Rob Roy 0-6-0T CR/LMS/BR

Overview
Rob Roy is an 0-6-0 Tank engine designed by Martin Evans and based on McIntosh's Caledonian Railway class 498. Originally designed as a beginner's locomotive and the subject of a construction competition to stimulate interest. The model has a round-top boiler, outside cylinders, and inside valve-gear. As drawn the model is over scale width to increase the side-tank capacity. The completed model's comparatively light weight allows it to be lifted by one person, however the corollary is that some find it lacking in adhesion when pulling passengers, though it should manage three adults.

Drawings, Publications and Castings
A very complete construction series complete with drawings commenced in Model Engineer (UK) magazine in Volume 124, issue 3110 16th February 1961, page 201. There is also a single-page article with drawings by Martin Evans titled 'Improvements to Rob Roy's Design' in Model Engineer (UK) magazine Volume 157, issue 3784, 5 - 18 September 1986, page 271. Current drawings should include these improvements. In addition there is a construction book complete with drawings,  'Rob Roy: How to Build a Simple 3.5" Gauge 0-6-0 Tank Locomotive based on the Dockyard Engines of the old Caledonian Railway'.

Drawings and castings are available from Blackgates Engineering, GLR Kennions, GS Model Engineering, Reeves 2000. Model Engineers Laser have a number of laser-cut parts available.

Drawing Errors
If built to the original drawings the valve gear and the valve spindles don't line up. The difference is approximately 1/8". The solution is either to make a stepped valve crosshead, or to make the valve face 1/16" further out from the cylinder, and the valve spindle 1/16" higher in the steam chest. The bottom section of the crosshead pump is too close to the cylinders.The dome bushing on the boiler should be 3/4" diameter bore.

Suggested improvements
Change the pitch of the thread on one end of the valve spindle; this allows easier adjustment of the valve geometry.

Fit thin lock-nuts to both valve and piston glands.

Increasing the height of the blast pipe by about 3/8" seems to improve draughting.