Bad surface finish 6x12 surface grinder spindle disassembly questions

Flyinfool said:
Start by getting your very best indicator on the surfaces the wheel mounts to, to see if they are round and/or have run out.
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Flyin, The first indicator I used must be sticking, as I did this measurement today. I'm getting ~0.00025 or so runout. Not just at the taper, but at the base of the shaft about an inch from the bearing. I also pulled and pushed, and I can deflect the shaft. I looked at the ball bearing, it is not some high quality spindle bearing but a common 6206Z NTN brand. ABEC1 quality most likely.
View attachment runout check.mp4
















I'm starting to take the rear bell housing off the motor, and hope the bearings are not too much of a press fit, as I would like to pull the whole rotor out. And set this up on my surface plate. Then I can see if there is a machining solution to fix it. I have a tool post grinder. But then I will see what it takes to set this up and make it better not worse.
I also did this runout on the taper, and got the same result.
 
Before you rip it apart, are the bearings preloaded correctly?

I'd highly recommend watching this video on spindle work:


It's long, but I don't believe there anything comparable available publicly. It might give you some things to look into.
 
@Flyinfool there's a lot to unpack by your descriptions. I don't have zillions of years experience, but I was mentored by a very good grinder hand. (oh, the tales he could tell!)

There are hundreds of factors about achieving a good surface finish on even a perfect machine. anything that goes 'wrong' affects the surface finish first, then the accuracy second.

One great thing that my mentor taught me is not to discount the value of hand work. A few swipes on a throwaway offshore surface plate with 400 or 800 grit W&D emery on it and the visual blemishes will disappear.

Frankly with runout on your spindle, you are talking big $$$ to fix, or you can live with hand finishing. I know what I'd choose. I am 100% sure that you have inferior bearings in the spindle, and changing the preload won't take your runout away. A set of spindle bearings for my Brown and Sharpe is north of 1500 US$, for instance. (it specifies ABEC9 bearing on my machine - you probably have ABEC 5 or 7 bearings)
 
I remember reading somewhere that a set of new abec 5's is better than an old wore out crappy set of abec 9's.
Joe
 
-- any wore out ball bearings are not useful in the spindle of a surface grinder, no matter what they are... Mine has seen tens of thousands of hours of on time, and my bearings are still just fine.
 
I removed the motor, and then got the spindle out of the machine. There is a double row of the 6206Z bearings. So it makes sense that the sides without the shield is put face to face.
20201226_202732.jpg
I don't see any special markings to indicate these are high tolerance ABEC bearings. NTN is the name brand.


The motor rotor appears to have been balanced, dynamically.
20201226_202747.jpg


I tried to clean up the centers on each end, and not scrape in new ones, I hope. I'm seeing 3.5 to 5 tenths on the taper, and main spindle bearing location.
20201226_205033.jpg

I think I'll put the steady rest on tomorrow, where the bearing runs, and see how true the taper is, where the wheel hub mounts. If it runs true, then that would mean the ball bearings introduced this runout.
 
Dont just look at the shaft. Mount the hub that actually holds the wheel and check it for run out and also the face for run out. There is no guarantee that the hub is machined concentric or perpendicular. By rotating the hub to different positions you may be able to find a spot wher the hub error cancels out the shaft error. then you just need to permanently mark the hub and shaft for that location.
 
Lo-Fi said:
Before you rip it apart, are the bearings preloaded correctly?

I'd highly recommend watching this video on spindle work:


It's long, but I don't believe there anything comparable available publicly. It might give you some things to look into.
Click to expand...
As you can see, I did rip it apart. And I did find I had a setup error in my original test indicator measurement. I used an electronic digital dial indicator, and it did not find the runout. Should have, Mitutoyo brand.

I started watching this same video last month, he took too damn long to get anywhere, so I quit. I'll have to see if he has anything pertaining to my problem.

As for preload, my understanding is for deep groove ball bearings, the preloading is typically done in electric motors and a wavy washer is used on one shaft end, typically the one with a slip fit to the bearing outer race. Mainly to keep the bearing outer race from spinning, and to keep the rotor from oscillating back and forth during run for noise reduction. And manufacturing tolerance has to be loose for motor production, or the bearing will get an unwanted preload from assembly too tight. At least that's what I have determined.
A real bearing that can be preloaded would be an angular contact pair, and that clearly is what should have been found here. I've found that 7206 bearings will be the same dimensions, and just need to find a pair that has shields on one side, and higher tolerance.
I can spend hours seeing these on eBay and then trying to reverse the "magic coding ring" of additional letters to this base number. Every bearing manufacture does there own.

The other issue is the bearing on the far end of this motor spindle. It has runout as well, and the shaft is part of that. Since it's a press fit, I can't fix the shaft there. That ball bearing is 6303ZZ. I need to find the same OD, with a larger ID, so I can put a sleeve on the shaft and grind that true to what I will grind on the mounting hub taper.
Assuming I can do this.
 
Flyinfool said:
Dont just look at the shaft. Mount the hub that actually holds the wheel and check it for run out and also the face for run out. There is no guarantee that the hub is machined concentric or perpendicular. By rotating the hub to different positions you may be able to find a spot wher the hub error cancels out the shaft error. then you just need to permanently mark the hub and shaft for that location.
Click to expand...
That was my next thing to do. I just got 3 new hubs off ebay. And don't know if they run a "swash plate" wobble.
 
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