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Fire Monitors Part 2

Some thought has to be given how to hold all these remaining parts, firstly I need to make sure that I can replicate an upward incline since there won’t be any up and down movement, only rotation. Here comes another jig, a simple block of ½ inch hardwood with the angle cut at 200 and the corner removed to allow all the soldering to take place. Carefully marking out a centre line I used small brass pins to hold the pre silver soldered pipes in position on the flat sides. I now used some clamps to hold the in place, check all the alignments then flux is applied. Very gently apply the heat with a soldering iron until the solder flows, it’s important to tack both ends of each pipe first on each side as at this stage the set-up is delicate to say the least and can be dislodged very easily. Then follow round to complete the joints making sure you don’t overheat the whole assembly and melting the parts already soldered. Next I need to test for leakage, if all OK I can carry on to fettle the joints, I don’t use files or abrasive paper to do this I only use a scalpel to remove any excess solder it’s so easy and better results are achieved. This also applies to cleaning up the white metal fittings; the main posts need to have a better base with some sort of fastening arrangement made, so an aluminium piece is machined up with three holes for fastening to the roof, this was then epoxied to the main post. The next job is to make the handles, for this I used some 3mm plate which I cut some slices off with a slitting saw. In its raw state it is hard and needs annealing before bending. The pieces were all cut to length and then drilled in a jig to ensure all the pieces were exactly the same, I can now leave a drill in both the end holes which keeps the pieces together while they are placed in the machine vice with a piece of round bar at the back to give a nice radius. The handles need a cross bar with “knobs on” so a little bit of machining and then the assembly can be done. The handles are soft soldered in place at the correct distance; I now need to drill and tap 10 BA the main body pipes to hold the handles in place. When these are assembled they will be put together with some epoxy on the screws and between the faces. Whilst using the epoxy I can glue the white metal exit pipe in place, this now completes the assembly. Next a coat of etch primer followed by a coat of grey primer then finally bright red, these will be left to fully dry before I attempt looking at the rotary system

5 years ago by mturpin013

Blog

Fire Monitors Part 1

The white metal items supplied are OK but really don‘t lend themselves to being working items. Graham93 has already completed a version which looks just like the drawing and photos available, and are the best I’ve seen. The bar has been set so here goes, whenever an item like this is been contemplated it’s always good to spend some time in planning a sequence of operations and assessing the problem area’s at the start of the work and if possible dealing with these parts first. Failure of the difficult process doesn’t mean you have wasted work on other parts that are now scrap. I think the most difficult and problematic piece is the pipework that sits at the top and curves round in two halves, this in reality is a casting, however replicating it can be done using brass pipe. Brass pipe can be purchased in annealed form; however my stock wasn’t so the first job was to anneal the tube. Heating to a dull red heat and allowed to cool, this treatment will soften the metal completely. In some books it is suggested that the brass should be quenched in water (which is what I do) after heating but this is to speed up the commercial process, and quenching has no effect on the annealing process. So tube annealed we need some method of retaining its tubular form during bending, in plumbing I use a spring but when you compare wall thickness/dia a spring would have to be mighty strong and so small. An easy alternative is to crimp one end of the tube and put some soldering flux down the tube, follow this by heating with a low temperature blow torch to melt solder and fill the tube, then allow to cool. You now have a soft tube which when bent will hold its shape. That’s the next challenge, the shape, and being able to replicate it twice, so an easy jig is required. Having marked out a scrap piece of hardwood I cut the “U” shape using the band saw and filled a groove along the top edge, this was then placed under my drill press with the appropriate dia bar (this must be calculated accurately as it helps to create the final form) on top of the tube, then just pull gently down (it takes very little force) this jig leave a small amount to finish bend to a complete a circle, the excess length is trimmed off and then I used a piece of hard wood with a small radius on the end to tap the final curve. Next the circle needs to be cut into two pieces I used a small slitting saw in the milling machine. Now it’s time to remove the solder, simply heat up holding in plyers and then shake vigorously to expel the solder. (Make sure you do this on your own and wear safety glasses.) The white metal “main pillar fitting” and the monitors final “exit pipe” will be used in the unit and all that is required is to mount them in the lathe and drill a 4mm hole through each and clean up the casting. Next I cut 4 pieces of 4mm brass pipe; these will form the main water passage. Two more machine turned items are the “pivot post top” that feeds water through the 2 into the “junction block” which then feeds into the exit pipe, sounds all very simple? Having made all the components, it’s time to think about fastening them all together. First items to be joined are the “upstand pipe” to the “pivot post top” X 2 also the “feed to exit pipe” and the “junction block” X 2, these four joints are all to be silver soldered. I mounted them in a piece of wood and placed a tight spring brass ring around the upright pipe to stop then sliding down when heated. Having the joints spotlessly clean is paramount, the flux is added, I insert very small pieces of silver solder into the holes at the top cross holes (less is more) a gentle heat, and watch as the flux goes “glassy”, this is closely followed by the solder melting, watching at the lowest point of the joint for the tell-tale shinny liquid metal. No fettling is required so the 4 parts are dipped for 45 minutes in masonry brick cleaner (dilute hydrochloric acid) the parts are now clean and ready for the next soldering activity. See part 2

5 years ago by mturpin013