Bolts or Studs when Fastening Parts

[J.L.]

Being very new to forum and in the company of very experienced model engineering experts, I hesitate to ask a question that may have been answered many times. But, if you want to learn something - ask.

So, my inquiry is about the use of bolts to fasten the base of columns and bearing blocks. I notice that almost all of the Stuart engines use bolts instead of studs to hold down parts. I thought that, back in the day, heavy parts were lowered onto studs - much like we put a wheel onto a brake drum or disk assembly. My example of the car wheel employs horizontal attachment, but the principle is the same. The studs locate the part and ease assembly. Is this historically correct with steam engine fastenings?

I also see a lot of very thick bolt heads being used and supplied in the Stuart line. They look out of scale to me. Are they?

Curious.

John

[jeff l]

Hi John , I feel that  some of the bolts that Stuart used are out of scale , as for the other question I think you are on track if a part had to be lifted or lowered into position studs would make the job easier ,I'm no expert though.

[derekwarner]

Hullo John......this is a very interesting point as it crosses a number of mechanical fastening conventions

One scenario is the application of an induced torque by the tensioning of the nut to stretch the un-threaded section of the stud.....however this also requires careful consideration of the depth of engagement of the threaded section of the stud in the base structure and also the thickness of the machine part which also is the mounting base of the removable part

A second scenario used less commonly in early machinery builds is the use of the locknut, however if the stud does not have the required applied torque moment attained when tensioned/tightened by the first nut,  adding and tightening the locknut against the first nut simply stretches the element of the thread between the two nuts

Potential mechanical damage to studs when lifting and lowering a heavy mass down over the studs was minimised by the use of pointed tall tapped taper alignment spears

Possibly the only enlightening consideration that computers have provided in stress analysis is that the thinner nut should be engaged and tensioned to the stud, then the second full size nut installed and then tensioned as the locknut    [......but it just looks wrong]

With the second point, a number of fastener manufacturers market ...
eg., 6BA threaded bolts with 8BA hex AF & head height

European [German] manufacturers also provide a similar scenario with non-ISO metric scale bolts & nuts  

Derek

[Jasonb]

I would not class Stuarts offerings as "Scale Models" back when they first came out many were used in small boats or steam plants so practicality for the user was more important than looks so would not base any thing on their use of bolts.

Back in the day when each full size engine manufacturer would have made their own fixings it was far easier and less wasteful of materials and time to thread a bit of rod and drill and tap a nut than it was to turn down larger stock to make a bolt/screw.

Also when errecting these engines with block and tackle the studs would take the weight of the part as soon as it was engaged on them rather than having to finely adjust a parts position while trying to line up bolts even with the use of a podger.

One thing I will say to those who choose to use bolts to assemble their engines, the usual convention is to have the bolt head on the top and the nut below when the bolt is vertical. The reason for this is that if the nut should work loose at least the bolt will remain in place and offer some location for the part.

As to nut thicknesses and A/F sizes they were generally taller and of a larger hex, take a look at old US hit & miss engines and you will find similar proportioned heads. For economy during the war years sizes were reduced and we have now ended up with the metric nuts which look very flat by comparrison. Though I use smaller than ISO hex metric fasteners.

I'm sure Jo will be along later to offer her thoughts on studs.

[pgp001]

I have just purchased another thread rolling tool for making metric studs and bolts, this one does M1.2, and I also have M1.4 & M1.6.
http://www.ebay.co.uk/itm/182069372002?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The seller has a variety of sizes available, these make a very good strong thread in the same way bicycle spokes are made, and if you have never tried them it might be worth considering.

Phil

[Jasonb]

Funny enough Phil I came across these the other day while looking for something else, fit in a standard die holder but roll the thread

http://minitaps.com/categories/Miniature-Threading-Dies/

[Alan Haisley]

...
Also when errecting these engines with block and tackle the studs would take the weight of the part as soon as it was engaged on them rather than having to finely adjust a parts position while trying to line up bolts even with the use of a podger.
...

Would they then leave the middle of the stud unthreaded and matching the hole size so they serve as locators? This would certainly seem to make sense.

[kvom]

Benefits for studs are that they are stronger than the same size bolt, and that over torquing doesn't result in breaking off inside the threaded hole.  For model builders the latter benefit is more important, plus those who seek to be authentic will prefer their looks.  As for connections to a concrete or masonry base, I'm guessing that the end of the stud is cemented in and that only the upper end is threaded.  Unless nutserts or concrete anchors were invented in Victorian times.

As an aside, modern vehicle wheels are hub-centered rather than stud centered, as this method is more accurate and safer.

[Dan Rowe]

Benefits for studs are that they are stronger than the same size bolt, and that over torquing doesn't result in breaking off inside the threaded hole. 

They both will have the very same root diameter so why is stud stronger? I have seen both studs and bolts break flush requiring an easy out to remove.

Dan

[Ian S C]

Came across an oddity, an English made caravan with a wheel that came off.  The wheel instead of being held on with nuts on studs, had bolts into a taped* back plate. The wheel on the other side had loose bolts too. The incident happened about 10K up the road from my place, we walked up the road and found one bolt, took one bolt from the other wheel, and bought the van to my place. Got the special shape headed bolts in Christchurch.
 next day.
*tapped
Ian S C

[Bluechip]

Que ???? 

Taped or tapped ? Quite a lot of vehicles have, or had, wheels held on by bolts. Often with a locating chamfer under the bolt head.

Normal practice to check any wheel retaining fastener on a regular basis.

In my case once every time I remember .... 

Dave

[kvom]

If you torque a bolt to failure then it breaks from twisting the shaft.  If you overtorque a stud to failure the shaft doesn't see any twist.  So it's a question of tension vs. torsion.  Since metals resist tension more than torsion, fasteners can apply more pressure n a stud and thus resist stronger forces.

Engineering rule of thumb is that a shaft is around 2x stronger in tension than torsion.

While it's true that lugnuts for vehicle wheels should all have a taper on the wheel side, hub centered wheels  and rotors are pretty universal these days.  The hub only centers the wheel on the axle; the lugnuts secure it.  In the past the bolt circle of the studs was often used for centering, but any variation or bending of the studs would cause an off-center wheel mount.

[sco]

If you torque a bolt to failure then it breaks from twisting the shaft.  If you overtorque a stud to failure the shaft doesn't see any twist. 

So the friction between the nut and the stud thread from the act of tightening the nut to pretension the stud goes where?  It goes into twisting the stud shank so it is wrong to say the stud doesn't see any torsional stress.

This is an excellent site to learn about fasteners: http://www.boltscience.com/pages/basics1.htm

Simon.

[derekwarner]

.... "So the friction between the nut and the stud thread from the act of tightening the nut to pretension the stud goes where?"

  .....so the real answer is elongation of the stud [understanding friction is a far more complex variable]

This is getting away from Johns original question, however one example  explains use over certain confusion

M64 diameter head studs & nuts on marine diesel engines are not subjected to nut flogging to attain pretension........the 6 or 8 head studs are simultaneously stretched in length by a hydraulic spider device. When the nominated increase in length [elongation/tension] is achieved,  the M64 nuts are spun down freely and seated....the hydraulic stretching device is removed....each of the head bolts are now subjected to the required uniform tension which is based upon a nominated % below the yield point of the stud material

So this example also relies on certain requirements as did the bolts or studs that John was originally questioning

The requirement is flatness of the surface that the nut is seated against

One final point of consideration in all bolted joints is understanding the degree of impulsiveness   that the joint will be subjected to

If we could close our eyes and visualize machines from yesteryear ....my best guess is that the majority would be secured by studs and nuts.......[the stud height above the nut would also be amazingly uniform together with a suitably machined stud top face surface & chamfer].........and very few with locknuts ............

Derek

[ChuckKey]

Another reason for using studs is that, for several maintenance cycles, they can stay put when dismantling, prolonging the life of the tapped holes in the expensive bits.