.

An excellent idea, Bazyle.

To my mind, the answer is very simple: If the manufacturer could achieve everlasting perfection, then the lathe should be made to face flat. In the real world, however, there are are tolerances for everything and Dr. Georg Schlesinger was right. …

For it to be useful; a lathe must face somewhere between "slightly concave" and "dead flat". How close to flat therefore depends upon how accurately made, and how resistant to wear the lathe might be.

MichaelG.

Edited By Michael Gilligan on 24/02/2014 20:58:43

Can anyone guess who wrote:

"Accuracy is a feature much to be desired in any machine tool, and the reputation of a lathe may stand or fall by its virtues in this respect. In recent years tstandards of accuracy for machine tools, including the well-known Schlesinger limits, have been set up to define the essential factors of concentricity, alignment etc. which are consdierd desirable in machines. Generally speaking, however these can only be observed in high class industrial machine tools; the types of lathes which have to be built at a competitive price are often sold without any guarantee as to accuracy … In the past, many small lathes have been manufactured in which accuracy was very dubious, but in view of their low cost, their imperfections could be tolerated, and they served the purpose for which they were intended quite well. It does not follow that accurate work is only possible if the machine tool itself is above reproach … the requirements of the amateur, to whom time is of less importance, may be adequatel;y served by a simpler and less expensive lathe."

And

"Lathe users, other than those with practical experience of machine tool fitting, are strongly advised not to attempt any modifications which might permanently affect the accuracy of a lathe. It is safer to accept the inaccuracies of the machine and learn to live with them. Even the most expensive lathe cannot be expected to remain in perfect adjustment indefinitely, and all machines have their limitations."

Neil

Check my 40 year super 7 mark 1 turns measure's 0.0003 " over "

Edited By Nobby on 24/02/2014 23:11:52

Edited By Nobby on 24/02/2014 23:12:27

Edited By Nobby on 24/02/2014 23:12:47

.

.

You did, just now.

Ironic though really when you think about it is that the old guy who taught me machining and had been in the job all his life, First job he ever did was rudder bolts on the arc, last job was brass turnbuckles for his coffin.

If you had asked him who Schlesinger was he would not have known.

Now if you had asked him how to tweak a hole 0.0001" either way with a reamer he'd have known.

I wonder if "Borderline Schlesinger" is another name for OCD ?

Edited By John Stevenson on 24/02/2014 23:31:53

Probably. I've no idea whether my lathe turns concave or convex but I have set it up so it turns parallel because that is important to the sort of model making I do. I sometimes wonder whether the people who obsess about these things actually make anything.

Rod

A lot of the work we do on a lathe is not between centres. Allowing the deflection demon to spoil our work even a say 20mm shaft will deflect away from the cutting forces. if it does the work will be a larger diameter as the cutting point moves towards the tailstock. Very annoying if you are fitting a shaft to an existing hole by feel. It will appear to be tight but when you finally get it to enter the hole it will be loose, Not good.

On the other hand if you are turning a base of some sort that has to sit on a flat surface you want it to be touching the surface all around its periphery not possible if it is slightly convex.

Both the above cases suggest that making the lathe turn very slightly concave is better then allowing it to turn convex.

Edward F connely In "Machine tool reconditioning" 530 pages

Recommends (For a tool room quality lathe) the end of a 12 inch test bar points .0000 to .0003" towards the operator

Boring is a different case you want it to be dead on however that is almost impossible, almost because. a few degrees change in the temperature can move the whole lathe frame out of alignment. I guess that is why many books on the subject suggest we err slightly away from perfect in the direction that is most likely to help us produce good work.

Regards
John

Edited By John McNamara on 25/02/2014 08:25:20

.

John,

Pithy, and very apt … My father was much like your tutor.

I have the greatest admiration for those who can do "fitting", and for the watchmakers that make [by hand turning] parts smaller than the chips of swarf we usually produce … But: the point is, surely, that Schlesinger was prescribing limits for Machine Tools.

MichaelG.

Edited By Michael Gilligan on 25/02/2014 09:16:11

This is true however even high end machines have adjustments, for instance to ball screw mapping and bed slope etc built into the software and setup at the factory, very small adjustments but still there, keep in mind, new machine tools are made by old ones……..

I don't know at the moment, but I am looking into it.

Martin.

In Euclidian geometry a plane can be defined by three points (provided they are not colinear), no straight lines, or calculus, needed. Since a plane is a 2D construct it must be flat, by definition, as there is no third dimension. Of course in the real world, which is inherently at least 3D, the concept of flatness has a tolerance.

As for badgers I think that BSI gave up trying to equate Ra to BA as there are too many variables, like culled or not, road kill or not, and if so what size vehicle. I believe that Rz, a peak to peak measurement, is now the preferred measure of surface roughness. Ra is an average value and can hide a multitude of sins, depending upon the crest factor of the surface.

Andrew

"Scratch and Dig" seems a very pertinent measure for the Badger.

MichaelG.

Edited By Michael Gilligan on 25/02/2014 12:03:46