Diving into spindle bearing replacement

Hello - I have a JCUT Router (chinese). After less than 200 hours my 4.5kw water cooled spindle (single phase, 220v ) wore out the bearings. There are a few factors that could have contributed including the quality of the spindle itself. On several occasions the water was not running and the spindle got quite hot, the application I use the machine for is pretty arduous (material removal with a long extension) and I don't have a dust extraction system. You will see in pics. I am relatively new to machining and so I just don't know what to focus on so that I can get better tool durability in the future. finally, i was told that this spindle should have a bearing ring to reduce wear caused by electrical "surges"? does that make sense and is it is a significant consideration?
Attachment 248630 this is the spindle with extension and 1.25 inch cutter.
https://www.youtube.com/watch?v=IrScC2Y9UkU general questions about re-assembly and bearing "tightness"

Any help would make a huge difference. Thanks in advance!

danielcoyle

The bearings should not be very tight on the shaft, as you have them mounted, how tight were the original Bearings, the fitting of the new Bearing should be the same fit, are your new Bearings Sealed, if they are then they already have the correct amount of Grease, no more grease is needed, if the Bearings are open then they will need the correct measured amount of high performance Grease ( kluber 15 )

When fitting Bearings like this, you have to measure the Spindle Shaft & the ID of the Bearing, & make sure they are the correct size before you press or slide them on, if they are to tight a fit on the Spindle Shaft, then they will not last very long

danielcoyle i was told that this spindle should have a bearing ring to reduce wear caused by electrical "surges"? does that make sense and is it is a significant consideration?

It has nothing to do with electrical surges, & it is a Grounding Ring for the Rotor, do a search about the use of VFD's & Rotor Grounding

mactec!! you are everywhere! thanks. the new bearings are the exact same type/id as the old ones. they are sealed bearings. they were installed/pressed on in the same orientation as the old ones. the old ones (before i pulled them off) spun on the shaft a little easier than the newly pressed on ones do. everything else seems/looks the same.

i guess i am wondering about the grounding ring because i have never heard of this before and, in addition to my wonderings about overheating the bearings by not having the water running and overworking the bearings because of the way i was using the machine this grounding ring thing is just another variable in the mystery of "how did i wear these out so quick". i guess i am really just overwhelmed at trying to figure out the best way to prevent this from happening again. why don't spindles just come with grounding rings on them (do other spindles, 3 phase for example, not need this)? if i had used the machine regularly at all the company would have been on the hook for a warranty situation, assuming it was the grounding ring that would have saved them? is there a way, from inspecting the worn bearings, to determine if the damage was mostly a result of improper mechanical loading, heat or lack of grounding ring?

danielcoyle

The Bearing ID can change depending on the tolerance the manufacture uses, if they were tighter than the one's that came off, then they had a different size ID than the old Bearings, it only take a very small number (microns) to be either to tight or to loose, that is why they have to be fitted/measured to the shaft the are going on, if they are to tight, they will over heat

The Grounding ring just Grounds the Rotor voltage, without it, this voltage goes through the Bearings to Ground, & eats away the Bearing surface, ( electrical discharge ) this happens in all VFD driven AC Motors

The running without water will also cause your Bearing to over heat, & the lube/Grease would run out, they will ware out quickly without lube, at the high RPM's they are running

It is easy to take apart the AC Bearings, to inspect the bearing races, you can rotate the center of the Bearing, outward, so you clamp the outside of the Bearing,(in a vice ) with a Steel Pipe or Bar a close fit on the inside of the Bearing, use the Pipe/Bar to lever the center of the Bearing out with a twisting action

Yes quality VFD driven AC Motors/Spindles have the Rotor Grounding Built in

The use of your long cutting Tools would not of been any part of early Bearing Failure, over heating would of been #1 then the Rotor Grounding as #2

OK. So, here are a couple videos of how the new bearings behave after being put on the spindle shaft and then after being tapped into the spindle body. In both cases they are tighter than the un altered spindle. What, if anything, should one do?
https://www.youtube.com/watch?v=QBwo8B1-as4&feature=youtu.be