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Centec 2A Rebuild

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mm289:
Wow, having read Pekka's thread and links I now know more about bearings than I ever wanted too  :doh:

Just out of interest, if you want to check the tolerances on Timken bearings you can use this page on the website http://www.timken.com/engineering-tools/bearing-tolerances/

You can out in your bearing reference and then select the bearing class and it will give you the tolerances  :beer:

Paul.

PekkaNF:
Felt pretty much the same....bearings are one thing - fit is another and measuring the shaft and bearing cavity reliably is pretty damn near imposiblle in typical home work shop. Best tu use a gauge - oversize or undersize bearing ring next best thing....most of the bearing shims and such are way to coarse to spindle - maybe fine for a gearbox.

Pekka

Pete.:

--- Quote from: mm289 on December 27, 2017, 05:03:49 PM ---Interesting input thanks guys. I will reassemble and run a set of tests with both bearings dry, then loosely packed with grease and take some new measurements. couple of thoughts/questions:

1. On the preload the reason I felt it was pretty high was because of the drag it was putting on the spindle rotation, it wasn't running freely and felt like it had a fair bit of resistance. Now I am more used to bearings in automotive applications where overtightening is a recipe for disaster so maybe I am being too cautious?

2.  The run out with no load I can live with at 1 thou. What concerned me is the deflection under load. To test this I was just gently pushing/pulling against the side of the chuck with a dial indicator on it and this is where I was getting the 7 thou. Is this a reasonable test?

3. Likewise the end play is the way I test end play on cranks in engines, set up a Dial Indicator then push/pull the shaft and read max deflection - in this case 10 thou. Again is this a reasonable test?

The cups look "ok" but not spectacular but the inner races feel very sloppy to me. The other thing I noticed which I have tried to show in the assembled pics below is that the inner race is not concentric with the outer. If you look at pic 1 you can see that the gap between the inner sleeve and  and the cage is less at 6 o'clock than 12 o'clock. In pic 2 I have rotated the cage and now the gap is less at 12 o'clock than 6. I may be missing something but doesn't that mean the bearings will run eccentric or do they only centre under load?

SLow progress so I have started swopping out the single phase motor for a 3 phase and VFD  :D
More on that later.

Cheers,

Paul.

--- End quote ---

1. Not sure
2. It's a reasonable test but the results are far from reasonable. I would expect it to be less by a factor of between 5 and 10.
3. The gap to the cage is unimportant. All it does is space out the rollers.

hermetic:
Just a little aside, the surface you are checking spindle runout on is not necessarily "exactly" concentric to the spindle, You really need to check the runout on the taper (Centec are int30?) Check the taper for chips, bumps and dings, carefully ream if neccasary, then fit an adapter or even better a test bar, lock it in with the drawbar, and check the runout on that.. This observation stems from realigning (or trying to) an Indian motorcycle crankshaft with the DTI fitted with an elephants foot and running on the outside rim of the flywheels. After about an hour of getting nowhere we swapped the DTI onto the shafts of the flywheel, and got instant results! Provided the oil level has been kept topped up, it is unlikely there is any problem with the main bearings unless this machine has had an exceptionally hard life.

timby:
1.    I would try to pre-load a bit more just to see if you can eliminate the deflection.

2.   I would expect to see almost no radial  deflection.

3.   I would expect no axial deflection, your 10 thou axial movement would cause chatter when cutting with a helical cutter.

The roller cage is only a spacer, check to ensure  it is not rubbing after assembly, you can true it up a bit in situ with a screwdriver or something else as a lever.   

One inspector that I met used to check the pre-load by trying to move the rollers  with a small screwdriver or a scriber,  he expected only a slight sideways movement.

Check spindle runout as advised in post 13  above inside the tapered bore.

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