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Newbie Exercise!
The theory usually (not always!) goes down well, but when we try to put it into practice, unexpected things go wrong, wrecking our confidence or trying our patience. This is an inescapable part of life, but we can
certainly reduce the instances or their intensities. By being in a position to recognise the danger-signals before the disaster actually arrives. Here, an ounce of "principles/theory" is worth a ton of
"how-to" manuals. So let us make a small beginning towards that big goal!
FASTNERS
No doubt, there is NOBODY here who hasn't tightened a screw/bolt/nut in their lives! But how many
would believe me if I said it is an art & science? Some of you are chuckling!! It is those that this part is aimed at!
You might have got a whiff or suspicion when I mentioned "torque-wrench" in
an earlier part. I still stand by my statement that they are unnecessary (infact, they are very much "passe" in the Advanced Engineering World, but that is a long story) but the fact remains that there is
MUCH more to the simple act of tightening a fastner than we realise. No, I am not going into the definations and formulae here, we will restrict ourselves to parts we need.
That is best done, like riding a bicycle, by actually doing it:
Go and buy a couple dozen of cheap fastners, say M8 nuts and bolts, and a few washers.
Find a firmly anchored plate or place where you can
fit and tighen one. If you look carefully, there will be many places in the house.
Get a box spanner with 2 sizes of tommy-bars, and/or a ring/C spanner with "extension-tube".
With each of the
tools, tighten the nuts till the threads break! Yes, that is why I said cheap fastners. And 2 dozen is not a magic number, you may get the point with the very first one, or else even after 2doz you may still go and
strip the threads of the sparkplug hole one day. (I take absolutely no responibility for that!) *As you tighten, concentrate on the "feel".
Observe the difference in the fit between different nut-bolt
pairs. (Another reason for specifying cheap fastners!)
Observe the effect of a drop of oil on a fastner tight due to tolerance as opposed to one tight due to rust.(Now you begin to understand why torque-wrenches
are not such a great idea!)
Observe the springiness when you relax the pressure while tightening the nut which has already "bottomed". *Observe the reduction of this springiness as you tighten even
further.
Observe the reduction of this effect (the springiness NOT reducing so much) if there are two greased face-to-face washers below the nut.
(Washers are often not symmetric as they are punched from
sheet; burred side is back, other the face) OK, now that we are in neck-deep, observe that the corners of the nuts are chamfered. Guess why! By now you are convinced that torque wrenches are a waste of time and
money!!! The thing to measure is extension of bolt, not resistance to turning of nut, as we are aiming at joint-clamping pressure, not nut-tightness which is not really a measure of joint clamping. This you have
just tried & seen for yourself; I won't labour the point.
From a practical viewpoint, it is the reduction of springiness before the thread snaps that you should observe and learn to recognise.
The matter
is complicated by the springiness of the assembly we are clamping in real-life; here there is none. But the feeling is not too different.
By the time you are thru with breaking a few, you will be able to predict
within half a turn the breaking point!
Stop at various points short of breaking and examine the damage to threads (if you are really getting curious and engrossed!)
Don't get over-confident, but if you
do this exercise right, you may not spoil any threads on your bike.
Until you get round to actually doing the above, remember this: The most common trap which causes broken fastners is because people try to
align the bolt/screw with another; to make the slot/face vertical or horrizontal, etc. Now that you know it, it should be easy to avoid?
Remember another thing: fastners are primarily tightened to clamp the
assembly, not to prevent them from loosening! There are various other ways of preventing them coming loose and falling off. Split-pins, spring-washers, anaerobic-sealants (loktite/anabond), lock-nuts, nylock-nuts,
tabbed-washers, etc. All this is quite interesting to learn, and very useful to know! Maybe this is a good time to do something about it?
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