NEW! Ultimate C/S Prop Wrench Anti Splat Aero

[PerfTech]

Originally Posted by rv8guy

The constant is the 3 inch extension. The torque is applied to it, not the nut.

Stimulating discussion

Very well said! Why couldn't I say that? Thank You, Allan

[Walt]

AC 43.13 is the bible, until someone can show me the math to prove it is incorrect (which I seriously doubt will happen), I will continue to go with the formula 43.13 shows with the exact length of my wrenches.

PS: I also ordered one of the wrenches, you can never have enough tools!

[nauga]

Originally Posted by Walt

AC 43.13 is the bible, until someone can show me the math to prove it is incorrect....

I can't do that, would you settle for the math to show you it's correct?

A torque is a force x an arm. If I apply a force F on a wrench L feet from a nut I will get a torque of T1:

F*L=T1

If I add an extension x feet long to the wrench and apply the same force F to the wrench handle I will get a different torque T2:

F*(L+x) = T2

Presumably T2 is the torque I really want. I would still measure a torque of T1 at distance L, the 'head' of the torque wrench. Think of this as the wrench setting, the wrench will 'click' (or indicate) when the torque at the head = T1 if the wrench is set to T1, but the torque at the extension will be T2. So...divide the first equation by the second:

F*L/[F*(L+x)] = T1/T2

The force cancels, move the bolt torque to the other side and get:

T1 = T2*L/(L+x)

Or as Walt put it:

Wrench setting = desired torque x wrench length / (wrench length + extension length)

I have two torque wrenches, one is ~10" to grip center, the other 14". If I use a 0.8 correction for a 3" extension on both I *will* get different torques at the fastener for the same torque setting.

[CMW]

Here's a simple diagram that shows the math. If the torque wrench is one foot long and the extension is 3in and installed in line with the handle then the .8 multiplier is correct if the wrench is two feet the multiplier would be .88 and if the wrench was three feet the multiplier is .92....if the extension is at an angle to the handle then the actual length E must be measured and used in the equation.



Here's a good calculator:

http://www.norbar.com/calculators/to...alculator.aspx

P.S. the wrench is awesome and I will definitely add one tot the tool box.

[erich weaver]

I'm just glad I already got my order in. Pretty sure Allan will be doubling the price tomorrow after all these posts These VAF guys are a bunch of tough customers huh? Just having a good product isn't enough any more.

Erich

[Garage Guy]

Originally Posted by L.Adamson

I agree with Allan. If a cheater bar is used to extend the length of any length torque wrench...........at the handle end, then the torque value remains the same.

But with an extension between the torque wrench and the bolt, there are two places where you need to know the torque: the head of the torque wrench, and the bolt. You care about the first one because that is what the torque wrench is reading, and you care about the second one because that's the torque you are applying to the bolt. Adding a cheater bar changes the torque at the two places differently, because the lever arm ratios are different, which is why you have to pay attention to "wrench length" when using an extension, even if you don't have to when you aren't using an extension.

Suppose I have a 12" torque wrench, with Allan's 3" extension on a bolt, and I apply 100 lbs at the tail end of the torque wrench. The torque wrench reads 1 ft * 100 lbs = 100 ft lbs, and the bolt gets 1.25 ft * 100 lbs = 125 ft lbs. So the wrench is reading 0.8 of the bolt torque.

Now suppose I add a 15" cheater bar, and apply 50 lbs to the end of it. At the bolt, I've doubled the arm and halved the force, so it is seeing 2.50 ft * 50 lbs = 125 ft lbs., same as before. But the torque wrench head is now seeing, and reading, 2.25 ft * 50 lbs = 112.5 ft lbs. The wrench is reading 112.5/125 = 0.9 of the bolt torque.

Which is what you get from the formula (wrench length)/(wrench length + extension), where wrench length now is 12" + 15" = 2.25ft. Length does matter.

--Paul

[PCHunt]

The reason length doesn't matter is that the torque wrench is indicating the torque on the nut, and not the force on the end of the wrench.

A wrench handle can be any length, and if the torque reading is calibrated at the nut end of the wrench, it will tell you the torque on the nut, which is what you want.

So, wrench #1 is 10 feet long, with a dial that indicates ft-lbs (or more correctly lb-ft) at the NUT. if you want 100 pounds of torque, you would apply a force of 10 lbs at the handle, and the dial would read 100. (10 feet X 10 lbs = 100 ft-lbs)

Wrench #2 is 1 foot long, with a dial that reads torque at the NUT. If you want 100 lbs of torque, you would apply a force of 100 lbs at the HANDLE, and the dial would read 100. (1 foot X 100 lbs = 100 ft-lbs)

You guys are confusing the nut torque with the force needed at the handle.

All torque wrenches read TORQUE AT THE NUT, not force on the end of the handle.

That's why the length of the handle doesn't matter for torque wrenches.

Taking all bets!

[Garage Guy]

Originally Posted by PCHunt

the torque wrench is indicating the torque on the nut

Not with Allan's extension, it isn't. It is indicating the torque at the torque wrench head, but the nut is 3" away from that.

--Paul

[The Paintman]

And here we are back at what Allan said right at the beginning. He has done the math for us and in order to achieve the desired torque on the nut one would have to set the wrench at .8 of whatever ft-lbs you require. The reason is that the point of torque on the nut has been moved by 3'' which will always remain the same as long as you are using Allan's prop wrench. In other words the torque wrench will "click" at the correct torque setting regardless of the length of the handle. If however, you were using an ordinary flat or ring spanner and extended the handle it would be a very different story!!

[nauga]

*sigh*

If I have a 12" torque wrench and I apply a 80 lb force at the grip there will be a 80 ft-lb torque at the head. If I add a 3" extension (0.25 ft) straight out from the head that 80 lb will still produce 80 ft-lb at the head but it will produce 100 ft-lb at the end of the extension. That's what everyone wants. Problem is, if I use an 18" wrench, I will apply a 53.3 lb force at the handle to get 80 ft-lb at the wrench head. The torque at the bolt will be 53.3lb*(1.5+0.25 ft), or 93.3 ft-lb.

Might be within tolerances, might not. It's better to know than to guess.