I would use rings. The solder is in exactly the right place and will melt as soon as the required temperature is reached.

I have built 3 boilers using this method and always put the solder on the work for other jobs as well.. I once attended a lecture from respected boiler maker Alex Farmer and this was the method suggested. The tubes should be a loose fit in the plate so the solder can penertrate.There is less chance of the flux boiling away before the joint is made too. I would also suggest using a large burner and getting the heat in quickly for the same reason. Hope this helps.

hi bill,

please put the rings on the ends of the tubes but on the inside (water space) where they fit into the tubeplate. make the clearances about 2 thou, with a few nicks in each hole with a swiss triangular file. flux up generously each side. heat from the opposite side from the rings ie the inside of the 'firebox', and you will see the silver solder flash around each tube once up to heat. this also avoids the risk of burning the tubes. i would silver solder up the inner firebox assembly first before silver soldering the tubes, or do all at the same time if you are a bit more experienced. for the 'smokebox' tubeplate you have to feed silver solder round the end of each tube where it protrudes slightly through the plate with the same clearances and nicks, silver soldering the 'smokebox' tubeplate into the boiler at the same time, making sure there is plenty of heat directed at the top and outside around the top of the boiler as you work around. do not make the tubes a 'press fit' and no need to turn the ends. just make sure absolute cleanliness by way of pickling and rinsing before each stage. when feeding the siver solder into the ends of the tubes at the smokebox end from the outside make sure the job has heated up to the right temperature and try and avoid the silver solder melting in the het of the flame. it should melt by way of the heat of the copper.

good luck,

cheers,

julian