Threaded rods vs headed bolts difference 4

[jarimasen]

I recently encountered a girth gear in an old ball mill with fasteners (to hold the sections of the girth gear) with threaded rods and nuts on both sides. I do not believe this to be the original design. And it got me thinking about the difference of fastening the gear sections with a threaded rod vs a headed bolt.

I did a bit of research but other than the rod having a lesser tensile strength (with the same diameter), it does not seem to be a difference.

I believe is easier for the rod to get loosen with a rod with nuts on both sides.


What do you think?

JM

 

[JohnRBaker]

Often a threaded-rod is preferred for no other reason than that using a conventional bolt would have been impractical due to the length required.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
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[EdStainless]

But you need to look at the hole also.
Was this designed for a smooth shank to help carry load or hold alignment?
Often threaded rod is crap for tolerances and strength.
The original design may be studs with threads on both ends, it would pay to find out.

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P.E. Metallurgy, Plymouth Tube

 

[rb1957]

I assume there was some portion of the shank unthreaded and with flats ?
and that the joint (ie the pieces being held by this) couldn't be clamped up, but could be controlled to a precise (ish) gap.

another day in paradise, or is paradise one day closer ?

 

[MintJulep]

Threaded rod or stud?

thread725-355979

 

[dik]

For anchor rods, I always spec threads to be cut on both ends to accept a heavy hex head nut... easier to obtain the mat'l and grade.

Dik

 

[GregLocock]

Another advantage of a bolt over a threaded rod is that the thread will have been rolled rather than cut so it has a better form (perhaps) and better fatigue properties.

Cheers

Greg Locock


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[JohnRBaker]

Are you sure that threaded rod is manufactured by cutting the threads? I ask because of this:

https://www.youtube.com/watch?v=dpt6RRiUccM

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[GregLocock]

I was going by dik's post, but you are right, rolling a thread on a rod is actually easier than on a bolt.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[jarimasen]

To EdStainless,

Sometimes these type of gears have 2 bolts for tightening (on each side, 4 total) and 2 to be used as guides (4 total), with a smaller diameter. In this case is an old mill, so who knows originally what was the case. But the 4 rods (on each side, 8 total) are the same diameter.



JM

 

[rb1957]

are these rods quite long ? what is the longest bolt you can get commercially ?

another day in paradise, or is paradise one day closer ?

 

[jarimasen]

The rod is quite long 13”, however, the length is in part because there is a need to place a nut, washer and a jamnut. When a headed bolt is placed, I’ll only need 10” length.



JM

 

[dik]

Greg and John... I cut 1"thread on one end and 4" on the other... I don't usually use threaded rod due to uncertain nature and supply.

For regular strength, I usually us 18x dia and for high strength 24x dia.

Dik

 

[dhengr]

Jarimasen:
In most moving mechanical joints, fatigue and vibration sensitive joints, significantly loaded structural joints, you want to keep the threads out of the joints and away from the faying surfaces, so you can use the full bolt dia. in shear and bearing. You don’t want to worry about the reduced cap’y. of the threaded part in shear, bearing or its fatigue sensitivity. Threaded rod is sold as a commodity and can be cut to any length, cheap and easy, but it is often not a good choice for many applications. Take a round bar of the appropriate material strength and dia. and thread both ends to eliminate the threads in the critical parts of the joint. Put a washer, nut and lock nets on each end, and be done with it, maybe add locktight or some such. Maybe drill and pin the lock nut on one end.

 

[DAVIDSTECKER]

jarimasen,
You say that a 10" long bolt would work but is there enough room to get the bolt in to the hole?
I deal with some old flange mounted motors that have pockets the only allow for a nut so we use studs in the gear box and slip the motor on then install the nuts.
Maybe your studs need to be installed before the 2 parts are brought together.

 

[tbuelna]

One thing to consider with bolts is that they typically have permanent markings on the head that provide information about their characteristics. This information will be very helpful for the next person who has to do this job.

 

[jarimasen]

Well my initial question was if there was a difference, regarding functionality or stress as to having a threaded rod instead of a headed bolt. Regarding dimension (David Stecker), there is no problem in placing bolts. I have already done it, the mill started and it seems fine. We have retorqued after 24hrs operation, and we will do so again in a month.

I'll let you guys know if I was wrong... hopefully not...

Regards,

JM

 

[DAVIDSTECKER]

One reason I've heard of in the past where a stud was used in a critical application is in bolting down the heads on dragster engines.
Since torque wrenches are an indirect method of reading the clamping force generated the engine builders went with studs and nuts so that they could measure the exact stud stretch with a dial indicator while tightening the nut with a wrench.
Of course each stud came with certified material records so the amount of stretch for each stud could be calculated.