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Lathe rigidity

And collet wobble

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JasonB10/09/2019 15:54:23
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This one has taper roller bearings " I replaced it a while back with Tapered roller bearings "

old mart10/09/2019 16:18:30
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Jason B, the bearing inner of the top bearing on that type of mill certainly has to move to take up the slack, exactly the same as the lathe in the thread. Changing to taper rollers from sealed ball races is a good idea, but sealing the taper rollers is slightly more of a problem.

When I changed the spindle size on the Tom Senor mill, I designed in a double lip oil seal for the bottom taper roller, not to keep the grease in primarily, but to keep the swarf out. I didn't fit the garter spring.

JasonB10/09/2019 16:34:37
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Posted by old mart on 10/09/2019 16:18:30:

Jason B, the bearing inner of the top bearing on that type of mill certainly has to move to take up the slack, exactly the same as the lathe in the thread.

And exactly why you can't bond it solid with bearing fit.

Neil Wyatt10/09/2019 16:37:51
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Posted by Michael Gilligan on 10/09/2019 13:51:29:
Posted by JasonB on 10/09/2019 13:13:37:

.

The need is for a close fitting bearing inner ring that can still move under the load applied by the adjusting nut/nuts. You can't do that with the ring bonded to the spindle.

.

Exactly that ^^^

MichaelG.

As they say! ^^^^^

Neil Wyatt10/09/2019 16:42:22
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Posted by not done it yet on 10/09/2019 14:46:49:
Posted by Michael Gilligan on 10/09/2019 13:57:51:

Infinitesimal, perhaps ... but definitely real : Any change of preload requires movement.

MichaelG.

Not true. If a force is applied, an acceleration should occur (Newton’s Second Law of Linear Motion) - unless that force is nullified by an equal force in the opposite direction. That is all that occurs when a preload is changed. No force, no preload.

Every preload force is opposed by an equal and opposite force - unless something breaks (and preload will reduce to zero). Bearings don’t move, only the force applied changes. You can’t actually have zero preload as the bearing races could be together or miles apart! If anything moves, it will be the housing, not the bearing, per se.

Bearings are not inelastic, correct preload implies a small amount of elastic deformation shared out between bearing, spindle and housing acording to their materials and design. This can only be achieved by the relative movement of inner and outer races.

Some high speed spindles are designed with the bearing a close sliding fit and a spring to apply prelaod.

Neil

old mart10/09/2019 23:14:33
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My advice to anyone thinking about replacing their lathe spindle bearings is to buy the new bearings, and make the tooling to reassemble the bearings without stressing them before taking the thing to bits. Aluminium rings which are a loose fit in in the bores and on the shafts, which press on both inner and outer races at the same time, and tubes if necessary to push with.

Howard Lewis13/09/2019 23:35:02
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When the time comes to fit the bearings, ensure that the tubular "dolly" only touches the part to be fitted (ie the inner, to press onto a shaft; or the outer to press into a housing ) Doing it so that both races are loaded , or the wrong one, risks damage to the bearing. Which rather defeats the purpose of changing the bearings!

Howard

old mart14/09/2019 21:04:07
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If you are fitting bearings where the inner and outer races are in line, then using a tool which presses on both at once cannot cause any harm. Taper rollers do not line up when they are assembled, but because they come apart, it is normal to deal with each part separately.

Iain Downs15/09/2019 16:48:09
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Well, I finally had a chance to get back to the spindle things today and have good news and bad news.

The good news is that the polishing has worked nicely. I can press the old bearing in with relatively little effort and there are no 'twangs' as it is pressed. Hoorah!

Next, following the advice in this forum I pressed the front bearing home. This was silly and I should have applied brains.

spindle pressed front bearing (wrong).jpg

I can see that the 'correct way would be to press in the front bearing (like this), then pull in the spindle (with the force on the inner race.

However, once the front bearing is in place there is no way to assemble the gears on the spindle.

spindle assembly.jpg

The only way you can actually assemble the whole thing is to press the front bearing on the spindle and the put on the keyway inner spacer and gears and press the spindle in place. this means that the pressure is on the inner race with the press going in on the outer race.

So now I need to unpress the front bearing. To do that I need to make a spacer (approx 56mm diameter so that I don't damage it on the way out. If only I had a working lathe!

I think I can make a suitable spacer on the mill and cut it off on the bandsaw. But I don't have the heart to start it today!

Old Mart - your advice is well taken, but you have to know what you are doing to know what tools to make!

Iain

old mart15/09/2019 19:04:00
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Bad luck, Ian, try to remove that bearing without damaging it, or you will be buying yet another. I made a similar type of mistake yesterday, I pressed two parts together and left out one procedure which would have been much easier to have done before they were assembled. Instead of taking a minute to do, it will take me 1/2 hour just to set up.

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