Pneumatic nut runners that draw the nut in

[Apokolipse]

Alright, given my profession as a manufacturing engineer, this is going to seem dumb. I am great with math but have very little experience actually selecting tools.

Why is it that some pneumatic wrenches can draw a nut in from the back but others just spin the bolt and nut around together? I am trying to get new nut-runners for one of my production lines and the one I purchased to try out a 90-degree angle requires the nut to be held in place while torqueing the bolt, but their current tools can be used one handed.

 

[APEowner]

The ability to tighten the nut without holding the bolt is going to be a function of how rapidly the nut is accelerated with each impact and how much it slows down between each one. When the nut starts turning there's a brief moment where the nut's threads slip against the bolt's. Kind of like a burn out. Eventually the friction of the threads is enough that the bolt is accelerated up to the nut's speed.

A tool like a conventional air ratchet has a steady speed air motor without an impact and accelerates once and then stays at a steady speed. You almost always need to hold the bolt with one of those.

Impact guns, as the name implies have an internal impact mechanism that sort of hammers against the nut once under load. Generally speaking the more powerful the gun, the faster the initial acceleration will be and the harder impact hits will also impart a faster acceleration. I think, but don't know, that a lower impact per second rating would allow the nut to slow down between impacts and therefore have a faster acceleration.

As far as how to calculate the requirements is concerned you'd need to look at the moment of inertia of the stationary bolt, the friction between the threads and the required acceleration of the nut. The problem I think you'll have is that acceleration rate is not a published specification on an impact gun. In addition the impacts per seconds changes as the load increases on the gun and that curve is also not published.

The bottom line is that you're looking for an impact style nut runner with a high torque and a low impacts per second and you're going to need to try it before you know if it's going to work. I'd start with the specs of the ones that you have that work.

 

[dstblj52]

Easiest thing to do is stop the bolt swinging

 

[Apokolipse]

The ability to tighten the nut without holding the bolt is going to be a function of how rapidly the nut is accelerated with each impact and how much it slows down between each one. When the nut starts turning there's a brief moment where the nut's threads slip against the bolt's. Kind of like a burn out. Eventually the friction of the threads is enough that the bolt is accelerated up to the nut's speed.

A tool like a conventional air ratchet has a steady speed air motor without an impact and accelerates once and then stays at a steady speed. You almost always need to hold the bolt with one of those.

Impact guns, as the name implies have an internal impact mechanism that sort of hammers against the nut once under load. Generally speaking the more powerful the gun, the faster the initial acceleration will be and the harder impact hits will also impart a faster acceleration. I think, but don't know, that a lower impact per second rating would allow the nut to slow down between impacts and therefore have a faster acceleration.

As far as how to calculate the requirements is concerned you'd need to look at the moment of inertia of the stationary bolt, the friction between the threads and the required acceleration of the nut. The problem I think you'll have is that acceleration rate is not a published specification on an impact gun. In addition the impacts per seconds changes as the load increases on the gun and that curve is also not published.

The bottom line is that you're looking for an impact style nut runner with a high torque and a low impacts per second and you're going to need to try it before you know if it's going to work. I'd start with the specs of the ones that you have that work.

Very clear explanation. Thank you for taking the time. Everyone at my plant uses terms interchangeably and I was having a hard time getting to the why of the thing.

 

[Apokolipse]

Easiest thing to do is stop the bolt swinging

Oh, lord, have we tried. We have very little clearance in the corner of this assembly. Two bolts go into a 90-degree corner bracket from each side. The only way we have found where the tools fit, is running the bolts through from the outside and (apparently) letting the impact draw the nut in on the inside. Tools don't have clearance to hold the nuts or drive them from the inside. Design for manufacturing was not a consideration when this product was launched.

 

[APEowner]

Oh, lord, have we tried. We have very little clearance in the corner of this assembly. Two bolts go into a 90-degree corner bracket from each side. The only way we have found where the tools fit, is running the bolts through from the outside and (apparently) letting the impact draw the nut in on the inside. Tools don't have clearance to hold the nuts or drive them from the inside. Design for manufacturing was not a consideration when this product was launched.

Can you use a flag nut?

 

[Bogie1632]

Some bolts that have restricted access for tools may also have a tab attached (formed with during production or welded on) to prevent turning while the nut is fastened. For the life of me I can't recall the proper name for them or find a picture but I've run into them often on vehicles and equipment with bolt used from inside the frame, out. More rarely I've used nuts with the same style tab on them.

V/R
Bogie

 

[Apokolipse]

Can you use a flag nut?

What a good looking question. I inherited this product. It has been running for years. I would assume we do not use flagged nuts or bolts because the design engineer did not find them pretty enough for a product sold at Home Depot.

The only issue with the tools they use currently are ergonomics. The team would prefer something at a 90.... without a butterfly trigger.... etc. I bought a 90 to test, but it was ratchet only, no impact. That was why I came here- to get people smarter than me to tell me what was wrong with the tool I bought. LOL

The tools they have now do not say impact on them anywhere, so I was a bit lost. Now I think I have enough info to get them something closer to the mark.

 

[tjansson]

Carriage bolts can be used too to eliminate the 2nd tool, though it sounds like that would not work here.

Make engineering change the bracket to have weld nuts, wait a few years for the new revision to show up in the container...

You could also use clip nuts ( such as McMaster 94850A150).

 

[BDT/NWMN]

Wonder if there is a "Hammerhead" that would meet Your requirements.. These resemble the shape of an air ratchet; but have the components of an impact wrench built into the drive end.