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Calculating Spindle Bearing Grease Volume

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macardoso

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#1
Quick question / request for links...

I am replacing the spindle bearings in my CNC (G0704) and I need to pack them with grease. I have an empty 7007B (https://www.vxb.com/7007B-Angular-Contact-Bearing-35x62x14-p/kit8891.htm) and an empty 7005B (https://www.vxb.com/7005B-Bearing-Angular-Contact-25x47x12-p/kit8889.htm). I have Kluber IsoFlex NBU 15 grease and a 1 ml dosing syringe. Both have Phenolic cages. I know that higher end bearing manufacturers have tables for these values, but any idea how I can figure out how much is needed in these?
 

TomS

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#2
When I installed AC bearings in my PM-932 spindle I estimated the amount of grease to get them 30% full. They have been running fine for the past two years so I must have guessed right.
 

Janderso

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#3
This might help. He packs the bearing 1/3 of the circumference
 

macardoso

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#4
When I installed AC bearings in my PM-932 spindle I estimated the amount of grease to get them 30% full. They have been running fine for the past two years so I must have guessed right.
Tom,

What method did you use to figure out how much free volume was in the bearing? I've read 30% but not sure how to find 30% of what.

This might help. He packs the bearing 1/3 of the circumference
Janderso,

That seems like a reasonable method to find 30%. My only concern is that since the grease isn't evenly distributed, once you spin the bearing, most will get squeezed out and you will end up with far less than 30% in the bearing.
 

mikey

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#5
I don't see an accuracy class ratings on the bearings you linked to but that's a separate issue. My understanding is that being accurate to the fraction of an ml is not necessary. Filling about 1/3 full should do it; the grease will self-distribute if the correct break in procedure is followed. Typically, this is a run-in for about 20-30 minutes at medium speed, followed by a similar time period at high speed. During these run-ins, you should check the bearing temps directly with an infrared thermometer to be sure they do not get above about 100degrees C.

You might also want to contact the seller for his recommendations on this process.

Have you considered going with a sealed precision angular contact bearing? Might be a good idea, and maybe specify an accuracy class of at least P5/ABEC 5.
 

macardoso

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#6
I'm certainly open to suggestions if they match the size of bearings. I need a 35x62x14 or 35x62x18 for the lower bearing (14mm + 4mm spacer) and a 25x47x12 or 25x47x15 for the upper (12mm + 3mm spacer). I plan on having a minimum rating of 8000 rpm.

Can you recommend where to find the bearing you described?
 

Cadillac

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#7
I've rebuilt acouple spindles recently. What I did was the 30% modo but I used a syringe and squeezed it between the balls all around spun and then did the same to the other side. I wanted to make sure their was a coating in the grooves of inner and outer races. Putting the grease in one section of the bearing leaves a lot of the bearing uncoated and wasted in my eye? Then after reassembly of the spindle I ran the spindles at low speeds for ten min. then stopped let cool then run another ten min. On two I ran in reverse to pull some grease to the other sides of the bearing cages. Biggest tip I have is be super clean be ready with all the parts to avoid delays. Be aware of runout marks on races and good to have spindle and bearings already checked for minimal runout on spindle.
 

mikey

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#8
I would contact Shaeffler and ask them for a bearing recommendation for your application. You can specify accuracy class, sealed, etc. https://www.schaeffler.us/CONTENT.SCHAEFFLER.US/US/products_services/inafagproducts/index.jsp

Shaeffler carries the FAG brand. Other good ones are SKF and Nachi (there are others but haven't used them).

Going directly to the bearing manufacturer or factory seller is the best way to find the right stuff for your application. Once you know which bearings you need then you can search for it for the best price. I can tell you that FAG precision bearings are very high quality. I have them on both my mill and they were OEM in my Emco lathe. Run out on my mill spindle is under 0.0001" with their bearings. Run out on my lathe spindle is zero.
 

TomS

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#9
Tom,

What method did you use to figure out how much free volume was in the bearing? I've read 30% but not sure how to find 30% of what.



Janderso,

That seems like a reasonable method to find 30%. My only concern is that since the grease isn't evenly distributed, once you spin the bearing, most will get squeezed out and you will end up with far less than 30% in the bearing.
What Mikey said below. When I greased my bearings it was an educated guess on the volume of grease I used. I don't think it's too critical as long as you don't try and pack every nook and cranny with grease.
 

P. Waller

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#10
Calculate the volume of the races minus the balls, then subtract the volume of the balls and separator, fairly simple really.
 

Kernbigo

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#11
rule of thumb has always been 30% i used to rebuild high speed spindles
 

macardoso

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#12
Awesome! I spent some time looking at the SKF and NSK bearing tables and I figure they are close enough to my bearings that it wont matter. They recommend 30-35% fill.

Large bearing: 6.5mL free space, 2.28 mL grease volume

Small Bearing: 3.5mL free space, 1.23 mL grease volume

I will use the syringe to evenly distribute the grease and run them in slowly.
 
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