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Guzziista 12-10-2012 06:50 AM

What keeps me awake at night!
 
Hi All

I am sat here bored and cant look at any of the websites I want to because the family are sat round me watching telly!!!!!!!!!

Anyhow I got to thinking about a longterm friendly argument that I have had with various friends and acquaintences over the years, and wondered if you might want to put youre take on the matter out there.

It came about when a friend had to make a one off spanner to fit on the end of his torque wrench in order to torque down his Harley Davidson cylinder base nuts.

He got a tape measure out and measured the total length of the torque wrench and added this to the length of the spanner and used the Torque=Force x Distance formula to figure out what to set the wrench at.
I argued that surely there must be a formula that DOESNT take into account the length of the torque wrench but instead uses the length of the additional spanner and the desired torque to be applied to the nuts. I gave the example that if the same spanner extension was used on different torque wrenches but to do the same job then surely all the torque wrenches would have to be set to the same poundage regardless of the torque wrench length. I further pointed out that as we know torque wrenches come in various lengths but it is accepted that providing the poundage scales overlap between wrenches then they will do the same job. There is the further factor that if the torque wrench is held ANYWHERE along its handle length, this will make no difference to the torque applied to the nut.

I have been on all sorts of websites and theire solution ALWAYS includes the length of the torque wrench in the equation.

I accept that the commonly spouted formula is the industry norm and it is used by people with far more wisdom and intelligence than me but I just think there has to be a mathematical solution that doesnt take into account ANYTHING regarding the torque wrench....other than the figure it is set to "Click" at, and I think the "NEW WONDER BILLY FORMULA" will express the percentage by which the torque wrench setting will have to be offset.

Unfortunately I am mathematically challenged and dont have the ability to prove my point on paper.
I have managed to get some people to see past the initial common formula and take up my point but eventually they come back to me and say there is no other way to do it, at this I say to the person that according to this formula, if the torque wrench were gripped in different points along its handle then each nut would be set to a different figure despite what the scale were set at (they then jump forward and say no that wouldnt be the case because the wrench would "Click" when the desired torque is being exerted on the nut (This is my whole point all along....torque wrenches deliver there desired output bang on the centreline/fulcrum point of there output (Usually 1/2" square drive) and so the length of the torque wrench is irrelevant in a formula to correct the setting in order to take into account the use of an adapting spanner or such like.

I would appreciate if you did take some time to see the angle I am coming from and try to help me get some sleep but would understand if you thought "Sod that he's thick" and just forgot about it all.
Take care

GunnerTHB 12-30-2012 08:16 PM

That's kind of a hard question to follow, but I'll try. The Distance term in the Force x Distance equation is the distance between the nut and the location of the force being applied (eg. your hand).

You can't calculate torque applied without knowing the distance from the nut to the location of the force being applied.

cobalt327 12-30-2012 08:32 PM

Couple thoughts:

An extension (like a crowsfoot), if used at a 90 degree angle to the torque wrench adds/subtracts nothing.

Using an extension straight out (or at anything other than a 90 degree angle) will need a correction factor. This is because the mechanical advantage is changed by adding length to the end of the wrench (where the torque is registered by the wrench.

A clicker torque wrench doesn't care where you grip it. That only changes the amount of input force required to get the same result at the other end.

A beam type wrench has to be gripped by the handle to register correctly because the shaft deflection is what's registering the torque.

Old Fool 12-31-2012 09:21 AM

I have thought about this same thing before.

The torque wrench is calibrated to display an applied force between the attachment point and a given point (beam type).

Add an additional length of leverage between the attachment point and the fastener and the displayed torque value is inaccurate as applied at the fastener.

The torque wrench is showing how much force is being applied at its end, not the end of the additional lever.

How to figure it out? I had an engineer tell me the math formula many years ago, but I remembered it for all of 2 milliseconds.

What I do remember is the displayed torque value was not the applied torque value at the fastener when additional lever was included.

One way to find out would be to take a torque wrench with an extension lever on it and directly couple it to a second torque wrench. mount one of the torque wrenches (t1)in a bench vise, apply a given torque to the other wrench (t2)and observe the value shown on t1 and compare to value on t2.

Now my head hurts :spank:


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