[Gnome]

For the past several months i have been in the process of retrofitting a bridgeport series 2 interact 4 cnc mill. The mill was made in 1989 and has sat for more than 8 years now as the control system was dead. I thought that the machine was mechanically sound as it appeared to have very little wear, however i am slowly learning that looks can be deceiving. The spindle must had gotten moisture into the bearings at some point or they simply rusted from sitting so long without moving because the spindle was basically locked when i started trying to manually turn it. I got the spindle to turn after a bit of massaging but there is a pretty substantial growl coming from one or more of the bearings.

After pulling the spindle cartridge from the mill i also found that approximately 50 of the 120 belleville springs in the drawbar had been reduced to pieces. At this point i realized that i would likely need to replace the bearings, have the taper reground, and the belleville washers replaced (and the drawbar force reset). The problem is that this is a fairly large spindle (~5.25 inches in diameter), with triple 7014 series bearings in the front and a single 6012 bearing up top. Apparently these bearings are expensive and i have received quotes ranging from $3,000 to $6,000 to do the full rework.

Its not so much that i am a cheap bastard, its just that this mill will only be used for hobby work and it honestly isn't worth as much as its looking like its going to cost to repair (given how cheap newer, nicer machines are selling for on ebay).

I am confident that i can replace the belleville springs and fabricate a tool to properly set the drawbar force myself. What i really want to know is if i can press the spindle apart, clean and regrease the bearings (and possibly replace the top 6012 bearing if it is the one causing the noise), and reassemble it. I know that this is unacceptable for anyone looking to get reliable, long life from their spindle and that NC_CAMS is probably rolling over in his grave right now, but honestly for how much i will be using this thing (maybe 1-2 hours a week, tops) i really would like to know if this is possible and what you all think. I have the tools to do this properly but am not sure what the results will be. At this point i can't see how i could make anything worse as the spindle won't work as is.

Does pressing the quill out of the spindle brinell the races and destroy the bearings? Is there any tricks to disassemble the spindle without destroying the bearings?

I have done a lot of reading about bridgeport's original bearing assembly/selection and i am also wondering if this will seriously affect the run out (ie: if the bearings aren't dead concentric and the outer races are not installed in the exact position as where they were removed).

I have included pdf's showing the cross section of the spindle. I really appreciate any and all advice.

Noam

[Gnome]

Bump... Anybody?

[gotis]

As you say you can´t make it worse.
The bearings should not be damaged IF they haven´t rusted to the spindlecartridge, in that case they are shot anyway, they should be a slidefit not pressfit, if you can press them out with minimal force (handforce?) mark how they are mounted, both inner and outer rings and refit them accordingly if you find anything other that might cause the spindle to growl.

Good luck!

[Gnome]

Hey Gotis,
So i took the plunge and decided to pull the spindle apart this weekend. All in all, the disassembly went a lot better than i thought that it would. I was really nervous about this as i had never pulled a spindle apart and wasn't sure what i was going to run into.

I had two main issues which were both caused by both unclear and incorrect cross section drawings of the spindle. I will summarize the process below for anyone that is interested.

1.) First i removed the front cap from the spindle nose. This has three threaded through holes. From the drawings it looks like it was press fit into the spindle housing and i assumed that i had to thread three fasteners into these holes to press the front cap back out. As it turns out there are actually two dowel pin holes as well and the part is actually threaded in (which makes a lot more sense in hindsight). It was held in with very little torque and i assume the three threaded holes are for setscrews to maintain a preload on the threads so that the front cap cannot back off! I made up a custom pin wrench for this and it popped right off.

2.) Having removed all the drawbar components and the circlip on the top of the top bearing, i put the assembly in my crappy homemade press. I then protected the front face of the spindle with brass shims as i was only just grabbing the outer edges. I started to press on the top of the quill and to my great surprise the thing literally started to fall out - very little force required. I marked each bearing relative to the housing as they came out one at a time.

3.) This left me with two assemblies: the quill with three bearing (with spacer) and the housing which still retained the top radial ball bearing. The bad news is that the spindle was full of rust!! It literally looks like it was underwater. The bearings are destroyed as the balls and inside races are pitted and corroded so much so that i can even feel it by hand. Knowing this there was absolutely no way these things could be reused which meant that they would have to come off.

4.) So... first i had to removed the nyloc nut that preloaded the bearing stack. Out of amazing luck or coincidence (or both) The custom pin wrench that i made for the front cap was a perfect fit over the diameter of the threads. I drilled and tapped a radial whole for a 1/4 -20 fastener which fit perfectly into the lock nut cut outs. This nut was very rusted and tight! I soaked it in loosen all and had to apply ~150 ft-lbs with a long bar to get it come off.

5.) The next step was to remove the A/C bearings from the quill. Now this is where the drawing definitely was wrong. It shows the shoulder which the lowest A/C bearing rests against as being one piece (ie: part of) the quill. This really puzzled me as i had no access to the inner race (as it was completely hidden by the shoulder) which only left the outter race to press the bearing stack off with. This seemed to be the only way to get the bearings off and i no longer cared about damaged them as they were clearly already destroyed. Pressing the lower stack off using the outer race resulted in the lower bearing exploding and balls falling all over the bench. This left the inner race of the lower bearing on the quill with no way to remove it. I didn't want to use a bearing separator or an air chisel for fear of damaging the bearing surfaces so i ended up using a piece of 1/2 threaded rod which i wrapped around the inner race (in a U shape) and bolted through a scrap steel plate. I tightened this carefully as this was actually compressing the race onto the quill further but it gave me a purchase to press on. The race came off without a problem using this method and didn't damage any of the surfaces. To my surprise, after i removed the inner race i found out the the surface it was sitting against was actually a ground spacer that was resting on a ground smaller shoulder on the quill. This makes way more sense and would have saved a lot of trouble in the whole disassembly. If i had known, i would have just pressed on the spacer to remove the whole bearing stack which also wouldn't have destroyed the bottom bearing.

6.) I knocked out the radial bearing that was in the quill housing with a cylindrical bar pressing on the inner race through the quill housing (from the bottom). This was a slip fit on the housing so it came right out.

An interesting thing that i noted while examining the assembly was the outer spacer (the one that was visible) was fairly loose before i even touched the nut which compresses the bearing stack. I could move the spacer radially very easily. This seemed very strange to me. Isn't this supposed to be a position preload that stacks the compresses the whole assembly when preloaded? I couldn't detect any axial play but i would have thought that the outer spacer should be compressed as well when properly loaded?

I am now searching for new bearings. Not sure what my plan on the rebuild is really right now. Luckily there is no rust or corrosion on the bearing surfaces. I will likely just clean the thing up (not touching the bearing surfaces) then start measuring. I have read some rebuild posts suggesting you grind the bearing surfaces, then chrome oversize (or undersize depending on the part), then regrind to size. I can't see the value in doing this if your surfaces are still in excellent shape (ie: no gouges, corrosion, dings, etc) and are in size. Maybe someone can enlighten me on this?

Does anyone know what contact angle the following part number from RHP england is: 7014 TAU EP7

RHP seems to have been bought out by NSK some time ago but i can't find any cross reference guide or info on these bearings.

[DougWoz]

I bought a Bridgeport Interact 720 O-Mate, that had bad spindle bearings. We rebuilt the whole assembly and replaced the seals and Bearings.

1. First the spindle has what is called a tri-set of bearings. These are ground at the very same time and kept as a set. the other bearings are of no significance you can find them on ebay, and probably at the same place as the TRI-SET. If you can. Mine had to come from Germany.

2. The original set should be scraped, and replaced. You mentioned greasing them, I have been told by very experienced Machine repairmen from GM that I worked at that you never grease them but just use spindle oil. I explained to them that the spindle Cartage had no way to insert the oil after the unite was reassembled. Well we created a hole in the spindle casting that holds the Cartridge, and then drilled another hole exactly inline with the casting hole into the cartridge. Then we hooked up a simple hand oilier and line to the hole we drilled.

3. Bridgeport designed the system of the spindles to fail. But now since Hardin or what ever there name that bought them out allot of information has been lost or just scraped. You cant even buy the bearings from them I tried, no go. I had to do allot of searching for the right parts. Just remember all the parts are Metric sizes this also includes seals and "O" rings.

4. We had to cut the inner-race off, we tried to press them off with a 20ton press but no way were they ever coming off that way. We found out that Bridgeport would use a bearing heating unit, heat up the bearing and then press them on. we then turned the spindle on a lathe for all the bearing surfaces. and pressed on the new sets. Since Bridgeport never installed any type of nut or some way to secure the bearings we decided to just tack weld four corners, and if we had to replace them again we would just grind the tack welds off.

the reason why ours failed was due to the fact that it was a 1986 Bridgeport and since there was no way to oil the bearings the coolant fluid had finally leaked into the cartridge and rusted the bearings. but it failed in 2007

Hope this helps.

[underthetire]

Most spindles are grease pack. Oiling grease pack spindle is never a good idea. Get some Klubber NBU15 grease for those bearings. Thats the #1 rated grease for spindles. It's about 15 bucks for half a toothpaste tube, but you don't pack spindle bearings like wheel bearings. A little goes a long way, and if you over-pack the bearings they will run-in hot, and possibly damage the new bearings.

[DougWoz]

Most spindles are grease pack. Oiling grease pack spindle is never a good idea. Get some Klubber NBU15 grease for those bearings. Thats the #1 rated grease for spindles. It's about 15 bucks for half a toothpaste tube, but you don't pack spindle bearings like wheel bearings. A little goes a long way, and if you over-pack the bearings they will run-in hot, and possibly damage the new bearings.

As I stated The Machine Repairmen I had talked to and the one I had help me repair this spindle says Spindle oil These are Master Repairmen with 30+ years experience. Besides if your claim was correct the inside of the Spindle Cartridge would have had grease in side of it. And it did not and the spindle Cartridge is completely enclosed. We had just a small seal leak from the the coolant into the cartridge. Which caused the failure.

[mactec54]

DougWoz

It sounds like your master repairman was a master hack, Those spindles were not designed to have oil, They did make spindles that have oil/air flow as do most, but for this spindle Grease only, he was wrong in doing this to your spindle,

Then you said you put weld on the spindle to hold the bearings in place. I have rebuilt most Bridgeport spindles old to new & all I can say is that you did a bad job & were missing some parts

They have never made a spindle that did not have some why to lock the bearings in place

They heated the bearing so they could slide onto the shaft,This is the correct why to do it, they were not heated & pressed on

[polaraligned]

The BP CNC knee mills all had grease packed bearings.

[machintek]

Spindle bearings are a science. I saw the clean room at Bridgeport where they were assembled. All CNC lathe and mill spindle bearings that I have worked with are Kluber grease injected with a syringe. So many CC in so many places. As it has been said, the bearings are not packed like a wheel bearing. I do not even rebuild S1STD spindles. It can be better done by a GOOD spindle shop. I use one in Oregon. They load new bearings, pre-load them, and regrind the R-8 taper so it runs true with the bearings (no run out).

George

[machintek]

Spindle bearings are a science. I saw the clean room at Bridgeport where they were assembled. All CNC lathe and mill spindle bearings that I have worked with are Kluber grease injected with a syringe. So many CC in so many places. As it has been said, the bearings are not packed like a wheel bearing. I do not even rebuild S1STD spindles. It can be better done by a GOOD spindle shop. I use one in Oregon. They load new bearings, pre-load them, and regrind the R-8 taper so it runs true with the bearings (no run out).

George

[DougWoz]

Spindle bearings are a science. I saw the clean room at Bridgeport where they were assembled. All CNC lathe and mill spindle bearings that I have worked with are Kluber grease injected with a syringe. So many CC in so many places. As it has been said, the bearings are not packed like a wheel bearing. I do not even rebuild S1STD spindles. It can be better done by a GOOD spindle shop. I use one in Oregon. They load new bearings, pre-load them, and regrind the R-8 taper so it runs true with the bearings (no run out).

George

I'm not here to argue with you, and you are absolutely right about one thing a good spindle shop is the way to go. But that would have cost me over $3000.00 dollars. on a CNC Milling Center from 1989. And I only paid $3000.00 for it.

"That was there Quote" the way we repaired the spindle is / and probably not the absolute best way, but we checked the spindle very carefully after the repair and there was no run-out that is significant some where around 0.0005 in. and all the work that the machine has done since then was with in specs. Now our repair costs was $850.00.

That's a considerable savings for a start up company with a small budget. Now you may not like the way we repaired it to bad. Some times you have to be innovative and save big money to use in other places. and your wrong as far as all spindles use Grease. I know from working in GM as an Industrial Electrician for 30 years, and being around the repairmen that I have worked with most are Hacks, But the ones I personally know are excellent repairmen I wouldn't associate with unless they were really good. And they have rebuilt hundreds of them and some do use grease but not all do. (Hobbs Gear cutters) for example. I have had spindle motors go bad just because the bearings have frozen up due to the oiller's wasn't doing there job.

Now I'm not saying that anyone should repair there mill the way we did, but it was a good repair no matter what you think. Because it has been running good since then and already paid for it self. now can anyone say after buying a milling center and have it pay for itself within 6 months or less. I don't think so.

Doug.

[machintek]

I do try and be careful as to what I say but..........I can and do screw up.
I said the CNC spindles I had to deal with. There are many varieties out there with different designs that work well in their particular application. This is a generality and thus exceptions apply. Did not attempt to put anyone down.
I have to give proper advice here. Yes, people have a freedom of choice and must work within their own parameters/envelope of budget and ability.
Basically you have done well, very well, and came out ahead. This does not mean that the next person would experience the same result with the possibility that there would be grounds for a law suit if I had advised differently from what I did.
I wish you a infinite amount of spindle hours with no heat, noise, and a good finish!
I also wish you a terrific year (my wish to the world actually).

George

[Gnome]

Wow... well i guess that's one way to rebuild a spindle but i definitely wouldn't recommend it. How did you preload your a/c bearings?

If you read through the bearing design manuals oil mist is only required on high speed spindle applications - pushing 10k rpm (depending on the preload, contact angle, etc)

The replacement of the bearings in my spindle actually ended up going really well. However, considerable time was spent making sure that the spindle bearing surfaces were cylindrical, in size, straight, perpendicular to the preload faces, and making sure the spacers were exactly the same height - which is extremely important.

I ended up using kluber isoflex NBU15 with 25 percent fill based on my max operating speeds. The spindle ran in perfectly with no real notable temperature rise. The thing is ridiculously quiet.

[mactec54]

Hi Gnome

Great job with the spindle rebuild, I new that you did not need any help by your second post, just the way you were going about taking your spindle apart, I new that you would not have a problem in doing a good job.

[DougWoz]

[QUOTE=Gnome;715182]Wow... well i guess that's one way to rebuild a spindle but i definitely wouldn't recommend it. How did you preload your a/c bearings?

If you read through the bearing design manuals oil mist is only required on high speed spindle applications - pushing 10k rpm (depending on the preload, contact angle, etc)]

As I stated we purchased a tri-set of bearings. After cleaning and slightly grinding the bearing surface with a OD grinder. +- .0001. all surfaces were perpendicular to the spindle Bearings after we pressed them on and set a spacer Block at the end (where the spindle should have had a bearing Nut installed.)
Roger, The machine repairman I wrote about, set the pre-load and tacked welded the spacer in place. I was not their when he did all of that so I cant tell you all of the details. As far as Manuals, this milling center is a Bridgeport Interact 720 from 1989. we had no manuals, No specs, Ect. I contacted Harding that bought out Bridgeport and all I got was a Parts break down of the spindle. No part Numbers no Nothing.