Push fit

This topic has 26 replies, 11 voices, and was last updated 29 May 2017 at 17:50 by Michael Gilligan.

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27 May 2017 at 18:52 #299856
Iain Downs
Participant
@iaindowns78295
I'm in the process of replacing the spindle on my Real Bull CJ18 – which is pretty much like all the 7×14 chinese lathes out there.

At the same time, I'm replacing the bearings with angular bearings.

So I've got the lathe in bits and finally got round to reading various instructions in detail. They say that the bearings should be a push fit on the spindle.

Well, the reason I had trouble with the lathe (and spindle and so on) is that the bearings are damned tight on the spindle and I ended up using a persuader with significant force which has probably done the spindle and bearings no good at all (I know it's damaged the taper at least a bit).

The new bearings do not just push on the spindle. I have not attempted to use more force than my fingers allow.

My calipers indicate the spindle is spot on 30mm and the angular bearings the same or possibly a thou (.03mm) less. I don't terribly trust the calipers to read the same internal and external.

The excellent guides by ARC and Neil say to polish the new spindle until the bearings are a push fit. I've taken the lathe apart. (Yes. Stupid. RTFM). And I only have one (lathe – I have two bearings).

With the original spindle and bearings I had to really crank on the effort with the C spanner to get them loaded – and I got creaking, cracking noises which sounded like it was just too tight.

So, How would I tell the bearings are a push fit? If my press pushes them on fairly easily? Should I be able to push them on with just finger pressure?

Or do I have to re-assemble the lathe and apply some fine sandpaper? And still, how do I tell they are push fit?

Many thanks

Iain
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27 May 2017 at 18:52 #8734
Iain Downs
Participant
@iaindowns78295
polishing my spindle for angular bearings
27 May 2017 at 19:38 #299859
Neil Wyatt
Moderator
@neilwyatt
The bearings are only a push fit (and quite a stiff one) on the threaded end of the spindle, once you get near the flange they become a force fit and you can use a puller or similar. I' can't see where you got 'polish' from – I can't see it in my article, X233 angular contact article, book or the Arc guide?

The front bearing will need 'persuasion':

"I followed the advice on the Arc website and drove the new inner race into place using a tubular drift – a section of 30mm light alloy scaffold pole, probably the ideal material for the job. Whatever you use, make sure that it fits the inner race without overlapping the caged rollers. It is also important to protect the face of the mandrel by resting it on a block of softwood."

The rear bearing should be a light press fit:

"Now load the rear bearing with grease and slip it onto the lightly oiled mandrel. You can now use the long spacer and one of the locknuts to draw it into place until there is no play, locking the mandrel with a bar in a chuck as before."

It's very important top make sure the spindle is clean, but it should not need to have its size changed as the original bearing fitted! You can oil or grease it to help the bearing races on. Keep the bearing square to the spindle, if it cocks over it will tend to jam. If there are any high spots caused by local bruising of the spindle, you can stone them off.

Slow steady force is best, mocking up pullers with angle iron and M10 studding is a good idea they don't need to be pretty.

Take great care that when fitting the outer races to the headstock that they are perfectly square, you really don't want to crack the casting.
27 May 2017 at 19:54 #299861
Michael Gilligan
Participant
@michaelgilligan61133
This will probably raise a few jeers … but I don't really care

A while back, I had a similar problem with the bearings on a Record wood-lathe.

Sitting outside in the sunshine, I laid the spindle on my knees and visually identified a number of 'lumps' in its ground surface [these had taken a polish when the bearing was fitted and removed].

So … I took a well-used Eze-Lap diamond hone, and eased those high spots.

It required patience, good lighting, and lots of trial-fits … but it worked beautifully.

Dare you try the same, Iain ?

MichaelG.
27 May 2017 at 21:51 #299875
John Reese
Participant
@johnreese12848
Bearing fits are critical for their proper operation. Too loose and the shaft will walk inside the bearing, wearing both the shaft and the ID of the bearing. Too tight and you reduce the internal clearance in the bearing, causing premature wear. SKF and other bearing manufacturers publish recommend shaft and housing fits for various classes of service.

Please go their online literature to find the correct fit information.
27 May 2017 at 22:25 #299880
steamdave
Participant
@steamdave
How about some warmth? Not heat.

I remember the leccies used to rest replacement motor bearings on a 40 watt lamp for about 10 minutes. This enlarged the diameter sufficiently for an easy (easier?) push fit of the bearing on the motor spindle.

These days, finding an incandescent lamp would be the hardest part, but you get the idea of the rise in temperature required for the job.

Dave
The Emerald Isle
27 May 2017 at 22:46 #299881
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Neil Wyatt on 27/05/2017 19:38:10:

It's very important top make sure the spindle is clean, but it should not need to have its size changed as the original bearing fitted!

.

I must just mention, Neil, that the bearings on my Record wood lathe must have only fitted because they had a big press or a big 'ammer. … According to the instructions, the spindle should have gently tapped out, leaving both bearings in situ in the headstock; but during removal the front bearing stayed on the spindle.

MichaelG.
27 May 2017 at 23:17 #299885
Neil Lickfold
Participant
@neillickfold44316
Bearings should always be pushed or pressed into place. Care should be taken that they are not hammered at all.

With a spindle, as it has a hole through it, threaded rod and various spacers and washers can be used to pull a bearing onto the shaft or into the housing.

Neil
27 May 2017 at 23:37 #299887
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Neil Lickfold on 27/05/2017 23:17:24:

Bearings should always be pushed or pressed into place. Care should be taken that they are not hammered at all.

With a spindle, as it has a hole through it, threaded rod and various spacers and washers can be used to pull a bearing onto the shaft or into the housing.

Neil

.

Wise observations, Neil … except that the Record DML wood lathe spindle is NOT bored through.

Here is a post [with pictures] by another user who encountered a similar problem.

http://www.ultimatehandyman.co.uk/forum1/record-dml-24-lathe-t80452.html

It was a cheap & cheeful little lathe.

[my spindle wasn't rusty, it was just badly toleranced]

MichaelG.

Edited By Michael Gilligan on 27/05/2017 23:46:20
28 May 2017 at 02:04 #299891
Iain Downs
Participant
@iaindowns78295
I guess I'm less concerned with getting the bearings in place than the process of 'pre-loading'. If the fit is too tight it will be hard (maybe?) to put the right load on or take it off. That's when I wonder if I should be concerned about the fit.

Neil (W) – the source of my informations is step 54 of **LINK**

Michael G. I don't have any concern about the smoothness of the new spindle, just the fit. However, I did manage to er, squash, the ends of my mill leadscrews by overenthusastic more wrenching when trying to to remove something at the far. End. The fix was a combination of a bit of scraping and quite a lot of filing with a fine diamond abrasives. Given I got myself in the mess in the first place it's nothing to boast about, but I do get your point.

Iain
28 May 2017 at 07:07 #299897
Neil Lickfold
Participant
@neillickfold44316
I have one of those wood lathes. Mine has circlips on each side of the bearings and the tunnel is through bored. Using castor oil on the shaft and on the inner face of the bearing itself allows them to assemble easier. When measuring the shaft, it wants to be about 0.005mm smaller than the nominal bearing diameter and it will be a push slide fit. The extra 0.005mm in diameter makes it a press fit. If the housing is heated to about 50 to 60 C, it makes it significantly easier to assemble the bearings into it as well. Making spacers to take up the inner gap and effectively preload it makes a difference as well. With mine I had a wood dowel keeping everything aligned sort of. Mine did not have a key on the shaft for the pulley, but had 2 grub screws instead.

Neil
28 May 2017 at 07:43 #299902
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Neil Lickfold on 28/05/2017 07:07:39:

I have one of those wood lathes. Mine has circlips on each side of the bearings and the tunnel is through bored.

.

With respect, Neil … That statement ^^^ is contradictory.

My wood lathe had no circlips, and the problem lay with the quality of the grinding on the spindle.

MichaelG.
28 May 2017 at 09:52 #299917
Clive Hartland
Participant
@clivehartland94829
As a young man I had to replace the crankshaft bearings on my Ariel NH 350. I warmed the Alu. crankcase on a stove and put the bearings out on the snow and it all, 'Fell' together.

New cylinder and piston and a new carburetter and it was a new bike. Unfortunately I was not to have it for long as I got posted abroad.

Clive
28 May 2017 at 10:39 #299921
Iain Downs
Participant
@iaindowns78295
I've pushed the old front bearing off the spindle this morning (or the spindle off the bearing). When I did so it did not come of smoothly but in a series of jerks. For the main part the press screw would rotate half to one turn, there would be a click and the spindle / bearing would move. So as far as I can see the stress builds up to a point and then the bearing shifts a lot 1 – 2 mm, perhaps.

This is fine if the bearing is to be pushed into position and just stay there (or at least I think so). However, if it needs a careful tension to be applied as a pre-load I can't see how that would work. The inner surface of the bearing needs to be able to move smoothly for this to make sense. If I press enough for it to slip half to one mm then that's not really a controlled preload?

This is what the old spindle looks like now

You can see the marks as it;s jerked through the next mm or so.

Incidentally, getting the front bearing off the back part was just as hard as getting it off the front part, though the middle section was relatively smooth.

Of course this may not apply to the new spindle and bearings, but I hope you see my concerned. I'm not bothered about getting the headstock, bearing and spindle back together. I am bothered about being able to apply an 'analogue' pre-load.

Iain
28 May 2017 at 11:10 #299926
Neil Lickfold
Participant
@neillickfold44316
Iain, you can rub it down with 320 to 400 wet dry paper to take the high spots off. It will not take that much to make it a little looser. With angular contact bearings , either the inner does the movement for taking up the clearance or the outer does. Normal is to have the outer contained and the inner is adjusted together.

Neil
28 May 2017 at 11:13 #299927
Neil Lickfold
Participant
@neillickfold44316
Here are a couple of links that you will find helpful,

http://www.arceurotrade.co.uk/machineguides/Mini-Lathe-Angular-Contact-Bearing-Change-Guide.pdf

http://www.hobby-machinist.com/threads/7x-spindle-and-spindle-bearing-upgrade.32865/

Neil
28 May 2017 at 11:42 #299937
Neil Wyatt
Moderator
@neilwyatt
Posted by Iain Downs on 28/05/2017 10:39:13:

This is fine if the bearing is to be pushed into position and just stay there (or at least I think so). However, if it needs a careful tension to be applied as a pre-load I can't see how that would work. The inner surface of the bearing needs to be able to move smoothly for this to make sense. If I press enough for it to slip half to one mm then that's not really a controlled preload?

The front bearing just sits in position, it's the back bearing thet moves as you adjust the preload.

The two spindles I have done (mini lathe and X2) the rear bearing was easily moved by the locking rings while the front one took a puller to get it in place.

Neil
29 May 2017 at 08:14 #300074
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Neil Wyatt on 28/05/2017 11:42:02:

[…] The two spindles I have done (mini lathe and X2) the rear bearing was easily moved by the locking rings while the front one took a puller to get it in place.

.

Neil,

I think that takes us back to where we came-in …

You have described an appropriate fit of each inner race on the spindle but:
- Ian's spindle is not ground to that toleramce, and
- he doesn't currently have a lathe on which to polish/lap it.
It is, however [as I described in post #3] possible to improve the fit by careful hand-work.

… An alternative approach would be to make a lap by cutting vee notches in two strips off wood; but we would then lose the abilty to observe progress.

MichaelG.
29 May 2017 at 08:34 #300077
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Iain Downs on 28/05/2017 10:39:13:

.

This is what the old spindle looks like now

You can see the marks as it;s jerked through the next mm or so.

.

Those marks are very similar to what I found on my wood lathe … and they should be your guide.

Just like a scraping job … you need to progressively remove the high spots, until the fit is as-you-require.

The new bearings will [hopefully!!] be much better finished than the spindle and you just need to work patiently … press the inner race on to the shaft until the point where it feels just too tight; then remove it and dress-out the witness marks on the spindle surface … repeat until you're happy with the fit [or ad nauseam].

MichaelG.

.

Edit: My tool of choice is

http://eze-lap.com/woodworking_shop_machine_use/hone-stone/

Edited By Michael Gilligan on 29/05/2017 08:55:40
29 May 2017 at 09:25 #300096
Hopper
Participant
@hopper
It seems a lot of these Far Eastern lathes have the bearings a very tight fit on the spindles. I have to wonder if perhaps the esteemed gentlemen of the Orient are using the tight fit to expand the inner race a thou or close to it in order to close up the internal clearance in a cheap, standard clearance bearing? This would give a low-clearance bearing that would aid smoother machining due to less spindle shake under cutting load. And it would be cheaper than using precision or low-clearance bearings.

Just a thought.

But if you do want to reduce the spindle diameter by half a thou or so without using a lathe, the traditional method is to use a long strip of emery tape looped around the shaft in a U shape, one end held in each hand and worked back and forth in long strokes. Rotate the job in the vice, or move your stance arond the vice, to ensure material is taken off the shaft evenly around the whole diameter.
29 May 2017 at 09:55 #300099
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Hopper on 29/05/2017 09:25:13:

… But if you do want to reduce the spindle diameter by half a thou or so without using a lathe, the traditional method is to use a long strip of emery tape looped around the shaft in a U shape, one end held in each hand and worked back and forth in long strokes. Rotate the job in the vice, or move your stance arond the vice, to ensure material is taken off the shaft evenly around the whole diameter.

.

I accept that, Hopper … I simply offered an alternative method which [for me] works better for this particular scenario [i.e. the spindle is poorly finished, rather than 'perfect but oversize']. A loop of tape will tend to follow the countour of the original defects, but the Eze-Lap is reasonably flat and rigid; which allows us to concentrate on the high spots.

MichaelG.
29 May 2017 at 10:33 #300108
Gordon W
Participant
@gordonw
There are tolerances on shaft and bearing, most factories seem to work to the maximum metal side of the tolerance. Get the new bearings and see what fit they are, if a bit tight rub the shaft down. I use emery tape on a file or strip of wood.
29 May 2017 at 10:55 #300113
Nicholas Farr
Participant
@nicholasfarr14254
Hi Iain, from the marks it looks a good fit to me, I would not worry about it moving in jerks as it is quite common in a lot of industrial stuff that I've maintained in my day job. As has been pointed out, the bearing at the chuck end should be pushed up against the shoulder and this one will not move during the preloading. If you are bothered about the back one being a bit tight, then give it a little rub down with emery cloth, but don't make it a shaky fit. The worst thing that you could have is an out of round, i.e. a significant oval-ness of the spindle, but that doesn't look the case on yours, as the evenness of the marks looks OK as long as they continue the same all the way round. When fitting the new bearings, smear the spindle with a light oil and also the inside journals of the bearings. The one at the chuck end should be pressed on with a press ideally, but I never press such things on in one hit, that is, I press it so far and then let of the pressure and then slightly rotate the spindle, say 1/8-1/4 of a turn and then continue pressing. I would do this maybe three or four times rotating the spindle in the same direction as this will even out any out of square-ness there may be in the pressing components.

Regards Nick.
29 May 2017 at 13:02 #300127
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Nicholas Farr on 29/05/2017 10:55:25:

… the evenness of the marks looks OK as long as they continue the same all the way round.

.

It's strange how we each interpret images differently.

What I noticed was the rippling in the circumference of what should be a circle … which are highlighted [as the witness marks that I mentioned] by local contact with the more accurately ground inner surface of the bearing race.

… Not arguing, just commenting.

MichaelG.
29 May 2017 at 13:09 #300129
Ian S C
Participant
@iansc
My old book of rough engineering suggests that for a push fit the clearance should range from .0002" to .0005", per inch diameter.

Ian S C
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