Reply With QuoteWhat is it? its a special type of socket wrench that gives and audiiable/visual indication when a preset tension is applied to it.
Who should have one? Every one.. yes even the guy who only uses it to change his tyres.
Hows it work? well that kind of depends on which of the 3 you buy..
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The first is common, its fast, its bidirectional, its a bit of a pain to set and it ratchets. Its the ratcheting, self resetting torque wrench...To set it you adjust the micrometer like spindle at the handle end, this adjusts the preload on and internal spring and then when you apply turning force (AKA Torque) a pin held in place rides up and over a ridge and clicks, the handle then "flicks: about 5 degrees letting you know that your at the right tension. when you return the handle to center the pin resets and your good to go again. It also has a ratchet head so you can tighten LH threads as well. These torque wrenches are the most forgiving to use and good ones hold their calibration really well. Setting the scale on the bottom does take a little getting used to. you can buy these ones almost anywhere. This is the one I recomend for home workshops.
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The next is almost as common as the ratcheting torque wrench isnt self reseting isnt ratcheting and isnt bi directional its the deflection beam torque wrench.(very top of pic) this is simplicity itself to use, simply undo the thumbscrew holding the wedge slide it till the little flat "t" is inline with the setting you want, depress the pin that pokes out of the beam and pull. The big advantage of these wrenches is the ease with which they are recalibrated, and they need to be, knocking one, variations of temperature, some dolt using it to undo nuts or tighten left hand threads will throw one of these out of whack... This is the one I reccomend for mechanics..
The last (and i dont have a pic of one) is the deflecting scale torque wrench. it works on the same principal as the deflecting beam but has an arc scale in place of the wedge and a thin pointer beam in place of the deflection beam. you pull the handle, the pointer stays in place and the scale moves under the pointer, they are not usually used for lots of torque but are bi directional and are just the ticket for measuring roatational torque between 5 and 30 ftlb.
Id only reccomend one of these to someone who was rebuilding diffs/gearboxes for a living and needed to asses the preload torque on a shaft on a regular basis.
Is there any thing I can use in its place.... Yes a spring gauge and a known lenght spanner will allow you to do the same thing...
torque is expressed as effort x distance.. 1 ftlb of torque is the eqivilent of 1 pound of weight pulling down on a spanner 1 ft long from center of rotation to the point of effort....Given that 1ftlb of force will also be developed by a 2 foot long spanner with half a pound of force applied, ditto 2 pounds on a 6inch spanner.. Want it in metric? simple replace ftlb with Nm, pounds with Newtons and foot with Meter.... the math is the same, the names change. (1ftlb is not the same as 1Nm tho...)
the reason for having a torque wrench becomes important when things have to be the same. could you imagine what would happen to your engine if 2 head bolts were finger tight 2 bolts were done up to just shy of snapping and the rest where who knows where.
All items that require tightening down with a torque wrench (infact almost antything with more than 2 bolts on it) will have a specified tensioning sequence... and the motto for tensioning is "in sequence in stages."
first the sequence theres 4 types of patterns youre likely to find
- Circular, like wheel nuts
- square/rectangular perimeter, like the bolts that hold the sump on the engine
- staggered rows, like head bolts
- 4 square, like the swivel pin bolts
in order the rough guide for tensioning bolts is
Circular, pick a bolt lable it #1 move to the bolt most immediately opposite it thats #2 go to the bolt next to #1 that is furthest away from #2 (try it on a landrover wheel youll see what I mean) and repeat till you run out of bolts. thats the sequence. on something that has an even number of bolts when you go back to bolt 1 pick left or right and then work the same way all the way around. (this should be in the tyre changing section of your users manual)
Square perimeters, Simple start in the middle of the longest side and thats bolt 1, the bolt in the corrisponding opposite side is #2 then the middle on the shorter sides is 3 +4, move one bolt left or right of bolts 1,2,3,4 and they are in turn 5,6,7,8 then leap frog back over 1,2,3,4 and thats bolts 9,10,11,12. what your aiming for is to tighen the middle of each side and then squeeze the plate down so the 4 corner bolts are the last ones you do.
Staggered rows If you dont have the template for an item you can use the generic rule of inside out in circles put your finger on the bolt closest to the center and call that bolt 1 then move your hand around in ever increasing circles and each time your finger crosses over a new bolt lable that bolt with the next number.
and 4 sqaures is easy, pick a bolt, thats #1, the one furthest away from it is #2 #3 is the one closest to #1 and #4 is next to #2.
If thats confusing I'll draw or obtain pics and post them...
naturally removing these items is a case of counting backwards.
thats sequence the next bit is in stages... IF you have to do a bolt up to 600nm theres no point doing one bolt up to 600nm while the rest arent even finger tight, thats how heads get warped, wheel discs get out of alingment and blance and stuff gets busted. you should do all bolts in stages... about 1/3 or near enough at a time...(the torque angle method is different and will be addressed later) so my 600nm wheel nuts would be tightend in sequence to 200 then 400 then 600 nm. The same goes for loosening. crack the bolts back a little (about 1/4 a turn, then back them off another 2/3 to full turn then remove them)
Take care of your torque wrench. if its out of whack you could be overtightening or under tightening all your bolts.. The jury is still out on which of those 2 is worse.
Originally Posted by matbor
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