Most people seem to opt for building the Rider Ericsson Engine with its four legged "table and furnace slung below” but I have always liked the look of the Denny Improved version. I decided to go back to basics and scanned in a patent drawing so that I could ‘trace’ it in Alibre CAD and pull the sizes directly off of that. This shows one of 5 sets of dimensions that were taken from the patent once it had been scaled to my chosen size which is a 40mm bore making the model approx 1/5th scale, this also kept the flywheel within the XY envelope of my CNC so I could cut that from a slice of cast iron bar.
I initially just drew the various rods and linkages as simple flat bars with holes at the pivot points and did a trial assembly to check how everything moved and once happy with that set about detailing the various parts that would all be fabricated or cut from solid. I found that setting them to 50% transparency and then assembling over the Patent drawing also made checking the proportions easy, sectioning the parts also made sure nothing was going to clash internally.
A quick check of what materials I had in stock and what needed to be ordered and this lot arrived a couple of days later from M-machine, the main items are some flat black bar for the base plate, slice of CI for flywheel, Brass tube for displacer (did not use it) and some thick wall steel tube that will become both Furnace and Cylinder Jacket and a piece of 70mm square for the furnace base.
