say THRUST and also say 07Q USA LOT#23076

Both the inner and outer races are marked with a tiny black dot on the same side as the imprinting listed above. That side also has an * marked on both the inner and outer race.

A line appears on the outside of the outside race of both bearings which I assumed was to indicate alignment of the matched pair for minimal runout.

I don't want to hijack the thread, but perhaps it would also help the original poster if someone could clarify for us the correct orientation of the bearing pair using these references. Yeah...I know...I should have taken more pictures..or made a diagram before disassembly :-) We are also back to the original "how do you set preload" question, too?? The .008 difference between the two spacers along with the .006 difference between the inner and outer races may, in fact serve to define about .002" of "preload", but I need an additional brain with some spindle experience to help out here. Those numbers were acquired with a caliper, so may not be that exacting.

I sure appreciate the expertise that comes from this group! This is a perfect example of being able to learn in general about spindles, and bearing pre-load whether we have a Bridgeport spindle to work on or not. Thanks
Paul in Illinois

[wierdscience]

From the NTN site-
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Angular contact bearings are designed such that a contact angle between the races and the balls is formed when the bearing is in use. The major design characteristic of this type of bearing is that one, or both of the ring races have one shoulder relieved, or higher than the other. In order for these bearings to function properly, they must be assembled with a thrust load. This loading (or preload) creates a line of contact (or contact angle) between the inner race, the ball and the outer race. The preload can be built into the bearing or created when the bearing is inserted into an assembly. The contact angle varies from 15آ° to 40آ° and is measured relative to a line running perpendicular to the bearing axis. Angular contact bearings are unidirectional thrust bearings that can withstand heavy thrust loads and moderate radial loads.
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[wierdscience]

The arrangement used in the B-port spindles-

Back-to-back arrangement
(DB)


[This message has been edited by wierdscience (edited 02-04-2006).]

[wierdscience]

Also from the NTN site-

---------------------------------------------
What is back-to-back and face-to-face in angular contact bearings?
Back-to-back (DB) or face-to-face (DF) are duplex arrangements of angular contact bearings (can also refer to taper bearings). Radial loads and axial loads in either direction can be accommodated by these arrangements. DB should be selected when shaft mounting rigidity is the primary factor. Select DF when shaft misalignment is a concern. The DB arrangement requires the inner rings to be clamped whereas the DF arrangement requires the outer rings to be clamped.
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[wierdscience]

Maybe this page will shed some light on what I am refering to.Read particularly the paragraph on"flush ground" bearings and why they are stocked.

Also,be sure and read down the whole length of the page.Then check and see if the old bearings don't happen to have an offset in the races.I'm betting they do.

http://www.ntnamerica.com/Knowledge/...ng_AngCont.htm

[This message has been edited by wierdscience (edited 02-04-2006).]

[wierdscience]

Also this page gives clues,I'm betting that B-port used the plain vanilla offset race angular contact bearings and not the flush ground duplex type.Cheaper bearings sold for big bucks,wouldn't be the first time.

http://www.ntnamerica.com/Knowledge/...ar_Contact.htm

[This message has been edited by wierdscience (edited 02-04-2006).]

[wierdscience]

Now,understand,I'm not trying to add any confusion to the issue,but rather figure out a solution to JCD not having to eat a $380.00 set of bearings he already OWNS.

BTW,the fact that they cost$380.00 a set means they are not conrad type deep groove radial ball bearings(electric motor ball).If they are common ball bearings,then the bearing house is guilty of fraud.

[Mcostello]

Holy smokes guys, I just replaced mine and did not have any trouble. Did not know there was so much that could go wrong.

[sauer38h]

Well, did you buy the right replacements? If you did, and followed the instructions on the back of the box, then nothing should go wrong.

[sauer38h]

<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
BTW,the fact that they cost$380.00 a set means they are not conrad type deep groove radial ball bearings(electric motor ball).If they are common ball bearings,then the bearing house is guilty of fraud.</font>

Conrad or deep groove ball bearings are the standard everyday ball bearing with a cage (that is, they're not full-complement bearings, the ones with filling notches). It's a popular type as it's easy to use - it takes both radial loads and axial loads, despite what some recent posts on a few threads here way. The name refers to the method of loading the balls, and was patented by Robert Conrad circa 1903.

You can get conrad-type bearings in all price ranges - cheapos for motors, REAL cheapos for garage-door openers, instrument bearings, turbine bearings, spindle bearings, carriage bearings, blah blah. As for size, I've seen them from little guys good for holding hairpins, to one that couldn't be shipped by air because the only C124 at that time allocated for civilian use was tied up elsewhere. You can't go by size or price to determine if a bearing is a conrad type or otherwise.

But how do you figure the vendors are fraudsters? From the first post it looks like the vendor found out which bearings were needed, but JCD bought something else cheaper because he thought the cheapos were somehow equivalent to what he should have bought. Now F.A. is trying to cook up a scheme to con the vendor out of some bearings. That's where I bow out - I'm an engineer, not a con man.

Have I overlooked something? The only fraud I see is the attempt to bamboozle the vendor.

[JCD]

I don’t know about the rest of the world but, my Bridgeport J head spindle calls for Bridgeport part number (code number) 11190238. I talked with a Bridgeport field service technician, he stated that, from the drawing of the spindle, the lower two bearings are: JM207K-PRB-DB/A/2729. I talked with a customer service representative from Bridgeport; he confirmed the number of the bearings. The bearings I removed from my spindle are marked MRC 207 S D1 ABEC X.
If someone out there has information from Bridgeport, I stress FROM BRIDGEPORT, that is contrary to this, please share with maybe contact name, location, position, Etc.

From the numbers above, and based on information I receive from the bearing suppliers, all of the bearings given above are single row radial ball bearings.
I don’t have a catalog, so I only believe what I hear during conversation. If someone has information from a catalog or data published from a bearing manufacturer, please share, maybe with the publication name and number.

[Charles Ping]

MM207 LU35T

From my Bridgeport Textron manual

Charles