Does anyone know what angular contact bearings are needed for the LMS3900 Hi-Torque mill? I have upgraded to higher spindle speed and am considering a bearing upgrade.
I have not seen a problem with the current bearings but am doing a CNC conversion and thought I may as well upgrade the spindle bearings.
IIRC the top is 30x62x16 (7206) and the bottom is 35x62x14 (7007)
I also bought some oil seals but had to make an adapter for the bottom.
I did some polishing on the spindle (borrowed a friend's lathe) such that the upper bearing was barely a slip fit.
I packed them with grease and may or may not have ruined the races when I installed them.
They run HOT. like 'can't touch the spindle for more than a second' hot...I've tried light/no preload and heavy preload. I will soon remove the grease and try oil/inspect for wear. I think the grease may be too viscous and causing viscous heating and or skidding, or maybe they just have a lot of friction in them.
DISCLAIMER: there isn't room to fit a traditional back to back AC arrangement like a true spindle warrants. However, I believe that with a little tinkering, I can make a cool running, reliable spindle with these. I also realize I won't get anywhere near a proper bearing arrangement's life.
I took the seals off last night and flushed the grease out as best I could (you knock the bearings out of their races if you pull it apart, so the spindle stayed in...) and squirted some oil in. I then ran the spindle with no seals and a decent amount of preload and lo and behold - almost no heat!
it looks like the lip seals were just too tight on the shaft and were generating the huge amount of heat. Surprisingly, they still looked good too.
I'm going to eventually pull out the spindle and turn down the sealing surfaces slightly and put new bearings in. for now i'll probably just rig up a shield and a drip oiler for the top bearing... but I say Great Success!
i'm running only a bottom lip seal, I figure the top is well sealed enough from chips by the motor mount, that i'd let it breathe... This was driven by the fact that if I wanted to add a drip oiler, it would have to be above the top bearing, which left no room for a seal, without making an adapter/spacer.
BUUUT, the mill runs cool, cuts beautifully (COLUMN BRACE FTW!) and is quiet. and that's after I've abused the bearings somewhat. for ~35$, this is a quick, easy win. I'll post some pics in my build thread that I haven't started yet...lol.
LMS3900 Hi-Torque Spindle Bearings
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