B.Hick & Son oscillating engine

[Jo]

Jason is not explaining what makes a good stud 

Lets start with washers (and "lands) around a stud. If the surface of the part is uneven then tightening a nut onto it will cause stress in the part which could lead to cracks. The easy solution is to put a soft washer under the nut, or to machine a flat surface like a land around the stud. 

Nuts: These come in various thicknesses. If your nuts are not big enough they might not work properly (crack the nut material due to stress). I have already mentioned dangly nuts  If the nut is too thin there is a risk it will strip its threads as you tighten it down . If it is too thick you are just wasting material  and you could possibly strip the thread in the part rather than the nut if you get over enthusiatic tightening.  A standard nut should be 0.8 to 0.875 times the nominal diameter of the thread, or about 5 to 6 times the thread pitch (the distance between thread peaks). This height ensures the nut has enough engaged threads to hold the joint tight without stripping the stud.

You will find some nuts are thinner: these are for locking the main nut. There has been many arguments over the years as to if this should go above or below the main nut that is providing the tightening force.

The bottom of the nut where it clamps to the material should be flat - it will not cut into the paint because you have a washer or paint free land under it  . As for the top you do not want any sharp corners that will get knocked off by a spanner monkey so they are chamfered.

As for the important bit: the Stud. The embedment threaded depth needs to be about 1.5 times the diameter of the stud. I personally use a figure of 1.5 threads visible above the nut on a stud. More than this, in either direction, is a waste of material which originally would increased the weight and the manufacturing cost. The ends of the stud should be lightly rounded so that the thread does not cause a sharp edge and for aesthetic reasons I normally polish mine.

I can go on but I am sure I everyone is going to get bored  A woman knows what makes a good stud   

Jo

[Sanjay F]

My goodness, I never knew there was so much to nuts and studs! 

Thank you all for the finessing information which is an area where I'm clearly lacking; I think I get too excited about the getting to the running engine stage that I don't pay enough attention to taking the engine from a good engine to a great looking one.

I must admit I didn't know a lot of the minute detail which has been described and will slowly start incorporating into my builds. 

[Jo]

I forgot an important fact: A stud has a plain unthreaded bit in the middle. The plain part prevents the stud being inserted too deep into the item and if threads are visible it indicates that it has pulled out of the work. It also gives a surface on which to hold the stud while machining without the risk of damaging the thread.

Some people cut bits off fully threaded rod or hack bits off long screws. There is a time and place for this if the diameter is too small to hold while cutting the thread but they are not true studs 


Hours of fun can be had making real Studs and their nuts 

Jo

[Chipswitheverything]

 I seem to remember seeing Jo at the Guildford show a good many years ago with the Cowell lathe set up in the marquee , using the ingenious arrangement she had devised of length and diameter? gauges to work away at the innumerable and assorted studs that were required for the three Stuart triple engines that were at the near completion stage just then. And indeed, they were true studs!

I would suggest the urge to sometimes resist slapping paint on fairly rough castings, so that the exciting assembly can be done forthwith. The process to bring castings to a decent finish is rather unexciting, repetitive and time consuming, but the engine model is something being made for posterity (?) , and what are some hours of tedium at the sink with wet and dry compared with that?  Dave

[Jasonb]

On studs that are not holding very thick material for example if the part is as thick as the diameter of the stud I tend to just thread the whole length. You would end up with such a short length between the two threads it won't give much to grip. Typical thing would be a cylinder end cover that is 2.5mm thick held on with M2.5 studs that is 3/32 and 7BA in old money. Longer studs such a sthos ethat pass through a steam chest and cover are threaded both ends and not in the middle.

As for the studs going in too far on the smaller engines that will just run for display I don't follow full size practice of screwing in the studs, placing the part in position and then adding the nuts. After making the studs they get a good rinse in solvent to remove any cutting fluid as do the usually commercial nuts. When dry I assemble the stud to the nut with a drop of Loctite with just the right amount of stud showing above the nut. Leave to set and then assemble as if you were using hex head screws.

[Jo]

Jason has reminded me of another reason why studs have a plain shaft: If the nut comes loose for any reason a plain shaft will not wear the piece unlike a thread which can act like a file on the piece

Jo

[Jasonb]

Yes they do provide some location without the risk of fretting, luckily we are not trying to assemble heavy castings with a basic block and tackle like the old fitters would have done so the location aspect does not come into it so much. If you need location then dowel pins are what is needed not studs.

But if you look at all those old aero and marine IC model engines and some small steam ones too of the past the vast majority of those used cheese or fillister head slotted screws so no plain shanks on those and the IC ones were subject to a lot more vibration than a steam engine ticking over at a few psi on air

[crueby]

Good point about the dowel pins. All the full size engine plans I have show pins used to locate parts for assembly. Usually not included on small models.

[Jo]

I was detailing studs but..

But if you look at all those old aero and marine IC model engines and some small steam ones too of the past the vast majority of those used cheese or fillister head slotted screws so no plain shanks on those and the IC ones were subject to a lot more vibration than a steam engine ticking over at a few psi on air

I normally use this type of Filister screws on my aero engines:



Available commercially or I prefer to make my own 

Jo

[Jasonb]

Do you have a source for commercial metric ones Jo? I have found them hard to find*, plenty with UN threads or much flatter heads like a pan head so I too tend to make my own. Which does give the option to only thread a smuch length as is needed, even the UN ones are mostly fully threaded.

Not including Accu who want silly money for them

[Jo]

None of my engines that I am aware of use metric fastners and I always make a point of using the same threads as per the original designs even if that means I have to buy the taps to cut the threads. (Any Male thread can be screw cut  )

I have stopped buying commercial fastners for any of my models as the tolerances supplied are what Eric used to describe as "they fit like a whore" and often are of inconsistent dimensions/shapes (there is a tale there  ),  unless I need several hundred in which case I get in contact with EKP.

Jo