Spindle bearing repair troubleshooting

joedesu1 · Apr 25, 2017

Hi All,
Seeking advice on a bearing repair on my VMC spindle. I have sourced some NSK bearings 3 pieces 7011CTRSUMP3 and two 7009CTRSULP3 , cleaned everything thoroughly, nd greased with a lube recommended by bearing engineering for the bearing called lubriplate FGL-1 which could be the issue (approximately 2.5ml measured as recommended by NSK see chart).

The problem I am having is with the bearings overheating during run in cycle. I even took them off and installed a new set due to over greasing the previous set. The spindle taper runs true to .00005" so I don't believe that I have a misalignment or a binding issue. I am having trouble finding information on my spindle, like how to tighten the nut other than "tighten as tight as you can then back it off".

I am attaching some information on the spindle and drawings. The maker of the spindle is no longer in business even though the mill maker still is around. I am trying to find out if this is an issue with the nut tightness or the grease I used.

Screen Shot 2017-04-25 at 8.56.47 AM.jpg

Thank you for any advice.

Vancbiker · Apr 25, 2017

Are the spacers between the upper BG64 and the lower pair of BG64 the same width? If using a "universal" bearing set which I think the "U" designation in the part number designates, then those spacers should be equal. It is not uncommon for a spindle manufacturer to not use matched bearings and control preload by adjusting the width of those spacers.

The Lubripate grease you used looks to be an approved grease for food processing machinery? I'm not sure why that would be looked as a machine tool spindle grease, but I didn't look beyond the first couple lines in the product description.

Kluber Isoflex NBU15 is a very popular spindle bearing grease used by many mainstream machine tool builders or their spindle suppliers.

ewlsey · Apr 25, 2017

You probably won't find a spec on how to tighten the nut. It just needs to be tight to preload the bearings. The pre-load is built into the bearings, so you the nut does not have to be adjusted for bearing preload. The nut should have 3 set screws. You can use those to tweak the runout. The nut will cause slight bending of the spindle which is corrected using the set screws (and sometimes a hammer...).

I thought Lubriplate was a graphite based grease. I would not use it. You want Kluber NBU15. There are other greases that can also work, like Mobil SHC32, depending on RPM.

We will have to wait for Machtool to come along and set us all straight.

HuFlungDung · Apr 25, 2017

Back when I redid my Haas spindle, I checked the bearing preload by setting up the bearings and spacers in a stack in the press, and then applied pressure through the stack to the inner races and inner spacer. This permitted me to still rotate the outer races with preload applied and get some kind of a feeling for how they were rolling. In my case, my first test showed that the outer spacer was easily moved laterally between the races, so the preload was non-existent, so I lapped the inner spacer and retested until I felt it took a firm pressure with my fingers to move the outer spacer laterally. The bearings must feel smooth on rotation, any sort of grittiness to the rolling is an indication of too much preload.

joedesu1 · Apr 25, 2017

Thank you for the replies. To start out the spacers between the bottom triplex set or not matched. I checked a .0003" difference with the outer spacer being smaller than the inner spacer. I thought about this before set up and it kept me awake at night but changing anything also seemed like a bad idea.

Regarding grease, this was recommended by a local "hero" of the spindle rebuild industry who works for bearing engineering. I forgot to order the Kluber grease initially, so I was looking for the local quick grease that would work, hence the choice for the fgl-1.

Joe

Richard King · Apr 25, 2017

Measure the amount of grease you use. Kluber says on there web-site 20% max fill. I usually use Modil Grease 28 or 32. It used to be called Red Horse Grease that has been used for years inside Heald and Excello boring machine headstocks. They recommend using 30%. Most of the time people fill the bearing full and the bearing (s) heat up. Also you should run in new packed bearings. Keep an eye on them, start with 500 rpm and run them for a hour, then increase it to 1000 for say 20 min, keeping an eye or temp gage on the bearing housings, if you can hold your hand on the housing your good, but once it gets to hot..I believe around 120 F stop the spindle and let it cool down, then ramp it up to 2000, RPM...watching it. If it gets to hot to touch shut it off until it gets cool and start up the process. If they get to hot, you have put to much grease in them.

Also not only run-out check the end play in the spindle. There should be 0 if they are adjusted right. The back bearing on the back of many spindles floats for end play to the heat of the bearings and shaft can grow and the back bearing is more for radical alignment.

Also did you check the TIR of the spindle to the run out of the bearings. They should be mounted 180 degree's apart. Stone everything. Also use a goor bearing heater to warm up the inner raises so they slide on the spindle and never use a punch to drive them in.

Your smart getting an expert to help you. I never use Lubriplate for anything as I feel it is a rip off, I might grease my boat trailer axels with it, might,,,,lol

Get Smart Too with SKF Maintenance Products - YouTube There many good you Tube shows on bearing instillation too

machtool · Apr 26, 2017

joedesu1 said:
I have sourced some NSK bearings 3 pieces 7011CTRSUMP3 and two 7009CTRSULP3 , cleaned everything thoroughly, nd greased with a lube recommended by bearing engineering for the bearing called lubriplate FGL-1 which could be the issue (approximately 2.5ml measured as recommended by NSK see chart).

That cant have been an NSK bearing engineer that recommended that?

That Lubriplate FGL-1. That must be a multi-purpose, multi-faith grease. I see its Kosher and Halal certified.

I have a book shelf wall of bearing manuals. Guarantee, I've never seen it mentioned, as a spindle bearing grease.

My NSK charts show's 2.4 & 1.6 CC's each, respectively for your 7011's & 7009's. That's at a 15% fill. Which is next to nothing to look at. So you would have had to significantly over filled them to produce heat on run in.

Can you send me a clean scan of that assembly picture? I'll P.M you with my email addy.

I'd assume you have a thread on the 7011's of an M55 x 2mm? 24Nm. Its not a lot, but will give you 10 MPa of side face pressure.

Your 7009's, Thread M45 x 1.5mm 12Nm.

Trick is to over - set them by 3 times the seating torque. Then release that, and torque back up.

I'm really short of minutes right now. Dinner wont be on the table, if I don't fuck off and get back in the kitchen.

You missed a really important step..

I'm going to back work this. You should have two sets of used bearings kicking around by now. Humour me, and run a Micrometer over the WIDTH of the outer bearings.Only the outer rings width. Granite and JO blocks would ever be better. You will be surprised how much the bearing width changes. Its a shock, because your gold NSK packets, Say D-4, d -4.

Measure the thickness of the two sets of bearings you should still have. I'll sort you out in the morning. (10 hours from Oz)

Regards Phil.

Mechanola · Apr 26, 2017

Two things appear important to me. First, the bearings must be clean, inside. Not wanting to frighten you in any way but your VMC is useless when the rollers bump over debris. I know of CNC machines that had thrust and radial bearings with optical mirror polished surfaces. Second, do not use graphite grease. Graphite is for slow moving parts under varying load, see my avatar. You want a first class synthetic roller bearings grease. The rest is adjustments. Preload according to manuf specs.

machtool · Apr 26, 2017

Mechanola said:
Second, do not use graphite grease.

He hasn't used a graphite grease. What he had used is a "food safe" white oil - non toxic goo. That wouldn't see 1750 - 1800 R.P.M in a 4 pole 3 Ph 60Hz motor.

machtool · Apr 26, 2017

joedesu1 said:
I have sourced some NSK bearings 3 pieces 7011CTRSUMP3 and two 7009CTRSULP3

Do you understand those numbers. Great bearing to be playing with.
7011 = 50 x 90 x 18mm. Its an ISO series 10 size.
"C" = Contact angle of 15 Degrees.
"TR" is just cage construction = Phenolic /Outer ring location. Neither of us could change that. It's how they are manufactured.
SUM = Single Universal - Medium. Meaning they are a Single bearing, that can be Universally mounted in any orientation, and will apply the preload. M for medium, in the case of your 7011's. L for light in the case of your 7009's.
P3 is your accuracy grade. One grade better than you need for a mill, (P4) As far as bearings go, there at least equal or better than the old ABEC 9 grade.

As bearings go, I couldn't wish for any thing better. So that's not your problem.

To start out the spacers between the bottom triplex set or not matched. I checked a .0003" difference with the outer spacer being smaller than the inner spacer.

What you have there in the nose end is what's called a 2TB combination. 2 bearings T (Tandem) facing the thrust & 1 bearing in a Back to back (Opposed) combination. You have to be absolutely sure they are arranged like that again.

Your 3 tenths reduced outer spacer. That reduces the preload on an arrangement like that. Its not pressing the outer's apart enough to apply designed load.

VanBC touched on it. With out knowing the speed and which pre-load you are changing out. I cant comment on that. Your putting Medium Pre-loads in. What are you replacing?

Do you understand how preloading works in an angular contact bearing.Free state, as the come out of the box, the inner ring will be proud of the outer ring. You can test this on a good slab of granite and a tenth clock. The inner ring will always stand proud of the outer ring, until its squished. (Technical term for axially clamped).

A 7011 in 15 degrees should have the inner proud by 11 microns, for a light pre-load. 26 microns for a medium.

I'll translate 0.0003" = 0.00762mm = 8 ish micron. I don't split the atom any more.

I think I see what they have done there by feathering off the pre-load. There is absolutely nothing you can do to change the pre-load on the first two bearings in tandem. They are just stacked back to face in tandem.

The opposing bearing if just a single. Via spacers. But it applies preload to the tandem pair. Not uncommon to tune that up to its capacity. Hence having it 0.0003" Undersize. I'm not going to lose sleep over that, until we tick a few more box's

Regards Phil.

joedesu1 · Apr 26, 2017

machtool said:
Do you understand those numbers. Great bearing to be playing with.
7011 = 50 x 90 x 18mm. Its an ISO series 10 size.
"C" = Contact angle of 15 Degrees.
"TR" is just cage construction = Phenolic /Outer ring location. Neither of us could change that. It's how they are manufactured.
SUM = Single Universal - Medium. Meaning they are a Single bearing, that can be Universally mounted in any orientation, and will apply the preload. M for medium, in the case of your 7011's. L for light in the case of your 7009's.
P3 is your accuracy grade. One grade better than you need for a mill, (P4) As far as bearings go, there at least equal or better than the old ABEC 9 grade.

As bearings go, I couldn't wish for any thing better. So that's not your problem.

What you have there in the nose end is what's called a 2TB combination. 2 bearings T (Tandem) facing the thrust & 1 bearing in a Back to back (Opposed) combination. You have to be absolutely sure they are arranged like that again.

Your 3 tenths reduced outer spacer. That reduces the preload on an arrangement like that. Its not pressing the outer's apart enough to apply designed load.

VanBC touched on it. With out knowing the speed and which pre-load you are changing out. I cant comment on that. Your putting Medium Pre-loads in. What are you replacing?

Do you understand how preloading works in an angular contact bearing.Free state, as the come out of the box, the inner ring will be proud of the outer ring. You can test this on a good slab of granite and a tenth clock. The inner ring will always stand proud of the outer ring, until its squished. (Technical term for axially clamped).

A 7011 in 15 degrees should have the inner proud by 11 microns, for a light pre-load. 26 microns for a medium.

I'll translate 0.0003" = 0.00762mm = 8 ish micron. I don't split the atom any more.

I think I see what they have done there by feathering off the pre-load. There is absolutely nothing you can do to change the pre-load on the first two bearings in tandem. They are just stacked back to face in tandem.

The opposing bearing if just a single. Via spacers. But it applies preload to the tandem pair. Not uncommon to tune that up to its capacity. Hence having it 0.0003" Undersize. I'm not going to lose sleep over that, until we tick a few more box's

Regards Phil.

Phil thank you for the information. I know about the bearings because I have been researching them for a while now and trying to figure out why I'm overheating. I made a note of how the original (replaced) bearings came out and checked that arrangement to the drawing provided by milltronics. The original bearings had the 7009's orientated wrong so I corrected them with this install. The originals were timken fafnir bearings and are supposed to be medium on the 7011's and light on the 7009's. That struck me as odd. What I pulled from the spindle were both light preload bearings but the book clearly specifies a medium for the triplex set, so I went with that.

Unfortunately I don't have the NOS nsk bearings that overheated. I took them back to the place I bought them from, as they recommended the grease and told me to fill the bearing "half way the diameter and packed top to back". I think this equated to about 10 times the actual amount of grease recommended by nsk. So they are at fault and wanted the bearing back for warranty purposed.

I will post a clearer scan of the plans here and email you or as well. Just getting the day going here as we have a newborn in the house and sleep has been scarce.

Joe

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