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You know what I hate!!

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  • You know what I hate!!

    When you get a set of plans for something and all the dimensions are in fractions it is nothing but a PITA, Micrometers and Verniers and Digital Verniers read in DECIMALS and always have, And the blokes that draw the drawings have to use these to make the item, so why the BLOODY HELL don't they put the DECIMALS in the drawing.Putting the dimensions in decimals would save those of us who are not constantly doing this from working it out.
    It is logical that the drawing should be dimensioned this way and I can't see any reason why not, unless of course the dimensions are quoted as rule size which to me is half a millimetre or 20 thou.
    Even on those measurements that are not critical it would be easier if the drawings were dimensioned in decimals.
    Will

  • #2
    I fully agree with you Will.
    Not wanting to start a imperial / metric war again but if all dimension on ENGINEERING drawings were done in decimal then it would go a long way.
    The problem is with Imperial there are two dimensions for every size.
    Take 37 /64"
    To most non anally retentive people this is a meaningless number, is larger than 32/64" which is 1/2" and that's about it.
    Taken to a decimal it becomes more usable at 0.578" To most of us who can remember the large way marks like 0.500 for 1/2", 0.625 for 5/8" and often the intermediate ones like 0.5625 for 9/16" this decimal then becomes more usable.

    So our indecipherable 37/64" becomes 0.578" which is a tad over 9/16" and many can even do the simple mental arithmetic to get 16 thou bigger.

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      To convert those damn fractions

      Hey Will, would those plans be from the good old USA by any chance?
      For those who may not know how to convert. Get out the old calculater and divide the numerator by the denominator, no probs. But you knew that already mate.


      had to amend that; it was arse about face
      Last edited by speedy; 04-01-2007, 08:06 AM.
      Ken.

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      • #4
        Just to muddy the waters further, why not dimension everything in HPGLU?
        40 to the mm, 1016 to the inch.
        Just got my head together
        now my body's falling apart

        Comment


        • #5
          It might seem funny, but I convert decimal measurements back to fractional much of the time mentally. If faced with 0.5781", I'll process it as around 5/8".

          Fractions and decimals are part and parcel of the Imperial system, and flipping back and forth between them is not a problem for me. If a drawing is dimensioned in fractions, it infers the dimensions are non critical, and the parts are to be made to fit one another.

          On the other hand, I find most metric dimensions meaningless, as I have to convert them back to Imperial for them to have any reference to me. 93.28mm is totally irrelevant to me unless I mentally divide by 25, and then I can think of it as between 3-1/2" & 4".

          Much of the time, plans, especially for the HSM, are not cast in stone, and can and should be freely modified to take advantage of materials at hand, or add the builders own modifications. For that reason, many are not much more then refined sketches, and fractional dimensioning is adequate.

          Engineering drawings, on the other hand, should be done in decimal dimensioning, as the fits and tolerances are inferred in the dimensions and number of decimal points they are carried out to. If the parts made are for multiple pieces, those dimensions are cast in stone.

          When first inspecting plans, all dimensions should be reviewed, and their importance determined. I think, with the increasing use of canned drawing programs, there is a tendency to allow the program to do the dimensioning. This can result in unnecessarally tight tolerances to end up in the drawing.
          Jim H.

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          • #6
            Originally posted by John Stevenson
            I fully agree with you Will.
            Not wanting to start a imperial / metric war again .
            It could have started already
            Ken.

            Comment


            • #7
              In case it matters, US folks have the same reaction.......

              Somehow, the rest of the world believes that the US uses fractional inches, which is completely wrong.

              In fact US "engineering" drawings UNIVERSALLY use decimal inches, when they don't use meter/mm dimensioning.

              The WOODWORKERS use fractions, largely because they can't buy a tape measure in decimal, and the wood is dimensioned (very loosely) in fractionals. It is also traditional and woodworkers are worse than cats for tradition. Plus, it does not matter much for parts that don't have tolerances and multi-part buildups that are critical. A bit over or under overall is no big deal to woodworkers, they adjust.

              I HATE fractional inch dimensions, and can't figure out why anyone uses them for items smaller than houses.

              Fractions would be at least a bit easier if one simply stuck with 64ths, and used them, but 9/64, 5/32, 11/64, 3/16, etc, etc.... that's bad.

              Stock is traditionally dimensioned in fractionals, probably to avoid being too specific about size. While each fraction has a spcific size to any number of decimal places, it is traditional to consider something like stock (or wood thickness) accurate only to a rough degree if given as 3/4" or whatever.

              If it were given as 18mm or 0.750 inch, it would appear to be more accurately held than as 3/4". (another tradition)
              Last edited by J Tiers; 04-01-2007, 08:48 AM.
              1601

              Keep eye on ball.
              Hashim Khan

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              • #8
                "with the increasing use of canned drawing programs, there is a tendency to allow the program to do the dimensioning. This can result in unnecessarally tight tolerances to end up in the drawing."

                Agreed, JC, but I'll tell you another tale of woe regarding a young "engineer" and a CAD drawing.
                This was told to me by an engineer mate (combustion) of the old school.

                The plant I know, it's just up the road. Aforementioned young engineer was told to knock up a quick drawing of a small part, a gas igniter bracket for a heat-shrink oven. A large heat shrink oven for pallets of bagged powder. The original aluminium bracket was not up to the job and he was told to spec it in 316.

                The part duly arrived, along with a $4500 invoice. (just the bracket, not the gas burner). Beautifully machined part, in G11 Ti.

                The young guy doing the drawing had just dragged up an old CAD file and annotated it "Titanium"

                The job was for the Ti-Di bagging line!
                Just got my head together
                now my body's falling apart

                Comment


                • #9
                  I agree that engineering drawings should be dimensioned decimally, but...

                  Materials are still sold in fractional sizes. Some of the parts I design require nothing more than cutting to length and facing, the mill finish and dimensions being suitable for the application.

                  Also, it is easier to call out a "3/16 drill" rather than ".1875 dia." if all that is needed is a 3/16 drilled hole. The four decimal places in the decimal callout could be interpreted to require extra precision.

                  All that being said, the drawings I submit for articles in HSM and DM generally recieve edits for before going to print, so I have been comparing the submitted vs. published drawings to learn where my style (or lack of) differs with that of the editor. I am trying to adjust, to minimize the time the editor needs to spend tuning up my drawings, but old habits die hard.
                  Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                  ~Practitioner of the Electromechanical Arts~

                  Comment


                  • #10
                    if that is the only thing that worries you you are lucky. i have worked where most people have not even been able to read a tape measure. and that was in a fab shop. one guy could only read little lines. you wanted 3/16 you had to say 3 little lines.
                    i went one place for a job and on the written test they only went as small as 1/8 becaus so many can not read smaller. i guess it goes back our school systems not teaching any more.

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                    • #11
                      Also, it is easier to call out a "3/16 drill" rather than ".1875 dia." if all that is needed is a 3/16 drilled hole. The four decimal places in the decimal callout could be interpreted to require extra precision.
                      Not around here. I lay the dial calipers to the drill bit and measure to make sure I have the right drill size.
                      Free software for calculating bolt circles and similar: Click Here

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                      • #12
                        Originally posted by Evan
                        Not around here. I lay the dial calipers to the drill bit and measure to make sure I have the right drill size.
                        Just good shop practice.
                        Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                        ~Practitioner of the Electromechanical Arts~

                        Comment


                        • #13
                          Back when I was doing mold design, we drew molds around the engineering drawing of the part. But the mold dimensions will be different to take into account draft and shrink. One of the first things I did with a new part drawing was to program the calculator for INPUT times (1 plus shrink factor), and pencil in new dimensions for everything on the drawing. In other words, multiply all the final dimensions needed on the part by the amount of the shrink factor to get corresponding mold dimensions.

                          I think that's what I'd do with an all fractional (or metric) drawing that hacked me off. Quickly get to dimensions that work in my head.
                          .
                          "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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                          • #14
                            "I lay the dial calipers to the drill bit and measure to make sure I have the right drill size."

                            Same here Evan, unless it's one of the pairs (drill and tap) I keep separate in a drawer.
                            Even when my eyes used to work a little better than they do these days, I'd check
                            Just got my head together
                            now my body's falling apart

                            Comment


                            • #15
                              Decimal inches are the norm,but a calculator solves the fractional problem.I typically go over a print and make my own rough sketch with decimal inch notes on it before I do anything even if the print is metric.

                              I only see prints with fractios on them from one old (Noah's ark era)company that makes steam pumps.I guess they figure if the prints have worked since 1870 why change them.

                              Checking tools with a caliper first is a good idea,you learn to do it quick when working in a shop with multiple people.Just because a drill is in the 27/64" slot doesn't mean it's a 27/64
                              I just need one more tool,just one!

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