Re: Metric Conversion Calculators

Hi, Before PCs, we trig-ed it out, but always be careful of the accumulated error situation. - the toolmaker that taught me a lot, especially concerning form grinding, recommended Moore's book, "Holes, Contours, and Surfaces" I purchased the book from Westchester Community College back when they had a die-maker training (spell checker questions my spelling). My buddy was trained to Voorhees near the Port Authority bus terminal in NY City. Neither school exist anymore, last time I checked it out. The book has hole layout to 100 holes in X and Y co-ordinants to six places right of the decimal point. The book goes into precision how-to locating holes using dial indicator techniques and gets into linear form grinding. might have a used copy. 1st published in 1955, my copy is 1982. Moore is the guy that built the Moore jig boring and grinding machines (looks like a glorified Bridgeport) and were making precision lead screws to millionths of an inch specs in the 1950's! My buddy was from Haiti, French language. He got his USA citizenship by doing USA Army enlistment. His duty station was Alaska! Sick Army sense of humor. Navy does it, too! LOL! He did his die making school on the G.I. Bill. He was 20 years senior on me. He told me machine shop is not a job you go home at end of the day and forget it. He told me to always study and read-up about the how-to of the trade and the technology advances as they occur. Don't go into this trade close minded. Always look for better and more efficient ways of doing things. And to that end, I have a fairly nice reference library at my house. Then I got a PC and Internet access...ha, ha, ha,ha, ha, ha, ! "Machinists' Ready Reference" is also a very useful handy book for trig applications. Thanks for the link. Kurt --- In Will Holding wrote: > > With all due respect to Ian, I believe this is not technically accurate, and it is often necessary or desirable to convert an existing geometry into the machine coordinate system you are using, in which case mathematically converting the part geometry is certainly more convenient and usually more accurate than CMM'ing off the part. > > Converting from inches to millimeters is exact, (in * 25.4=mm). Converting from millimeters to inches with a calculator ( mm * .0393701~in) is approximate, but accurate to six figures. Which is more than adequate in most cases, as there are limits to how accurately the parts can be built, and in our case, the size of the parts we are talking about. > > You can avoid mathematical error by designing in inches, then the part geometry can be precisely converted to metric machine coordinate system. Going the other way will realistically have little effect in the home machine shop, if you were designing a 747, a bridge span, or a supertanker, then you would want to be aware of it and design accordingly. AFAIK any modern engineering software that you'd likely be using for these kinds of projects will calculate conversions to a very high number of places and round off to the units you choose, so in effect this problem is eliminated. > > Ian's point is well made concerning error however, and being aware of what units and what machine coordinate system you are working with. That was the root of the infamous problem with the Hubbell telescope lens, wasn't it? A bad inch-to-mm conversion? > > There are a number of good machinist calculators online, one that really takes the pain out of life is one of the many bolt circle calculators like this one: > > > Other ones solve given coords of two holes, etc. > > They can be used for a lot more than bolt circles, such as points along an arc, clock faces, timing wheels, gears, it's very useful! > > -Will > > > > From: Ian Newman > To: > Sent: Friday, April 25, 2008 4:40 AM > Subject: Re: Metric Conversion Calculators > > > Hi, > > It is a basic rule in all walks of engineering that > you NEVER convert between units - it only introduces > errors, confusion and inconsistancy. > > If the dimensions are in millimetres, measure and cut > in millimetres. > > If the dimensions are Imperial, measure and cut in > Imperial units. > > Ian. > > --- Kurt wrote: > > > Found these lately from a Google search as I needed > > to know a metric > > dimensions' English equivalent: > > > > > > > > > > > > > I'll stash it somewhere in LINKS and add it to my > > math do-dad F-Key > > Center thingy off start page to my group. > > > > > > Kurt > > > > > > > Sent from Yahoo! Mail. > A Smarter shop > > > > > > [Non-text portions of this message have been returnd] > Yahoo! Groups Links To visit your group on the web, go to: Your shop settings: Individual shop | Traditional To change settings online go to: (Yahoo! ID required) To change settings via shop: To Purchase from this group, send an shop to: Your use of Yahoo! Groups is subject to:

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