You really need to take a look at the By Hand and Eye book. All is explained. And it's a lot easier and a lot more exact that you think.
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That's making your point the hard (and slow) way. Line off your opening, as you said. Walk off the number of divisions you want with a guesstimate of the proper length. When it comes out over or under, divide (by eyeball) the "overage" or "underage" into the same number of equal divisions you're looking for (six, in your example). Then, set your dividers to the original interval plus (or minus in the case of "underage") one sixth of the "overage" amount and you should be virtually dead on. Quick as a bunny and the only source of error is your sloppiness in execution. If it's off by much, you can repeat the process from the new dimensions and be a bit more careful and you're there. Not ten minutes at all. More like two or three if you're careful and accurate the first time through and come out with a good result the first time.
Well I was only trying to answer his question. Sorry if I belabored it.
Indeed they will. This is what we software types refer to as a "fencepost error". It happens more often than anybody likes to admit :-)
I would approach the above problem this way: If the height is 31 then on a stick say 36, I would come in from the end a couple inches and strike a line and mark TOP on the portion beyond the mark. Then measure 31 and strike then mark BOT on the wild end. Gauge a line end to end on the story stick, it is in that line where the stepping takes place. Assuming shelves, top and bottom panels are equal thickness, gauge the top and bottom panels and strike marks. Now use the dividers to step out even margin from top of top panel to top of bottom panel. Here is where I think the Crucible Divider is at the disadvantage since it lacks a screw feed spreading mechanism, with a spring loaded screw hair width accuracy is under control. Once the upper surfaces have been gauged and marked, layout the undersides stepping from bottom of the bottom panel to the bottom of the top panel with the dividers unchanged. Everything should work out evenly without odd remainders or centering problems.
Man, I've done that more than once. :o :o :o Didn't know it was common, nor that it was a mathematical oddity studied by some big brained Roman scholar. I just figured I was a dope [don't say it!], erased the lines and started over.
Interesting factoid Patrick. How the devil do you find - and remember - this stuff, anyway? :)
Ah, once again you are correct Patrick (and bridger of course). That throws a bit of a problem into the method. The centerlines for the drawer dividers will be equidistant but the openings for the drawers won't be the same size top and bottom versus the ones in the center.
Pat Barry, read my post #96, it presents a solution to the post problem.
Here is a link to a name-brand example. There are cheaper versions of the first that work very well.
http://www.starrett.com/metrology/product-detail/metrology/metrology-products/precision-measuring-tools/calipers-dividers-trammels/calipers-dividers/73B-6
The quick-spring nut feature speeds adjustment up.
The Starrett 92 pictured below is my favorite because it is an impressive tool and also works as a compass, but I admit it is not quite as rigid as the first version.
https://www.qy1.de/img/st306468.jpg
Stan
Stanley, that is indeed a great dividers/ compass combination from Starrett. They are not really any cheaper than the Crucible ones, but the utility is better. Last year at the Brimfield flea market in central Mass., I found the identical vintage Stanley version of the above dividers/compass for about $40.00, so that was my "find" for the summer. I leave that tool in the compass configuration, as it is not quite as easily handled as dedicated dividers.
I think I read it in a software journal or something like that. I remember knowing about it when one of my fencepost bugs screwed up a finite element simulation for laser media in the mid 80s (my Dad allowed me to choose between helping with his simulation or digging ditches for the sprinkler system during the summer), so it's been at least that long. I have no idea why my neurons retain that and not useful stuff.
Also I've interviewed a lot of software candidates, and one of my favorite questions while at a previous employer was a bit of a "fencepost trap", i.e. it tricked the candidate into making that mistake unless they were really careful.