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Odd Spindle bearings, Sealed 7905 Angular contacts.

firebrick43

Plastic
Joined
Nov 22, 2009
Location
Indiana, USA
Hello, I have run up against a problem I need help with.

I am a CNC mechanic, hand have a Junkers CNC cam grinder that one of the small belt drive spindles has had the sub spindle go out on. We have 6 of these grinders(really two grinder put together as one half does journals and the other does lobes)

It has a JB belt that goes to a small stub spindle and then transfers through a flex coupling to the actual grinding spindle with a 3"~ wheel running around 11k rpm.

The little stub spindle has 4 bearings that appear to be 7905 angular contact bearings but they are sealed. I am the only one here that has any spindle rebuilding experience (from a previous job) but it was very very large milling spindles under 1500 rpm with very good documentation. We have no good docs from Junkers, they don't want to give us any, and a replacement assembly is not available till 3/2023:angry:

Any way one of the other mech replace the bearings with 6905 bearings without my knowledge and it subsequently failed a few days latter without surprise. I explained that they have to be angular contacts and I made some tools and partially disassembled another machines spindle to see what it had and found 25x42x9 angular contacts. They were sealed(i have never seen any sealed angular contacts before except 1 30tac something ball screw support bearing) and I was not going to remove them from the shaft and ruin them(to look for numbers on the race) but the arrows on the side, while faint, were in a Tandem Back to Back arrangement. Even then they would have the preload and precision class marked on the race it it was even visible.

I found and had them order an NTN 7905CDLLB/GNP4 bearing, which is supposed to be sealed, and the next day the supplier had provided 7905CDUL/GNP4 bearings which are open.
https://www.ntn.co.jp/jimtof2004/eng/pdf/PrecisionBrgs-e/PrecisionBrgs-e-162.pdf

Problem is the bearing housing is not sealed and grinding oil(coolant) and swarf can get in. They had another mech put it together(with the unsealed bearings) and it lasted a shift before catastrophically failing. There may of been other factors but long term unsealed bearings won't work. Motion and Applied Tech say they can't get sealed bearings that NTN doesn't make them any more or doesn't sell them in the USA????? I may have to contact a tech rep directly.

The more I think about it, the bearings should probably be Light preload instead of Normal preload but according to the NTN link about they are good to 36000 RPM.

Does any one know of other 7905C bearings available with seals?
 

4GSR

Diamond
Joined
Jan 25, 2005
Location
Victoria, Texas, USA
Without seeing a section view of the spindle be hard to determine what to do here. If it is possible to build a dust shield on front of the bearing housing and spindle to would keep dust/grit out of the bearings? Next, rather than use grease in the bearings, is there a way to install some kind of drip oil feed to the bearings. I used to use a Bijur continuous oil feed pump to feed spindle bearings on the special machines I used to deal with. Ken
 

mottrhed

Plastic
Joined
Sep 23, 2013
Location
nh
You should be able to get those bearings-maybe a different oem- but sealed angular contacts, should be on the shelf, if your bearing vendor cant cross them, find a new vendor. I wouldnt go modifying a system that works.
 

trevj

Titanium
Joined
May 17, 2005
Location
Interior British Columbia
Any room for installing an extension to the output housing, and putting a standard style oil seal on it?
Or is space too tight?

Per mottrhed above, I'd be shaking a few more trees as far as finding someone that can find a suitable cross reference, or has them on the shelf somewhere.
 

13engines

Hot Rolled
Joined
Jun 30, 2015
Location
Saint Paul
It has always been my experience that Super Precision Sealed Angular Contact Bearings reside only in the catalogs and not on the shelf. It doesn't surprise me for a minute that the OP asked for sealed and received open type. What I figured was unless you're a big time OEM, they're only allowed in your dreams. I mean who wouldn't want pre-greased sealed bearings? You could practically rebuild your spindles on the back porch, instead of having to be all super clean about things.
 








 
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