Help please - Firebox stays

I am building an 3.5" gauge 'Schools' - I have drawings from Clarksons of York dated 1935 by H P Jackson and LBSC Roedean from Mechanics dated 1948.

For the firebox stays in Jackson's design he calls up 13 off 3/16th x 40 tpi per side at 1 and 1/16 th centres. The LBSC design calls up 50 off 5 BA stays on 5/8th centres per side. In both cases the firbox wrapper is 13 gauge.

Which is the better design and recommended staying?

Mike

I would go with the LBSC option or use 1/8" copper rivets. But either way, I would discuss it with your boiler tester first, as he (she?) will have the last say.

Geoff

Mike,

What working pressure is specified? What material are you intending to use for the stays, bronze or copper?

Eddie

Hi Eddie,

Working pressure is 80 psi and was planning to use copper for the stays.

I found another variation this evening - Martin Evans suggests 4 BA at 7/8th pitch for 13 swg wrappers in his book - 'The Model Steam Locomotive'.

Mike

Hi Geoff,

Thanks for the reply. I'm amazed at the variations from different designs. My 3 1/2 gauge Jinty (LBSC Molly) was a lot simpler!

As regards a tester - I have n't joined a club yet - not much going on in the West of Scotland methinks as regards loco building. I hope I'm wrong on that one as there used (20 years plus back) to be a fair amount of loco works and running tracks of which there were three within a fifteen mile radius of where I live.

The 'Schools' was started over twenty years ago and now fully retired just picked up again.

Mike

hi mike,

the clarkson pitch of stays is way too big. i would stick with LBSC's pitch of stays.

if you are a 'lone hand' dont expect to finish the boiler then join a club and get a boiler certificate - these days club boiler inspectors will expect to see the internal joints of a new boiler and inspect construction as it progresses. and if at some stage you intend to sell the completed loco if it has no club boiler certificate it is basically a loco without a boiler.

cheers,

julian

Hi Julian,

I'm only getting the materials together for the boiler at the moment and studying it's construction. Hopefully I will find a club to join long before I build it. The chassis work is keeping me pretty busy at the present.

I thought the Clarkson design a bit odd with its choice of staying when comparing so many other round top boiler/firebox designs in the same gauge by others.

Mike

Hello again Mike,

My calcs put the maximum stay spacing for 13G plate at 80 psi as 15/16". If you go to 2.5mm plate then 1" spacing is possible. Problem then is the stays need to be quite big so you'd need to go to 1/4" x 40TPI in copper - not an easy prospect in relatively thin copper. Alternatively you could stick with LBSC's 5/8" spacing but I'd recommend increasing the stays to 5/32" x 40TPI. Modern thinking though is that the stays do not need to be threaded as this goes back to the days of riveted and soft solder caulked boilers where the stays needed mechanical fixity in the plates. The strength of silver solder allows the stays to be plain, but for someone with limited experience of boiler construction I would recommend threaded stays silver soldered, so that if the silver soldering is not perfect and the odd stay leaks then it is safe to caulk them with a high temperature soft solder like Comsol.

Do join a club and liaise with their boiler inspectors, For the boiler to be operated legally you need to comply with the construction and test proceedures agreed by the ME organisations such as the Southern Federation and Northern Association and of course the club membership brings with it third party insurance cover.

Best of luck with your boiler.

Eddie

Hi Eddie,

Many thanks for the data. I am hoping to join a club - few and far between now in the West of Scotland.

Mike