How thick is a sharpie mark?
April 22, 2016 7:30 PM   Subscribe

 
This may seem like kind of a trivial question, but when I'm measuring thicknesses of rock formations in the field in a stratigraphic sense using contour lines on a topo map, this is super duper important. One of the more difficult parts of doing that is that you don't want your pencil marks to smear, so you have to use graphite that's harder, yet you want to be able to erase it when you fuck up (as you inevitably do) and then later when you Sharpie it in you want to know what that thickness means, especially when you're using contour lines that are really close together and making cross-sections.

So thanks! This not only interesting but useful.
posted by barchan at 7:46 PM on April 22, 2016 [21 favorites]


I watched all the way to the end waiting for him to crush the fancy indicator in a hydraulic press but no such luck :-(
posted by indubitable at 7:47 PM on April 22, 2016 [13 favorites]


The mark-as-shim remark at the end reminded me of balancing a carbon fiber propeller by spraying an extra pass of clearcoat on one of the blades.
posted by indubitable at 7:49 PM on April 22, 2016 [3 favorites]


But he's measure the thickness of the ink on paper, isn't he? So I don't know if this is useful for what you're describing, barchan...

Anyway, I'm impressed because a 'statistically significant number of measurements' usually means 3 for me, because I am lazy, so way to go for going all the way to 10!
posted by maryr at 7:55 PM on April 22, 2016 [2 favorites]


Sharpie does not blend, indubitable.
posted by maryr at 7:57 PM on April 22, 2016


Oh, that thickness. Wow!
posted by jjwiseman at 8:07 PM on April 22, 2016 [12 favorites]


Yeah, the, erh, precision versus accuracy versus both precise and accurate is an interesting question. But I'm always wondering when I'm doing this shit how much I'm throwing off when I bring in the Sharpie, especially when my measurements don't match. . . when you're measuring in feet + inches and trying to bring it to scale it can be super duper frustrating. And since I may be measuring IRL but bringing ink to paper, I'm always aware that the medium I'm using may throw it off. So I'm excited to try this!
posted by barchan at 8:07 PM on April 22, 2016 [1 favorite]


"Oh, that thickness. Wow!"

Yeah, when I read the post I was wondering what the deal was or why this would be interesting. But the height of the of ink, not the width. Yeah, that is pretty cool.

Reminds me of working with an antique precision balance scale in college (the enclosed kind) and weighing a short word written in pencil on a piece of paper.
posted by Ivan Fyodorovich at 8:13 PM on April 22, 2016 [3 favorites]


Yeah, gauge blocks are good for winning bar bets, too.
posted by 2N2222 at 8:30 PM on April 22, 2016


Reminds me of working with an antique precision balance scale in college (the enclosed kind) and weighing a short word written in pencil on a piece of paper.

So could you determine the weight of "the soul"?
posted by maryr at 8:38 PM on April 22, 2016 [6 favorites]


The sharpie could attack at any time, so we must deal with it.
posted by Slap*Happy at 8:41 PM on April 22, 2016 [5 favorites]


This immediately reminded me of Rob Cockerham's attempt to find out how much is inside a Sharpie.
posted by cardioid at 9:08 PM on April 22, 2016 [8 favorites]


I remember that you can make a very sensitive (but not accurate) scale out of an analog meter movement, putting the object to be weight on the end of the pointer, and measuring the amount of current required to bring the meter back to the starting point. It might be interesting to weigh a sharpie mark in this manner.
posted by MikeWarot at 9:17 PM on April 22, 2016


My first thought when I saw the title: "you could figure that out with a good indicator and gage blocks". My second thought was "probably about one ten-thousandth".

I guess my time working in the machine shop of an aluminum foundry wasn't a complete waste.
posted by double block and bleed at 10:51 PM on April 22, 2016 [15 favorites]


There are smooth jaw pliers. TIL.
posted by GuyZero at 11:06 PM on April 22, 2016 [1 favorite]


Knipex parallel jaw pliers are amongst my favorite tools.
posted by flaterik at 12:19 AM on April 23, 2016 [1 favorite]


Smooth jaws are the best type. You can pry my Lindström 726-501's from my cold dead* hands…

(*Or more likely, since the insulation wore off them 20 years ago, "my warm carbonised hands…")
posted by Pinback at 12:22 AM on April 23, 2016 [1 favorite]


My knipex cobras, which are the OPPOSITE of smooth jaw, are also amongst my favorites.

(I have no connection to the company other than the money I've given them for the pliers I really like and use all the time!)
posted by flaterik at 12:32 AM on April 23, 2016 [1 favorite]


Whoa. I thought this would be about width, but it's about height.

However, they made the Sharpie marks on a block of metal. If they're made on paper, don't they get (partially?) absorbed, so the height would be less?
posted by Rangi at 12:43 AM on April 23, 2016


If they're made on paper, don't they get (partially?) absorbed, so the height would be less?

Only if the paper doesn't expand as it soaks up the ink!
posted by aubilenon at 2:08 AM on April 23, 2016


He maybe could have also done an analysis of variance to test if the computed averages are different statisically. Variance does seem low per column of data, just with eye-balling.
posted by JimDe at 3:54 AM on April 23, 2016


That was surprisingly cool! I wonder if he checked the zero on the test block between tests to control for temperature changes or other sources of variation. I dug the vintage HP calculator he was using. I still have the 15C I used in college in the 1980s, although it has needed batteries for a decade or more. I also really want one of those fancy dial indicators even though they are probably pretty pricey and I have absolutely zero reasons to need one.
posted by TedW at 4:29 AM on April 23, 2016


I went to their website to see how much the Johansson measuring tool cost, and couldn't find it anywhere. Looks like it's old gear that you can get used on Ebay for somewhere between $40 and $200.

What I wonder about when I watch the video is the compressibility of the Sharpie marks. Would they be taller without the gage block resting on top of them?
posted by clawsoon at 5:17 AM on April 23, 2016


So blood is thinker than water, at least in part, because of the color!
posted by Obscure Reference at 6:19 AM on April 23, 2016


Looks like it's old gear that you can get used on Ebay for somewhere between $40 and $200.

Or a bit more if you buy them from sources who might actually be able to tell if you if they still work :-)

The mikrokator was invented in the thirties (just like the gauge blocks, it's a fine by-product of the Swedish weapons industry -- the inventor later designed the Carl Gustaf) and manufactured & sold by the company run by the block inventor. The original company is no longer around, they got gobbled up by Hexagon iiuc and seems to have left very few traces on the web. I think Mitutoyo manufactured some of their stuff under license (and they still make blocks), but I suspect this kind of instrumentation is all electronic these days.
posted by effbot at 6:45 AM on April 23, 2016 [2 favorites]


If they're made on paper, don't they get (partially?) absorbed, so the height would be less?

are inks a mix of "solid" pigment and liquid solvent? if so, maybe teh solvent gets absorbed and the pigment stays on the surface? (but paper isn't as smooth as the polished gauge block, so some will go into hollows).
posted by andrewcooke at 7:09 AM on April 23, 2016


All well and good, but LIGO's routinely measuring 4km light beams down to a thousandth of the width of a proton, so step your game up guys.
posted by Devonian at 7:33 AM on April 23, 2016 [1 favorite]


The presenter in that video (OxToolCo) has done some really neat machining and manufacturing work on YouTube. He's been in the business for ages and knows a lot of tricks yet somehow manages to make videos that are both friendly to novices and interesting for experts. Also, you gotta check out the beginning of the "wabble drive" (cycloidal gear drive) he made for a litho (?) press for his wife's art work. There are a lot of video series there that follow a project from start to finish.
posted by introp at 8:08 AM on April 23, 2016 [5 favorites]


Oh, that thickness. Wow!

Skimming the front page before really waking up all I saw was "thickness" and "Johnson". Needless to say I thought they were measuring something entirely different.
posted by inflatablekiwi at 8:39 AM on April 23, 2016


I'm not discounting this important science, but I feel like we get a lot of these videos this time of year trying to get the attention of the Nobel Prize committee. I hope he wins, he seems like a nice guy.
posted by Slarty Bartfast at 9:13 AM on April 23, 2016


I hope he wins, he seems like a nice guy.

Should be a shoe-in for an Ig Nobel.
posted by clawsoon at 10:35 AM on April 23, 2016


Oh, hey. Someone showed me the Sharpie-as-shim trick on a fiddly Wire EDM job last week. (Not my video.) Neato.
posted by qbject at 10:47 AM on April 23, 2016


  Gauge blocks … kind of mysteriously stick together

It's what any two very flat, very clean, hard, compatible surfaces would do. If you leave steel ones together too long, they cold-weld together just through molecular diffusion. Mitutoyo used to have a nifty display of two fused blocks sectioned and etched, showing the crystal growth across the blocks.
posted by scruss at 12:01 PM on April 23, 2016 [3 favorites]


thanks Barchan, cause my first thought was "why do we need to know this?" and your answer is perfect.
posted by supermedusa at 12:40 PM on April 23, 2016


Sharpie ink consists of a pigment, which is a fine ground solid, glued to the substrate by a polymer adhesive. Since the thickness of the sharpie mark varies by color it's probably determined by the size of the pigment particles, and thus probably not very compressible.
posted by Bringer Tom at 1:09 PM on April 23, 2016 [1 favorite]


I... still can't tell if barchan is missing something, or I am.
posted by jjwiseman at 1:10 PM on April 23, 2016 [2 favorites]


This is great, thank you for posting it.
posted by LobsterMitten at 1:24 PM on April 23, 2016


A 'Sharp' is a kind of grifter (a card sharp, for example - 'shark' is a derivation of this), and a sharpie is just a diminutive of it, a lovable rogue, if you will. A grifter's victim is a 'mark', and thus a thick mark would fall for such tricks as those of a sharpie.

How thick is a sharpie mark? Depends on the Sharpie, I guess.
posted by eclectist at 2:03 PM on April 23, 2016


But a grifter in UK parlance is also called a wide boy, so I'm not sure if a wide boy's mark would have to be particularly thick.

These are deeo waters. I do not wish to dwell on how deep.
posted by Devonian at 2:14 PM on April 23, 2016


... any two very flat, very clean, hard, compatible surfaces ...

I once had two pieces of some tropical hardwood that I had flattened and polished with successively finer sandpaper up to 12,000 grit. (Yes that's 12,000, not 1,200.) I could wring them together and they would stick for about two seconds.
posted by Bruce H. at 5:02 PM on April 23, 2016 [1 favorite]


I could wring them together and they would stick for about two seconds.

That effect is probably due to air pressure -- the same thing that lets you upend a glass of water with a piece of cardboard over the opening without spilling it. As air manages to get between the pieces, though, they finally separate.

The effect with really flat clean metal is different. The atoms actually diffuse cross the boundary between the two pieces, welding them together. Left long enough it becomes impossible to separate them.
posted by Bringer Tom at 7:45 PM on April 24, 2016 [1 favorite]


So blood is thinker than water, at least in part, because of the color!

Mostly the blood cells though.
posted by maryr at 2:52 PM on April 25, 2016


The effect with really flat clean metal is different.

I'd be interested to find out the wringing behavior of gage blocks of dissimilar materials, like one steel and one ceramic. My intuition is that it's not very different from two blocks of the same material.

(But not interested enough to buy some blocks and design a test.)
posted by Bruce H. at 9:31 PM on April 26, 2016


Wikipedia says the exact cause is unknown, but it's believed to be a combination of air pressure, surface tension from oil/water vapour, and molecular force, and points to an article by the chairman of the ASME's Working Group for Measuring Gage Blocks by Comparison Methods that says the same thing.

NIST thinks wringability is zombie technology.
posted by effbot at 3:20 AM on April 27, 2016 [2 favorites]


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