torque wrench

elwdo513 · 05-29-2011, 02:40 PM

would the accuracy of a torque wrench be effected if you use a 3/4 inch wrench with an adaptor to convert to 3/8? thanks in advance

DrIoannis · 05-29-2011, 03:04 PM

As far as I know yes.Any adapter that is been used can effect the accuracy of the torque wrench.

lfoggy · 05-29-2011, 03:15 PM

No problem so long as the adapters don't allow the assembly to flex and move - the fastener always needs to be kept in line with the centre of the wrench. I often use my 1/2 inch torque wrench with 3/8th sockets. However a 3/4 inch torque wrench is very unlikely to have the right range for motorcycle applications....

moman · 05-29-2011, 03:32 PM

As long as you are not changing the length between where you grasp the wrench and where the torque is applied you are fine. An example would be if you are using a crows foot. Placing it at a 90 degree angle from the wrench handle will not affect the applied torque. If you place the crow's foot straight out or straight back it will alter the torque.

LiterBoy · 05-30-2011, 09:40 PM

Quote:

Originally Posted by moman

As long as you are not changing the length between where you grasp the wrench and where the torque is applied you are fine. An example would be if you are using a crows foot. Placing it at a 90 degree angle from the wrench handle will not affect the applied torque. If you place the crow's foot straight out or straight back it will alter the torque.

Your example is a good one, but the explanation is even simpler: as long as you don't change the pivot point, where you grasp the wrench has no effect.

Theoretically, a solid, non-articulated adapter remains concentric with the pivot point and will have no effect on the torque reading of digital or beam scale wrench, or where the "click" occurs on a micrometer type wrench.

Change the pivot point, you change the torque.

moman · 05-31-2011, 07:40 AM

Where you grasp the wrench will definitely have an effect on the torque applied. You would be changing the length.

LiterBoy · 05-31-2011, 08:50 AM

Quote:

Originally Posted by moman

Where you grasp the wrench will definitely have an effect on the torque applied. You would be changing the length.

Don't confuse the force applied to the handle with the force applied to the bolt head. You will have an effect on the force applied to the wrench handle, but it will have no effect on the setting of the wrench.

Set a micrometer style wrench to 50 Ft. Lbs. Slide a 3 foot pipe over the handle. Grasp the pipe at the furthest point to tighten a bolt and the wrench will still click at 50 Ft. Lbs.

You have changed the amount of force needed to twist the wrench, i.e., you increased your leverage, but as long as you don't go further than the click (or the 50 Ft. Lb. reading on a digital or beam display) the amount of torque applied to the bolt will remain 50 Ft. Lb.

**1000RR** · 05-31-2011, 09:23 AM

LiterBoy is on the right track...

Torque is a measurement of how many feet from a pivot point a specific weight/force is applied. As far as changing the distance from the pivot point and applying force, it has no affect on the torque wrenches I've seen. Their internal mechanism that calculates the torque is taken at near the head of the the ratchet. So if you grab the handle you're fine, if you grab half way down the handle, you're still fine. The closer you get to the head, the more force it will feel like you need to apply for the same result. If you were to use a crows foot or extension connected to the end of the handle, the torque wrench will still react the same, you'll just end putting less force on the end of the extension/crows foot than you would if you weren't using it. The internal mechanism still reads and reacts to the force being applied the same. It has no understanding if you used a big extension on the handle.

As far as using socket extensions or reducers, you should not have a problem if you're using quality tools. If you are needing to torque something down pretty tight, say 70 ft-lbs or more, I would just stick with the normal sized extensions and not use reducers. My experience for motorcycles is that you pretty much need a big torque wrench and a small one too. The axle and steering head certainly use a big torque wrench, whereas most smaller bolts (clip-ons, fork clamps, etc.) use a smaller one.

LiterBoy · 05-31-2011, 12:16 PM

Thanks for the more thorough explanation, Don. In an effort to be brief, I may not have been detailed enough, and this is an area where lots of folks--even auto mechanics--aren't quite familiar with how a torque wrench operates.

lfoggy's advice is spot on.

moman · 05-31-2011, 12:56 PM

Quote:

Originally Posted by LiterBoy

Don't confuse the force applied to the handle with the force applied to the bolt head. You will have an effect on the force applied to the wrench handle, but it will have no effect on the setting of the wrench.

Set a micrometer style wrench to 50 Ft. Lbs. Slide a 3 foot pipe over the handle. Grasp the pipe at the furthest point to tighten a bolt and the wrench will still click at 50 Ft. Lbs.You have changed the amount of force needed to twist the wrench, i.e., you increased your leverage, but as long as you don't go further than the click (or the 50 Ft. Lb. reading on a digital or beam display) the amount of torque applied to the bolt will remain 50 Ft. Lb.

This is absolutely true if you are using a concentric attatchment. My comment was regarding when nonconcentrics are used. You have to make your calculated torque based on where you are applying the force on the handle. You could do that with a three foot pipe if you want but it may be a little difficult. However, the point of force applied on a flexible beam-type torque wrench pivoted grip will not affect the calculated torque applied to the fastener. This is the only exception I'm aware of.