Lathe Levelling - how level?



Before I retired several years ago I heard an interesting tale of levelling a machine.
The guy installing a new machine at a major engineering company worked at various adjustments to get the machine level. He had got very near the desired result then went of lunch or maybe it was overnight. Anyway on his return it was not a level as when left. This puzzled him especially when the effect was repeated later. It turned out that the site was on a tidal estuary and the land moved as the tide came in and out!
Henry
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Try Rollie's Dad's Method of Lathe Alignment (Google for it). Worked for me.
Iain

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That is the method I alluded to, although I didn't know it by that name. I also found it eminently effective, and confirmed my levelling using a 10sec level on the carriage.
Richard
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Richard Shute wrote:

Possibly a dumb question: is it fair to assume that lathe levelling is not so much of an issue when the bed is attached to a humungous and solid base? I have a Holbrook C10 (1500kg, or so) and have it mounted on machine feet. It's level'ish, but not to the accuracy discussed here.
Dave S
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wrote:

Hello Dave, Broadly, Yes. It's not so much a matter of the lathe mass, but whether the base is itself very rigid with a comparatively smaller bed on top so that the machine is a rigid whole. If that is so there's usually not much to be done about any apparent bed twist. In effect, the base is part of the bed or bed is part of the base, either way, it makes the whole machine a very rigid structure. You can measure for twist, but probably not do much to adjust it, jacking the feet of the base will/should have little effect, 'though it may be measurable and unbolting the bed from the base is also unlikely to improve matters and might easily make them worse.
When you get to MUCH bigger machines, the case is often different again. Very often for a machine that has, say, a 10m bed, you would expect to use multiple jacking feed along the bed/base against a suitably serious concrete floor so that the concrete floor effectively becomes part of the machine.
I had not realised when I replied to the OP that it was a fairly serious machine (6.5" centre height), I was assuming something 'home workshop' sized and probably bench mounted where the appropriate levelling is pretty well mandatory. Likewise, an old machine mounted on legs rather than a monolithic base (eg a Southbend Heavy 10) will also need levelling as legs at either end can induce significant twist into a bed having no other support or 'external rigidity' added.
As Bob said, you are better off testing for taper without the tailstock and then setting the tailstock afterwards. There are plenty of write-ups on how to measure machine straightness and to partially account for wear, it depends on the construction of the machine and also what tools you have to hand. You can get accurate results using just a DTI and a bit of ground round bar that actually doesn't need to be especially straight if you look for the mid point of the DTI range and compare that at each end of carriage travel.
Richard
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wrote:

The Heavy 10's bed rests on a pivot pin under the tailstock, allowing it to be set to cut straight without shimming the feet. It pretty much straightens itself when the two opposing adjustment screws are loosened.
jsw
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On Mon, 8 Nov 2010 04:09:48 -0800 (PST), Jim Wilkins

Fair enough, my fault. I haven't actually palyed with a Heavy 10 and assumed too much from its appearance.
Richard
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wrote:

I owned mine for ten years before noticing the pivot and its adjustment screws under many layers of trade-school paint, applied yearly in lieu of real maintenance.
Rollie + other goodies: http://www.neme-s.org /
jsw
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"Dave S" wrote...

Humungous is definitely the word - I have a C13 (2 tons) and I reckon the base alone weighs as much as a Chipmaster! I still want to check the bed for twist though, Just In Case.
Are you also a member of the Yahoo Holbrook group? Lots of useful info there (particularly on the C's) and some very helpful folks with advice on rebuilding my C13! I'm working on hooking an ABB VFD/inverter to the 3-speed motor (not too far off the final design now), are you blessed with real 3-phase?
Cheers, Dave H.
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Dave H. wrote:

Yes, I joined the Holbrook group as soon as I bought the lathe.
I struggled to get the C10 to run at top speed - initially from a Transwave static converter, then a rotary converter, then a 3 phase inverter (415 3ph in/out, with the input stage modified to act as a voltage doubler). I haven't had time to do much for the last year or so but I'm fairly certain that the headstock oil is too viscous (the spec is very thin indeed!) so when I get the right round tuit I'll replace the oil.
Dave
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Dave S wrote...

Hmmmm, sounds very much like my hacked 5HP ABB 301 inverter (2 sets of series-connected electrolytics, neutral to the 1/2-way pads between 'em) - which I've had some fun and games with, it had been "drop tested" by DHL on its way to me, so it was a 200-piece jigsaw puzzle by the time it reached me... Only cost me 20 though! I've had to replace the LCD screen (2 from a nice Chinese gent on Ebay, hooked the backlight up and it's a pretty blue colour now), do a lot of gluing and sticking, un-munge the connector from VFD to programming panel, but it's all working as intended now! I was a bit disappointed with ABB though, no service manual / circuit diagram available because it's "obsolete", only 10 years after production ended - I guess they didn't supply them to the military, then?
Have you hooked up the interlock switch on the C10 speed lever to "coast" the motor during changes? On the ABB I can set up 2 sets of acceleration / deceleration ramps under control of a switch, so I'll put in a nice slow ramp for speed changes, something fairly savage for E-stop / threading stop, although I'll need a braking resistor... All that will come once I've done a bit of renovation, poor thing had been neglected in a leaky shed :(
Re the headstock oil, I'm told that LHM fluid (for Citroen / Rolls-Royce suspension systems) is a fairly good choice, possibly with a hint of paraffin to reduce the viscosity a touch? Like the Holbrook, they have a fair bit of bronze in 'em so it's formulated to protect that as well as steel.
Cheers, Dave H.
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Dave H. wrote:

Yes, that's exactly what I did
... snipped

I did when I tested the whole thing but I've been waiting for time to finish the job and do it all properly - a shortage of tuits.
On the ABB I can set up 2 sets of acceleration /

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