How do You Fill a Bearing to 30%?
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  1. #1
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    Default How do You Fill a Bearing to 30%?

    I removed solidified grease from a Fafnir 2MM203 WI CR DUL bearing that goes in my Gorton 375 tool grinder. I located a suitable replacement grease. Now I have a problem. I don't know how to fill the bearing correctly.

    My understanding is that this bearing requires a 30% fill. How am I supposed to know when a bearing is 30% full? It's not like it has graduations on it to tell you how full it is.

    I have a big new cartridge of grease and some dental syringes. Just waiting to find out how to gauge the amount.

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    Here you go:

    How to Calculate Grease Quantity and Frequency for Bearings

    If you really need that 30% here's a PDF from Klueber that is a little more detailed:

    https://www.google.com/url?sa=t&sour...=1581961599918

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    Wonder if fafnir could tell you by volume for that part number. I know how i would do if i needed to and wanted to keep it as close to 30 percent. fill 100 percent of empty space 30 percent around . Blow all back out and put same volume around entire circumference .

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    If he is positive about that 30% number and has a graduated syringe he can just fill it 100% with a light oil while the bearing is lying on a piece of painter's tape or something to seal the bottom. Then use 30% of that number for the grease fill.

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    Even better! should even seal with some grease. You know how nasty that tape gets around oil.

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    Ask customer support of any bearing manufacturer for that particular size.

    If I was desperate I would get the dimensioned drawing for the bearing and calculate the volume of the toroid that houses the bearing balls.
    Then is it 30% of that? Not sure but I would find out.

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    How to determine grease percentage for bearing packing.

    1 Flush bearing clean and free of grease

    2 Weigh the clean, dry bearing on sensitive scale - note reading

    3 Pack bearing completely solid with recommended grease - weigh and note reading

    4 Subtract reading 2 from reading 3 - this gives you weight of grease at 100% fill

    5 Calculate desired weight of grease from percentage times result determined in 4

    6 Add weight of clean dry bearing from 1 to result in 5

    7 Remove excess grease with soft tools to achieve total weight in 6. Alternative. Remove 70% of the grease by weight.

    8 Distribute grease following Robin Rinzetti's tutorial:

    YouTube

    Note how Robin stresses the need for strict cleanliness in his remarks and demonstrates how to work clean in an open shop environment.

    Adding: BTW, never ultrasonic clean an assembled bearing. Consider the effect of 40,000 impacts per second between balls and races.
    Last edited by Forrest Addy; 02-18-2020 at 06:49 PM.

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    Or just thouroughly clean the bearing, then palm in grease to fill just under a third of the circumference. reassemble machine, then go on making money.

    The 30% is a guideline. Mucg too little is bad. 100% is expensive. (£25,000 for repair of the emergency generator for our data centre after I'd asked the service 'engineers' why they were completely filling a 7" od 3000rpm bearing during a 'C' service and they told me to get back to my computers).

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    Fafnir is part of Timken, so I sent an inquiry to Timken. I didn't hear back from them, but it looks like I don't need to now. Thanks for the help.

    In case anyone is wondering, Mobil 28 red synthetic grease appears to be suitable for this bearing. Should be easier on the wallet than the caviar-priced Kluber product that was initially recommended. I paid around $22 and got almost 14 ounces.

    I don't have a clean room. I'm just a human being who lives in a house. I will do what I can.

    I hope the bearings aren't fried, but the cost of new ones doesn't look too scary. Whether I can install them correctly is another question.

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    Quote Originally Posted by Steve H. Graham View Post
    Fafnir is part of Timken, so I sent an inquiry to Timken. I didn't hear back from them, but it looks like I don't need to now. Thanks for the help.

    In case anyone is wondering, Mobil 28 red synthetic grease appears to be suitable for this bearing. Should be easier on the wallet than the caviar-priced Kluber product that was initially recommended. I paid around $22 and got almost 14 ounces.

    I don't have a clean room. I'm just a human being who lives in a house. I will do what I can.

    I hope the bearings aren't fried, but the cost of new ones doesn't look too scary. Whether I can install them correctly is another question.
    Page One:

    To get a 30% fill, just leave 70% void. Once there is grease in there, it is permitted to rotate the bearing and distribute it. Pointless to call it a "bearing" if either of rotation or resulting distribution is to be prevented in any case.

    Page Two;

    Klüber's claim to "magic", priced accordingly, isn't because their greases are slipperier.

    It is becauuse their chemistry resists age effects, separation, varnish, weird-ass bacteria and hardening for one and a half to two or even three times as many years as most other greases.

    Price your savings vs Mobil red against the downtime and labour cost of having to clean and re-lube two, three, four times as often, and Klüber might be CHEAPER.

    That's how Klüber live and prosper with the makers of the pickiest spindles and their bearings on-planet. Not because they have nice tits and a great ass.

    If you and your application are less picky or your bearings not costly? Save yer money.

    Some apps with generously spec'ed - read "understressed" - bearings really, really do not much give a damn, will serve sixty years just about as well on Yak butter, peanut butter, Arco graphite, or anything else much slipperier than bunker C or road tar cutback.

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    Here's what I'm wondering now: how will too much grease hurt the bearing? There is plenty of room around it for excess grease to fly into. Is it possible the fill percentage is only for sealed bearings?

    Hoping to get the bearing reinstalled today. Then all I have to do is find out how to work a tool grinder. And fabricate a rolling base.

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    Too much grease will cause excessive heat build up, so you have to keep an eye on the bearing temps when you run it in. As far as 30 percent, I don't even go by percentages any more but I have rebuilt a lot of spindles and have a feel for the right amount. It would be better if a bearing manufacturer would tell you the amount of grease, as in 10cc, or 7ml etc. for each bearing.

    I would error on a bit too much, but keep an eye on the temperature. When it gets to 140 degrees, stop and let it cool down to room temps then start at the rpm that you left off at.

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    Yeah too much causes excess heat and that can damage the grease (separates out the oil and thickeners). Once they separate the lubricant just seeps away and the hardened thickeners are left behind, just like with very old grease.

    A good analogy I've seen to help get a feel for this is thinking about the difference in exertion it takes you to wade through a 1" deep mud hole and one up to your knees. Excess grease is like the knee deep mud hole. In addition I've read that excess grease can cause individual bearings to skid rather than roll, damaging them as well.

    Apparently there are fancy ultrasonic devices that listen to the bearings as you add grease out there now. As grease is added the bearings get quieter. At the point where the high frequency noise starts to climb again is where you stop for optimal greasing. Temperature is monitored as well.

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    Quote Originally Posted by Steve H. Graham View Post
    I removed solidified grease from a Fafnir 2MM203 WI CR DUL bearing that goes in my Gorton 375 tool grinder. ....
    You are not putting in a new bearing?
    Bob

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    No new bearings yet. I was advised to clean and grease the old ones first.

    I did my best. The grinder runs cool now. Whether it's truly fixed, I don't know yet.

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    Em ..
    there is a speed rating for bearings used in machine tool spindles, and similar.
    Number k, maybe ?

    Anyway, using the kluber magic grease the rating for critical speed is very very much higher.
    Around 20.000 rpm rated load for a 25 mm D (iirc) 7205-AC-DUP-P4.
    Somewhere in that ballpark.
    A single bearing costs about 540€ online typically P4.
    A P2 might cost double.

    The kluber magic grease resists very high rpm and loads better than other greases.
    That is why most-all machine tool builders specify it for their 1000€ spindle bearings, and up, along with only 2 alternative greases, typically.

    I have 2 sets of both and 40 mm both P2/P4 bearings for very high end spindles.
    Had them 2 years, stuff got in the way.
    My ground high end shafts need a final lap, to bring the 2 micron high spot down.
    And kluber isoflex 10 grease.

    I´m testing my own-import bearings, and hope to have decent results on 1000 hour run-in tests via ac servos.
    7205 and 7210 bearings, aka 25 mm and 40 mm inner D.
    Goal is for 1-2 micron tir, or better, on honed in place fits.

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    All I know about my spindle's speed is that it's not too far from 1725 . The motor turns at 1725, and the spindle pulley is a little smaller than the motor pulley.

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    Quote Originally Posted by Steve H. Graham View Post
    Here's what I'm wondering now: how will too much grease hurt the bearing? There is plenty of room around it for excess grease to fly into.
    The open space is how you can do a good approximation of 30-33% fill. So long as the beaing is NOT sealed nor sheided, you can place a spot of grease, skip two same-sized increments, do it again and you've got roughly 1/3 - 2/3'rds filled/open ratio. Now at 'hand operated' speeds you use the bearings and race to distribute the grease for you.

    Damage comes at HIGH speeds, where so much grease that the rolling-elements can't push it aside fast enough. The bearing then "wedges" up off the race on excess grease and skids, rather than rolls... to another point where there is NOT a cushion of grease - so it "lands", speed mismatched to skid metal-on-metal.

    So long as a grease is still "healthy" that's a fairly RARE situation on precision machine-tools.

    Given even a skosh of room and healthy, not cruddy grease that can flow, the bearing generally clears itself as a byproduct of ordinary use.

    Uber-precision spindles, BTW commonly call for a warm-up of 15 to 30 minutes, speed slowy ramped-up where the drive supports that.

    This is good for stability once put to work as well as reduced risk to costly bearings.

    Overheat from churning that degrades the too-full grease pack faster than "the plan" is more likely than skidding, and even that primarily off the back of folks who believe a bearing should be STUFFED SOLID with grease.

    Maybe that works for boat-trailer wheel bearings that may get water into them?

    Pass. Got trouble enough without investing in a hole in the water to toss money into!

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