On Jun 23, 1:43*pm, "DoN. Nichols" wrote:
On 2011-06-22, Andrew VK3BFA wrote:

* * * * [ ... ]

things, but not getting the machine time to get competent. So, I ask.
Hence my question - whats better to align between, centres or chuck
and centre?

* * * * Actually -- you don't want the center involved at all at first.
It is good for turning long flexible workpieces, but it confuses the
issue with alignment.

* * * * So:

1) * * *Level the bed with a precision level (to take the bed twist
* * * * out of the equation).

2) * * *Chuck a beefy piece of stock in the chuck alone -- free length
* * * * no longer than say four or six times the diameter. *And hope
* * * * that the jaws of the chuck are not worn bell-mouthed, which will
* * * * make things more difficult.

3) * * *Turn down the middle of this enough to allow you to do a final
* * * * turn of just the ends with a light cut, and measure the results
* * * * with a micrometer.

* * * * There are precision bars with a Morse taper to fit the headstock
* * * * spindle and you measure this with an indicator in the carriage.
* * * * But these are quite expensive -- it is cheaper to turn the
* * * * two-collar bar in the previous paragraph. *It does not even need
* * * * to start out with a good finish -- you're making surfaces
* * * * centered around the axis with your turning.

4) * * *If the two ends measure the same, this part is done.

* * * * If not -- then the mounting of the headstock to the bed has a
* * * * twist in it (not the bed has a twist -- you eliminated that with
* * * * the precision level). One end of the headstock points to the
* * * * front and the other end points to the back, and this needs to be
* * * * fixed before you attempt anything else.

* * * * Some lathes have setscrews which push on the headstock at the
* * * * front and the rear to adjust the alignment. *These are easy to
* * * * fix.

* * * * Other lathes have the V-ways extending under the headstock, and
* * * * used for the alignment. *Probably, the headstock was first
* * * * mounted to the ways, and then bored for bearing placement to
* * * * assure that the spindle is parallel to the ways. *If you have
* * * * parallelism problems with this type (probably a different
* * * * headstock mounted on the old ways), you'll have to work with
* * * * very fine shim stock to bring it in to alignment. *Or do some
* * * * precision scraping. *Or something else serious.

5) * * *Once the lathe is turning with no taper in the chuck, you then
* * * * adjust the tailstock offset so a bar turned between centers has
* * * * no taper. *(You really don't want to do from chuck to tailstock
* * * * center, as this will bend the workpiece if the center adjustment
* * * * is not quite right.

* * * * Note that tailstock center height on a good *new* lathe is a
* * * * little *above* headstock center height. *(maybe 0.0005" or so).
* * * * This is so as the tailstock wears through a long life, the
* * * * tailstock center height gets better for quite a while before it
* * * * starts getting worse.

* * * * [ ... ]

Still trying to "see" the lathe in 3-dimensions, see how they all
interact. Always was crap at geometry.

* * * * That is a handicap in the world of machining. *Both the number
part of geometry (working with angles and sines for setting precise
angles) and the visualizing how things interact.

* * * * [ ... ]

So, another question - what came first, the lathe or the precision
level needed to set it up? If it was the lathe first (I got a drawing
of a tree branch one in a book) then how did they set it up? - before
precision levels were invented.

* * * * Well ... the bent tree branch one was not a precision lathe.
The cutting tool was not guided by the machine -- it only provided some
form of rest, and the tool was guided purely by the operator's hands.
(And the workpiece material was wood, after all. :-)

* * * * I would say that the precision level came into being somewhere
along the progression from the bent branch powered wood lathe to the
precision industrial machines -- and its presence made it easier to set
up a lathe once it was moved from the factory to the machine shop where
it was expected to spend its life. *Before that, machines were mostly
built where they were going to be used, so during the construction
errors wre tuned out.

* * * * This is my take on it all.

* * * * Good Luck,
* * * * * * * * DoN.

--
* * * * * * * * * Remove oil spill source from e-mail
*Email: * | Voice (all times): (703) 938-4564
* * * * * (too) near Washington D.C. |http://www.d-and-d.com/dnichols/DoN.html
* * * * * *--- Black Holes are where God is dividing by zero ---

Hi Don - long time no hear. Granted all of the above, still need a
precision level. As soon as I figure out how to do it, I will give it
a try.

Made a test bar at school, measured accurate to 2 microns. (yeh, pure
chutzpah) as my reference point.
Stuck dead centres in both ends, with a dial gauge, checked them for
concentricity. (replaced one) Butted em up close for a loose pre-fit.
(if the whole thing looks like getting good, will use the finger
indicator for greater resolution) Also checked for any devaition or
runout in the headstock shaft - its accessible - was spot on. So the
headstock is probably aligned // with the bed.
the supplied MT3 dead centre at the headstock was crap - bought a new
one. Much better. The tailstock - always been problematical in that
under load it would spin the MT2 tapered shaft. Finally fixed that by
blueing the bore against a known good MT2 plug, then setting up the
dead centre(and the live centre) on the cylindrical grinder and
cleaning up the original supposedly MT2 taper - blueing it till it was
a good, even fit. it was out heaps - much better now, doesnt spin.
Checked // alignment in tailstock by measuring run out on the edge of
a live centre. Crude, I know - but at least an indicator of no major
stuffups. But now the tailstock ram thrashes around as the grub screw
(cheese, made of) locating it is too bloody small for the job...makes
drilling a bit difficult.
So, I do know a bit about machining, its tying it all together -
without a bloody precision level - and yes, it will still be a crap
lathe when its fixed, I know that, too much flex to use a
conventional knurler, dont do bit cuts if you want any accuracy - but
I want it to be better than it damm well is at the moment. And if I
totally stuff it up, it doesn't really worry me, I will by then know
enuff to be able to go out and appraise a used lathe. Dint know
anything before I started all this. Thanks fellas, a lot of knowledge
here.

Andrew VK3BFA.