From: Robert Bastow <"teenut"@ hotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Taking the mighty Myford for a test drive this evening
Date: Tue, 16 May 2000 09:50:03 GMT

Not a cut rate way to use the same indices Janos..but an indexing
method..preferred by some...hated by the true cognicenti.

It is called diametric indexing.  The CROSS slide is indexed in such a way that,
say to reduce a diameter by 1mm, you move the index 1mm, that moves the cross
slide 1/2mm and the resultant reduction in diameter is 1mm.

The Topslide is usually used for LENGTH reduction..a sort of fine adjustment on
the CARRIAGE Slide...They are therefore Directly indexed..1mm on the dial means
1mm of movement.

This, at first sight might seem a perfect arangement...It means you don't have
to take every diametric measurement, deduct it from the finished diameter
required and divide the resultant by 2 to determine the cross slide movement
required to achieve that.

For that reason, it is a prefered arrangement on training lathes and those to be
used by semi-skilled labor  (in the UK..a lathe or a milling machine
operator..in fact any specialised machine operator, is or certainly was
classified only as semi-skilled!!)

Fully skilled tradesmen..including Tool and Die Makers however expect and wish
to use a lathe for quite few operations where the ability to diectly call off
cross slide movement is as important as any diametric movement they may wish to
use.  To them the Diametric Indexing is a Pain in the Butt!!

To Jobbing Machine shop owners..who most often have a crew of skilled and
semiskilled Tadesmen moving daily if not hourly arround a bevy of different
lathes, milling machines, grinders etc., It is a total disaster!!!!

I don't care how "accustomed" any  operator is, to moving to and fro from direct
indexed mills and lathes to a diametrically indexed lathe.  Sooner, rather than
later, the arrangement will cause a mix up, and double the quantity required
will be removed from a diameter.

Murphy's Law Dictates that it will happen.  It also dictates that it will be on
the single most valuable and difficult to repair or replace component going
through the shop at the time.

For these reasons..I personally..as a Skilled Tradesman.....hate diametric
indices..As a Machine Shop Owner, I will not have them within a country mile of
my shop!!!

teenut

Janos Ero wrote:

> The other oddity on my metric Myford is, that
> the cross-slide's wheel is scaled to the
> half: moving from 0 to 10 does not move it
> by 1mm, as usual, but only 0.5mm! One turn,
> 40 units means then 2mm. I think this is
> simply because they use the same scale for
> the cross-slide's diameter screw: there
> the movement means diameter, 10 units, 0.5mm
> movement removes 1mm in diameter.
>
> Janos Ero