Making studs

[Jasonb]

2. the nominal [minimum] depth of thread engagement is 1.5 x the thread diameter

No thread engagement is not how far the stud/bolt or screw is turned into the tapped hole.

It is the relationship between diameter of tapped hole to the major dia and is expressed as a percentage. eg how much flank contack there is not how far the stud is screwed in. If the commercially produced rolled studding is undersize then the percentage engagement will be reduced.

3. I simply noted that BA is a metric thread form

The term "form" relates to the shape of the thread and as BA is not shaped the same as metric it can't be the same form. It would have been better to say something like "BA is a metric based system"

J

[Jo]

Now let’s look at the production methods. First thing is look to use a number of pieces of rod to make these, I normally use 4 or 8 rods and cut studs on both ends. The reason for this is that once you have your lathe tool set up and calibrated (on your DRO/dials) on a quick change tool post if you change tools the chances are you will need to recalibrate the measuring technique.



Tooling: for the smaller studs I use a tailstock die holder, for larger ones I have now moved over to using a Coventry die head but for now let’s focus on using the more normal tailstock die holder. I also use a mandrel handle, sometimes a collet chuck, sometimes a three jaw SC chuck and others a drill chuck fitted in the nose of the lathe.

[

The example I am going to use is some of the 6BA studs I need for the Double Tangye. These are made from 1/8” 303 stainless rod, so the 1/8” will fit nicely into a collet but once they are reduced to 2.8mm they won’t.

Jo

[NickG]

Thanks for the spreadsheet Jo, will come in handy 

[Steam Haulage]

Thanks Jo,

That's just the sort of detail I would value, not only why but also how to achieve the desired result.

Looking forward to the next post.

JerryNotts

[Jo]

So the starting point is to face the end of the rod and turn the threaded part of the stud that is going into the work piece. Why this end? Because this end is normally longer than the end for the nut so gives you more to hold on to later (and if you get overly enthusiastic and put too much pressure on the threaded end when you hold it later and damage the threads they will be hidden in casting). The distance required to be turned down is the length of the required thread, plus the lead on the die (that’s the tapered bit at the entrance of the die that helps you start the thread). We also need to chamfer off the end of the turned section to help the die start, I do this with a file as I do not want to disturb the lathe tool.



This can now be threaded under power if you so desire or as there is not many threads required the mandrel handle can be used. A bit of cutting compound first won’t go a miss and don’t forget to clear the swarf to prevent damaging your next threads.



Now it is worth just running a file over the end to get rid of any new burrs caused by the die then we can take the shank to length. The length is the remaining length of the stud plus a bit for your parting off tool. And don’t forget to get rid of any burrs raised on the outside of the rod otherwise it will not fit back into the collet chuck.



Before we get excited and finish this one we need to do the same on the ends of the other bits of rod:



Now we can part them off, not forgetting to deburr the stock material before disregarding it.



The other half finished stud you can see in my patented (egg) stud tray  is a 2BA/4BA opportunity which you can't buy commercially. Great for when the standard sized nuts look oversized but you have already drilled and tapped to the drawings before you realised how hideous the size specified looks .

Now the second halves.

Jo

[Jo]

Now we have to decide how we are going to hold these to continue. We are limited to the amount of material we have for holding by the same rule we mentioned earlier we need to leave hanging out of the holding device as a minimum not only the length of the top thread but also enough for the lead on the die. As for holding the watchmaker’s trick is to use a drill chuck in the mandrel:



This works well with very small studs  . Last chance to correct the length of the studs… if you are like me they vary a little, it doesn’t really matter (if it is a little) as when they are inserted they need to be fitted to the correct length, you just need enough threads to let that happen. So go and find the file and taper the edge to help the die start. I normally count the threads in to get the correct length, but if you do don’t do what I did on the DT valve rod studs and forget the plus 1.5 threads for the lead otherwise you will find that your nuts bind before you get them where you want them



And repeat for each:




The alternative technique I use for larger studs is to use a Coventry die head. These are wonderful. But not as easy to set up for smaller threads. My Coventry die head has been fitted to a 2MT and fits into the lever fed tailstock on my Prazimat.



In use I close the die head, introduce it to the work and then count the thread turning the mandrel handle. Once I am at the required number of threads (plus 1.5 for the led) I push the tailstock lever and magically the die head lets go and withdraws itself  .


The only other thing I can add is don’t do more than about 8 at a time otherwise it can get boring  .

Jo

[b.lindsey]

I didn't think you ever got tired of making studs Jo, much less bored with them   Thanks for the great write up !!

Bill

[derekwarner]

Jasonb.......

1. I did not invent  the term "thread form" as applied to BA threads ....& I certainly was not here in 1884....
2. however many authoritive references group the words together as below
3. I certainly am not qualified to question the British Association for the Advancement of Science 

Having said this, I quite enjoy using BA fastners in model building......Derek
___________________________________________________________________________________________________________________________________________

"In 1884 the British Association for the Advancement of Science adopted a thread form and series, primarily for use in precision equipment. It was inspired by one used in the Swiss watch and clock industry, and was formerly sometimes called the Swiss Small Screw Thread System; but is now just referred to as the BA series. Like the Whitworth thread, it has a rounded root and crest, but the included angle is 47.5° and the radius was originally 2/11 (0.1818…) times the pitch, but at some later point was changed to 0.18083. The gauge numbers and pitch are related, roughly, by pitch = 0.9 to the power of the gauge number.


Despite the date of origin and the British sponsorship, the BA is a metric series. Not only is it based on the meter, but the thread frequency is specified in terms of round numbers in the pitch sequence, with threads per meter allowed to fall where it may"

[swilliams]

Great thread Jo!

So far I've learnt two things

1) If you are making small studs you need a Cowells lathe
2) If you're pulling the head off your car, notice the proper use of studs, and you should wear a bikini

Hmm, I'll have to ignore these two points. Heading back to my old methods 

Steve

[derekwarner]

Jasonb.......just thinking more about rolled threaded bar & your note......."If the commercially produced rolled studding is undersize then the percentage engagement will be reduced"

This is not the case for the final product....the parent bar stock may well be intentionally undersized, however the rolling process takes from the rich to give to the poor & increases the diameter of the threaded section

eg., an M24 x 3P ISO metric rolled thread formed fastner may be created from bar stock negative of 24 mm diameter, however the final thread sizing & tolerancing is to the appropriate Standard...in this case being ISO 898/1......Derek

[Jo]

2) If you're pulling the head off your car, notice the proper use of studs, and you should wear a bikini

  I thought that you guys were meant to forget things as you got older.

Jo

[Jasonb]

Totally agree with the theory there Derek.

But in practice the majority of commercial studding and small non graded bolts for that matter that the average model engineer buys tends to be of far eastern origin and certainly in my experience a bit of a slack fit. I can get a far better fit by adjustment of the die than using bought in fixings. Even the good quality model engineering fixings that are machine cut are usually to a slacker fit than making your own.

The other reason we are discussing this is that studding in the smaller ME sizes if not that readily available, over here about the smallest you can get is 8BA or M3. If you have  a source for commercially made smaller sizes such as M1.4, M1.6, M2 & M2.5 that would be of use to members who want to use commercal studding.

[Arbalest]

Those of us old enough to have maintained their own cars will recall how the cylinder head studs were unthreaded through the head and the washer not only allowed the nut to turn without twisiting the bolt but also would not tighten down unless the washer was in place.

JerryNotts

I used to work as a Mechanic at a Ford main dealership many years ago and one thing you got hold of as soon as posible was a couple of head BOLTS to cut the heads off so you could use them as temporary studs. A saw cut aids removal once the head is located and a couple of bolts loosely inserted. Not sure about other makes but all the fords I ever worked on only used bolts. One of my old bangers - a Corsair with a Vee 4 engine had double hexagon (12 sided) heads on the bolts, not seen that since but it's been a long time since I worked on cars!

[Steam Haulage]

Ah but those were bolts not screws. Certainly BMC used studs. My current Ford has bolts as well.

JerryNotts

[steamer]

Nice write up Jo!   

Dave