Alibre Workshop

[Lirim Collard]

Whilein still working for a living I decided that as a company we needed to move into 3D CAD. We are already a very software savvy outfit and used as many tools as we could to give us a competitive edge. Getting into 3D CAD seemed like another useful step to take.

After some research on the interweb I found a downloadable 3D program called Alibre. You could get a fully working licence for around USD750 and I began to play. It was a bit of a learning curve but gradually it began to sink in just what the process was.

Following our 3D experience in software we decided we ought to investigate a CNC milling facility for our military standard ruggedised enclosures. I imposed a Bridgeport VMC on the team in the sheet metal facility and told them to learn how to drive it. Which they did.

We employed a 3D CAD engineer to streamline the design and he demanded SolidEdge as his software tool so Alibre lapsed with us. (In fact Alibre was bought out by Geomagic and has only recently reverted back to an independent entity again).

Sadly when our company was bought they closed down our superb CNC facility and killed off the 3D CAD but for me the seed had been sown and I judged it only a matter of time before CAD and CNC raised its attraction to my home workshop.

Once retired I became a regular reader of various forums and YouTube sites. The program Fusion 360 seemed to be respected as a tool and was becoming more and more popular. For a hobbyist and one man band company it is possible to get a free full package licence to use the product. I downloaded it and was blown away by how advanced it was compared to my distant memory of Alibre and free compared to SolidEdge.

An eclectic mix of mechanical engineering, clock making, Fusion 360, CNC, 3D printing, live steam locomotives, amateur radio, golf, garden and France. It is more to remind me what I have been doing but if it helps stimulate you then a double bonus.

Spending a good deal of time overhauling a steady stream of Romuli, Bagnallsand Hunslets that came through the workshop, I had the idea two years ago ofbuilding a robust, powerful and easy to maintain 7 1/4 inch gauge engine,suitable for either larger garden railways or club running, combining the bestfeatures I've found on the hundreds of engines that have been through my handsover the last ten years whilst trying to eradicate the weaknesses.

A specification was mapped out and I talked to one or two possible buildersfor a batch - suffice to say that after wasting twelve months waiting for anoutfit who pottered about producing small quantities of finished work and largequantities of excuses, I cancelled the contract having decided that, if you want a jobdoing you've got to do it yourself.

Having bought a new machining centre and CNC lathe to beef up the existingworkshop kit (already owning a CNC Bridgeport mill I'd bought new several yearsago) we set to designing the new locomotive. Never one for the easy life, at thesame time Ichanged CAD systems from AutoCAD, which I'd used for the last fifteen years, toAlibre Design - one of the latest generation solid modelling packages. Thisrequired quite a shift in mindset - you tend to draw a block on screen andmachine it away with the CAD tools to produce the part, exactly as you wouldmake it in the workshop, rather than draw it from scratch in third angleprojection, as I'd been used to doing up until then.

Taking a bit of a leap into the unknown, Geoff and I designed this enginefrom day one with Alibre, using it to produce workshop drawings and testassemble virtually everything before machining. I set out the valve gear usingDon Ashton's formulae and associated spreadsheet by Alan Gettings before runningit using Allan Wallace's excellent simulator to check valve events.

The parts werefinally drawn up in Alibre and the assembly checked for collisions before machining on the VMC. It was more than a little satisfying that theengine was substantially completed bar paintwork in time to show at Alexandra Palacein January, twelve months after we started the project, the engine running onair "straight out of the box" (there's a short clipof the first time it ran here, in the excitement to open the regulatorI forgot to plug in the camera microphone so what Geoff said when the wheelsactually went round is lost to posterity).

The design is along the lines of a freelance narrow gauge 0-4-0 tank engine,with a nod towards Bagnall's engines of the 1920s, giving a large engine to anotional 4 inch scale running on 7 1/4 inch gauge track. A marine boiler isused, a type I have found particularly free-steaming and easy to clean in thingslike Sweet Peas and Bagnalls - working pressure was set at 120psi, a pair ofbronze pop safety valves are fitted to the design Geoff developed (and fitted asreplacements with great success to a Fowler ploughing engine we had in a whileago with pathologically poor safety valves).

Valve gear is Walschaert's. Although not the cheapest or simplest to make, Ilike it for lots of reasons - it is very efficient, it gives a fast-openingexhaust whose blast, I believe, makes the boiler easier to handle, it notches upwell which allows large full-gear cutoff for reliable starting (and there'snothing worse than seeing 7 1/4 inch gauge engines requiring assistance from thedriver's foot to get off a "dead spot" leaving the station with aloaded train) whilst still allowing for economical high-speed running. And it'salso quite the best looking valve gear ever made.

The rest of it is specified for robustness and ease of maintenance - sealed self-aligning roller bearing axle boxes,TIG-welded stainless steel water tank, stainless ball valve regulator andinjector water valves, full-sized bronze steam valves, steel wheels, cast ironcylinders fitted with Clupet rings. Whilst the detail design and any errorstherein are mine alone, it is only fair to say that Giles Favell has been agreat source of inspiration and information (probably more than he knows andcertainly less than he's been thanked for) both with his half sized Bagnall"Alice" and the current "No.2" currently under build.

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