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 >>>> >>>> ______________________________**_________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to https://www.febo.com/cgi-bin/** >>>> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> >>>> and follow the instructions there. >>>> >>>> ______________________________**_________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/** >>> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> >>> and follow the instructions there. >>> >>> >>> >>> >> ______________________________**_________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/** >> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.