10 Replies Latest reply on Feb 12, 2014 11:10 AM by Bjorn Sorenson

# Holdovers from days gone by

So in looking at a design with lots of holes for mounting ziptie clips to hold wires in place I got to wondering...

How many other people still locate holes that do not require precision based on fractions?

Having grown up using a tape measure to quantify distances I find myself drawn to fractions by default.

Why locate a hole at 5.25 instead of 5.2?  Because .2 just looks weird compared to .25

And I know this is an American thing because most of my European counterparts are not used to using fractions.

Am I alone in this neurosis or is it common even though everything is now machined on equipment that allows any decimal you desire?

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I think it goes back to K.I.S.S.   .... and just because you can make a hole series at 1.215315646 spacing, why would you?

Our company is metric, when I design stuff in metric, I like to use round numbers for most things, makes it easier on the eyes and doing the math.

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Chris

I think I've finally shaken free from that habit. Dimensions like .938 or .094 used to feel natural and right. I'm happier with millimeters.

Dwight

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I did a mercifully brief stint with a furniture manufacturer that did all their wood parts with fractions.

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I confess to this neurosis myself.  Most commonly I work in metric, yet when specifying otherwise neutral values I try and use numbers that come out even in both.  I have chart on my wall that has fractional and decimal inches and their metric equivalents.  I guiess my real issue is that I like to have things come out even.  I hate having supposedly aligned features that are off by .000372948567.

Thankfully, I have learned to resist these urges when it takes more than a very small amount of time, or when it interferes with more important things, but I always feel the subtle pull...

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We were just having a similar conversation here at work.  We produce architectural products; canopies, glazing systems, skylights, bus & smoking shelters.  For the most part production personnel are more a kin to carpenters than machinists, as are the tools they use.  We do a few pieces of equipment that can work with high tolerances, like an awesome miter saw that can cut to .0001" (or so I am told).  When we create our models and drawings we try to think about who is fabricating each step.  When we layout hole locations our guys use tape measures and they are all the typical fractional versions.  So if we say .2 we are getting .25 anyway.  Who knows what your going to get if you put something like .6486.  Maybe 5/8" or 11/16", maybe even 21/32".  But I can guarantee the the phrase '\$#@%ing engineer...'  will come up at least once.  We still put everything in decimals but are discussing dual dimensions so we can eliminate having to make our fabricators convert it.  Its a simple conversion most of the time given that we try to keep them logical but it's just an extra step someone has to do for no real reason and an opportunity for a mistake.

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I've spent more hours than I like to think about with a tape measure hanging off a toolbelt, so I'm also more comfortable with fractions than decimals, though that's gradually changing.  I also have a chart hanging above my monitor like Carl.

And it also depends on who you're designing for.  Most of the stuff I do involves off the shelf material that's fabricated in fractions, so that's how I design.  If I handed our construction supervisor a drawing with dimensions called out in decimals of an inch instead of 1/16ths I better have a good reason or he'll throw it right back at me.

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My chart is just to the right of my monitor. It includes inches as decimals & fractions as well as mm since we get polycarbonate panels in metric.

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Like others, it comes down to who the final "customer" is for me. If it's going to the machine shop, then certainly I can put decimal precision to three places on a part and expect results. But if my drawing is going to the fabricator or the assembler, I use fractions because they use a standard tape measure for everything.

That being said, I still try to give them nice "round" dimensions to work from. Metric dimensions to the nearest .5 mm and inch dimensions to the nearest 1/16.

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Okay, at least it's not just me who sees it as a gray area.

I prefer the simplicity of less digits but my mind automatically assumes it was truncated from being a fraction.  I guess I'm just an old school framing square guy in a high tech caliper world...

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At my last job, we used to call them "Stanley" numbers, because one of the Sr. engineers maintained that the bigger the number on his old Stanley measuring tape the better.  It makes logical and economic sense, too- as engineers/designers, we all learned our decimal/fractional equivalents at least down to sixteenths (so we knew what .188 meant when we saw it, for example), our fabricators could program their machines quickly, QA knew when to reach for a tape measure vs. a more precise measuring tool, and the assemblers weren't mumbling under their breaths (as Joe mentioned above).  If you don't have to, why would you design to oddball numbers?  How many tape measures have you seen that resolve to 1/10ths of an inch rather than 1/16ths?