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Question about torque

BGordon

BGordon

Well Known Member
Good afternoon everyone,
I am looking for the advice of an A&P or IA concerning torque. I read in the Standard Aircraft Handbook that an AN3 bolt should be torqued to 20-25 inch pounds. However I am having a hard time finding a torque wrench that will go that low. Is there any harm in torqueing them to 30 inch pounds (seems to be the starting point on most wrenches I have seen)?

Thanks
Brandon
 
You will want to get a good torque wrench which has that range. Actually #8 structural screws are even lower. They are available online (Amazon for example), and I've seen them at Home Depot and Lowes.
 
There are lots of torque wrench options- just few cheap ones. Check snap on for a dial or digital type. Find the snap on one you want and check eBay.

It is typically not recommended to use a click type torque wrench at it's lower limits, although technically acceptable.

Keep in mind that torques values for most bolts is driven by the nut type- ref AC43-13-1B table 7.1.

Hope that helps
 
I've got a Snap-on that goes from 5-30 in/lbs. I think it is best to spend some $$ for a torque wrench for the correct range. Most people tend to "over torque" verses under torque .... especially small AN3 bolts. Remember to add any torque required for locking nuts....might add a few in/lbs depending on situation. You will not be able to torque every single bolt ....sometimes you just can't get to it with the wrench. But, with the experience you'll gain, you will be close.

Ellis
A&P/IA
paid 2017
RV7a slow build Canopy phase.
1977 Tiger owner
 
Some place like Sears will sell torque wrenches calibrated in Ft-lbs or inch-pounds. You'll need both, but most of the time it's the inch-pound one you'll be using. Don't forget to add in the 'free running torque' (what you need to smoothly turn the nut all by itself) when using locknuts.
 
I had a cheap 1/4" drive click torque wrench and didn't feel that it was very accurate or repeatable so I bought a cheap digital 1/4" drive one and it seemed to work fine until I dropped it once and it was done (cheap plastic). I should have just bought a good one in the beginning. I have a Westward digital one now that was about $260 and I never worry if I am under or over torqueing the bolts. When you look at how many places a single bolt failure can cause a catastrophe, it's really cheap insurance to buy a good one.
 
In my experience, the primary difference between an expensive torque wrench and a cheap one is the sound the owner makes when the expensive one hits the concrete floor in the hangar.
 
I like this style, easier to measure the "drag torque" and work after dropping on the floor. :)

https://www.purecycles.com/products/park-tool-tw-1-torque-wrench

10772245-1363093550-975430.jpg


The Park TW-1 is apparently discontinued by the manufacturer so it's existing stock being sold.

Zero to 60 inch-pounds is just right for our smaller bolts.
 
+1 on that, Gil.

Amazon sells several similar beam-type torque wrenches. They are reliable and rugged. Look for 1/4" drive.

I've got a similar one and use it in preference to my click-type one. With the beam-type, I can find the running torque, add it to the planned tightening torque, and torque that thing down quickly.

Dave
 
Torque Wr

Harbor Freight has an electronic gauge that makes your ratchet a torque wrench. Comes with 1/4 and 3/8 ratchet adaptors in a nice plastic box and sell for under $40.
Very accurate and repeatable. Electronic is the way to go in my opinion.
 
CDI

Get a 1/4" CDI. Check Amazon. $100 or so. You'll also need a set of crows foot open end and a 3/8-1/4 adapter.
 
swordtail said:
Harbor Freight has an electronic gauge that makes your ratchet a torque wrench. Comes with 1/4 and 3/8 ratchet adaptors in a nice plastic box and sell for under $40.
Very accurate and repeatable. Electronic is the way to go in my opinion.
Click to expand...

Yes, this is very accurate...... But, it needs a lot of space to be used. It is great for installing cylinders. Not really good for lower inch pounds.
 
I like my dial type torque wrench

I looked at a number of styles of torque wrenches and settled on a dial type rather that a click type for smaller fasteners and I'm very happy with it.

Here's a link... https://www.protorquetools.com/cdi-1-4-dr-0-75-in-lbs-dial-torque-wrench/

It wasn't cheap ($158), but the dail lets me see the actual torque being applies as I work up to the desired point. It also allows me to measure drag (typicality 3-5 in-lbs for a -3 nut) as I'm tightening a nut. You're supposed to add the drag to the final desired torque...

-Ivan
 
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