Taper bearing fit

[John Rudd]

Guys,

On my minimill, I replaced the standard bearings taper rollers some years ago....

Recently things havent been so good with the machine so I decided to strip it... 

I find the bottom bearing has parted..That is the inner race has come away from the cage and rollers...

I have two questions for the collective..

1)...Does the above mean that the bearing is broke and I should fit a new one or clean/grease/reassemble/refit the bearing? ( the top brg is fine, the one that is at the motor end...)

2).. The outer race is housed in the mill body, does this mean that the inner races should be a tight sliding fit on the spindle to enable the bearing preload to be set? 

I'm guessing at no.2 that if the brgs were tight on the spindle then I wouldnt be able to adjust them for correct preload and this has maybe led to the (early demise ? ) bearing coming apart?

As always your help appreciated....

( now be quick to answer me wont you... )

[John Swift]

Hi John
 
having decided to takeup this hobby at the start of the year
I am rebuilding a CL300M minilathe
taking notice of various forums I have replaced the ball races with taper bearings
the bearings where in three loose  parts  - inner , outer and the cage
the outer is a tight fit in the headstock ,  the inner is a press fit on the spindle , but will move when the nuts on the spindle is adjusted to pre-load them



           hope it helps


   John

[John Rudd]

 while the inner is a press fit but will move when the nuts on the spindle is adjusted to pre-load them

John

John,

Thanks for the reply, yup your comment above confirms my thoughts that the inner races should slide on the shaft to allow preload adjustment...

The orig brgs were ball raced brgs which were a tight fit on the shaft, moving to TR's I would have expected the races to be adjustable relative to one another but didnt realise it at the time I installed them....

I guess I need to 'adjust'the spindle to accomodate the taper bearings..

[John Swift]

Hi John

I gave the spindle a quick polish with some 1200 grade emery just to ease the fit ( just taking a bugs whats it off )

packed the bearings with the same grease you use on a cars cv joints

 not knowing just how you should  adjusted the pre load
 
tightend the nuts a bit at a time , until the spindle stopped after about revolution
when you spun the spindle by hand

run the spindle for an hour at 1000 rpm , or so checking it was only warm

re checked the preload and retested it ,while slowly increasing the speed to 3000rpm


 so far so good

   John

[Brass_Machine]

Good questions John.

I don't have the answer, but I want to hear it. I have tapered bearings for my mill and lathe. Just haven't gotten to it yet.

Eric

[John Rudd]

Now I have it all stripped, everything looks fine.....Except the bottom bearing isnt seating fully.

I think this is where my problem stems from.

I did a bit of research and found the following text over on one of the files at the 9*20 lathe group...Ok the text refers to the lathe spindle but applies equally to the mill setup..I hope it is of use..


Quote..
Dependant upon the difficulty in removing the Inner Races and bearings it is essential to
make sure the new bearings are a hand press fit on the spindle bearing journals.

The fit of the bearings on the spindle bearing journal is CRITICAL! A tight fit is acceptable,
but a too loose fit or non-concentric spindle is a rejected lathe! Because these lathes are not
made to high quality tolerances, the bearings are intentionally made too tight on the Spindle
shaft journals. This prevents you from adjusting the Pre-Load. Before replacing the bearings,
you should make sure that you can slide the left side inner bearing race (closest to the pulley)
over it’s journal with medium to firm hand pressure.

The right bearing inner race may be a bit firm as once it is in place it doesn't move in relation to
the spindle. Only the left side moves when adjusting the preload. But the left end needs to
move when *cold* with a gentle tap of the mallet in order to make adjustments.

When sizing the spindle journals, how tight is too tight? Well, if you can't move the inner race
on the spindle with a gentle tap from a nylon mallet, then how do you think you are going to
adjust the preload? That inner race needs to move along the shaft. When setting the preload,
you may find you are only turning the spindle nut 1 or 2 degrees to get the proper tension.
How loose is too loose? The races should not slip easily. They should be a firm interference fit
so there is no play when things warm up. The fitting must be approached very cautiously. If
you go too far you will have to take the spindle to another lathe and knurl the spindle journals
or replace the spindle.
When everything is assembled, be sure to do a run-in at low speed for 30 minutes to an hour.
Check the spindle and head stock every five minutes during this run-in period to make sure it is
not too hot. If you detect heat, stop the lathe and back off the preload. If things are just warm
after an hour, increase the speed for 5 minutes and check again.
After using the lathe for a few hours, the preload may need additional tightening as the bearings
seat. The temperature should never get warmer than a warm cup of coffee.
Unquote.

[John Swift]

Hi John

thanks for that
that confirms my instinct was right
but its nice to know just how it should be done

    John

[kwackers]

Just to add something to the mix - on the off chance someone is staring at their bearings and wondering why this thread isn't making much sense...

I replaced the tapered bearings in my mill when I first got it, mainly because it's previous owner had taken to cleaning the quill with an airline which looked to have forced shrapnel into the bearings.

The bearings come in three's, two at the bottom and one at the top. The top bearing is just a radial load bearing and can be replaced for a few quid from almost anywhere, the bottom are a matched pair of precision taper bearings with a list price of £400! (I'd expected to pay £50, saw the actual price and thus was made up how cheap they were when I finally got a pair for £130...)

Anyway, basically these two bearings fit back to back and are made such that when they're tightened up and the gap between the inner races taken up the pre-load is automatically set.
Another thing is try to use a press to fit bearings, hitting them with a hammer and drift isn't a good idea, it damages the balls and the seating reducing the life of them.
(Since discovering all this I've stopped knocking seven bells out of my drawbars to loosen them too!)

I doubt any of this is relevant to the OP, but thought it might be worth a mention.

[John Rudd]

Just to add something to the mix -

(Since discovering all this I've stopped knocking seven bells out of my drawbars to loosen them too!)

I doubt any of this is relevant to the OP, but thought it might be worth a mention.

My spindle has been cleaned up and the bearings are a nice tight sliding fit...

Outer races have been pressed into the housing and it is now ready to accept the spindle/bearing assembly after greasing...

Kwackers,
If you dont knock 7 bells of unowot out of your draw bar, how do you remove it?

I suspect that repeated striking of the db on my mill has probably contributed to the bearing issue? (guilty as charged M'lud.. )

[kwackers]

If you dont knock 7 bells of unowot out of your draw bar, how do you remove it?

I've made a U shaped tool where the thickness of the two prongs is tapered, placing that between the quill and the tool means a gentle tap replaces a hefty whack on the top of the drawbar!

Of course this is all IMO, there may be a good reason why hitting the drawbar isn't the same as drifting the bearings into place (e.g once 'fitted' they may better withstand a few knocks. But I'm guessing anything that means you don't have to hit something is good (?))
The tool needs to be a nice fit though otherwise it'll just damage the edges of the spindle and/or tooling.

[John Rudd]

The tapered tool sounds a good idea and will working with my Clarkson style cutter holder but not with my drill chuck... 

The mill cutter holder is one piece whereas the chuck is chuck + arbor....Hmmmmm thinking time needed...

[kwackers]

Yeah, I can see the drill chuck may be a problem...

I've moved away from drill chucks and Clarkson holders, I just use one of two ER collets, either an ER25 for general use or an ER40 for the big cutters.