Tailstock height

[AjohnwParticipant @ajohnw51620]

The other thing that's important Ian is that the change in height is even along the bar so say it's such and such at 200mm or what ever the length of the bar is. It should 1/2 that at 100mm and also proportional at 50 and 150. If not there is an error in the bar or bed. Centres need to be in both ends.

It must be done by running the dti across the top of the bar with the cross slide – if you run it along the bar it can drift off the centre making it look lower than it is. If that shows it flat to the bed on the top then running along the side makes more sense.

I don't know how you made the test bar but with rather careful fixed steady setting up on a length of silver steel it will be as accurate as you have set it up. A good number to aim at is under 1/2 thou. Just grip a short part in the chuck, say 1/2" on 1" dia bar, no tighter than needed and then get the other end running true via the steady. Then face , recess the end a bit, centre drill and chamfer the end corner. Reverse the bar and do the same to the other end. The chamfer and recess are to just protect the centre hole from knocks

If you use one of the centre drills that are about 6mm dia it doesn't matter if the tailstock is out a touch. They are happy cutting on one side, just go gently.

Setting this up is tedious which is why I have never made one at home. I bought one a long time ago. No fixed steady for the lathe I had either.

John

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[MWParticipant @mw27036]

The tailstock on my clarke can lock up in some weird ways, i've seen the same happen on a colchester master and yeah well sometimes it can just sit askew to the headstock if theres enough movement in the gib and clamp in a funny way, there isnt really much other way to explain it.

The optical error could be true because it isnt a direct measurement (physical contact) which is always preferable.

I bet i'm not the only one who's noticed the aforementioned funny placement of the tailstock that can occasionally occur.

PS. i probably wouldnt want to check the runout of the tailstock to the head myself, i know i'd just be opening a can of worms, i'd rather live in ignorance for the time being 😛

Michael W

Edited By Michael Walters on 03/03/2016 21:47:35

[Neil WyattModerator @neilwyatt]

Posted by Ajohnw on 03/03/2016 17:58:05:

I have seen spec's of other makes with things like -0 +0.05mm. Boxford use that as well – high at the tailstock end over 380mm centres (15" checking all along.

Schlesinger says 0.00-0.02mm, rising towards tailstock end.

Neil

[AjohnwParticipant @ajohnw51620]

The blokes at Boxford must have never met him Neil. Wabeco haven't met him either.

I can never make my mind up why the limit isn't +/- other than high means that it could be lapped out but with errors this low it isn't how I would cure it if the lathe is generally ok. Wear on the tailstock slide might mess things up even then.

The other aspect about it being corrected by lapping is still no saying how accurate the alignment of the morse cone is and the lapping might make that worse which will matter when things like reamers are used.

The best spec I have actually read on a machine was a long bed DSG. Centre work in relation to the tailstock was guaranteed to be better than 0.0015" over I would estimate 5' if installed correctly and that one really was a high spec machine. Going on some work I did on it around 3ft long it was a lot better than that.

It's an interesting area. My father was a production engineer, senior at the sharp end not desk tied. Mostly very high volume stuff. His stance was that once a centre is involved it's not possible to hold a ROUNDNESS tolerance of <0.0005" reliably so use centreless processes if that.is needed. That might just be a cutter box on a bar or 2nd op auto. This was from actual direct experience as well.

John

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Edited By Ajohnw on 03/03/2016 23:37:52

[Neil WyattModerator @neilwyatt]

My thought was that if Myford lathes don't meet the Schlesinger limits, why fret if a relatively inexpensive one doesn't?

The reason for high is that the weight of the work can only depress the tailstock rather than raise it, so it acts against any error. Many of the limits are toleranced against the way the machine bends or the work shifts under a cut.

This is the standard for lathes with up to 15 3/4" centres, into DSG territory.

Bear in mind the tests are only valid when the lathe is installed set up to the same standard as in the factory and in practice this rarely applies.

This is why many prefer practical tests to Schlesinger – if the lathe turns round, and parallel and faces flat within acceptable limits, that's all that really counts.

N.

[John FieldingParticipant @johnfielding34086]

When I had a similar problem with my Super 7 the hardest part was measuring the difference in height. And then I had a "magic moment" whilst puzzling it out during a cup of coffee.

All you need is a piece of round bar, say 1/2" silver steel you grip in the headstock chuck. Make a similar 1/2" diameter bar to hold in the tailstock chuck with about 50mm sticking out in both cases. Then a piece of other rod with an adjustment screw tapped into one end and a lock nut. Say another bit of 1/2" round bar faced off truly at one end and the machine screw in the other. This is attached to a piece of square bar with a countersunk screw drilled up through the square bar so that it will span the lathe bed and set perpendicular. It looks like a T upside down.

This is a variable height (telescopic) pillar. Place the pillar under the headstock rod and adjust the screw so it just touches the underside of the bar in the chuck and tighten the lock nut. Now move it to under the tailstock rod and if everything is OK it should have a similar feel as you move if under the rod. To measure the difference in height reach for your feeler gauges!

I use this gizmo to divide out 3 and 4 radial holes on things I need to drill on a PCD, by adjusting the screw to catch the outer of a chuck jaw. Mark the hole and then slip out the pillar and move the chuck around and catch the next jaw on the top of the pillar.

[LambtonParticipant @lambton]

John,

Neat idea but will only give a true reading if both the main lathe chuck and the tailstock drill chuck are perfectly accurate.

Unfortunately both these types of chuck usually have errors. You could of course take a number of readings with the chucks rotated a bit and find the average.

Eric

[BubbleParticipant @bubble]

Does anyone know the correct amount that a myford tailstock should be higher by? Im'e thinking of myfords original spec tolerances.

regards

Stephen

Myford (Beeston that is) used to selectively choose the base plate thickness on the tailstock on assembly of the machine, to give the proper alignment of centre height. The design error was zero plus minus.

Jim

[stephen.Participant @stephen]

Thank you Jim

I believe the reason for the tailstock to be higher rather than lower is because of the reason Neil gives and to allow for bed and tailstock base plate wear. Thinking back to when i checked my Myford, the tailstock was between 1.5 – 2 thou higher. Is this an acceptable amount?

I checked it by using the test bar between centers and clocking the highest point of the bar at each end, measuring the difference. As John said, you must use the cross slide rather than just running along the top.

Many thanks for your comments, i have often wondered what is an acceptable amount.

Stephen

[AjohnwParticipant @ajohnw51620]

It's cost Neil – what they can realistically expect to achieve. Shaublin managed to 10um and claimed any tail stock could be fitted onto any of there (small) lathes as a result.

I'm inclined to say yah boo tory style to theories about the way machines flex etc. Maybe we could calibrate quill deflection against extension with certain weights of drill on the end and also how fiercely the drill is being used and a host of other things. It just doesn't wash.

Evenly changing readings along the bar when it isn't level are important as well – warped / worn bed. A plain bar without the morse taper is better for that as it gets in the way and the only solution is to reverse the bar to allow the whole length to be done.

John

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[MWParticipant @mw27036]

"I'm inclined to say yah boo tory style to theories about the way machines flex etc."

I agree with you that people can sometimes over think things and come to some strange conclusions with theories. However, i think now that the quality of castings has probably improved over the previous century, the "flex" issue is more of an old fashioned concern, which i have no doubt was genuine in the minds of users, It probably was true that some lathes were made rather haphazardly and that sometimes you could get warpage from the poor quality of iron casting. I remember Sparey once remarking that there were an awful lot of badly made lathes for home usage at the beginning of the 20th century of questionable origin, alot of them were simply flat bed slides with no lead screw and therefore no screw cutting. People still dont believe me to this day that water was the most common coolant at one point.

Most modern made machines now, even the very cheapest ones, are likely to be as flat and true as a proverbial pancake.

Michael W

Edited By Michael Walters on 04/03/2016 17:13:41

[Ex contributorParticipant @mgnbuk]

Most modern made machines now, even the very cheapest ones, are likely to be as flat and true as a proverbial pancake

There is a long running thread on here for an inexpensive Chinese made lathe with a German sounding name that suggests this is cannot be taken for granted !

Having spent nearly 40 years (where did it all go !) working with machine tools in industry, I can only suggest that similar methods to those used when (quality) machine tools are built are used to systematically track down errors. All the fitters I have worked with (trained the old fashioned way at the likes of Asquith, Butler, Stirk, Crawford Swift etc. ) have been quite emphatic about building & checking machines from "the bottom up" – each part, starting with the bed & working upwards, is "right" before moving on to the next. While there will no doubt be howls of protest about the need, that starts with a precision level to make sure that the bed is indeed without twist or bow. The headstock is aligned to the bed using a test bar in the spindle taper, any error to be upwards & towards the toolpost only. Likewise the tailstock is aligned to the bed using the testbar & again any error to be upwards & towards the toolpost. Without being systematic & eliminating errors as the build progresses, it becomes very easy to start chasing your tail to eliminate errors later on in the process.

"Rollies Dad's method" may well "get you by" if the machine is not too bad to start with, but I wouldn't want to track to down the root cause of a problem using it. Introducing an unknown amount of twist to the bed to try and get a machine to perform satisfactorily does'nt seem the way to go to me, but seems to work for some.

Latterly at my last employment most of the rebuilds of CNC machines were larger centre lathes & vertical borers. They look very substantial (upwards of 16 tonnes for a 48" -54" vertical borer) but can be twisted quite easily & getting the final alignments "to spec" relied upon the machines being bolted securely to a substantial floor and "tweaking" the levelling bolts to twist the machine to get the levels & squareness within tolerance. Machines vary considerably in their stiffness – as an example I had a customer in the West Midlands who had 3 centre lathes of similar capacity (about 500mm swing / 3.5 m between centres IIRC). One was of British manufacture at the lower cost end of the market (no names !), which required bolting to a substantial foundation block cast into the floor to get (and hold) alignment. The other British lathe (up the price scale) was just bolted to the factory concrete floor. Finally was a Russian machine, which had a massive cast coolant tray integrated into the bed – this sat on the floor unbolted, with the only levelling required being to ensure it didn't rock & the coolant ran back to the pump ! Of the three, the Russian lathe was the most used & most popular with the operators.

Take nothing for granted !

Nigel B.

[MWParticipant @mw27036]

"Take nothing for granted !"

I can honestly respect this opinion entirely, i know where you're coming from when you say that all the individual components of a machine need to be correctly toleranced in order for it to work. But when it comes to the issue of "bed flex", nothing but my own logic tells me this is something i can't agree with strongly.

First of all, the issue of asian machines, i reckon they've been making this business of home machines since around the 70's or 80's. Thats given them alot of time to catch up with the quality practices we have in the west and so i'm inclined to believe they've got it right by now and my own machines seem to be quite flat. The end of the day, they want our money and if a healthy dose of skepticism around quality convinces them they arent going to get it, then theyll move heaven and earth to correct it.

With that out of the way, the idea of a solid cast iron lump being able to bend like it were playdough. It just seems a bit fanciful to me, thats all. I mean, you would need arms like pop eye to put that much pressure on to a few bolts. I've never tried crushing cast iron before but i'm sure it's pretty hard. I do agree however, that with an extremely long bed machine would present some bending thats more likely to be true. In my experience, the wood of the bench itself would sooner give way to bending than the machine itself.

This moves me onto another problem of "bed leveling". Ok, if you can see it's going up and down like a yoyo then you should consider a flatter surface. If you can see that its pretty much flat, i dont see where the issue is. The tool moves relative to the level of the work piece, meaning that so long as the relative level of the tool and the work piece are the same, it's not going to make 1 iota of difference to your work. The absolute level, if anything will just put your mind at rest, thats all but the machine will still behave the same because everything is moving relatively to each other.

I hope you can see why i would disagree and fully respect the opinion you have of the high standards of british tool makers.

Michael W

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Walters on 06/03/2016 10:21:28:

But when it comes to the issue of "bed flex", nothing but my own logic tells me this is something i can't agree with strongly.

…

With that out of the way, the idea of a solid cast iron lump being able to bend like it were playdough. It just seems a bit fanciful to me, thats all.

.

Michael,

First; please forget any comparision with playdough … that's not how cast iron bends.

Second; please explore the concept of "stiffness to weight ratio" … it's very relevant.

MichaelG.

[MWParticipant @mw27036]

I obviously cannot speak for everyone, that would be silly. But my own machines are literally almost solid cast iron, no gaps in the bed. My bones are probably going to give out sooner than this machine bends. Also, if rigidity, stiffness, hardness and weight were all they cared about. You could justify making a lathe bed from stone, it would just take forever to make.

Ps. I rather rudely forgot to mention my machine in question is a clarke CL430

Michael W

Edited By Michael Walters on 06/03/2016 11:11:06

[Tim StevensParticipant @timstevens64731]

There is a fallacy behind the 'beds must be level' idea, in my view. What is needed, surely, is that the bed does not twist, or the toolpost will rotate as it moves from one end to the other, cutting a taper as it goes.

In practice, a proper level is an easy way to get the bed free from twist, but it should not matter, should it, if the whole bed is a degree or two off horizontal, as long as it is the same angle all along?

Are there lathes on some ships, I wonder? if so, do they have to wait for a flat calm?

Cheers, Tim

[Michael GilliganParticipant @michaelgilligan61133]

Tim,

You're right, of course, and I thought it had already been 'done-to-death' on this forum.

MichaelG.

Edited By Michael Gilligan on 06/03/2016 12:31:45

[MWParticipant @mw27036]

"There is a fallacy behind the 'beds must be level' idea, in my view. What is needed, surely, is that the bed does not twist, or the toolpost will rotate as it moves from one end to the other, cutting a taper as it goes."

You're too right! How is it possible to maintain total level? for us mere mortals its unlikely, ok there is a point there, when its so "unlevel" that gravity inevitably comes into play.

I'm sorry for kinda spamming this thread with my digressions, as Michael G has pointed out, I'm relatively new here, so maybe this idea has just piqued my intrigue so to speak.

I even measured my own bed with a trusty vernier, and i will concede, it isn't perfect. Theres about 0.010"(0.25mm) difference in thickness between the front and the back over a distance of 300-400mm. I'm not really too bothered about it because i know this can happen from wear. And its likely that the casting itself was a little thicker and thinner here and there. I can see with my eyes that its really flat though.

with respect,

Michael W

[AjohnwParticipant @ajohnw51620]

My comment on flex was aimed at Niel's theory that centre heights are high to account for "flex" when in use. There will be flex but it's not possible to specify the amount because it depends on what the machine is doing and if it was significant in relationship to the work that is being done something for a problem.

The Opti thread keeps cropping up but people seem to miss the fact that one fault – lead screw alignment lead to a catalogue of disasters. I'm not sure what other work Hopper did on it. The point here really is many people who might be a little conversant with machines would have spotted that pretty quickly. Instead all sorts of suggestions on fixes relating to the saddle were suggested that these people wouldn't need. These were done and eventually because of the shear force on the lead screw needed to move the saddle along caused it's parts to pop out. Take that away and my impression is that Hopper would look at the lathe and wrinkle his nose and say not bad – it;s weight, size and power have obvious limitations. I wouldn't even buy one for that reason. If it was for watch / clock type work I might.

The banana bed thread fault probably cropped up because the bed casting was some combination of cooled too quickly or machined too soon after casting. It will have been as flat as the machine used to make it could produce when that was actually done but internal stresses would soon fix that. The other possibility is clamping forces when it was mounted on the machine distorted the bed, bits if swarf under the feet. Could be all sorts of things including the machine slides being worn out or even just set too loose-that does give banana surfaces. The OP lapped the tailstock base then oh dear. He had done several silly tests that didn't tie the problem down. The only fix for this problem would be to send the machine back. He might even have mounted it incorrectly who knows.

It all boils down to really finding out what is wrong before doing anything else. I don't think this area is helped by all of the titivation type pages that are about, talk of casting kits etc. People leap in looking for faults rather than getting some bar and turning with it and then proceeding from there. I've owned 2 chinese machines. All I did on both before using them was adjust the slides correctly. On one this meant cleaning up the point on a mail dovetail a bit. That was the miller. It was fine. On the lathe I turned some bar. Rather a lot of taper not due to the bar bending so the spindle alignment was obviously well out. I then tried turning a longer piece with a centre in. Oh dear that was out too. One thing I didn't do was to bring 2 centres close together. No point I wouldn't be able to see the sort of error levels I want or expect. I part sorted the headstock out and made a mistake of trying to dowel it as it was stupidly short along the bed. I didn't really have the kit needed to dowel it well. The tailstock proved to have too many problems to sort so I had to put up with that.

The moral really is don't mod anything until sure of what the problem really is and maybe Ollie's grand dad might have added check the bar in several places along the bed – side and top. His uncle might be aware that it isn't as simple as that, use a test bar. Me – I am not sure about that. The method isn't new to me but the name is. I am pretty sure I have been told no use a test bar. There used to be some web pages about that showed very clearly what various alignment errors and problems did to work as it's turned or ground etc. I can't find any now.

John

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[AjohnwParticipant @ajohnw51620]

The reason for levelling a bed to very high precision is pretty simple really. It allows a high precision level to be used to check the bed for twist. That is sometimes mentioned but it can be used for another reason. Not twisting the bed when it's mounted. Actually I don't think that the lathe needs to be precisely level to do this providing the level has adjusting screws.

Or probably if it's from Chine – removing a bit of twist that is built in.

John

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[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Walters on 06/03/2016 12:53:16:

I'm sorry for kinda spamming this thread with my digressions, as Michael G has pointed out, I'm relatively new here, so maybe this idea has just piqued my intrigue so to speak.

.

Michael,

It shows that you're thinking !

… generally seen as 'a good thing'

The only trouble is that this thread's original question is in danger of being forgotten whilst people discuss their pet theories. … It was ever thus.

MichaelG.

[Neil WyattModerator @neilwyatt]

> literally almost solid cast iron, no gaps in the bed

When you get a really big dig-in and the tool is stuck in the work, you may be surprised just how much everything twists.

Neil

[Ex contributorParticipant @mgnbuk]

I can see with my eyes that its really flat though

Define "really flat" ? With all due respect, your Mark 1 eyballs cannot compare to a 0.02mm/metre level whan it comes to sensitivity for detecting a bow or twist on your lathe bed.

Does it matter if a machine is absolutely "level" ? Apart from that being a requirement (the first test actually) of the much quoted "Schlesinger tests", probably not. More important is that the use of the level indicates with great sensitivity whether or not the bed is twisted or bowed. And your Clarke bed will almost certainly be a 5 sided box & not solid, so it will be capable of being twisted (it would be capable of being twisted even if it were solid – it would just take more force to twist it).

A couple more examples :

A fitter had been struggling to bed the crossrail onto a vertical borer column – if you are unfamiliar with vertical borers, I have put a photo in an album on here (I think !). Basically a lathe sat on the end of it's headstock with the bed pointing upwards, the cross rail is the "saddle" & the part is cut with the equivalent of the compound slide on a standard lathe (the crossrail is clamped while machining & is moved to suit the height of the component).

The column was about 2 metres square section by about 4 metres long (high in normal operation), opened ended & hollow but extensively ribbed internally and had been laid on it's back on a couple of sleepers. I would guess it weighed about 5 or 6 tonnes. The crossrail (a hollow, ribbed casting) would have weighed a couple of tonnes – far too heavy to push on the blued-up column ways, so a pulley system had been rigged to pull it using the overhead crane. The (experienced) fitter had been on with bedding & aligning this for about a fortnight & I was asked to find out what the problem was. Turned out he was "chasing his tail" – couldn't get consistent results & didn't know why. First question I asked was had he levelled the column – no came the reply, something that big won't move, so didn't think it necessary & hence just placed it on two sleepers. Not convinced, I found 4 levelators (precision wedge type levelling blocks) & we set to and levelled the column. Two days later the job was completed – bedding / aligning had gone the way the fitter had expected due to consistent, repeatable readings from the now stable column casting.

A Butler Elagmill milling machine was sent to us for a rebuild & retrofit (basically re-machine the slideways, replace ballscrews & bearings etc. and rewire the machine with a new CNC control & drives). In the works (& before return to the customer) the alignments were repeatably within spec, but on site they could not be consistently demonstrated. The rather gung-ho fitter was all for breaking out his scraper and diving in, but the MD wanted a second opinion. Turned out the customer had moved the machine from it's original location (on a purpose installed foundation block) and had rag-bolted it to the factory floor. Unfortunately, the position chosen had put the machine bed across two concrete floor slabs & the machine moved whenever the gantry crane moved across the joint. When this was pointed out, the machine was moved back to it's original foundation, where it was then stable & we could show the same alignment results that we had seen before shipment (and with no further scraper action !).

With regard to my physical capabilities, be assured that I am no Schwarzenegger ! At 5'9" and about 12 1/2 stone & with both wrists having had carpal tunnel decompresion operations, I cannot bring a huge amount of pressure to bear on a spanner – but I can twist a vertical borer to tweak the alignments without too much effort.

No problem at this end with trying to answer "piqued interest" questions if my experience may help.

Nigel B.

[MWParticipant @mw27036]

Thats quite an interesting tale you've got there, Nigel, i only wish i could've been in your shoes to see it. Since i dont have that much experience in industry, and never seen or really understood vertical boring machines. I know that my clarke isn't completely solid but it's atleast a good few inches deep even if the base is hollow. I didnt have much time to look at it as my main concern was hoofin' the damn thing into place.

I have to say it's an unfortunate habit of mine to ask and pontificate a little bit more than what i consider the average joe would. Context seems important but also tends to wander.

I'll have to take that as a compliment, Michael G, and at the risk of taking this conversation even further from the authors intention, i'll leave it at that.

Michael W

[Author]

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