Mechanical / Maths sort of question.
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thom
____
- Location
- The Borough
[QUOTE 2505306, member: 9609"]I was checking the calibration of a torque wrench, which (i think) is quite straight forward. Hold wrench in vice, add weight until click, calculate weight and distance and check against setting.
Now not that the following makes any real difference, but I wanted to improve my accuracy by including the weight of the wrench in my calculations. But not really sure how to do this.
Length = 466mm
Turning point 25mm form end (a)
(CoG) centre of gravity230mm from end (a) {205mm from turning point}
weight of wrench =1250g
So with the turning point held in a vice, and the wrench parallel to the ground, what torque is being applied at the vice.
Lets ignore the fact that when the setting is changed the wrench becomes longer. And lets ignore the 25mm sticking out the other side of the turning point
I was thinking half the weight x distance from turning point to CoG
0.205*0.625 = 0.128kg/metres (0.92 lb/feet)
I will give @thom a shout, but I'm sure others will be able to explain how I should be calculating the effect of the wrench its self.[/quote]
Why half the weight ? I reckon you just need to add the full weight of the wrench multiplied by the distance from the COG to the centre of rotation of the wrench/turning point.
Now not that the following makes any real difference, but I wanted to improve my accuracy by including the weight of the wrench in my calculations. But not really sure how to do this.
Length = 466mm
Turning point 25mm form end (a)
(CoG) centre of gravity230mm from end (a) {205mm from turning point}
weight of wrench =1250g
So with the turning point held in a vice, and the wrench parallel to the ground, what torque is being applied at the vice.
Lets ignore the fact that when the setting is changed the wrench becomes longer. And lets ignore the 25mm sticking out the other side of the turning point
I was thinking half the weight x distance from turning point to CoG
0.205*0.625 = 0.128kg/metres (0.92 lb/feet)
I will give @thom a shout, but I'm sure others will be able to explain how I should be calculating the effect of the wrench its self.[/quote]
Why half the weight ? I reckon you just need to add the full weight of the wrench multiplied by the distance from the COG to the centre of rotation of the wrench/turning point.
Just hold the square drive vertically in the vice (ie wrench body horizontal) then there's no need to worry about it's weight at all. Either use a spring balance to pull the handle or use a peace of string hung over a pivot point so that you can just hang weight.
thom
____
- Location
- The Borough
[QUOTE 2505336, member: 9609"]I was thinking the vice will be carrying some of the weight of the wrench, but come to thing of it, I think your right. All of the weight is having a turning effect. (sometimes my brain fails me)
so 0.205*1.25 = 0.256 or about 1.85 lb foot (which is about 5% on a 40 lb foot setting, so worth adding in)[/quote]
A part of torque i get confused about is with regards to power output in cycling. There was some notion that Wiggo produced a higher torque for TTing by using larger gears, while still providing the same power output from his body. Maybe it's a bike efficiency thing...
so 0.205*1.25 = 0.256 or about 1.85 lb foot (which is about 5% on a 40 lb foot setting, so worth adding in)[/quote]
A part of torque i get confused about is with regards to power output in cycling. There was some notion that Wiggo produced a higher torque for TTing by using larger gears, while still providing the same power output from his body. Maybe it's a bike efficiency thing...
Matthew_T
"Young and Ex-whippet"
- Location
- Prestatyn, North Wales
Get a normal wrench and get fit. You dont need any of this torque setting stuff unless you are fitting car wheel nuts.
Custom24
Über Member
- Location
- Oxfordshire
Here is my write up when I did this, including how to account for the torque exerted by the mass of the wrench alone.
http://custom24.blogspot.co.uk/
http://custom24.blogspot.co.uk/
The correct torque is used in order to achieve 2 things. 1. To get the part tight enough that it doesn't move/undo (think slipping seat post) 2. To ensure that you don't apply too much torque and damage the component or fastener (think crushed seat post or stripped threads).
With practice and experience it's possible to get a feel for this which is why many people don't bother with torque wrenches but if you don't 'have the feel' a torque wrench is a good thing to have in your tool box. Most components give a torque range (a min and max setting) by setting your torque wrench mid-range you eliminate the danger of under/over doing it (unless the torque wrench is very out of cal).
Always store torque wrenches wound back to their minimum setting to reduce wear and help keep them in cal.
With practice and experience it's possible to get a feel for this which is why many people don't bother with torque wrenches but if you don't 'have the feel' a torque wrench is a good thing to have in your tool box. Most components give a torque range (a min and max setting) by setting your torque wrench mid-range you eliminate the danger of under/over doing it (unless the torque wrench is very out of cal).
Always store torque wrenches wound back to their minimum setting to reduce wear and help keep them in cal.
Jesus, that's a hell of a sweeping statement
Anyone with a carbon frame had better make their own mind up on this one. If you're mechanically minded and confident (and prepared to pay for replacement parts if you get it wrong) go for it
Davidc
Guru
- Location
- Somerset UK
Absolutely. I'd add that a torque wrench is a seriously good idea with aluminium too. It cracks easily when overstressed.Jesus, that's a hell of a sweeping statement
Anyone with a carbon frame had better make their own mind up on this one. If you're mechanically minded and confident (and prepared to pay for replacement parts if you get it wrong) go for it
On a steel frame you can usually get away with a bit of over tightening because the stuff is more elastic and also deforms gently and generally reversibly. Still a good idea to know what you're doing though.
Not sure about bamboo.
Night Train
Maker of Things
- Location
- Greater Manchester
mark st1
Plastic Manc
- Location
- Leafy Berkshire
Take it to an lbs they are insured against ham fistidness !
vernon
Harder than Ronnie Pickering
- Location
- Meanwood, Leeds
neil_merseyside
Guru
- Location
- Wirral
You might be thinking of a breaker bar?
Arch
Married to Night Train
- Location
- Salford, UK
I think he's studying civil engineering, so he'd probably thinking of 6" sewer pipe or something....
