Coffeepot locomotive - 0-16.5 scale - on Hornby mechanism

thingiverse

A locomotive of an unusual "coffeepot" design, built in England and found in the USA. Based on a drawing and a photo of a model once made by Backwoods Miniatures (no longer trading but still on the internet.) This model is designed to fit on a Hornby 0-4-0 chassis (Caledonian Pug) that has the right wheelbase and now uses an improved motor that gives good control and slow running. Attempts to buy this motor as a spare part have been unsuccessful. This model has a lot of parts but is not a complete kit as quite a few brass and steel fittings had to be made. This model may also involve some frustration getting the moving parts aligned. The basis is a footplate with dummy outside frames (so the wheels are inside) and a set of wheel discs with axle extensions and cranks. For strength, I centre drilled these axle extensions and epoxy glued 1.6mm rods in. The disc adapters are aligned carefully using a drill through each crank hole and into the hole in the original wheel. The cylinders, guides, piston spindle, and cross head are all brass but no machining is needed. (Stl files for a rough idea are included - detail below) The crosshead is fitted to (shortened) original connecting rods with 14BA screw, nut and washer. The connecting rods and coupling rods are fitted to the external cranks with M2 screws that look horrible but permitted repeated disassembly but the idea is to use the original crankpins. The tank and the top of the boiler are filled with lead for adhesion. Steam pipes are PVC insulated mains cable and 0.9mm MIG welding wire provides rods and the strength of the roof supports. These are clad with U-section styrene. The motor and its mount are removed and the new motor is glued to a small printed mount so that the worm engages on the other side of the pinion (having cut a hole for it in the base of the chassis) The wiring is reversed because of this. A modified (adjustable) motor mount has been added, to try and improve the meshing of the worm and gear. The hacked-about Hornby chassis is secured to the footplate with M2 screws into tapped holes in the blocks moulded into the footplate. The connecting rods etc are part of the chassis while the cylinders are fixed to the footplate, so fitting the two parts together is rather fiddly. It might be easier to add the connecting rods after fitting the chassis to the body. NEW MOTOR MOUNT "Coffeepot motor mount.stl" has been designed to allow a slower motor (around one third of the speed of the earlier Hornby "Smokey Joe" motors) This motor (https://www.aliexpress.com/item/1005003788528466.html?spm=a2g0o.order_detail.order_detail_item.2.5ed7f19cLbbFpO) costs £1.26 for four + postage from China. The cylinders are made from brass tubing of successive sizes that slide into each other and the crosshead and spindle part is filed from 1mm brass (approx) 7mm OD tube forms the basis and is filed down on one side to reveal the crosshead. A length of 8mm forms the outside of the cylinder, and inside (to guide the spindle) are short lengths of 6, 5, 4 and 3mm tube. Stl files are included for the end covers, valve chests and front support. The corrugated iron roof was printed flat and formed over a jar in a saucepan with boiling water. This sheet is very flimsy and relies on the frame for protection (fixed with plenty of epoxy adhesive) The roof and its frame are cut down to finish above the rear of the boiler. The frame is drilled for 3 MIG wire supports, at the back and into the two frame ends for supports forward to the top of the boiler. I have included end views but I must point out that these are based on guestimation on my part. I have no photos or drawing of the ends. Fearing that current pickup with only four wheels could be unreliable, I produced what I refer to as a pickup truck :-) This is built like other CaderIfor trucks and has curly phosphor bronze contacts (bearing on the wheel backs) soldered to a strip of PCB that is wired to the loco so it follows it everywhere. (mine is disconnectable but that is a bit difficult to explain)