As near as I can tell (and remember the language barrier), our regulations have not changed since the 1960's, and I suspect we do not have well described policies on welding of locomotive boilers. Or, it may be that the certification requirements for boiler welding are so high that we do not dream of attaining them. Education and training expectations for licensed trades are pretty high here.

But yes, standard staybolts start at 26 millimeters when new, and renewals typically move up two millimeters each time. We have taps for all sizes in one millimeter increments up to about 33. Even though I have seen some very clean threads after some removals, I have not seen us re-use those threads. The explanation given to me is that the expanding and peening process expands the hole, and it is too much effort to try and turn a new staybolt to compensate for the non standard hole. So, we always tap out to a standard hole size.

On our HHB #4 tank engine project (which I have posted about previously) there are some staybolts that have been renewed often enough to require bushing the hole back down to a starting size. The bushing is maybe 50 millimeter.

Also, what are some control factors that determine how hot the metal is, and how to limit heat flow beyond the point you are cutting?

Does using a smaller tip make it easier to limit surrounding heat, and or make it easier to limit the cutting zone?

You can start practicing by just threading some cheap nuts onto some cheap bolts, used even? Cut the nut off the bolt and leave the threads undamaged. That will at least give you a feel for how the 'joint' gives you a bit of resistance to allowing the cutting to jump the gap. I cut a LOT of nuts off of 8mm studs and rarely damaged the threads. You don't need to remove ALL the material, you can leave a thin shell which usually is pretty brittle slag, and that protects the mating part.

You do need a nice, clean, straight cutting tip, probably a medium size. We're not trying to cut up a battleship....

Well, the Mark I eyeball usually worked pretty well. Try this. Set up with some scrap plate, relatively clean with no heavy scale on the surface, inside the shop, or at least in the shade so you can see when the steel starts to glow dull red. Aim the torch at a spot like you were going to pierce a hole (not at the edge) and when the steel just starts to glow, press the cut lever. The glow should go away as the stream of expanding oxygen cools the surface. Now try heating it a bit higher, and try it again. At some point you get that yellow flash of the steel igniting, and the cut starts. You can't cut steel that is too cold to burn... learn what that color looks like.



Skimming one part off another with a torch relies on the fact that heat transfers into a single piece of steel faster than it transfers to an adjacent piece. You need to get in and go fast, before the adjacent piece heats up. In my experience, a too small tip won't have the oxygen flow to blow completely through a thick plate, and that leads one to piddle around in the puddle trying to get it to pierce through, meanwhile everything is soaking up heat, and you are losing that temperature differential. If you want to pierce through a bolt and have it come out the side of the bolt completely below the plate, you need a tip sufficient in size to cut through plate as thick as that distance will be. Sorry, it's been way too long for recommendations on tip numbers, pressures and the like.

Quick correction, we go all the way up to 36mm staybolts. They are brutes and feel huge in your hand! The other boiler my dad referenced had about 3 of them changed to this size. 2 more holes were candidates for 36's, but we deemed the threads to be insufficient after tapping, and bushed the holes.

On the K, All original staybolts are 26mm. The locomotive received a new copper firebox a few years before being pulled from service. On the steel shell, its possible to see that nearly every staybolt has a bushing around it. When it comes to radial stays, they are not standard like the side sheet stays. They are designed to fit the needs of the holes. Some can have both sheets tapped, just the firebox, or just the shell. This makes for a large amount of annoyance when locating the taps. We ended up having to borrow around 12 different taps and reamers from the state railway shop to get what we needed. Our collection of radial stay taps and reamers are mostly for leaving the shell threads alone and only tapping the firebox threads. It was decided to leave the firebox threads alone since they were still good, and to only tap the shell. We ended up with a 26 thread remaining in the firebox, and a 31 thread in the shell.

All of the threads are eleven threads per inch (yes per inch).

Nothing but "this is the way I do it".

1 Grind off as much of the bolt head as possible without grinding into the sheet. This way you can see exactly where the actual center of the bolt is instead of using a off-center headed over lump. It's also that much less you have to burn through.

2 With the gas and oxy turned up kind of high (loud hiss) start slightly off center and heat the bolt up to cutting temperature (usually bright yellow)as fast as possible, pierce in slightly off perpendicular towards the side of the bolt opposite from where you started heating.

3 Slowly hit the cutting lever and start the pierce, increasing the oxy as the pierce deepens. Until the pierce punches through. You'll know when. The lava like flow will stop and the sound will change

4 (the tricky part) Quickly reduce the flame on the torch (turn down oxy and heat fuel) until you can barely hear the hiss - if at all. Continue to "wash" the molten steel though the pierced hole as you center the tip with the bolt. You should be able to watch inside the pierce to see your progress. Always maintain a nice flow of molten metal as you carefully wash the center of the pierce out, angling the nozzle slightly (about 10 degrees) as you proceed around the bolt leaving a cone shaped hole that is about 3/8" on the pierce side and bigger on the inside (where you cant see).

5 Take a break. That's right. Either go onto about hole or take 5 to 10 minutes to let things cool off -especially the sheet. This will prevent the sheet from getting too hot - close to cutting temp and, more importantly, it will allow the now ring shaped slug that is left in the hole to pull away from the sheet as it cools. This will provide an insulating gap of air between what is left of the bolt, and the sheet.

6 With the torch turned down low - almost no audible hiss, start cutting three evenly spaced notches in the ring. Looking carefully, you will see the thread point appear as dark ribs in the molten metal. Once you just see the points of the threads, go onto the next slot. When all three slots are done, take a punch and hammer and try to peel the now weakened ring away from the sheet by collapsing it into it's center. Don't worry if you cant get the ring out, just separating it from the sheet a little more makes it a lot easier to cut without damaging the threads.

7 Again, take a break to let things cool. Then go back after the ring, washing and punching until the ring segments fall free.

Summary: Be patient and let the hole cool off. You should never see the sheet or the threads in the sheet turn red. Oh yeah. One other thing. BE PATIENT. The locomotive is probably approaching 75 years old or more. A few 10 minutes breaks from your work to let things cool off are going to pay off in the end.

P.S. I don't know if I mentioned this yet. BE PATIENT.

I know this is an old thread, but I just ran into an article on burning out staybolts in a 1923 issue of Railway Mechanical Engineer where they claim a man can burn out four per minute:

https://archive.org/stream/railwaymecha ... 5/mode/2up

Go to page 60 of the scanned file; page number printed on the page is 42.

Thanks, Dennis -- I had been looking for the preceding article on "Mechanical Drafting" for some time.

Just in passing: while finding the sacrificial-anode reference entry in the Puffing Billy blog, I found a potentially-interesting discussion of their practice in welding staybolts after the drilling and alignment as described here has been completed. In particular, they have designed a jig to keep the stay 'centered' in its hole, for at least the time needed for effective tack-welding, the stays being made longer than usual 'for welding' and apparently machined to at least partially align the jig properly during operations. What versions of this are in current practice in United States preservation and restoration-to-operation communities?