My Model Engineering
As the coupling rods are going to be silver soldered together, and I haven't done any silver soldering for quite a while, I made up an assembly to experiment on using some offcuts. These are the same material as the actual coupling rods, but other than the joint itself the metal was just filed to a better (but still rough) finish, rather than machined accurately to size. I ended up pleased with the joint, but glad I had a test run. Here's the assembly about 5 minutes after removing the heat, still hot and flux everywhere: newly soldered test assembly And then after a bit of cleaning up, this is pretty much how I was hoping the joint would turn out: newly cleaned joint, showing a neat line of silver solder between the steel parts I put a little too much silver solder into the joint as I wasn't sure there was enough to fully penetrate through to the other side of the rod. This is why I'm glad I did a test joint, as now I know how much solder to use, so I won't get this big lump on an actual rod. Still, it's nothing that couldn't be cleaned up with a dremel-like tool: the other side of the cleaned joint, with a lump of silver soldering showing that too much was applied The task basically required heating the steel to red hot, applying the solder, then adding a little more heat to the metal till the solder had flowed nicely into the joint. It took a lot of heat, I had to use my largest burner on the propane torch, and still took about 15 minutes to get up to heat.
Today I made the retaining collars for the rods, these were relatively simple turning jobs on the lathe. The front collars are completed, the rear/driving ones still need to be drilled and tapped for a grub screw to hold them in place. the retaining collars assembled on the crankpins
Here's a really rough set of adjustable coupling rods, these were fitted on the loco, then adjusted till the wheels rotated freely, and will be used to jig drill the second crankpin hole in the coupling rods. an adjustable coupling rod on the bench beside the loco frames I've just recently turned up the two pins at the front, the front one goes through the existing coupling rod hole, and one end of the jig, the second fits in the other hole of the jig and has a 5mm hole to spot drill the other end of the coupling rod. the adjustable coupling rod jig, assembled on a coupling rod
Here's the first coupling rod partially assembled, at this point I had only machined and threaded one end of the rod, but both ends are now done. The pic' does give a good idea of how the finished rod will look though. A partially assembled coupling rod
So I got some 12x7mm BMS offcuts from ebay, and am using these for the centre part of the coupling rods. A relatively simple matter of cutting to length, then turning the ends down to 6mm and threading them M6, so as to screw into the bosses. Only relatively simple as this is about as long as the little Taig II lathe can take between centres; the centre drilling being done by careful marking out, then drilling in the bench drill. Here's the rod being set up in the lathe, tool post still missing from the cross slide. A length of Bright Mild Steel for the coupling rods mounted between centres in the Taig II lathe
So I'm having to restock/refit parts of my workshop as I get back into model engineering, and in the process I've left myself wondering about BA threads. Back before my dad sold off a large chunk of the tools, we had been in the process of switching to an entirely (or mostly) metric workshop; metal stocks, drills, taps, dies, etc. Of course it never would have been entirely metric, as most (older at least) designs are drawn in imperial, and most fittings are ME threads; but new machine tools are metric, as are most metal sizes. Thus things like axles are 20mm instead of 3/4", use a M5 tap instead of 3/16" and so on, with imperial dimensions used only where necessary. This brings me to where I am now, and particularly in replacing smaller taps and dies. The smallest tap/die I currently have is 3mm, below that I need to buy new as the old sets got sold off (or were claimed by my brother, and thus either lost or broken by now). So I'm wondering if I should get new BA taps/dies, or switch to the metric equivalents. Going all metric would simplify some things such as identifying a thread, and the idea of a "standard" thread type feels somewhat more organised to me. Anytime a BA (or other) thread is specified on a drawing, I'd just use the nearest metric equivalent, as there's metric thread at 0.2mm (or less) intervals in the smallest sizes, down to 1mm; equivalents to 0-14BA, plus some in between. But, smaller metric fasteners are not necessarily easy to get hold of, so I'd likely end up having to make a lot of nuts and bolts myself. On the other hand if I stick with BA for small threads then fasteners are easier to get hold of, compared to the smaller metric sizes. Plus there's no need to deviate from the design. But there'd also likely be a crossover point, either in the case of a project having larger threads in metric, and smaller in BA; or in having both metric and BA tools and fasteners on hand, and choosing one or the other depending on the project. I've been dithering on what to do for a while, but I'm going to need to buy one or the other (or both) soon, so a decision needs to be made. Basically this is my chance to go all metric, if I want to, which I'm not sure if I do.
Currently drilling and tapping the joiner holes for the rod bosses, I need to get a M6 plug tap to finish this off. Also gradually cutting the centre sections for the rods, this is 4 x 9" cuts in 6mm plate, so is taking a while. Just doing a bit each day so as to not wear my arm out or get bored and rush it. Also contemplating building a 16mm scale loco as a side project, this would be built to sell to help fund a bigger lathe. The little Taig isn't big enough to machine the blowfly cylinders, and the crowdfunding campaign I have going is not going very far.
Dad came into the workshop tonight as I was boring out another coupling rod boss. Even though it was late (about 11:30PM), and he was a bit sleepy from getting out of bed, we still were able to have a good chat for about 30 minutes about what I was doing, and what's next, and so on. Considering his dementia has progressed to the point that he often can't remember where he lives, even when standing in his bedroom, this was really great to see. It's been a couple of years since I was able to regularly just chat with him like that.
Yey, 2 hours work and I have a hole. Just bored out the crankpin hole in one of the front coupling rod bushes, this includes a 2mm deep 20mm counterbore for the retaining collar to fit in. one of the front coupling rod bosses, showing the completed crankpin bore
That was quicker than I expected; all the boses are now machined to size, so I can get on with boring the crankpin and joiner holes next. Will have to sharpen up a boring tool first.
That's one boss machined to size, and now all nice and square and shiney. Five more to go. A completed coupling rod boss sitting on the bed of a Taig II MicroLathe Hey look! I cleaned the lathe benche (didn't realise how messy it was till I say that last photo). Sitting on the bed is the finished-to-size boss, with another mounted in the 4-jaw chuck ready to be machined to width. Lathe belt is off, as I took the pic' just as I was done for the night.
Just to show I am actually doing stuff, here's the coupling/connecting rod bosses (as per earlier drawing) getting machined to size in the lathe; to give some idea of scale, that chuck is 4" diameter. The other 5 bosses are sitting on the cross slide for the photo. All have been machined to length, currently machining to height, next machine to width. Then I'll bore the holes for the crankpins and bushes, and then drill the holes for connecting them together into a finished rod. one of the rod bosses mounted in the 4 jaw chuck of a Taig II Micro Lathe This all looks messier in close up.
Well that's one dead (or at least blunt) hacksaw blade, now waiting for some new ones to arrive, which should be a few days. I could get a pack of cheap blades froma local store, but those cheap carbon steel things are utterly useless; akin to cutting a steak with a stick of butter. So I've ordered some good high speed steel blades. But as I've got a couple of the coupling rod bosses cut to (rough) length, I've started machining those to square them up; the combination of rough drawn black steel and my battling on with a blunt hacksaw blade on the last one means they're far from square now. As I was setting the job up I gave the 4 jaw chuck a good clean and some fresh oil; apparently went overboard on the oil as I got a face full of it when I first started the lathe, oops. But none-the-less the little Taig lathe is good for this kind of small job, and even with mild steel it cuts without fuss. Still took an hour to face the ends of one boss down to size, 6 to do total (4 for the coupling rods, plus 2 for the connecting rod), so longer task than one might think for something so simple. Plus that's only 2 faces done, 4 more faces per boss to do, then bore out the pin holes, and make the bushes. Hopefully I can find plenty of time to work on it though.
My arm is threatening to go on strike, still cutting metal. Still at least when I've got it all cut the rest of the work on these rods will just be machining; which I can pretty much sit down and do. On the plus side it's still less than half the cutting work needed for the original design, so I shouldn't complain too much.
Giving the coupling rods some thought, I'm considering deviating from the plans; partially so they're easier to make, but also to give them a bit more shape, and centre the bearing surfaces on the rods' forces. The standard Blowfly design calls for 25x7mm steel, shaped into a dogbone, but I'm thinking of using 2 pieces of 25x10mm for the rod ends, joined by a length of 12x6mm which would be threaded and silver soldered into the ends. This would give what to me is a more pleasing shape, while resulting in considerably less hacksaw work. Also, unlike the original design which has the bushes overhanging the rods by several millimetres on one side, this would centre the forces of the rods on the bearing surfaces, which could reduce wear (would also centre the oil hole in the bush, thus better lubrication). Here's a quick workshop drawing I made tonight of the intended coupling rod design. photo of a side elevation of the coupling rod design, drawn actual size
So I realised after much experimenting that the taig II just isn't a big enough lathe to machine the cylinder castings. After some mild panic, I decided I'm going to need some help and have set up a crowd funding campaign to try to finance a bigger lathe. Hare and Forbes / Machinery House have their L160 lathe on special till the end of the month, hopefully I can get the lathe and some necessary accesories for it. The Lathe. The Campaign. In the mean time, I can continue working on the brake gear.
Firstly, a quick pic' of assorted bits that arrived from Hobby Mechanics: an assortment of metal rod and bar, plus a circular iron casting From left to right; bronze rod for bushes, brass rod for steam and exhaust pipes, brass hex for glands and various other things, 2xBMS square for slide bars (and some parts of the valve gear), stainless steel rod for the piston rods, stainless steel rod for the valve spindles, silver steel rod for the crosshead pin, brass flat for valve nuts, some BMS angle for the motion brackets, more silver steel rod for valve gear and parts of the brakes, more brass rod for steam pipes, copper blast pipe, and finally the ring of cast iron brake shoes. Last night I did a bit of work, and am greatly missing having a bandsaw; a quick 20 minute job ended up taking over an hour. This is just the pull crank for the brake gear, it's not pinned in place yet - that can wait till after the hangers and pull rod are in place. under the loco frames, showing the new pull crank for the brake gear Next I'll turn up some pins for the brake hangers, make the hangers themselves, then machine the brake shoes; the pull rod will be done last, with everything else assembled, so I can get the length right.
Well I've placed an order with Hobby mechanics for the brake blocks, as well as most of the steel, brass, and bronze needed to get the chassis on air. Forgot to get cylinder rings though, which they stock, but I can get them later when I'm closer to needing them (along with anything else I might've missed). A chance mention to a neighbour has given me a potential line on some bright mild steel; turns out he's mates with one of the higher up's in one of the states biggest steel distributors, so says he'll be able to get me what I need without problems, brilliant! I've also been fiddling with potential setups for machining the cylinder casting in a lathe that's really too small for them. Looks like it'll take a bit of fiddling with pipe centres and the fix steady, but will ultimately be doable.
Currently swapping emails with Hobby Mechanics to get some materials (and brake shoes) for the blowfly. In the meantime, I found this rather handy chart for imperial <-> metric conversions:
Well the Blowfly manual arrived from A.M.E. It's pretty much just direct copies of the original articles though (including the old ad's on the pages, and some errors in the drawings), but at least it saves damaging the old magazines. Currently waiting to hear back from a steel distributor who's trying to hunt down some BMS for the coupling/connecting rods for me, I'm likely just going to end up using black steel. Also the lathe needs a new belt, and I'd like to get some new jaws for the 3 jaw chuck, unfortunately there's no belts in stock, so I'm waiting on those as well. It looks like the Hobby Mechanics' A10 brake blocks will work nicely though, so I'll probably order those along with a few other bits and pieces (stainless steel rod, maybe bushing materials, various sundries) from them this (next) week.
I've been trying to find some bright mild steel for the coupling and connecting rods; so far I've found suppliers of sizes too big and too small. Why is BMS so hard to get? I might end up just pickling some black steel again. Putting together a list of materials needed to get the chassis to the 'on air' stage, so I hopefully won't have to stop half way through doing something. At least bronze is easy to get. Also, the brake shoe castings I had on hand seem to have gone missing at some point, there's none included in the blowfly casting set, but I had some spares from when dad's sweet pea had brakes fitted. So I might see if Hobby Mechanics will sell a set from their A10 which should suit. Waiting for the Blowfly manual to arrive from A.M.E., I've still got the original series, but don't want to risk damaging the near-30-year-old magazines. Besides, there might be some updated info in there that could prove useful. Thoughts have also turned to a driving/riding truck, I don't want yet another of those ugly things that just about every blowfly builder seems to have, current thinking is to make two 4 wheel wagons, an open wagon for coal and riding on, and a box tank wagon for water. This would at least make for a more interesting train. But that's a long way off, so ideas may change greatly before I get there.
I dug out an old set of frames for a 5" gauge Blowfly that had been sitting under a bench for over a decade; this had been started just before dad sold most of the workshop machinery, and thus never got finished. 5 inch gauge blowfly chassis The rolling chassis as it was left years ago, I had to clean it up a fair bit as, aside from some spider's making a home of it, there was a lot of rust. The hornways had rusted so bad that one of the axle boxes had to be knocked out with a hammer and drift. 5 inch gauge blowfly chassis Another view of the chassis, the rust on the front axle is plain to see. After much cleaning, degreasing, and a bit of polishing it's now in a much better shape; and some fresh oil should keep it that way. Here there's some temporary adjustable coupling rods in place, and the valve gear - what little of it there is with slip eccentrics - is also visible. some of the break linkages for a 5 inch gauge blowfly Some of the brake linkages after cleaning, as there's no drawings for brakes these were designed by me. The cylinder will allow for steam brakes, hence the elongated lifting link with spring inside, The hand brake standard is fitted to the foot/running plates, which I don't have a picture of at the moment. The two pins at the bottom of the image are for the couplers.