ML7 headstock reallignement.

[Martin DowingParticipant @martindowing58466]

[Martin DowingParticipant @martindowing58466]

After long investigations of certain peculiarities in my ML7 work I have concluded that there is a headstock allignement issue.

Fault is severe enough that usual bedways twisting doesn't wash anymore.

So lathe was leveled with precision level as accurately as possible 2thou/foot deviation was achieved with minute propeller like twist of entire machine.

Then a fine cut across bobbins on bar held in chuck spaced 6 inch apart was taken.

Taper of 9.5 thou per foot, narrowing towards a tailstock was reliably produced after several trials.

This obviously qualifies machine for headstock reallignement.

Now, does anyone knows a procedure, how to do it with ML7 lathe?

I know that headstock needs to be twisted, can even calculate how much but I would appreciate to leard about step by step procedure very much.

This could make life so much easier.

NB. these 4 high tensile screws used to mount headstock to bedways are really tough to undo. No one did it for 48 years, I suppose.

My first go at those have failed, next week will try again with more robust spanner.

Is there any headstock adjustment (twisting) mechanism to play with in ML7?

Many thanks for any comments.

[Brian OldfordParticipant @brianoldford70365]

I've never had the need/courage to shift the headstock on my S7 but can suggest you mount a longish test bar and shift the headstock, with great care, using a DTI for reference.

[HopperParticipant @hopper]

IIRC, there are two jacking screws, like long grub screws, that go in sideways on the front of the bed just below where the headstock casting sits. You slacken the hold down bolts and use the jacking screws to move the headstock. They should push the headstock casting machined base lugs up against the machined bed surfaces and that should be properly aligned. But on an old machine you may have to add shims etc.

[not done it yetParticipant @notdoneityet]

This obviously qualifies machine for headstock reallignement.

What rules out simple chuck misallignment?

[Tony Pratt 1Participant @tonypratt1]

Posted by not done it yet on 03/12/2016 05:59:09:

This obviously qualifies machine for headstock reallignement.

What rules out simple chuck misalignment?

What do you mean by simple chuck misalignment? Chuck run out etc. will have absolutely no effect on the lathes ability to turn parallel.

Tony

[HopperParticipant @hopper]

BTW, have you checked the condition of and play in your headstock bearings? No point in aligning the headstock if the bearings are slack. Slack headstock bearings can allow the job to move away from the tool, or ride up on the tool, or even get pulled into the tool if enough rake on the top surface, causing a taper.

A common way to check is to grasp a bar about a foot long in the chuck, put a dial indicator on the chuck backplate or preferably right on the spindle, and then push and pull the end of the bar up and down and side to side and observe teh dial indicator. Should be less than a thou movement. Preferably well less.

[Martin DowingParticipant @martindowing58466]

@Brian,

Well this idea is what I will try with great care, however due to a lack of test bar I will have to rely on bar with 2 bobbins mounted in 4 jaw and used for test turning. Aternatively I have 1in diameter and 20 inch long high precision round grounded, hardened bar which is not bent for sure and this one mounted and centered in 4 jaw may do as replacement for a more usual Morse taper ended test bar.

@Hopper

Bearings are OK. No play really and not long ago parting of 1 inch diameter steel bar 2.5 inches from the end of chuck and without tailstock support went with not much fuss and this indicates good bearings. My understanding of a bearing is that there is about 1/2 thou of oil clearance there, so longer steady pressure would at the end displace this oil and even good bearing would give in this 1/2 a thou or so.

As I have written, my measured misallignement of nearly perfectly levelled lathe is in excess of 9 thou per foot. Bearing fault to deliver that would be substantial, machine would produce a horrible chatter (but my cuts clean) etc.

Also bed twisting can reduce taper to 2 thou per foot, unfortunately taper narrows to tailstock end. However bed twisting has its limits and I got there shiming with 50 thou under far end foot of the tailstock end. IMO it is a cut off. Such a shiming doesn't correctly allign lathe either as certain diameters tend to be turned more paralell than others and at this point it is time to address real issue and not pretend that something is done if it is not.

Headstock allignement done intelligently is the way forward here and I have decided not to approach it as a tabu subject and no go area, as many of us are doing.

Important are details, about procedures used by Myford, as those may save much trouble and effort.

For me it seems certain that such work need to be done with decently levelled lathe to begin with. Precision level is a must here. Later it is a matter of *twisting* headstock until the tapers are within a range of thou per foot or better (Myford works were happy with 3 thou per foot albeit majority of lathes got much better deal than that).

Most what matters then is horizontal misallignement. Vertical one (business end looking up or down) is much less likely and consequences are not as severe, unless substantial.

@not done it yet

It was turning test, not bar in the chuck + dti test

Edited By Martin Dowing on 03/12/2016 21:22:19

[AjohnwParticipant @ajohnw51620]

If the bearings are loose things usually widen towards the tailstock and there may be a degree of recut if the same cut is run again – amount depends on the play but the saddle can slop around if the part of the saddle that runs on the back of the front rail wears round which it generally does. The same thing probably happens elsewhere on the none narrow guide beds. It can cause the tool to lift off as the saddle is wound back.

It might be worth doing a bar test, now called so and so's uncle or dad's test to see which way the head is miss aligned – parallel to bed and parallel to the sides of the bed rails. I'm assuming that particular test can do both but personally I would use a test bar in the morse socket in the spindle 'cause I am not sure if the other way can check both orientations.

When the bearings on these lathes are adjusted a shim should be removed from under the caps and then the bearings scraped back into truth. Both of them are likely to need scraping to maintain the alignment. As I understand it once done there should be slight resistance when the spindle is turned by hand and decent contact over most of the bearing surface. I't's a right pig to do especially with myford phos bronze bearings when they left much to much scraping allowance. The horizontal aspect can be checked with a dti on the spindle resting in the lower bearing halves providing the contact is good. Might be another option rather than buying a test bar.

Personally I would worry more about getting the horizontal aspect right as the screws that come in from the side are capable of bending the bed a bit and shims could be used to correct alignment.

You'll probably need a breaker bar plus a short extension and the correct socket on the end to undo the bolts that hold the head down. Get the longest one you can find. I always buy 3/8 drive as it's more useful than 1/2". When I worked on cars myself I just bought 1/2" drive stuff as needed or borrowed them. Some nuts were rather large at and the socket rather expensive to buy.

John

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[Martin DowingParticipant @martindowing58466]

@ john,

Many thanks for your comments. These are valuable.

Regarding my bearings.

These *are* phosphor bronze bearings working with hardened spindle. They were not scraped in, however I have bought them new as a set in old Myford works , in Beeston nearly Nottingham in 2004.

Peoples there have advised me that they have made certain rectification of manufacturing process and as per their belief it is unlikely that I would need to do hand scraping before bearing adjustment due to wear is needed.

Lathe had some rather light use but recently, during last year or two it is used more (interest in precision mechanics grows with age and it seems to be inversely proportionate to interest in women 😀 ).

Bearing surface was inspected occasionally at the time of belt change and pulley slipping trouble and nice shiny contact areas have developed, may be not as nice as those in properly scraped bearings but still reassuringly large.

There *is* some resistance of a spindle when I attempt to hand turn it by pulling a chuck. After a moment system gives in and begin to turn. No "double cuts", unless initial one was rather heavy or even more so if heavy and done with slender boring bar.

Bedways and saddle scraped by professional fitter to bring machine to its former glory.

Btw, this 7/32" Allen spanner to undo head bolts already ordered and guess, it will come with 3/8" square socket. One with 1/2" square socket would be too clumsy.

Regarding horizontal and vertical misallinement.

It seems that first is the one to look for and second must be catastrophic to matter, unless very small diameters are turned.

For 1 inch diameter horizontal misallinement of 10 thou per foot would give 20 thou total taper over said foot of distance.

With vertical misallignement of the same magnitude on 1 inch bar error would be 2 x  0.0000999 of thou (say two tenths of thou of total taper over foot).

On 0,1 " diameter error would grow to 2 x 0.99 thou, say 2 thou per foot total taper, still acceptable. Based on those it seems that in normal work undertaken by model engineer vertical misallignement matters little, but those attempting to turn a hair a bit could really fret aboit it – they could end up turning nothing at all.

Martin

Edited By Martin Dowing on 04/12/2016 20:32:55

[HopperParticipant @hopper]

Posted by Martin Dowing on 04/12/2016 19:53:34:….

…There *is* some resistance of a spindle when I attempt to hand turn it by pulling a chuck. After a moment system gives in and begin to turn. .

Something is not right there and should be rectified before you spend time aligning the headstock. It sounds like you may need to scrape the high spots off those bearings.

..

"Bedways and saddle scraped by professional fitter to bring machine to its former glory."

Scraped by a professional fitter to give a misalignment of 9 thou per foot? Something is not right there. Can you talk to him about your taper problem? He should have aligned the headstock as part of any bed rescrape. No point in scraping ways flat but out of alignment.

Edited By Hopper on 05/12/2016 06:09:36

[Martin DowingParticipant @martindowing58466]

@Hopper,

Yes , it was done by professional fitter 12 years ago.

He advised me that job on bedways, saddle and tailstock would be done but bearings are in such a poor state that I really need to replace them.

Actually I did not need a fitter to find it out – spindle was "wiggling" under pressure. So he has advised me that headstock would be left as it is and I need to keep fingers crossed and hope for the best and with some bed twisting it might be acceptable if not perfect.

However I have been warned that I might need to allign a headstock once bearings are changed. In his opinion for ML7 it is rather trivial, so I should cope. As I have said it was long time ago and contact is lost.

BTW, by principles it seems trivial, but I try to gather knowledge how to do it the coorect way and find out about any tricks there, just to save myself fiddling and piddling for a week, before arriving at correct setup by chance.

Regarding bearings.

Now I live in quite secluded area (and a country) which is really beautiful and charming but entirely devoid of peoples capable to do bearing scraping or most of other industry and I am not yet up to the task myself.

Such a job could certainly make them a bit better but up to date observations are not revealing obvious troubles from this source.

So I would either need to take machine 200 miles to outlet which does it (tedious) or pay for them to delegate worker to me or find a fitter and fund him a week of holliday in my place and meantime job would be done (I have terminated my professional careeer in chemistry and now run small hotel for a living).

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