Harrison lathe accuracy ?

[blowlampParticipant @blowlamp]

David.

The general act of setting up a machine tool in a geometrically correct condition, which also includes removal of twist from its structure, is known as leveling. That said, I'm afraid I can't be held responsible for anyone being confused by my use of the proper terminology.

Martin.

[David LittlewoodParticipant @davidlittlewood51847]

Martin,

Thanks for clarifying. Shows the problems that can be caused by one person's special meaning of a word not quite aligning with the one in everyday use; we are not all professional machinery erectors.

David

[RICHARD GREEN 2Participant @richardgreen2]

Thanks everyone for your comments and ideas, I think I've decided what I am going to do with the Harrison M500,

At the moment it's turning about 3/4 of a thou tapered over 4 ",( with the shimmed headstock ) this is more than acceptable for the work I'm doing with it at the moment,

However when the work for this lathe eases off later in the year, I think I would like to seriously investigate the problem further, by removing the headstock completely, thoroughly cleaning the headstock clamping faces, going back to basics, and checking everything out as I work my way through the lathe, (without the shims ).

There are a few other minor jobs that need doing , so I can do those as well,

The bed checks out OK with a dial gauge, it's level, no detectable wear in the bearings, the saddle had a bit of lift on the rear , about 10 thou, I've adjusted this back to a nice sliding fit,

The cross slide and topslide were clamped, so I think the only place to check now is the headstock itself.

Although I've been latheing for almost 40 years, I never seen to stop learning, this lathe is a problem, but it's an interesting problem.

Thanks for all your advice,

Richard.

[Harold Hall 1Participant @haroldhall1]

As I consider there will be some reading this thread that setting up a lathe to turn parallel is rather a grey area, because of this I feel a little more detail on the subject may be helpful.

For issue 10 of MEW I made a College Engineering Supply precision level using their most sensitive vial. To put an easily understood value to its sensitivity, it is 200mm long and if raised by 0.05mm at one end the bubble moves by about 2.5mm. This would equate to 0.025mm across the width of my Myford and as much smaller movements of the bubble could easily be detected, say 0.5mm, accuracy within 0.005mm should be possible. In the case of my Starrett general purpose level of the same length the bubble hardly moved if the end was raised by 0.2mm.

From this it can be seen that their sensitivities are vastly different. However, there is also another important difference. With the general purpose level there are just two lines between which the bubble sits if the object is level, with the precision level there are five pairs of lines and these are at about 2mm spacing making it easy to note the values being tested, 1 space, 2 spaces, 1/2 a space , etc.

If therefore the lathe owner has such a level, and the lathe has jacking screws, using it to set the lathe level would be quick before moving to the essential stage of turning a test piece and making further adjustments until it turns parallel within acceptable limits.

If the lathe has though to use shims then the process would be very much slower and testing to check that both ends read the same, rather than level, would be sufficient as the bed would be equally straight/flat?. This is acceptable as it is not essential for the lathe bed to be level. From there it will again be a case of turning a test piece making further adjustments as this demands.

If though a workshop owner has purchased his, or hers, first lathe, be it a second hand Myford, or similar, or a budget new one, than having spent say £1000 it would be foolish to spend another £100 on a precision level for what is likely to be a very occasional use. Those advising such workshop owners should not therefore, as I have witnessed, encourage them to go the precision level route, but to turn a test piece and adjust the mounting accordingly.

Using a general purpose level could be used to set the lathe nominally level but will achieve nothing in terms of setting the lathe to turn parallel as the above regarding their sensitivity shows.

Richard, is there any chance that someone in the past has foolishly placed shims that you haven't spotted at the front of the headstock for some reason.

Harold

[RICHARD GREEN 2Participant @richardgreen2]

Harold,

This had crossed my mind, but until I lift off the headstock I cant see anything.

The shims that I fitted might have pushed any previous shims further in.

I'm positive that the only option now is a complete removal of the headstock, investigate it all further, and go from there,

It's no good me keep guessing what the problem might be, I've got to get stuck in and sort the problem out.

Richard.

[blowlampParticipant @blowlamp]

In this context LEVEL = PLANAR.

Like a surface plate is PLANAR, even if it's stood on its side or propped up with a bit of wood – the surface is PLANAR so it is LEVEL but not necessarily parallel to the Earth's surface – if we accept the Earth is flat  .

Martin.

Edited By blowlamp on 02/06/2012 10:21:57

Edited By blowlamp on 02/06/2012 10:22:24

[Anonymous]

Quite so, it's got nothing to do with the earth's surface; the plane is being set perpendicular to the local gravity tensor.

Andrew

[David LittlewoodParticipant @davidlittlewood51847]

Martin,

You said:

"In this context LEVEL = PLANAR."

Only in your eccentric view. I press this point because I think it is distinctly unhelpful to beginners if you use a word in a different way from the one understood by the average person; they are very likely to receive the wrong message. You agree with the general view of what is needed to adjust a lathe to turn parallel, but persist in using a word more or less guaranteed to cause confusion.

David

[Clive HartlandParticipant @clivehartland94829]

A plane level device ( Flat bed lathe or a milling bed) would only be level if it was at right angles to a vertical line going through the center of the Earth. this applying to x and Y planes in the horizontal.This brings us back to the bubble vial where we attribute levellness to the bubble being in the center of its run when end for ended and any error adjusted out until it stays in the center in both directions.

Acceptable errors are are the sensitivity of the bubble.

A far better system of proving flatness/level is Auto Collimation and is measured every 200mm and graphed out using one station as a base point or even off the bed being measured.

Clive

[David LittlewoodParticipant @davidlittlewood51847]

Hm, but how many of us have an autocollimator? An autocollimator (even second-hand) in working order costs more than many small lathes. I have several, but I'd still doubt it was worth doing compared with the cut-and-try method.

David

[KWILParticipant @kwil]

If anyone is particularly interested in the actual figures, I do have a copy of the 600 Group charts for checking Harrison Lathes. Ask about what you need to know.

[RICHARD GREEN 2Participant @richardgreen2]

Hello KWIL,

What does it say about the M500 lathe ?

Richard.

[KWILParticipant @kwil]

The standard 600 Group chart does not differentiate about which model, the limits are shown for various bed lengths etc. PM me and I will try to answer your particular questions.

[Clive HartlandParticipant @clivehartland94829]

By now I would have had that head off and had a look to see whats what!

It does not seem possible that a lathe of that quality has such a large error and it comes to mind that the head was misaligned before you had it.

Who knows what someone else has done?

Perhaps that was the reason for its sale? Is there not a reason to go back to the seller and query what is going on as such an error would be obvious to a donky.

Clive

[Ex contributorParticipant @mgnbuk]

I would like to think this is simply a matter of terminology, i.e. you really mean "removing wind (twist)" rather than levelling. Otherwise I'm afraid you are just confusing anyone new to this.

You appear to be the only one getting confused ? The terminology is well established in industry, but some model engineers appear to want to use different terms, or seem to think that the industrial methods & terminology doen't apply (thinking particularly about the ME affliction for calling a lathe spindle a "mandrel" here).

A precision level does not have to be particularly expensive (Ebay 290723844611 – or for a little bit more, a box level 360464357901). Such a sensitive instrument for relatively little compared to the cost of machines.- & using one makes installation of and subsequent checking of a machine much easier.

But to each his own.

On the point of slant bed lathes – recently had one delivered at work (Gildemeister CTX500), along with all the original documentation. First requirement when the machine is sited ? According to the supplied manual – level it ! First entry in the alignments ? Confirmation of levels ! Only then on to the other geometric checks.

It has been the same with all the machines I have worked with over 30+ years – the confirmation of levels is the first entry in the alignment checks. On some of the bigger machines, like Webster & Bennett vertical borers, it can be "interesting" getting the levels correct and the squareness checks within spec. – often requiring much tweaking to get the levels to one side of limit to get the squareness within the other side. Particluarly as the "levels" also include the front & side of the column and the cross-rail, as well was on the table top (faceplate or chuck in lathe parlance – a vertical borer being effectively a lathe sat on the back of the headstock, with the bed pointing upwards from the floor). And putting "borer" in the machine description appears to be shorthand for " reduce all values from a "normal" machine by half " !

One thing I was suprised to see not commented on was that the OP said he purchased the machine from a dealer – was the dealer not contacted to rectify the problem ? The error described seems to be a long way from acceptable & should have been reasonable cause to seek redress.

Nigel B.

[RICHARD GREEN 2Participant @richardgreen2]

Clive, The reason I've not yet removed the headstock is that I've got too much other work going on at the moment !

If you read one of my previous posts, it says I'll sort this lathe out when work eases off,

At least I know how to spell donkey !

Richard.

[Clive HartlandParticipant @clivehartland94829]

You are right Richard, work takes priority and the lathe must wait its turn, I was not being nasty and today I have fat fingers.

I apologise if you think I was having a go.

A bit frustrating today when I reamed 10mm and tried to fit something in the hole and it would not go and its too much work to make another two parts.

I have had to make a female hone and reduce the male part to size and it did not help as it was brass. I have just now come out of the workshop having done the job.

Clive

[David LittlewoodParticipant @davidlittlewood51847]

Nigel,

The problem is surely that most hobby engineers do not work in industry installing machinery. Even the rest of your – very interesting – post indicates a distinction between level and squareness, as you say it can be tricky to get both within limits simultaneously!

Since you are clearly very knowledgeable about machine installation, perhaps you could clarify something. I estimate that a deviation of 1 minute of arc over 10" would give a shift of about 3 thou. Now I realise that a bed which is out of square by 1 minute may not result in all of the error appearing in the turned diameter, but – and here is the question – just how much precision can you get with a typical engineer's level; and assuming that you can use that to get the bed at the same inclination (which I'm afraid I still decline to call level) and thus have removed wind from the bed as best one can using this method, what would be the resulting worst-case error in turning parallel? And how would that compare with the "cut and measure" method, which could detect errors of say 0.0001 – 0.0002" depending on skill of micrometer user (and using only equipment every model engineer is likely to have already)?

David

PS – still getting the bloody stupid smileys when you type " followed by ). What a POS.

David

Edited By David Littlewood on 06/06/2012 23:32:38

[Ex contributorParticipant @mgnbuk]

David,

I have never worked in minutes of arc, all the levels I have used have been graduated in the form of a slope – typically either 0.05mm or 0.02mm per metre per division. As a divison is typically around 5 or 6mm wide, it is easy to read to less than quarter of a divison – 0.005mm in a metre (around two tenths of a thou in 40" in old money) or better. As the length of the bubble varies with temperature, the position of the bubble is read relative to both ends of the scale, the aim being to get it central. From memory, most machine specs. have called for level to be set to a maximum error of 0.04mm/metre – less than one division on a 0.05mm/metre level. As with most things engineering, there are tolerances given for levels, as it is rarely possible to achieve perfection. When I was involved in putting rebuilt CNC machine in at customer premises, we normally aimed for around haf the permitted error or better, but "within spec." is all we were required to supply & if the levels had to be sent to one side of the tolerance or the other to get all alignments with spec, then so be it.

As I said earlier. setting level is the first part of checking the overall alignment of a machine. What could reasonably be assumed, though, is that if the machine was initially levelled during manufacture & the alignments adjusted so that they were within specification while the machine was in a levelled state, when the machine was installed at the customer 's site re-levelling should also put the machine in to it's as-built alignment. Most of the time this is how it worked, though some "tweaking" of levels & alignments within the allowed tolerances may have been necessary.

The "cut & measure" bit was usually done on the first component that went on the machine – I can't recall having had a customer requesting test pieces being cut after having had the alignments demonstrated. The main bit of cutting I did was on rebuilt vertical borers, where the machine was used to face the top of it's own faceplate. This was pretty well the last operation, after I had been through the levels & alignments with the fitter who had done the machine. A slow operation – 0.1mm /rev, running in constant surface speed but most machines had a top speed on 300 rpm or so & tables of 1500mm diameter or larger & programmed tapered to produce a concave surface.

When I put my ex-school Myford in at home I used a 0.02mm/metre level. Checked across the bed at headstsock, mid bed & tailstock ends & along the bed on both shears it levelled to better than the width of the division line (maybe 1/10th of a division) at all points. This suggests to me that a). that Myfords did a good job of grinding the bed initially, b). that the casting must have been pretty much stress free when it was ground and c) that the school didn't use it much. I did a "dumbell" turning test after installation. but cannot recall the numbers – I guess it was with the limits I was expecting, as I have not made any headstock-related adjustments.

Regards,

Nigel B.

[David LittlewoodParticipant @davidlittlewood51847]

Nigel,

Thanks for that detailed and helpful reply. I recall reading many years ago that Myford used to leave the bed castings out in the open for several years before machining them, to alow them to de-stress. However, it is quite astonishing (to the uninitiated) just how much twist you can put in a light bed like a Myford 7 by adjusting the supports; even my M300 shows quite measurable changes on adjusting the feet.

I still feel the average amateur is best served by what you describe as a "dumbell" test, as (a) they probably wouldn't have a level of sufficient sensitivity, (b) they may not have acquired the skill to use it, and (c) they will still need to do the dumbell test anyway. But …. we've gone over this, there are different views, and we'll have to agree to differ on the best way to do it (and the best words to describe it).

David

[Harold Hall 1Participant @haroldhall1]

I have to say Nigel that my sentiments are with David's approach. In an early post you referred to precision levels being available at an economic price, comparing it favourably to the price of the machinery being purchased.

I think it is incorrect to assume all workshop owners, and budding owners, have spare cash available. This is confirmed by reading items in this forum where newcomers have obviously stretched his, or hers, budget to the limit with just the purchase of a lathe. To add another £60 to the initial costs for something that will get used initially, even though it can be done without, and then rarely, will not be a wise choice in terms of ones bank balance for very many.

If I can be allowed to give a personal experience. When I purchase my mill/drill, I was horrified that the drill chuck supplied was totally inadequate for holding end mills, such was my ignorance. Even more so when I found that my £600 mill/drill needed a £100 cutter chuck as any additional expenditure was out of the question. I had two options, owning an expensive drilling machine or making a cutter chuck myself. I did the later and it is still in use some 25 years later.

Please do not expect that every new workshop owner has plenty of cash to finance it fully, especially to purchase something of very limited use. It is the reducing costs that have opened up the hobby to those that would not otherwise be able to afford the move. In this case, any unnecessary expenditure would only make it more difficult for those who are stretching their budget. It often being said that we should do more to encourage younger people into the hobby, but most of these will have families to feed and mortgages to finance, workshops will come well down the list.

I will finish with a question I mentioned to a contact recently. How do you level ( as most people understand the word) machines that are installed in workshops on board ship. Quite unexpectedly, he came back and told me he had first hand experience of this having worked on board a merchant navy ship for fifteen years. The answer is of course, you cannot.

Harold

[Sub MandrelParticipant @submandrel]

> Quite unexpectedly, he came back and told me he had first hand experience of this having worked on board a merchant navy ship for fifteen years.

The knack is, of course, to ensure that sea conditions at the time you turn the part are the same as when the part will be used.

Alternatively you wait for a calm day and get the mateys to move heavy weights back and forth until the plimsole line is properly aligned with teh surface of the water.

Neil

[Sub MandrelParticipant @submandrel]

> Quite unexpectedly, he came back and told me he had first hand experience of this having worked on board a merchant navy ship for fifteen years.

The knack is, of course, to ensure that sea conditions at the time you turn the part are the same as when the part will be used.

Alternatively you wait for a calm day and get the mateys to move heavy weights back and forth until the plimsole line is properly aligned with teh surface of the water.

Neil

[blowlampParticipant @blowlamp]

Posted by David Littlewood on 02/06/2012 12:46:01:

Martin,

You said:

"In this context LEVEL = PLANAR."

Only in your eccentric view. I press this point because I think it is distinctly unhelpful to beginners if you use a word in a different way from the one understood by the average person; they are very likely to receive the wrong message. You agree with the general view of what is needed to adjust a lathe to turn parallel, but persist in using a word more or less guaranteed to cause confusion.

David

David.

Level: Google Definition

A lathe needs to be installed in the same unstressed state in which it was manufactured and that's why it is levelled before use. Levelling ensures that the working surfaces at each end of the lathe bed are on the same plane. It doesn't need to be done with a spirit level, but it does need to be done somehow, or else how is one able to be confident of the truth of the lathe ways?

I would never recommend a lathe to be be 'set parallel' purely by jacking the feet without being sure it was very close first, because there's a fair chance of putting a twist into the bed that could easily cause other problems.

If you check for yourself, you will see that the words level, levelled, and levelling are a fair use of the language and in my opinion, shouldn't confuse anyone that truly wants or needs to understand what is being explained.  

Martin.

Edited By blowlamp on 09/06/2012 17:34:21

[Ex contributorParticipant @mgnbuk]

Harold,

I can see where you are coming from, but starting up a home workshop is never going to be a cheap occupation regardless of how you try to do it & the cost of a precision level as described is not much more than 10% of a fairly basic entry level lathe. If I had put links to the kit used at the last employment, that would be a very different matter – IIRC the M&W block level was £250ish+Vat, and the Level Developments magnetic box level over £600+Vat, both prices being probably 10 years out of date. It would be impossible to justify such an investment for a home workshop. The changes to supply that have made small machine tools far more affordable have also been at work with the metrology side of things.

Again, perhaps it is my industrial background that makes me aware of the ongoing requirement for "extra" kit to make a machine useable – the rule of thumb I was told when I started out that "you will spend as much again on tooling & workholding equipment for a (CNC) milling machine as the machine cost" is probably not far off the mark if you buy new, reasonable quality items.

How often a precision level gets used is dependant upon your individual checking regime – if a machine is initially set level, it is a matter of moments work to check it has not moved (and they do move) before committing to a particularly accurate or demanding job.

All setting a lathe up by turning & measuring will tell you is that it can turn a 4" or so piece close to the chuck parallel. What is happening further down the bed ? A lot of small part turning may well be done within the 4" or so from the chuck, but what happens when you want to line bore a casting bolted to the cross-slide, working further down the bed ? Or set up a vertical slide – extra length for a milling chuck + vice on the veritcal slide + component = out of the "tested" area ? If you have introduced a twist in the bed to compensate for localised wear close to the chuck, how will you know ?

I wonder how many would-be home workshop practitioners start out with a tired lathe, install it using the "turn, measure & tweak" method, then get disillusioned when parts don't come out as expected & subsequently give it as a bad job ?

Having set my machines with a level, and regularly re-checked them, I can be fairly confident when something goes awry that it is most likely to be "operator error" rather than "machine error" that is to blame.

This appears to be (yet another) area where the exponents of two different camps (industrial methodology versus ME methodology) use different means to get to nominally the same end – and neither side will budge on their prefered method !

Nigel B.

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