A question for those who have set up industrial machine tools.

[John CParticipant @johnc47954]

As seen in another thread (Boxford Spindle Play) i have been chasing my tail trying to reduce the play I thought I was experiencing in the spindle of my Boxford STS10.

In a flash of inspiration, I moved the indicator from the cross slide to the headstock – and presto – no more play! So the play I was seeing was movement between the headstock and the bed. Clamping an indicator to the bed confirms this – pushing the spindle shows movement between the lathe bed and the headstock.

I have carefully tightened the headstock clamping bolts and the TIR movement is now about 0.004 mm – that's 1-1/2 tenths in old money. I can get this same deflection by leaning almost anywhere on the lathe, and over twice this if i apply a spanner with only moderate force to the headstock mounting bolts.

So my question is how much flex is acceptable, and to those who have set up industrial machinery, did you experience similar movement?

I am just off to read Schlesinger's 'Testing Machine Tools' to seek inspiration, and perhaps sanity too!

many thanks,

John

[John CParticipant @johnc47954]

How much should a lathe bed flex?

[Neil WyattModerator @neilwyatt]

Dr Schlesinger's tests say nothing about rigidity, your lathe could be made of rubber and still pass.

That's why many would say Colonel Salmon's practical tests (based on the work produced rather than testing the machine itself) are far more valid than Schelsinger's.

Sadly Salmon is largely forgotten, which is a great pity as his approach is far more applicable to the home workshop.

Neil

[Nick_GParticipant @nick_g]

.

I have the same lathe and don't have the same issue.

This :-

Sits on this :-

And although the diagram does not show it the bottom of the headstock is groved so that it sits onto the V of the bed.

I am wondering in at sometime the headstock has not been tight and crud has got between them. I cannot check ATM until I get home later but I 'think' there are 2 clamps front and back where only one is show. (prob for clarity of the drawing)

Nick

[John McNamaraParticipant @johnmcnamara74883]

Hi John

A true story it starts off topic but I will get to the point ….

When I was in my late teens I helped my uncle restore his 57 Chevrolet, it was his pride and joy having purchased it new.He lived in the country and did a lot of miles in it, it finally needed a full engine recondition and rebore of the big 6 cylinder engine. Being in the country has its advantages…. just down the road was a Alex a first class mechanic of the old school. His workshop was amazing! a couple of lathes included. The engine was removed to be rebored on site. naturally he would do it there on the spot, he had a bolt on boring rig similar to this one: **LINK** I spent a week working on it, it was fun and I learnt a lot. Now getting back to the point as each cylinder was carefully bored and then measured using an inside stick micrometer

It was then I learnt a lesson I have never forgotten. Alex carefully set micrometer in the bore just holding by its own weight. I guess it was set parallel to the crankshaft, He then pressed against the sides of the block and the micrometer dropped out. With hand pressure alone he was able to distort the heavy block enough to release the micrometer.

All materials deflect when subjected to a load.

Regards
John

[John CParticipant @johnc47954]

Thanks all!

Neil – do you have a link to Colonel Salmon's work? Google brings up this page and then goes on to fish!

Nick G. I have the diagrams – there are indeed 2 clamps for the headstock, spindle end and rear end. The bolts for the rear are accessed by removing the change gear quadrant. All are good hand tight.

John M – thanks for your story! It reinforces my belief that I am probably looking too hard. I have now less than 0.002mm defection at the spindle nose, but a 25mm steel bar clamped in the chuck shows 0.04mm deflection at about 100mm – which has to be due to bending.

I fully agree that the proof of the pudding etc, so will try some more turning tests later.

Once again, thanks for talking the time to reply.

Regards,

John

[jason udallParticipant @jasonudall57142]

Industrial machines?

150 k cnc lathe?
Machine bolted to floor. .
Test turned…adjust bolts ..test turn…
Repeat.

Machine display limit ( consequently programed) 1 micron.

True -ness check on installation. 0.1micron.

Re check after ten years…0.2- 0.1 micron..
Some of that might be ground move or possibly wear…35 000 hrs on clock

Edited By jason udall on 16/09/2015 17:43:06

[jason udallParticipant @jasonudall57142]

Of course one 20 year old HARDINGE..
No leveling..hardcrete bed..test turn….mmmm is this clock bust?…
No visable move on dial …
Hardinge…awesome. ..

[martin perman 1Participant @martinperman1]

Gentlemen,

As I've said before I've worked with all manner of machine tools and various other machines all my working life and where I served my time the company used many grinders and one particular make was Studer and we had several which had the bases made from concrete with machined plates set in to fit the various components of the machine, the purpose of the concrete was its dense and doesnt need stress relieving, they were very accurate machines.

Martin P

[AjohnwParticipant @ajohnw51620]

Posted by John C on 16/09/2015 16:39:59:

Thanks all!

Neil – do you have a link to Colonel Salmon's work? Google brings up this page and then goes on to fish!

Nick G. I have the diagrams – there are indeed 2 clamps for the headstock, spindle end and rear end. The bolts for the rear are accessed by removing the change gear quadrant. All are good hand tight.

John M – thanks for your story! It reinforces my belief that I am probably looking too hard. I have now less than 0.002mm defection at the spindle nose, but a 25mm steel bar clamped in the chuck shows 0.04mm deflection at about 100mm – which has to be due to bending.

I fully agree that the proof of the pudding etc, so will try some more turning tests later.

Once again, thanks for talking the time to reply.

Regards,

John

Just how accurately do you expect a chuck to run?

John

–

[Ady1Participant @ady1]

So the play I was seeing was movement between the headstock and the bed.

wow

Take the head off and have a look, don't just screw it down tighter

Boxfords are good gear and shouldn't have this kind of issue

[Nick_GParticipant @nick_g]

Posted by John W1 on 16/09/2015 23:03:48:

Just how accurately do you expect a chuck to run?

John

–

.

He does have a point 'original John' I originally got my decimal point position wrong on my first reply.

As I said I have an STS 10 20 Boxford and an 'Industrial machine' you state in the thread title they are certainly not. But to be fair they were never intended to be.!

On the scale of things as lathes go they are a paperweight. They just don't have the mass for one thing. Mine certainly needed fixing down to the floor and properly leveled before it started to tick. And then only in it's capacity envelope of intended design use.

Cast iron does bend and flex. Other wise one would not be able to get rings onto a piston as just one example.

You could of course to improve things if you wished by going a little step larger in machine size and buy a Hardinge as previously said. However I think a mint fully and properly refurbished one (not just a paint job) will put a hole in your pocket in the region of £20 – 25,000. There is a company in the States that will even export you one in original factory condition. You may also need to budget to reinforce your flooring.

I love my STS, but a precision machine it ain't. It is however more accurate than I will ever be. I am the weakest link in the chain.

Regards, Nick

[MuzzerParticipant @muzzer]

Posted by jason udall on 16/09/2015 17:41:45:
Machine display limit ( consequently programed) 1 micron.

True -ness check on installation. 0.1micron.

Re check after ten years…0.2- 0.1 micron..

Jason – when you say "micron" I suspect you mean thousandth of an inch? A micron is a thousandth of a millimetre. I doubt you'd be able to measure that….

[Neil LickfoldParticipant @neillickfold44316]

Hardinge made special machines from 1 about 1978 and onwards that had offsets of 0.00001 inches, yes 10 millionths of an inch. Hard to believe how long that technology has been around.They are sub micron machines.

Neil

[AjohnwParticipant @ajohnw51620]

Things these day will seem to measure 1 micron Muzzer. I have a dti for instance that will. Trouble is that at best even at this level it's really digital and probably the limit of resolution so in real terms is +/-1 digit and then there is the tolerance on the scales themselves when measurements are made with digital mic's and digital readouts which are very likely to be worse, getting even worse as the length goes up. Often that tolerance isn't even given.

Lastly lathes are not micron devices, most of the metal turned on them isn't either.

As well as mentioning how accurately a chuck hold I should have asked how straight does he think the bar is. Even on ground stuff a tolerance of 0.001in per foot is by no means unusual.

The best way to check a lathe is via turning and even then actually measuring all aspecta to 1 micron is beyond the ability of most people really. Even a digital mic in really terms is only a comparator at this level if used very carefully.

John

–

Edited By John W1 on 17/09/2015 09:30:52

[jason udallParticipant @jasonudall57142]

Muzzer.
I do mean 10^-6 m
Or a thousandth of a mm.
Could I measure 0.1 um ?
With some of our gear yes.
Routinely 1um believing it to +/- 3 u m on a mick in ws.
The fitter brings his own clocks for thouse tests quoted above…
Effectively clocks reading to 0.005 um/div

These were in effect much more sensitive instrument than used in production ( typically 1 um).

That said one lathe ..hardinge gt sp..worked to 0.1 um
And against thermal would hold that all day
Tool “wear” not withstanding..differentialthermals ccould be a problem…if tool /holder expands more/less than machine..
And if “wear”-change of keeness – changes cutting force thus part deflection…
We delivered hundreds of parts a day to +/-3 microns at a cpk of 6 or higher.
CPK..Capability index…a measure used in statistical process control…

[jason udallParticipant @jasonudall57142]

That said one short coming of the hardinge manuals.
The usal dodge of taking a final cut with a thumb on the tool post to finish your part..doesn’t work..even the manuals are to ridged for that.

[Neil WyattModerator @neilwyatt]

This is the only thing I have ever found on Colonel Salmon, I suspect most of the history of this is on paper, not the net

Schlesinger%20limits1.pdf

No, ether is more out there:

IEEE

This lathe is to 'both Salmon and Schlesinger limits':

http://www.lathes.co.uk/mondial/page5.html

Plenty more, especially from the UN, but you have to search for 'schelsinger salmon machine tools'

 

His reputation seems to have suffered from being French, which seems to automatically bias web searches against someone!

Edited By Neil Wyatt on 17/09/2015 12:43:44

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