TRUSS and Bolt Torque Specs

[Tshaka]

I have worked primarily with 12"X12" General Purpose Aluminum Box Truss in Motion Picture rigging. So far everything has gone as it should without incident. It's been a few years now.

 

This Truss goes together with 15/16th Grade 8 Nuts and Bolts. I typically use a stubby box wrench to hold the nut in place while tightening with a 1/2" drive ratchet. Some people use cordless drivers. I usually tighten the bolt as much as I can. I've never used a torque wrench. I never learned that way.

 

I'm talking about Rigging here. In Rigging nothing is left to chance and there is always a redundant system in place. There's all sorts of research and regulations, specs., values and stats.

 

Who knows what the Bolt Torque value should be for the Truss system I just described?

 

I'd just like to know.

 

Tshaka

[peter kantor]

i believe that would be 296 foot pounds torque IF you needed it to hold up to a stress of 150,000 psi. this is overrating in most cases.

[Tshaka]

i believe that would be 296 foot pounds torque IF you needed it to hold up to a stress of 150,000 psi. this is overrating in most cases.

 

 

Thanks Peter. What is your source?

 

So I've asked a few other grips on set what their thoughts were on the topic. The general consensus is to fasten the bolts firmly and not to strip them. Different grips on different sets agree.

 

It's a dry topic. I also realize this is a fairly obscure subject. It's more trivia I guess.

 

I'll post here if I find out any more on the topic.

 

Tshaka

[Hal Smith]

This Truss goes together with 15/16th Grade 8 Nuts and Bolts. I typically use a stubby box wrench to hold the nut in place while tightening with a 1/2" drive ratchet. Some people use cordless drivers. I usually tighten the bolt as much as I can. I've never used a torque wrench. I never learned that way.

Tshaka

Bolts are not described the size of the head, but by the diameter of the thread. For instance the Thomas and Tomcat trusswork I work with from time to time uses 5/8" bolts with 15/16" heads.

 

There's a general Grade 8 torque specification page at:

 

http://www.teleamerica.net/reference/Mecha...bolt_torque.pdf

 

If you're using the truss in a way that creates a life and limb safety issue I suggest calling the manufacturer and consulting with an applications engineer for tightening specifications.

[peter kantor]

good point made about the actual bolt size.. referencing the mechanical trades pocket manual; 3rd edition

3/4"grade 8 bolts require 296 foot pounds torque

5/8"grade 8 bolts require 180 foot pounds torque

 

Note: these differ from the values listed in the PDF Link mentioned above.

[Hal Smith]

good point made about the actual bolt size.. referencing the mechanical trades pocket manual; 3rd edition

3/4"grade 8 bolts require 296 foot pounds torque

5/8"grade 8 bolts require 180 foot pounds torque

 

Note: these differ from the values listed in the PDF Link mentioned above.

An even better point!

 

I raced sports cars for 12 years in the 60's and 70's and learned that one always consulted manufacturers when in doubt because a given application might have a required safety margin quite different than reference values. I'll bet the mechanical trades pocket manual is using a 20% additional safety margin because they obviously don't know the end application being referenced. That's why I recommended "Tshaka" (real name please Mr./Ms. Tshaka, it's not a requirement of this forum but is one of its courtesies) contact the trusses' manufacturer if they're using the truss in any sort of a human safety application - which on stage and set is most applications! :)

[Tshaka]

An even better point!

 

I raced sports cars for 12 years in the 60's and 70's and learned that one always consulted manufacturers when in doubt because a given application might have a required safety margin quite different than reference values. I'll bet the mechanical trades pocket manual is using a 20% additional safety margin because they obviously don't know the end application being referenced. That's why I recommended "Tshaka" (real name please Mr./Ms. Tshaka, it's not a requirement of this forum but is one of its courtesies) contact the trusses' manufacturer if they're using the truss in any sort of a human safety application - which on stage and set is most applications! :)

 

 

Tshaka is my real name.

 

This post is addressed to manufacturers as well. It's in the heading.

 

As soon as I learn more information from the manufacturers I'll post it here.

 

Thank you for the attention. Racing sports cars must have been exhilarating.

[Tshaka]

Spoke with a represenative of Tomcat Global USA today. They called me back after checking with [ I assume] the shop staff and told me 80 ft/lbs of torque.

 

Really good of them to make time for me since today was a big inventory day for them sprinkled with meetings.

 

Just to review I asked them only about the lightweight aluminum 12"X12" General Purpose Box Truss that fastens with 5/8th Bolts Grade 8 (15/16th Bolt Head).

 

I got the sense that they fastened a couple sections of Truss together using a torque wrench until it was tight to what they know feels right and then they called me back. I didn't ask if that was in fact what happened.

 

To be honest I didn't ask very many questions after that because it was the final work hours on a Friday afternoon before labor day weekend. They really had a lot to get done too.

 

Honestly I felt the question was somewhat trivial and not worthy of lengthy discussion.

 

We could explore this further and call other manufacturers.... I am satisfied.

 

Also after speaking with co-workers (Grips), Mentors (Grips), and Arena Riggers the general consensus is to fasten the nuts and bolts until they feel secure without stripping the threads. This is how I learned and how I've always done it. I plan to continue doing it this way.

 

So 80 ft/lbs of torque.

 

Tshaka

[Hal Smith]

Spoke with a represenative of Tomcat Global USA today. They called me back after checking with [ I assume] the shop staff and told me 80 ft/lbs of torque.

 

So 80 ft/lbs of torque.

 

Tshaka

Another racing story: I got real lucky the second year and was taken under the wing of a semi-retired Indy car master mechanic - he had two winners after WWII. He invited me to come over to his shop while he was rebuilding the engine out of a very similar car to the one I was racing, just a little bit bigger motor. He let me assemble a lot of the engine, but insisted I use a torque wrench on everything, including things like 1/4" pan bolts. His "lesson" was that after a month or so using a torque wrench on everything, I'd know what "tight" felt like and afterwards only need to use a torque wrench on highly critical bolts like on connecting rods. To this day I can tighten things up to just a bit more than listed torque values, but not too much. And I've got a built-in calibration for aluminum versus plain steel versus alloy steel, etc.

[Guest david west]

i think that the numbers from the references are the Max Torque values before you damage the thread of the bolt, or stretch the bolt and change it properties.

 

the mfg says 80, then 80 is probably derived from the engineering specs for the product. i doubt that they ever expected anyone to torque to nearly 300ft lbs with a box end ratchet.... (at least not all day long).

[Hal Smith]

i think that the numbers from the references are the Max Torque values before you damage the thread of the bolt, or stretch the bolt and change it properties.

 

the mfg says 80, then 80 is probably derived from the engineering specs for the product. i doubt that they ever expected anyone to torque to nearly 300ft lbs with a box end ratchet.... (at least not all day long).

It's quite possible that Tomcat and other truss manufactures use a 5/8" bolt not for it's ultimate torque capability, but as a dowel pin to align truss sections. So their 80# figure is what it takes to safely connect sections, corners, etc. together and not related to the ultimate bolt strength. Also, I suspect it would be a pretty rare stagehand or grip gorilla who could break off a 5/8" grade 8 bolt with a 1/2" wrench! :D