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    Discussion in 'The main mechanical design forum' started by xmechanic, Jan 23, 2011.

    1. xmechanic

      xmechanic Active Member

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      I am curious as to how working Engineers measure/prefer to measure things. English or metric or a combination of the two? It seems like metric would be superior in small size applications but I'd like to hear what works in the trenches.

      In construction English is the only way to go. Foot references are only used to describe say building size or material size. One carpenter doesn't say to another I need a piece 7' 10", he says I need a piece 94". Why? Well its just easier. In such things as framing a house an 1/8th" is often as close as it gets. In woodtrim we go with 16th heavy or 16th light, nobody uses 32nds. There is another term we use for small increments but I'd probably get banned if I said what it was, universal use coast to coast though ;)

      In laying out house plans I use a cobbled system of metric and english. Like 1 cm equals = 2 feet or whatever works on whatever size paper I'm using. This isn't normal practice, just how I like to do it.
       
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    3. xmechanic

      xmechanic Active Member

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      In construction feet, inches and fractional inches in 16ths work extremely well, for more precision such as in cabinetry 32nds and 64ths do the job if needed. An inch broke into decimals wouldn't be as user friendly or functional given the demands of jobsite communication among everyone involved in it.

      I guess my question is what is generally used in ME for various scenarios. Decimal inches or metric or both depending on the situation/use. The reason I'm asking is to see if there are measuring methods I should start employing now as I start learning how to lay stuff out in CAD. For example as a cad beginner I am designing a 2 wheeled powered utility vehicle. To keep things simpler as a beginner I'm wondering if I should go with metric all the way or inches. When I get around to building it the goal will be to source as many US made commonly available parts as possible.

      Thanks for tolerating an old dog trying to learn new tricks :)
       
    4. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      Old habits are hard to break..... Having grown up using English inches.... I don't relate as well to MM. However as I got older, I never could understand why here in America we never gave up the inch and adopted the metric system.. So for me, it's decimal inches..

      Source
       
    5. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      Having grown up using both metric and imperial units I do prefer metric units where measuring and component inspection is concerned, however I always think back to imperial with regard to tolerances, ten thou seems easier to imagine than 0.25mm.

      Source
       
    6. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      I grab whatever tool is handy and use whatever units it is calibrated in. I also keep my handy unit converters close by. I often receive information from others spcified in English units that have to be converted to metric for computer analysis programs- I have one CAD package that allows me to draw in English units, then, when all is done, a quick "scaling" converts the entire drawing to metric...Except the text...

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    7. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

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      Well this is result globalization of engineering.
      it is better to keep small booklet of conversions which is available at a very reasonable rate.
      Google search engine also does the conversion. you can simply type "500 km/hr to m/sec" or something similar, it will do the conversion for you.

      Source
       
    8. guy

      guy Member

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      I remember someone telling me that if the American manufacturers adapt and use the metric units, Chinese and Japanese companies will become very tough competitors in the domestic market.
      I don't know if it's true, and if it is then to what extent, but it sounds reasonable.
       
    9. JC_Biggs

      JC_Biggs Active Member

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      I draw everything in inches, unless a specific part im getting made is done by a company over seas. for example the company that supplies and manufactures the MMC metal i use, get all their drawings in metric. but the assembly drawings, and the "rest" of the stuff I do, is mainly English.

      I Tried using the engineering system for a little while.. but it confused me .. lol. so i gave up on that. Good thing i dont build highways i guess :D
       
    10. xmechanic

      xmechanic Active Member

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      Thanks for the inputs, I think I'll stick with inches where ever possible. As a mechanic from 1980-90 I saw the gradual implementation of metric fasteners on some components of US autos, a weird mix really. Metric in bolts/nuts did seem to offer a better variety then fractionalized inches, well unless you went to 32nds which would be hard to standardize I think. 1000ths of an inch were easy to visualize and use.
       
    11. 47ford

      47ford Guest

      It is best to do your CAD drawings in whatever units are NATVIVE to where you are sourcing your parts/assembly. Sometimes that means a metric drawing (when sourcing outside the US). But if you are in the US that is primarily going to be decimal inches for machined (mill/lathe/etc) parts and fractional inches for construction/woodworking, and foot/inches/fractional for architectural drawings. You should never mix SCALE (ie 2cm = 1foot) as that will really mess people up. Engineer drawings are typically 2:1, 1:4, 1:16, etc and architectural drawings are typically 1" = 1' or 1/2" = 1' etc. These match the engineering and architectural scales (that look like 3-d rulers, but are marked appropriately).

      Occasionally you will have something that you will need to dual dimensions (ie the part is sourced outside the US, but used in an assembly that is assembled in the US). Typically the secondary units are enclosed in square brackets "[]" so it might be 23 [584.2] where my primary units are inches and my secondary units are millimeters.

      For engineering CALCULATIONS I prefer to stick to SI (metric) units whenever possible. It is a lot easier when converting units in SI (say from meter to kilometer) than in Imperial (say from foot to yard or mile) for consistent units in calculations. HP calculators are great for unit conversion (I have both a 48G and 48SX). For myself I currently work in a manufacturing facility in the construction industry. Our shop drawings (CAD) are done in fractional inches (to the 1/16th with typical tolerance of +/- 1/16 though some times you can get away with an 1/8 or even 1/4 for fit). Our CNC mill came from Italy and is in millimeters (mm) so all of our CNC programing (CAM) is done in mm. I am the unlucky person who typically has to work in both so of course I am very familiar with either multiplying or dividing by 25.4 (mm/in) even on a standard calculator. I also use tape measures that have both on them (inches on top, mm on bottom) and digital calipers that can toggle between inches (decimal) and mm. While European machines sold in the US typically have an Imperial (inches) mode the ones I've worked with have had problems and it is safer/easier to use them in their native SI (mm) mode.
       

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