Quill bearing Burke Mil-rite

[BDriscole]

I purchased this mill quite a few years ago. Its a great little mill. Recently the the chatter has been getting to the point that I need to replace the bearing. I have the quill out, put now have to idea how to get it apart. From what I' have read its supposed to have a Timken bearing, but I believe they have been replaced at some time. Any help would be greatly appreciated

.

Bob

 

[Ischgl99]

I attached the Millrite manual in case you don’t have it yet. What spindle nose do you have? It looks like a 30 taper of some sort? I didn’t realize they were available with that, mine is an R8. The manual I attached shows the quill arrangement for the collet spindles. To remove the spindle on mine, you need to unscrew the bottom cap that would be just above your spindle nose. It is left hand threads and you need a pin wrench to do it, but a strap wrench might get enough grip on it as well. It looks like you have a bottom cap that is bolted on, so I would take those bolts out and see if you can do the next step. I’m not sure if they would have threaded it like with the collet spindles and the bolts are just to lock it in place, or if they go all the way into the quill and the bottom cap just slides out.

After taking that cap off, or loosening it as I think in your case, the spindle with the bearings can come out that end. You will need to tap the top of the spline to drive it off the upper bearing ID. Once its clear of the bearing seat on the spindle, it should come out easily.

 

[BDriscole]

WOW, I was not expecting left hand threads. I would have been hammering a long time. Thanks for the manual. Your correct the spindle nose is a #30 NMBT. The four hole in the nose are tapped, but do not go through, see attached. The plate under the nose is bolted to the nose nut. I'm not sure if the go all the through to the nut. I can loosen them and the plate, but not take all the way out as they hit the nose. There is a slot that I'm going to enlarge. Doesn't need much. I've often thought about removing the plate, but never got around to it. Besides it an easy place to attach the dial indicator.

By the way who am it talking to.

Bob

 

[Ischgl99]

Hi Bob, I’m Mike. Yes, left hand threads take you by surprise the first time, but it makes sense since the normal rotation direction will keep that cap tight if anything rubs. I didn’t notice the plate in your original pictures, do you know why that was installed? I can certainly see it being helpful for putting an indicator base on, I often struggle getting it to firmly attach to the quill housing.

When you get it apart, check the bearing nut and make sure it is not loose, that could cause your chatter problems. You can actually check that without taking the spindle out of the quill through the hole in the backside. I had to replace the upper bearing, it was going bad, but the tapered bearings were fine, so I reused them. I didn’t want to spend $600+ at the time to replace them when they still looked good. The upper bearing was a standard precision bearing when I took it out, I am not sure if that one needs to be a higher precision class or not, I wasn’t able to find an answer to that when I replaced it, so I put a standard precision back in.

 

[BDriscole]

Pleased to meet you Mike. I have no idea why the plate was added. It does have a threaded hole in it and it been handy, once I learned to not smack my hand on it. So I figure I'll keep it. The machine came out of a tech school in OH and was originally set up with a punch tap operating system. I removed all that stuff. I'm not sure I have any of the old photos. If I do I'll post them. When I get it apart I'll likely replace both bearings. The top definitely needs it, it wobbles. I'll keep you posted.

Bob

 

[BDriscole]

Hi Bob, I’m Mike. Yes, left hand threads take you by surprise the first time, but it makes sense since the normal rotation direction will keep that cap tight if anything rubs. I didn’t notice the plate in your original pictures, do you know why that was installed? I can certainly see it being helpful for putting an indicator base on, I often struggle getting it to firmly attach to the quill housing.

When you get it apart, check the bearing nut and make sure it is not loose, that could cause your chatter problems. You can actually check that without taking the spindle out of the quill through the hole in the backside. I had to replace the upper bearing, it was going bad, but the tapered bearings were fine, so I reused them. I didn’t want to spend $600+ at the time to replace them when they still looked good. The upper bearing was a standard precision bearing when I took it out, I am not sure if that one needs to be a higher precision class or not, I wasn’t able to find an answer to that when I replaced it, so I put a standard precision back in.

Mike, I got the guill apart yesterday. See photos.

As the shaft came out of the quill. I'm not sure what the ribbon of metal is. It appears to be shim stock.


Things laid out it order they were removed.


Lower bearing seat.


Upper bearing seat.


The lower bearing seat was snug and the bearing seem to be in good condition. I'm not sure if or why the one side of the lower bearing cover was removed or if that the way they are supposed to be. The upper bearing seat is loose, and either poorly cut or damaged sometime in the past. It is rough and the bearing was loose and pushed out easily. I'll be shopping bearing today.

Bob

 

[Ischgl99]

This is completely different than my spindle. Are those angular contact bearings, or ball bearings? They look like standard ball bearings and someone popped the seal off on one side. If those are ball bearings, I don't see how they were preloading them enough to take out the clearance in the bearings, unless what you are calling a shim was supposed to be in there and worked its way out. I'm not able to see any part numbers on the bearings, can you see any markings showing what they are? Mine uses tapered roller bearings without any seals on them, and where you are showing a shim is where a grease slinger is in my spindle. I don't know if your mill came from the factory with angular contact bearings in there, or if someone changed that out. The locknut is also different, since my bearings are open, they are greased by the hole in the back of the quill, and my lock ring is designed to direct the grease towards the bearings.

What I would do if this was my quill. The hole for the top bearing needs to get repaired, that is badly worn from the bearing spinning and with the loose fit, that could certainly be causing your chattering problem. It will probably need to be machined and a sleeve added to the proper fit for the upper bearing.

Next, I would put the proper bearings in there, if these are ball bearings, look into replacing them with angular contact bearings with the correct preload built into them so a shim is not needed. Unless there is a path for the grease to get out, you may need to use sealed bearings in this application so that it doesn't get packed with grease over time, but if you look at the manual, you will see there is a grease slinger between the bearings and the end cap for the tapered roller design. That keeps the proper amount of grease in the quill, but allows excess to get out. Without seeing yours in person, it is hard to say if you can do that, or if you need to do things the way it is now.

 

[BDriscole]

They are ball bearings. There is no way to put grease into the bearing once the shaft is inserted back into the quill. I do see bearing #s. Top is a MRC 206 SFF. The two lower bearings MRC 207 SZ. Next the this number there is a DB that looks like it has been hand scribbled. I assume I can get tapered roller bearings to replace the lower.

There appears to be sufficient material on at the top of the quill to allow for cleaning up the bearing seat if I can get the appropriate bearing to match. As for the lower bearings I'm inclined to stick with the way it is. I have no way of knowing what modification may have been done to inside of the quill barrel. Finding a pair of tapered bearings to replace the ball would be fine. I would go with sealed, again I see no way to get grease into them. I might only run my Mill a total time of 2 -3 days during a month.

As for per-loading of the bearings, I'll have to admit I'm not quit sure what that is. I'm thinking pressure is put on the bearings so the actual roller bearings are pressed firmly against the race. I can see where a shim or spacer between both would aid in this. I'm in the ballpark on this.

Top bearing. Lower bearing.


Lower bearing.

 

[Ischgl99]

Preload is axially clamping the bearings together to remove clearance between the ball and the races of the bearings, this makes the spindle rigid and suitable for machining. It's important to take up any clearance in the bearing and add a slight load on them so that in use you have a rigid spindle. Angular contact bearings can come in various styles that do this depending on the application, tapered roller bearings do it as shown in the manual I posted, the outer rings are locked in place by means of the spacer ring and the locknut is tightened on the inner ring until the proper load is on the bearings.

The 207 SZ bearings are metric, so you won't be able to put the tapered roller bearings used in the other spindles in there, those are inch sized. I'm thinking the 207 SZ with the DB added indicates the bearings were modified for this application, I couldn't find any info on that in my MRC catalog. The only bearings in that with DB are angular contact. Ball bearings can have their rings specially ground to take up the internal clearance and give the proper preload on the bearings, I believe I heard that is how Bridgeport does it on the older heads. It could be the spindle with the 30 taper is supposed to have these bearings. I have never seen a manual for the 30 taper spindle, so I can only go by what is in the standard manual. Hopefully there is someone else here that has this spindle and can confirm what should be in there, but since someone would have needed to do a bunch of machining to change it, I am thinking this might be correct for the 30 tapered spindle.

Before putting this back together, I think you are going to need another shim. Can you measure the thickness of the one that came out and see if you can make another one? I don't know if you have the equipment to test this, but I would also check and see how much end play these bearings have, if they were modified, you might be able to treat them as angular contact bearings and just clamp them together without the shim. You can elevate the bearing off of a surface plate on something like 1-2-3 blocks and check with a tenths indicator the difference in height between the outer ring and the inner ring, I would do both sides of the bearing and see if it is different, that will tell you how much play each bearing has to take up the internal clearance. You can also measure the width of the inner and outer rings and see if they are different. A normal ball bearing, they would be the same, but if they were modified, they could be different.

 

[Beckerkumm]

I would also verify the correct bearings before putting stuff together. A 30 taper spindle will incur both radial and axial load so using standard deep groove bearings seems like a poor choice as they are primarily for radial load applications. Angular contact are proper when both forces are in play as on a mill. In addition, A/C bearings come in different angles from 15-40 degrees or so. I've found more machines with improper bearing replacements than I care to count so those may not be original. The numbering systems aren't totally consistent. I think the old Hoover deep groove bearings were numbered 7xxx vs 6xxx for most other brands which led to confusion as 7xxx were A/C . I've seen both types swapped but usually not for good results. A/c bearings should be bought as a set and the proper angle used for the application. Dave