Adjusting the ML7 spindle bearings (New bronze version)

Hi I am look for some help with adjusting the spindle bearings on my ML7.

A little history: I bought a ML7 a few yeas ago and I have been fixing bits and pieces over time. The spindle had some bad dings on the nose and internal scratches so I decided to swap it out for a new one. After remortgaging the house to pay for the new spindle it finally arrived.

The first issue I had was that once installed it locked solid I had not even torqued up the bolts!! I was expecting to have to take a few layers off the Shims. Any way 3 sheets of post -it notes and I was good to go.....well it turned. I did not understand the criticality of getting the bearings adjusted just right. so Fast forward about 11 months and I was having big issues with turning a 100mm long 10mm shaft. without a taper. It would be right at one end but not at the other.

So I set about trying to find the source of the issue. I leveled the bed to within a gnats. I could then adjust the back foot to get it to turn parallel but then the bed was skew, not level and most of all not co-planar. I felt that I was twisting the bed to fix another issue. Eventually I got a MT2 test bar, re-levelled the bed and ran a dial along the test bar in various rotational positionsthe results were all over the place..... that was when I realised two things 1) I needed to get the bearings adjusted first and 2) the lathe needed a thorough clean.

The lathe is now clean and I started adjusting the bearings.....well I think I am adjusting the bearings correctly but but I am not sure. So here is what I have done.

I got a 2"x1" batton about 1m in length and another block to act as a fulcrum and put a moderate amount of force in the upward direction, I had installed a DTI which reads to 0.005mm (well those are the smallest divisions) the spindle moved 0.095mm so almost 4 thou.

Next I removed all but one of the pieces of paper (there were 3 at 0.06mm (2 thou) each) from the Front bearing and tightened it up....it locked. I kept adding equal amounts of Ali foil shims (0.015mm) to each side until the spindle was free to run and there was about 0.01mm (0.0004" ) play using the 2x1.

I repeated this on the rear using the drive belt to lift the back end. After Tightening up the slop in the spindle bearings I used the test bar just in the spindle (no tail stock ) and found that the head stock was out about 0.07mm (3 thou) out at the end of the test bar roughly 220mm from the end of spindle nose. I shimmed the head stock to pull it straight and was berry chuffed with my self .

However, pride comes before a fall and....all was well until reassembled and I moved the spindle speed up to maximum rpm the front bearing stayed cool the rear got warm. I ran the lathe for 30 min and the temperature stabilised at 32C for the rear and about 26 for the front. Ambient in the garage is about 18 today.

Ok so now the questions:

1. Does this all sound right? I am a novice when it comes to these things I have researched, watched videos and read loads about it, I understand the theory but I have not done it before.
2. What is the right procedure for adjusting these bearings what is the tolerance? and how is it measured? is the 2x1 lifting method even appropriate?
3. What is the tightening torque for the bearing half Hex screws?
4. Is the rise in temp significant.
5. If the temp rise is significant what do I do? add shims until I get to the outer limits of the tolerance
6. Finally how is the End float adjusted? I realise it is done with the screw colar and the grub screw but how do you check it what is allowable?
7. One more.... Is there a service manual with all the Bolt torque settings, methods of testing etc.

Thanks for reading all of that any help would be most welcome.

Alastair

Edited By Colin Seggie on 26/10/2013 17:00:42

Edited By Colin Seggie on 26/10/2013 17:01:11

I too am in a similar position to you

I've even considered ringing the ex myford setup boys. but personally I think the best way to learn is by doing it yourself. alas i'm still struggling but getting there slowly (I hope)

The main thing for me is belt tension, If too tight & it pulls the test bar out of true. Too slack and the belts slip

even under very little load. My machine is old and well worn though might even be me expecting too much of the old girl.

hopefully there may be some informative replys

You will need to scrape the bearings to mate with the new spindle.

Martin.

Martin could you elaborate please.

The new spindle comes with new Bronze bearings. Are you saying I need to scrape these even thought they are new? How is that done and to what tolerance?

Or are you talking about martins Issue?

Alastair

Alastair.

Yes, the bronze bearing shells will need scraping to the spindle.
Because these are new components they should already be quite close to size, so things should be quicker and easier to fit than might otherwise be the case.

I'd install the lower halves of the shells into the headstock after giving it a thorough clean and inspection to be sure they're correctly and fully seated in position - no dirt or burrs under the shells. Then, with a smear of engineer's blue on both bearing journals, drop the spindle into the lower bearings and rotate rotate it half a turn or so. Lift out the spindle and see where the blue has been transferred to. Chances are that there will be spots here and there and these are what you attack with your bearing scraper until you achieve an even coverage of spots.

The upper shells are done in a similar way, but are a little more awkward because you need to achieve a close running fit with the bearing caps pulled down onto a thin stack of shim. So it's a matter of installing just enough shim to leave the bearing too tight to turn until the upper shells have been scraped to provide the necessary (minute) clearance which allows the bearing caps to be fully tightened down.

If the lathe now turns a taper its usually a matter of removing the headstock and scraping its mounting surfaces until things come back into line.

Martin.

Martin,

Thanks for taking the time to explain that. It is aprieciated.

I understand most of what you have explained needs to be done. I will have a look for bearing scraping videos before having a go. I think there was one on youtube . The only thing that I am still not sure about is what am I aiming for play wise and how is that best tested? i.e. what do i do to test and when do I stop and think well that is it done.

Sorry for the dumb questions but this is all very new to me.

Alastair

Edited By Colin Seggie on 26/10/2013 23:50:36

You will be looking for a very slight drag on the spindle when it's rotated by hand and the bearing caps are fully tightened against their shims. You should really aim for slightly less contact at the very bottom and the very top of the shells so that the spindle isn't 'pinched' top & bottom whilst potentially not as well supported at the sides - think of a bar sat in a vee-block to see what I'm getting at.

There's not really any need to try and measure any play, just try to get even coverage of blue (which equals contact between spindle and shells) once everything is tightened down along with the proviso of free spindle rotation.

Martin.

Rather than running at high speed once reassembled, think of itas an old car, after an overhaul, run slowly, until run in. Keep the oil up to the bearings. Ian S C

Hi all

thanks for the responses it really does help guide me.

Martin thanks for all the info I am now on the hunt for a scraper!

Ian - I did a running In process slow at first then slowly went up to full speed with 2x the normal amount of oil over about 2 days but it is only at the higher speeds that the bearing starts to heat up.

I think that I need to look at the contact areas like Martin suggests just need the tools.

Alastair

Martin describes the method to use. I did my white metal bearings that way a long time ago. Of course, you must go carefully because if you go too far...

I carefully scraped mine to a really accurate fit then found to my dismay that when I bolted down the bearing caps, the shells expanded into their housings giving about a thou more clearance than intended. The shells were not as tight a fit as they should have been. As an expedient, I cut out some rectangles of cooking foil (0.4 thou thick, 0.8 thou on diameter) which I 'stuck' onto the outside of the shells with oil, put them back together and it came good. The static clearance measured using a clock gauge while pushing and pulling a bar in the chuck is still only 0.5 thou after 40 years of use.

Andrew M

Andrew its the going too far that worries me! especially as I have never done anything like this before.

Thanks for the tip I will keep an eye out for that!

Alastair

Hi just a quick note if when testing a fit on a spindle you force the spindle in one plane ie the back of the machine m/c and read the error what you are reading is the max diflection this is an error that includes the rigidity of the m/c as well as the spindle play. What i check is the non returnable error similar test but remove the presure and then take the reading then repeat at 180deg. The opposite way then at 90deg and 270deg ghis will give a much better understanding of the error.

As for scraping practise on the old bearings first read up on blueing up and do a little the assemble and test repeat till required fit is acheved ive used this methord to scrap in high speed spindle bearings for production grinders

Phil

Just a quick question on bearing scraper size what size do I need the front bearing is fairly large but the rear bearing is much smaller. So I am supposing you need a fairly small scraper?...or have I got this wrong?

Anyone able to give me rough dimensions of the scraper needed

Colin

I used a small worn-out half round file, ground off all the teeth then smoothed the cutting edges on an oilstone. The file is about 4" long overall and has been useful for all sorts of model engineering jobs since.

Don't let my earlier tribulations put you off; scraping is not difficult. The amount of metal you take off and ends up on your scraper is tiny compared to the amount you would remove by taking the finest of cuts with the lathe, so progress is naturally slow. How accurately you work depends on the thickness of engineer's blue you apply and you can use less as you home in on the final fit. There is something very satisfying about achieving a really good fit by hand methods that is better than you can achieve by machine - at least the sort of machines a model engineer uses.

Good luck!

Andrew M

Hi Colin,

I have some scrapers listed on ebay at the moment. See 301001204131 and PM me if they would suit you. They are all useful scrapers and one could be right for your Bearing/Spindle fitting.

Mike

I have made scrapers from triangular, half round, and flat files, the local second hand shop has a good supply of worn out files for a few cents each. Ian S C

Andrew, I am up for the challenge I love doing new things, in fact that is my biggest problem i never master anything!

Mike would those not be too big?

Ian and andrew, I have never seen a scraper up close so I don't think I would be able to make one even if I had the file to make it out of I think in the first instance I am going to buy one. I have a marine engineer friend who has scraped bearings before so as soon as I get the scrapers he is going to come round and see if it comes back to him after 25 odd years.

Alastair

Hi All I seem to be having some issues.

I've been scraping for about 17 hours now and I have good contact on the bottom bearings, and the tops are coming along.

Now I ve removed a lot of material, far more than i was expecting, since myford say that the spindles and bearings & shaft are paired?

My issue is that I am getting lots of side to side play about 2 thou. I also note that at the same time the top bearing housing moves about the same, which does not seem right. Even when I torque the bolts up tight.

I've tried to scrape more on the bottom to in effect drop the shaft down a bit and get the V block effect Blowlamp alluded to

Can any one shed any light?

Alastair

Hi Colin, did you ever get to the bottom of your problems? Thinking about doing this myself!

Martin