I have small British lathe (Myford) with a 1/8 inch leadscrew, and a
127 tooth gear is inconveniently large.
By examining the ratio of every gear for every thread required (with
a simple basic program) I found
a solution within 50 parts per million for all metric threads.
The wierdest threads are not metric but imperial, 19 threads per inch?
Incidently the Whitworth threads, with included angle of 55 degrees
and coarse pitch are ideal
for soft materials like Plexiglass (perspex, methyl methacrylate).
cheers,
Neville Michie

On 17/12/2011, at 5:48 AM, J. Forster wrote:

Hi, Brooke,

To cut metric threads on an inch machine, I mesh the 127 tooth gear with the 100 tooth gear that came with my Sherline lathe threading attachment. Works great.

Don Couch

--- On Fri, 12/16/11, Brooke Clarke brooke@pacific.net wrote:

Which works very well, but unlike all of the English
thread combinations, you must keep the lathe's half-nuts
engaged to the lead screw ALWAYS.  That means when you reach
the end of the thread, you must stop the lathe, and back
it up to the beginning of the thread to make the next cut.

With English threads the following rules exist for using
the thread dial indicator:

Even threads - engage half-nuts anytime
Odd threads  - engage half-nuts on any numbered line
1/2 threads  - engage half-nuts on any odd numbered line
1/4 threads  - engage half-nuts on the line you started with.

Metric threads are miserable to cut on English lathes...
and not much better on Metric lathes.  Metric thread dial
indicators are complicated and easy to get wrong devices.
With English threads, you would have to work to get it wrong.

-Chuck Harris

Don Couch wrote:

On Sat, Dec 17, 2011 at 4:48 AM, Chuck Harris cfharris@erols.com wrote:

That method always works.  But another might.  There will always be
some integer number of pitches that get you back exactly without
error.  But it might be say 5 inches back so there is almost always a
way to run only forward you method might be the best.

But are people still using these old machines for production work?

Chris Albertson
Redondo Beach, California

I suspect turret lathes are still used for shortish runs of some of the
simpler parts, like bushings and similar parts.

Not every shop looks like a NASA facility.

-John

==============

Chris,

You must be kidding!  How old are you?

Lee  K9WRU
----- Original Message -----
From: "Chris Albertson" albertson.chris@gmail.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, December 17, 2011 11:00 AM
Subject: Re: [time-nuts] metric / English

On 12/17/11 9:14 AM, J. Forster wrote:

Oddly, NASA facilities aren't necessarily the most modern or sophisticated.

It takes an act of Congress to build a new building or make non-repair
improvements.  My office and lab at JPL is in an 3600 square meter 2
story semi-temporary building (161) built in 1954 (before NASA even
existed). The frequency and timing lab is in building 298, an 1800
square meter building built in and was built in the 70s. Our big highbay
spacecraft assembly building was built in 1961. (To be fair, there is a
general plan to demolish a bunch of small buildings and replace them
with larger buildings sometime in 2020-2030 time frame, if Congress
approves).  Much of the infrastructure at Johnson Spaceflight Center
(and KSC, as well) was built for Apollo and followons in the 60s and
early 70s

We don't depreciate equipment, it's bought with capital expenditure or
project funds, and then we pay for maintenance and calibration. A big
project might buy a whole bunch of some piece of gear (e.g. HP8663A)
which we will then use for the next 20-30 years (I just counted about 30
HP8663As in inventory.).  I think we bought a whole pile of those 8663s
in connection with upgrades for Voyager or maybe Cassini.

As a result, we tend to keep gear forever..

Students coming on interviews are always amazed (and not necessarily in
a good way).

At least we've moved beyond slotted lines for the most part.

The manual machines are still in use for limited production runs,
such as are used in prototype manufacture.

Screw machines, and second op lathes see extensive use in
manufacturing because they are quicker than CNC machines...
that and very cheap to use.

I use manual machines because it is quicker to whittle out a prototype
chassis or do-dad on manual machines than it is to do a formal
CAD drawing, and then work out the tool paths to do it on a CNC
machine... and then find you have made it a mistake... wash rinse
repeat...  CNC machines are like printers.  In theory they save
time and materials, but in practice, they can burn time and waste
materials like no human running a manual machine ever would.

[As a tree farmer, who sells trees into pulp production, computers
and printers have been a godsend.  More trees go into paper
production today then ever did before the advent of the "paperless"
office.]

-Chuck Harris

Chris Albertson wrote:

You might want to consider the possibility that there is a whole world of
manufacturing that does not deal with millions of a single item.  And
prototypes are not part of the process.  When a product life might extend
over ten years and you can expect to get orders for two or three per year
(you know there are products  that cost tens of millions of dollars)  then
high volume is of much less interest.  Of course, a single part might
require a five axis machine and then things are again different.  I vividly
recall one sales visit  when I was only 35 or 40, and still hadn't learned
anything, and found that a very familiar product was still being
manufactured in a room with a dirt floor.

Lee
----- Original Message -----
From: "Chuck Harris" cfharris@erols.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, December 17, 2011 9:31 PM
Subject: Re: [time-nuts] metric / English

Up till three or so years ago the VLA (Very Large Array radio telescope)
was using a PDP 11/70.  Most of the workstations were Sun Ultra 1 systems
that were horribly outdated to a point where I had already sent mine to
land fill a few years before.  Now they have a spiffy Linux cluster on
modern hardware, but the old system was as old as me.

-Bob

On Sat, Dec 17, 2011 at 6:44 PM, Jim Lux jimlux@earthlink.net wrote: