Harrison lathe accuracy ?

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:

**LINK**

- 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