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:
There is no "error" with the change gears. The ratio of inches to
centimeters is exactly 1:2.54 or 100:254 or 50:127. It is often
done with
a train of 3 gear pairs to get the center-to-center shaft spacing
right.
-John
=================
Not that hard, actually. My 1984-vintage lathe has an inch lead
screw, but
the quick-change box that drives the leadscrew will do all of the
inch and
most metric threads directly. The few "weird" metric pitches are
accommodated by changing two gears on the input side of the QC box. I
suppose that at some very small level, there is some "error" in
the metric
threads produced (and I've never bothered to calculate it for my
lathe)
but
it's a VERY small error that has never been an issue for me.
73,
geo - n4ua
On Fri, Dec 16, 2011 at 11:48 AM, Brooke Clarke <bro...@pacific.net>
wrote:
Hi Don:
Sure converting lengths is easy and I have metric, English and weird
taps
and dies, but how do you turn metric threads?
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.**end2partygovernment.com/
**Brooke4Congress.html<http://www.end2partygovernment.com/
Brooke4Congress.html>
Don Couch wrote:
The idea that conversion to metric would require replacing all
of the
machine tools (lathes, mills, etc) is a myth. Any U.S. machine
shop has
walls and toolboxes covered in conversion charts, converting drill,
screw,
wire, sheet sizes from one crazy measurement to another. One single
additonal conversion chart, inch to metric, and you can keep
using your
inch machines on metric projects.
My mill has inch lead screws. I added a low cost digital readout
with a
little button to show inch or millimeter movements, and now I do
everything
in metric. No problem.
Don Couch
--- On Thu, 12/15/11, Dan
Kemppainen<dan@irtelemetrics.**com<d...@irtelemetrics.com>>
wrote:
From: Dan Kemppainen<dan@irtelemetrics.**com
<d...@irtelemetrics.com>>
Subject: Re: [time-nuts] time-nuts Digest, Vol 89, Issue 51
To: time-nuts@febo.com
Date: Thursday, December 15, 2011, 10:29 AM
On 12/14/2011 3:59 PM, time-nuts-requ...@febo.com
wrote:
It's not like metric is totally absent. We drink
2 liter cokes and defend
ourselves with 9mm pistols. Our cars
use mostly metric parts. Even ham
radio operators, arguably the most jingoistic and set
in the past bunch
around, get on the 80, 40, and 20 METER bands.
I agree with you, and funnily enough the rest of the NATO
world uses 7.62mm and 5.56mm rifles. (Both were originally
based on standard inch sized rifle cartridges designed in
the US)
The problem in converting to metric would require replacing
a lot of tools. For example Mills, lathes, and other
machining tools and measurement devices are expensive, and
last for decades. I doubt many of the small tool shops
around here could afford it.It's a great idea to standardize
in theory, but in practice it becomes difficult. Maybe the
whole world should standardize our language. We could all
switch to Spanish or Latin or Chinese to speak with so we
could all talk with each other. That would probably be more
helpful to me on a daily basis, than having to switch
measurement systems.
While we're on the subject, let me throw time back into the
mix. We use months and days for scheduling projects.
Meanwhile some of our counterparts use calendar weeks. This
is much more difficult to convert between than inch and mm.
When is CW 36???
There I threw some wood on the fire too!
Dan
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