[time-nuts] metric / English

Neville Michie namichie at gmail.com
Fri Dec 16 21:21:08 UTC 2011


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 <brooke at 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 at irtelemetrics.**com<dan at irtelemetrics.com>>
>>>>  wrote:
>>>>
>>>>  From: Dan Kemppainen<dan at irtelemetrics.**com  
>>>> <dan at irtelemetrics.com>>
>>>>> Subject: Re: [time-nuts] time-nuts Digest, Vol 89, Issue 51
>>>>> To: time-nuts at febo.com
>>>>> Date: Thursday, December 15, 2011, 10:29 AM
>>>>>
>>>>> On 12/14/2011 3:59 PM, time-nuts-request at 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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