.

Are you taking that measurement when both the tailstock and it's quill are tightened.?

Nick

Usual tailstock problem wear causing tailstock to be low is common,never had a high tailstock, I assume the lathe was used when you acquired it,if it had been supplied to a training establishment there could be the possibility of tailstocks getting swapped, though I would have thought that centre height between similar lathes would have been very accurate ,I once replaced the tailstock on a round head Colchester with a tailstock from a later square head lathe which aligned very accurately with the headstock, you state that the barrel is .15 mm high, did you measure the error on the o/dia of the barrel or on the the bore of the morse taper, just wondering if the error was in the tailstock bore or if the morse taper was not central to the barrel,worth checking. Yes I too would be wary about taking metal off the base of the tailstock,once off not easily rectified. So I would get a knowledgeable friend or colleague to do an independent check,using his equipment ,just to make sure there is an error and does he get the same error, then come the decisions about rectification ,a very goof surface grinder would be required.

I bought the lathe secondhand but the dealer had acquired it off a model engineer and I can only assume its the original tailstock.

I measured the error with a DTI mounted in the chuck and read off the error on the OD of the barrel, with and without the tailstock (and the barrel) locked. Interestingly when the tailstock is clamped to the bed the DTI takes a second or so to stabilise as the oil is squeezed out of the bed mating surfaces (the effect is not present when I did the same test 'dry'

I also saw the same 0.015 error when I had the DTI checking the Morse taper bore so at least I know its concentric.

The barrel is locked by a cam pushing the key upwards so increases the problem, however when using a centre drill, the quill is free so would not matter.

Ian P

Thanks to Graham who has suggested to me (in a PM) that I shim up the headstock rather than remove metal from the tailstock.

On reflection though I think shimming the headstock might be a lot of work on an M250. Apart from the difficulty of getting shim two thicknesses that work out correct (on the 'V' and the flat of the bed) actually stripping down and installing them would be a major task.

The tailstock has a separate soleplate so seems a good candidate for surface grinding (not that I have one) although there is a raised (crossways) tenon which separates what would a plain flat surface.

Ian P

When clocking from headstock to tailstock error will be half clock reading,

So your tailstock barrel is 0.003' or0.0003'high depending whether clock TIR is 0.15 mm or0.015mm.

Also this check does not account. Which way the tailstock is pointing !

Could the problem be that the tailstock is actually pointing upwards? Its pivoting on the crossways tenon and needs some shims at its back end?

Frank

Not forgetting the runout of the DTI being held!

Since its a quality machine and unless abused Harrison wouldn't send out with that error, perfectly fine for imports. Steel far superior to Asian imports and wont wear either but the ram will in the casting.

There may be adjustment front and back on the bottom, two grub screws. Bigger Harrisons can tilt the tailstock via this a small amount.

Are you sure the tailstock and or barrel has not been strained or bent by somebody using it to lift the machine ?

Maybe you could remove the barrel and do your DTI test in the bore of the tailstock casting.

Phil

The difference in reading between the top and bottom of the barrel is 0.015mm so surely I need to lower the tailstock by that amount to correct the error (rather than only half that amount).

I did check the barrel at another position after I extended it and did not see much difference. However tomorrow I will check more carefully as a tilted barrel is a possibility.

I need to make some Hooke joint shaft couplings to fit a non standard (and non changeable) shaft which is 3.270 diameter (measured with two different high resolution micrometers). I don't want to have reamer made but was hoping to make a D bit or modify a twist drill by trial and error so that I can get a very close fit otherwise the joint will be notchy if not exactly on centre. If when drilling, the drill is not on centre it will bend and I will end up with a bell mouthed hole. One temporary solution might be to mount the drill chuck on a boring head in the tailstock so that I can offset it and correct the error.

Ian P

Has the headstock been shimmed?

Many lathes are made with the tailstock slightly higher than the mandrel so that when the tailstock wears it is still within reasonable limits. Even the Schlesinger limits are -0 +.0008' or so for this measurement. And note, this measurement is actual alignment, which is half of Total Indicated Runout. So if you have .003' TIR, that is only .0015' actual shaft offset and probably is just how the manufacturer intended it to be.

I would not be too hasty to remove metal from the tailstock or to tinker with the headstock alignment. If you can put a piece of 1' bar about 6' long between centres and turn it parallel within .001' you really have nothing much to worry about. And if it does turn a taper greater than .001', you can adjust that out by offsetting the tailstock sideways without touching the vertical alignment.

Those concerned that if we want to drill a .010' diameter hole and the TIR is .003' the drill will be .003' off target and snap etc, should remember that it is only .0015' off centre and no hobbyist tailstock chuck is going to hold a drill to any greater accuracy than that anyhow.

Leave well enough alone, I reckon.

Edit: PS, just read your correction post. If TIR is .015mm (aka .0006' your misalignment is .0003'.

And if you are worried about this affecting a 3' diameter drilled hole, just stop it and get turning.

If you want those sorts of accuracies you will need a toolroom cylindrical grinder, not a lathe.

But in the real world, I would drill undersize and bore to the final diameter. This is the usual way of machining couplings and uni joints of this size. You should be able to bore to .001' to .0005' accuracy if you take small final cuts and allow for spring in the boring bar by taking several cuts at the same setting to get final size.

Edited By Hopper on 01/09/2015 06:09:23

Edited By Hopper on 01/09/2015 06:11:34

Edited By Hopper on 01/09/2015 06:16:25

PPS, just reread your last post again. If that coupling shaft diameter is 3.27mm, not inches, disregard my misguided waffle about boring etc. D bit makes much more sense at that tiny size! Doh. Getting our inches and MM confused here.

But even so, .015mm TIR between mandrel and tailstock is well within the Schlesinger limits and you are not going to get closer than that on a lathe. That is .0075mm misalignment. I'll bet that if you run your lathe for 30 minutes at high speed, heat in the headstock will lift the mandrel by that much. Likewise, I'll bet that your dial indicator set up has more sag than that amount, no matter how rigid you think it may be.

If it has I want some of that negative shim material for the tailstock!

Ian P

Hopper

Boring a 3.27mm hole is a distinct possibility and might be my best option as its not to a great depth. Watchmakers regularly bore diameters below 1.5mm, although it usually only in thin brass plate rather than SS bar.

I'm slightly confused now about TIR numbers in respect of tailstock alignment. If the barrel is 0.015mm high, to me that would be a total error of 0.03mm in terms of the diameter of the rotating workpiece, so a 1mm drill would make a hole 1.03mm diameter (neglecting drill flexure).

Ian P

If you put a 3 morse blank in the tailstock, drill it out and finish with a 2 morse taper reamer you would have an adapter that you could use for fine work. You would need a witness mark on it as it would only be true in one position. Not the best solution maybe but cheap and easy.

Regards.

David

Was it my imagination or on the Harrison group didn't you say it was 0.15mm out?

Chris, not your imagination. I carelessly used confusing and contradictory readings in some posts.

I have just done some more careful checking, this time I used a plunger type DTI which has half thou resolution (0.0005'. The results are very consistent and and I have tested with barrel locked and free and with the tailstock locked to the bed each time.

Love strange love 1982 stream. With the plunger reading the OD of the barrel I get 0.000' at the East and West positions. North reads 0.005' positive and South reads minus 0.005'.

Out of interest, with the barrel unlocked firm finger pressure gives 0.001' lateral movement whereas the clamp pushes it 0.002'. The action of clamping the tailstock to the bed seems to lowers the tailstock by 0.003' very consistently.

Good news is that I get exactly the same N, S, E & W readings with the barrel fully extended, only difference is my finger pressure gives more deflection as the barrel moves further out of the tailstock bore.

For expediency I will solve the current problem by mounting a chuck on a small boring head so I can offset it the right amount.

Ian P

I think maybe we are talking at cross purposes on TIR vs misalignment. Kind of hard to explain clearly in words so here is a diagram that maybe will clarify it some.

So if you have a Total Indicated Runout on your dial gauge of .015MM it consists of the .007MM at the top plus the .007MM at the bottom. So if you move the solid blue circle (tailstock) downwards by .007MM the tops of the two circles will line up. The bottoms of the two circles will line up. Shafts aligned.

It's like when you set something true in the four jaw chuck. You measure the TIR - the total movement of the needle on the dial gauge in a 360 degree sweep - then rotate the job to the high spot and move the job in by HALF the TIR and the TIR will then be zero. You can try this yourself at home.

Either way, even if the tailstock is .03MM higher than the headstock spindle (aka .001' ) That would be exactly how Harrison made the lathe, in order to allow for wear as is normal practice wiith quality lathes. I would not be messing with it. Your drill chuck is not going to be any more accurate than .03MM concentric.

But at .015MM TIR, aka .007MM misalignment, count yourself fortunate, very fortunate, to have a lathe with such good alignment. In old money that is 'two tenths of a thou' or exactly three fifths of five eighths of a gnat's left 'un.

And you could always try drilling a 2.7MM hole in a piece of scrap with your current set up and measure what size it comes out. If you round the sharp outer corners of the cutting edges with a rub or two on the oilstone, you will be surprised how close to size a drill bit will drill.

Or you could make a 'toolmaker's reamer' by cutting a piece of silver steel bar of the correct diameter at an oblique angle and hardening and tempering it.

Edited By Hopper on 01/09/2015 11:41:20

How do we know that the 'error' isn't due to an eccentricity of the chuck used to hold the DTI?

Andrew

Hello everyone,

I've got a Harrison M500 lathe, I bought it from a dealer last year , and after proprely levelling it up with a Moore and Wright machine level, it was turning about 30 thou tapered over about 6',

I have discovered that the headstock is not adjustable like the two Colchesters that I've also got,

It was suggested by a machine tool fitter that I might be able to shim the headstock to get better acuracy,

The headstock is clamped down firnly on the rear 'V' of the bed,

After several evenings experimenting with shims and taking many trial cuts I have an accuracy of 1 thou tapered over 4 inches, on both boring and turning, also betwen centres is the same,

Is this accuracy about what can be expected from a lathe pushing 30 years old ?

Am I having a mid life crisis, or have I got a lathe thats OK ?

It seems unrealistic to expect a lathe to keep It's accuracy for it's entire life with a non adjustable headstock,

What sort of accuracy do you men get with the Harrison 'square head' M250 or M400 lathes ? I presume they are also non adjustable as well,

Or am Imissing something ?

Apart from this It's a nice machine.

Richard.

If you have leveled the bed and were getting 30 thou, what have you done to reduce the error to 1 thou?

I have an M250 and it turns as near parallel as I could want - I can get the taper to go either way, depending on the material and the tool combination, so if your machine is with little wear and abuse, then I don't see why you shouldn't get similar results.

Martin.

Richard,

I have an M300, and the accuracy is a lot better than that! I got it down to a thou or two per foot, but I haven't finished fine tuning it yet.

The fixing of the headstock to the bed is definitely not something I would recommend fiddling with, and neither (in the case of the M300 at least) would I want to mess with the fixing of the lathe bed to the stand. What I did was to fit some jacking feet to the bottom of the stand, and to adjust them to remove any wind in the bed. It is perhaps surprising to the uninitiated that something so rigid, and weighing over 2/3 of a tonne, that there is enough flexibility to do that, but there is.

Levelling the bed is, in my opinion at least, a delusion; you will never get it spot on by this method. The only method to do this is to keep taking small test cuts while adjusting one pair of feet to remove wind. If it cuts small at the headstock, raise the front foot at the tailstock, and vice-versa. Do this with a very stout bar of MS, not supported by the tailstock, and take very small cuts to avoid bending the test piece.

David

Edited By David Littlewood on 30/05/2012 23:17:41

Probably looking at a thou last year on my M300 and dependant upon material turned.

What feet are you using David? Supplied M20 bolts i think they are sink in to the concrete. Ideally need something to spread the load.

Agree Harrison went to great lengths scrapingand checking everything in tolerance before leaving factory. Whether machines been picked up by the head or disturbed in any way would affect, they have mentioned it some where.

Jon,

My M300 stand has threaded M12 holes in its feet. I used adjustable feet like these:

- not these exact ones, I got mine from Key, but can't find them now on their website. Thread them into the holes and then adjust with a spanner.

David

I put a piece of 1 1/2' silver steel in the chuck and it ran concentrically, but was high on the outer end, so I've raised the rear of the headstock to compensate for it, thats how I got it from 30 thou to 1 thou.

The bed looks to be in very good condition, so I think my real trouble is possibly in the main spindle bearings, possibly being worn.

There is no movement in the main spindle when I check it with a dial gauge, but whats happening at 300rpm I dont know.

Richard.

The one way of reducing error is to introduce a slight degree of twist into the bedway, this is not scientific as you need to jack up one of the tailstock leveling screws, take a test cut and occording to the direction of any taper, slacken or tighten either or both of the clamping screws untill the reading is papallel. That's the only real way of adjusting an older machine and is a proven method in industrial workshops. Good luck

Unfortunately Richard I have no experience with a Harrison M500, I have to manage with a Myford series seven. Before Myford owners take that the wrong way its a fine machine.

As I cannot add much to the thread, my main reason is to agree with David as it is good to see someone adding some common sense to the subject levelling the lathe. So often we are given here, or in the magazines, the impression that this is the be all and and all of the subject. For me, if you do not have a level do not worry, turning a test piece and adjusting the lathes mounting is the all important requirement.

When I placed my workshop in a new garden the only suitable position required a large area of the space to have the soil built up by around 1 metre. It is still settling after 30 years and if I were paranoid about the lathe being level I would probably be resetting it every few months. As a result the bed of my lathe is far from level but still turns parallel within very acceptable limits. That is achieved by turning a test piece and making the adjustments to the lathe's mounting as the results indicate.

Harold

You don't mean that you have unbolted the headstock and shimmed it do you?

If there is no play in the headstock bearings, then you'll gain nothing by touching them - you certainly won't want to buy any when you find out the price either!

So with no wear in the bed and no play in the bearings, it would seem we are down to an alignment problem. First thing to do is be 100% sure that the bed is without twist, i.e. it is 'level' when gauged against the working surfaces of the bed.

Once this is done, the lathe should turn to close limits of parallelism that are similar to those obtained by the manufacturer. If the results are still unacceptable then you need to find out why the headstock is not properly aligned to the bed, which would probably involve separating the two and checking for signs of tampering.

Martin.

I should add to my answer about the jacking feet by saying that the M12 nut shown in the link is redundant, at least on my M300 cabinet; the M12 stud screws into the threaded hole in the feet, and a spanner on the bottom nut (which is actually fixed to the stud) will adjust the height. I guess the M12 nut is for use when there is only a plain hole to use, or as a locknut.

Harold, thanks for the comment, glad to see I'm not the only one who thinks levelling is unnecessary. In fact I do try to keep the bed of my lathes reasonably level, but only so I can use it as a reference if needed - and I can't remember actually so needing!

David

Edited By David Littlewood on 31/05/2012 12:06:52

'Spare' nut is for locking against machine base to prevent movement should your machine vibrate.

The preload on the main bearings is measured with the machine at running temperature. Best advice, do not touch unless you know what you are doing and have the right tools. As Blowlamp says Super Gamet bearings are very 'pricey'

KWIL,

I did suggest the locknut use - though just how much vibration it would need to cause a foot to rotate under 1/4 tonne of compressive load must be left to the imagination.

David

There are however some machine mounts which do not have a fixed foot and a ball ended threaded shaft bears in the centre of a cup. This type could be affected by vibration. The fixed foot types are more stable but perhaps more difficult to adjust accurately because you are trying to rotate the foot on the floor under your 1/4 tonne compressive load, hence perhaps the two nuts?

Hello Blowlamp,

I've done all things that you suggest last year,

The bed is level, the bearings seem to be OK, the bed looks to be in good condition, so the only option left was to shim the headstock, which I've done , at least it's made the lathe usable, although I'm not really happy with it, I didn't have much choice, I had jobs to do with it and had to do something.

Who dares wins ?

It's a big lathe, 10' centre height and 80' between centres, it's probably done some heavy work in it's life, but as Michael says it shouldn't move much in 30 years of hard work

Richard.

Hi There

The feet I use are supplied by J&L industrial. They are quite solid with rubber on the base.

They really work well even on wooden shed floors (I know that is not perfect).

The ones used by the old Myford company (no idea what RDG use) are awful.

Like standing the machine on a bit of rubber.

regards David

KWIL,

The feet I use (and the ones in the link I posted) are made so that the steel stud rotates independently of the black foot, so it is easy to rotate the hex nut at the base - well, it's a bit stiff, but definitely do-able by normal spanner/hand power.

David

Hi Richard,
I Agree with David Littlewood's first reply. Here are some more thoughts on the problem. The bed will be machined all the way along from the tailstock end to the headstock end so the surface that the headstock aligns to has got to be in line with the rest of the bed. The spindle axis of the headstock will have originally been machined in line with the surface that mates with the bed. I can not see how this alignment can have changed unless the lathe has been dropped. If this had happened I think there would be visible damage. Even if the headstock was from a different lathe The spindle axis would still be aligned with the bed. ( The spindle height or front to back alignment could be different to the original but that would not cause a taper on something mounted in the chuck. I would cause a taper turning between centres as the headstock would not line up with the tailstock.) I think these points show shimming the headstock is not the correct approach to the problem.

Les,

Hi Richard

I wonder if the bed is an issue?

One way for a quick test, although not completely accurate (the tail stock ways may be worn) is to attach a dial indicator to the saddle, setting it to bear on the face of the tail stock v sides and flat. then run the saddle along the bed. If the bed is in good order there should be very little change. If not the bed is worn. The tail stock ways near the head stock are not likely to be very worn. They tend to wear further away as the tail stock is not normally needed as much to support short work that is held in the chuck alone.

This test is a very good indicator of bed condition.

Another point to check carefully is the back and front saddle retaining strips particularly the back one, Speaking from experience my lathe a VDF RO80 has a very heavy geared saddle apron. if the back strip is not set correctly the saddle can lift at the back. Causing strange cutting errors.

John

Setting a machine so it's 'level' is the only good way to know where you are starting from. By being level you are removing as much twist from the bed as possible and restoring the surfaces of the ways to a planar condition, i.e. about as smooth and flat as it was machined by the maker.

A turned part may still not be exactly parallel, but there is now a starting point from which to work and small corrections can be made by invoking a very slight twist back in to the bed, but large errors should be investigated and corrected by the proper means, or else many other alignments will the thrown into doubt.

Martin.

Hi Richard.

Using a silver steel bar To check if the axis of rotation of the spindle is parallel to the axis of the bed ways is problematic. It is very difficult set the bar in the 4 jaw in such a way that the bar is truly concentric with the spindle axis, it may be at one point but is it true at every point along the bar?, and is the bar perfectly straight? very difficult to achieve without an elaborate adjustable test bar.

There is a way around this.. Set the bar in the chuck (set it to run true in the middle of its exposed length) and then use a dial indicator mounted on the saddle, set on the centre line of the bar then rotate the spindle by hand to measure the high and low point as shown on the dial indicator as you rotate the spindle note the two values in a high and low column in a spreadsheet or on a piece of paper. Do this say every 20mm along the bar or 10mm if you want to be more accurate. Mark the points along the bed with a soft pencil or on a piece of masking tape stuck on the bed.

Now subtract each high value from each low value on every pair. If the relationship of your spindle to the bed/saddle is perfect you will get the same answer for each pair otherwise you have mapped the bed/saddle to spindle error measured along the bar. If you did it with Excel you can even graph the error.

There are a number of errors that can affect the results using this method one is the bar varies in diameter? you can check for this using a micrometer you can compensate for this in the unlikely event you measure a significant error.

The bar itself sags by gravity Connelly in Machine Tool Reconditioning page 113 Says
'The effects of sag in test bars is often overlooked and unless allowed for becomes a major source of error in alignment tests.
A solid bar 1' dia 12 inch overhang
has natural sag of .00038

Ideally your dial indicator is fitted with a flat contact point to keep the contact with the bar in the same plane otherwise there will be small errors if it moves off the centerline of the bar However if these errors start to affect the results there are serious problems with the alignment

There appears to be some conjecture on the set up of the spindle. Many text books state that the spindle should point up about .00015 and towards the operator a similar amount to allow for sag and the pressure of the cut using a 300mm bar. certainly never down or back. In reality it will never be perfect.

The same test can be used from the top of the bar and the face of the bar to establish the two planes at 90 degrees needed to check the alignment.

Cheers

John

Edited By John McNamara on 01/06/2012 10:33:12