Lump in Lathe MT3 Spindle

<Light bulb moment>

If you hammered the end of the spindle to get the bearings either out of the headstock or off the spindle, they are probably damaged by hammering the ball bearings into the ball races.

This could well be the cause of your problems.

Neil

Light bulb? Hopper spelt it out last night?

I missed that one

Neil

Easily missed when you are looking to at all posts across the whole board.

I thought, early on, thaf this was likely a scrap spindle, but it is difficult to post that on 'gut feeling' alone. Hopper got there before me on the bearing scrappage issue. Hopper has my high regard on practicality. There are engineering ways of doing things, mostly which don't include the use of extreme hammer force.

Controlled force is the way to go. With bearings it is force applied to the appropriate race, taking care not to transmit force through single contact points (of balls for instance),. Differential expansion is another means to an end, but needs some degree of speed. This thread is surely one of how not to attempt a repair. Sorry, but it needed saying.

This has thread has turned into a nightmare and my sympathies are with Iain.!

When I needed to replace the gears on my mini-lathe the advice was to tap the spindle out with a large raw-hide mallet. (Judging by the picture the mallet head was 6" diameter and about 10" long.)

Not having such a thing I used a lump-hammer and a block of wood. The bearing was tighter than I expected and needed more force to shift than I was comfortable with, both coming out and going back.

I'm pleased to report that I got my lathe back together without doing any damage, but that was more luck than judgement. It seems that Iain's spindle was even tighter than mine.

Noting that Iain unsuccessfully tried to shift the spindle with a home-made puller what's the best way of dealing of with this kind of 'jammed solid' problem?

Thanks,

Dave

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Reading back over the recent posts ... I think Hopper beat me to this thought too.

MichaelG.

For the record, here are some pics from when I changed my bearings that may help those who come after.

I used some of these tools when I changed my X2 to angular contact bearings as well. For the record although I did use bit of rubber mallet & wood to get one bearing free, it was very light taps and I think all four of the removed bearings are still in good nick.

Honest.

Neil

The puller in your last picture but one is what I made. I rather think that was advice you gave at the time (the same picture included). My angle iron was a little thicker than in your picture and it deformed in a big way without the spindle moving a micron. As well as bowing, I couldn't get any more force on the spanner. More gym, perhaps.

As SillyOldDuffer says, the manufacturer's advice is to bash it with a hammer. I too ended up with a lump hammer and some serious blows to get it moving.

So. I wouldn't do that again.

The spindle has pretty certainly had some compression artefacts. most of the bluing was round the throat at first, particularly right at the edge. once I'd scraped for a bit I quite quickly got coverage half plus the way down the taper.

What I see now on the blued taper is a set of small cleared blue areas mainly in a line pretty close to the axis which is the high point of the run out and a few more high spots here and there near the bottom. I can't really see the blue on the spindle though.

So I think there is evidence that The throat collapsed on the re-assembly bashes and possibly an off-centre hit pushed a ripple down one side.

One of the things I tried briefly was to wrap some 1500 grit paper round my taper and lightly lap. this actually appeared to clear off some of the worst of the high spots. However, it's had little or no effect on the run out and I then reverted back to the forum for words of wisdom (not mentioned this before as it's either a bit clever or really dumb...).

It seems to me that I probalby have two options. Replace the spindle and bearings or leave it alone and make the best of it.

Anything that's smallish a thou or so out isn't going to make a lot of difference. Any thing I need long and accurate I would turn between centres.

I'll see what the spindle costs.

Iain

Heat. Depending on the set up, you can heat the headstock housing to loosen the grip on the outer race of the bearing, or you can heat the inner race of the bearing to loosen the grip on the spindle.

You can use a propane torch to heat the headstock/race. Or you can use an electric heat gun available from any hardware store. Even a hair dryer will work, just takes a bit longer to get up to temp. Recommended temp is about 120C (250F). Roughly, hot enough that if you spit on the heated job, the spit sizzles and evaporates instantly.

With a real sticky job, you can use a combination of methods. Put tension on the bearing/shaft with the puller as shown in the pics posted above, then if the bearing will not move, tap judiciously on the end of the spindle with a soft hammer or hammer and soft drift. (Be aware though that this destroys teh bearings and they should be replaced). Or, better option, put tension on the shaft/bearings with the puller and then heat the housing until the bearings move. If desperate, do all three, puller plus heat plus hammer persuasion.

On assembly, small bearings like these should be able to be installed on the shaft with light pressure from an arbor press, or from a piece of tube slid over teh spindle and tapped with a hammer so that all the impact is on the INNER RACE ONLY.

If the fit is too tight to do this, the spindle diameter needs measuring and emerying down slightly and carefully until the fit is right. Too tight a fit can expand the race -- or indeed crush a thin walled hollow spindle -- and adversely affect bearing clearance and life.

Likewise, bearings should tap easily into the housing on the OD. If not, burrs and maybe some metal need removing to get the right fit. Again emery tape or paper should do the job. We are usually only talking half a thou or so. And you can warm the housing, and even freeze the spindle and bearings overnight, to ease assembly, providing sizes are right.

In view of the trouble you had getting the spindle out last time you might be best to try to make do with what you have in place already as first option.

Just use a soft centre when turning between centres and take a clean-up cut over it before each time you use it. This will make the centre run true regardless of whether the taper is running true or not.

And if the lathe is turning a thou or two tapered,  with no  tailstock centre in place, you can adjust the headstock alignment regardless of the condition of the spindle's internal taper.

I prefer turning a test piece over Bob's Dad's method because the test piece gives you a real world result of what you will get, taking into account any headstock bearing play etc under real-world working conditions, which may be different from static conditions when checking bars with dial indicators etc.

Edited By Hopper on 27/10/2016 05:41:06

Thanks Hopper.

With the soft centre, I'v marked position on the chuck plate and the centre so that i can re-assemble in the same orientation each time (after an initial skimming) which means (I hope!) that I don't have to re-skim for each job.

The headstock adjustment is basically tightening up the securing bolts more or less so it's a bit of a blunt instrument. I will most likely use Rollie's Dad's as a starter because it's quick. Depending on results I may end up tuning with a test bar.

Most likely I will leave any spindle / bearing replacements for now, though I will have a try at aligning the headstock. In particular if it's too far vertically from the tailstock it makes centre turning pointless.

If I'm going to replace the bearings / spindle then I most likely don't care how hard it is to get out. I did have in mind to put the headstock in the oven (cook for one hour at 120...) to warm it up, rather than a blowtorch as 1) it should give more even heat and less stress and 2) I don't have a blowtorch.

Iain

George Thomas says in one of his books that inaccuracy in machine tools becomes very much less important when you know what they are. You can compensate for many of them by the way you work. Many people have produced good work on very old worn out lathes.

Don't heat the headstock, put the spindle in the freezer and do the job on a warm day.

regards Martin

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Tricky ... when you're removing the spindle

MichaelG.

I meant when fitting the new one obviously. You can cheerfully hit the old one with a sledge. Sounds like you can't do it much more damage.

You could of course put a bung in the end, tip it on it's back and fill it with liquid nitrogen. It should drop out on it's own then.

:0)

Martin

I did realise, Martin ... Sorry; just couldn't resist.

Seriously, though: If [as it appears] the parts are not toleranced properly, who knows what the best approach will be?

As you say ... for getting the old one out [again], brute force should suffice.

The new spindle can [and should] be 'fitted' to suit the bearings [*] but things may get more intersting if the bores in the headstock casting are undersize for the O.D. of the bearings.

MichaelG.

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[*] ... on a Record Wood Lathe spindle, did this by hand, using a very fine diamond hone to remove the peaks of the grinding marks !!

**LINK**

http://www.ezelap.co.uk/tools/Diamond-Hone---Stone.html

Well personally I would fit as many bits together as I could individually. Inner races to spindle, outer races to headstock etc. That was I know that everything that should go together will go together and I would get a feel for 'fits' and any high spots on the way in. I realize that nothing is ever in perfect alignment so it's going to be a little tougher doing everything at once.

Having said all that it occurs to me that if the bearing outer races are not seated well in the headstock and they are at all on the skew it's going to be really hard to get the spindle in so maybe that is what has happened in this case.?

regards Martin

You should care how hard they are to get out. Headstock castings are not indestructible.

Best to use a torch or heat gun (cheap to buy) so you heat up the housing from the outside but not the spindle and bearings so much. The housing will expand away from the bearings. A wet rag slapped on the bearings periodically helps keep them cooler than the surrounding housing. Soaking both housing and bearings/spindle in an oven will result in them both expanding about the same amount and so the interference fit will remain about the same.

I wouldn't rely solely on freezing in the domestic fridge to contract your spindle a great amount. Freezers are usually only 10C below 0. So only 30 degrees or so below nominal room temp of say 25C. Heat with a torch to 120C gives you 95 degrees above room temp. About three times the expansion. In extreme cases , housings can be heated to about 200C for another three times the expansion. "Freezing" of bearings in industry is done with liquid nitrogen to a temp of about -200C.

Edited By Hopper on 27/10/2016 12:28:08

Ideally, if the spindle comes in and out from the righthand end of the headstock, the main bearing (righthand end) should be mounted on the spindle before fitting into the housing. The lefthand bearing should be mounted in the housing before the spindle is installed..
Then when you slide the spindle in, the lefthand bearing guides it into the correct alignment before the righthand bearing is tapped home in its recess. So all should line up within the amount of clearance between the balls and races.

Edited By Hopper on 27/10/2016 12:38:16

Liquid nitrogen is for shrink fits mostly. What we are talking about here is gentle fitting. You should not have to resort to millwright methods on a little lathe so the fits need to be sorted out first. I am, as I said talking about reassembly not getting it out.

Martin