Fuseblower's picture

I'm sure that most automotive engineers have to design like this - or they do, whether they have to or not. Why? Because as far as I can tell from the units on the estate around us, this is how car repairers/fitters fit most things... a typical case in point being exhaust systems. I almost don't believe the amount of hammering that goes on during the fitting of them!

In the UK, this has almost been formalised; the acceptable alternative name for a hammer is 'Birmingham Screwdriver'...


To be fair, a lot of mechanical parts are designed to fit within a thousandth of an inch (even back in my grandfather's day as a tool and die maker). Realistically, mass production size variations are generally going to be around that no matter how good your equipment is (and probably several times that). So it's very common for parts to fit more snugly (or less) than intended. If it's too snug, it will bind and the mechanism won't work properly, but if it's just a little snug, it requires a lot of persuasion to go in. (If it fits too loosely, it vibrates and makes a hell of a racket, possibly destroying the machine if it's too bad. Vibration can do nasty things.)

Also, even when things do fit exactly as designed, it can sometimes be difficult to get in. Applying enough force (the hammer) will either force it to go in, or destroy the part and possibly the opening you're trying to shove it in. Anyone who's ever tried to install a CPU on a motherboard can likely attest to this. The clipping mechanism for the fans is designed to create a _very_ tight seal for the thermal conductive paste and hold a very fast fan still to keep noise levels down. I've never managed to destroy a motherboard in the process, but every time I've done it, that's been a major concern.

Fuseblower's picture

Well, I sort-of agree up to a point - but there are some generally accepted limits to fit. A 'light press' fit is about half a thou of interference, a 'standard press' fit is about a thou. And if you achieve either of these fits with a hammer, you're likely to distort the parts anyway. Don't think you're quite in touch with tolerances though; in these days of CNC manufacture, you can easily hold these levels of tolerance - it's pretty much down to tool wear, so if you take account of that, it's the step size on the machine that determines the accuracy (assuming the part's held accurately, blah, blah...). Even on manual machines, using check gauges you can hold production values at this level - although I don't want to make too many like that, because it can be time-consuming.

What you are *supposed* to do is tolerance drawings correctly... which rather makes me wonder what's going on in the cartoon!


You're probably right about my understanding of manufacturing tolerances. I'm not very experienced in mechanical systems, and the areas I am more familiar with have far less need for exact precision. (For instance, nothing bad happens if a 355mL can of beer happens to have 355.001mL of beer in it. A processor with a pathway that's a couple of nanometers out of place may not work at all.) All of the examples we covered in the relevant QA classes were for the trivial side of things, so errors tended to be relatively large. I'm a mining engineer, so I'm part of the process that gets the raw materials to the people who need to worry about such issues.

My grandfather's work with thousandths of an inch dates to World War 2, which probably means he was working more or less by hand. (I know this because it's why he wasn't a combatant in the war - they needed his skills in the weapons factories.

And yes, the idea of having 0 (or as this comic appears to be suggesting, negative) tolerance in the design stage does seem rather questionable.

Homer's picture

A day you spend assembling parts with a mallet is a good day in my book.

EiceBleu's picture

My Airforce father-in-law has informed me that the technical term for that is to 'malletize' it.

CrazyAlmostCanuk's picture

LOL, I was Army, we referred to it as "using the field wrench", or "grab the attitude adjustment tool!"

jbaltz's picture

We always called it "percussive maintenance" when we would "malletize" previously working kit back into working condition.

Pharmer's picture

Our general note was: Cut to suit. Beat to fit. Paint to match.


That way is much too imprecise. It should be: Calculate to 10 decimal places, measure with a micrometer, mark with chalk, cut with an axe, beat to fit and paint to match.

AckAckAck's picture

The wise words of Eddie Izzard:

"You take the instruction manual, throw it out the window. Then you assemble your device, and SMASH IT WITH A HAMMER!"

Zweihander's picture

Oh hé j'ai juste lu votre dernière partie de 600 bandes dessinées (au sujet de #250 à #600) dans une nuit avec le cople gentil des martini. Je suis ainsi -- ok je ris nerveusement hors de l'enfer pour lui. Maintenant je suis-- est-ce que je suis réellement du type ceci vers le bas en français ? Mauvais !

I ayant l'amusement lisant votre comique. Vraiment.

Pierre Lebeaupin's picture
Pierre Lebeaupin

In case anyone here does not understand the above, don't worry. As far as I can tell, it's bad French that seems to have been automatically translated from English*, and nicely translates back to English using Google Translate.

*unless it was specifically written for the purpose of translating back to English well, in which case my hat is off to him.

JohnnieCanuck's picture

I note that his or her handle is from the German and translates as 'two-handed', as in a sword or axe. It appears in Diablo II, for example.


For the benefit of those who don't have a translation tool on hand (including the one called "being fluent in french"), it doesn't translate all that well in English, assuming Google Translate isn't way more sophisticated than I think it is. Here's what it spits out:

"Oh hey I just read your last part of 600 comics (about # 250 to # 600) a night with cople of nice martini. I'm so - ok I giggle out of hell for him. I am now - is that I'm actually type this down in French? Bad!

I had fun reading your comic. Really."

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