Background

Mechanical drawing machines have been around in various forms for centuries if not longer. One of the first such uses was to reproduce the pen stroke of a writer by means of a pantograph which mechanized the facsimile process which up until that point had been accomplished by painstakingly by hand. The pantograph in particular was engineered such that the output would exactly match the input, which was accomplished by means of parallelograms, though they could also scale curve larger or smaller they otherwise did not deform or morph the input in any way as the intention (and name) of the device was to reproduce or copy writing. Later uses however came up for much less serious a task, such as was the case with Spirograph in particular, which was my first experience with any drawing devices, its purpose was to simply produce unique roulette curves for pleasure. It accomplished this task via oddly shaped gearsets which with pen holes such that you could trace out different curves. My machine is similar to this in output however it accomplishes the task via a four bar mechanical linkage coupled to a rotating platter. The result is any number of roulettes which are defined by the geometric properties of the four bar, as well as the gearing relation of the platter to the crank. My machine is deliberately simple so as to be readily simulated however, as shown in Figure 2 the curves possible can be arbitrarily complex by simply adding motion constraints via additional gears linkages or both. 

Figure 2. Drawing Machine by James Noland Gandy 2018

Project Scope

For this project my goal is to synthesis and build a functional drawing machine. Which I will allow me to validate position analysis plots based on course work in four bar mechanisms coupled with gear train analysis. The drawings that I will produce will be simple coupler point paths of a open assembled crank-rocker linkage , however they will be subject to a rotational transform as defined by the gear ratio which connects the crank rotation to the platter rotation. The effect will be to create smearing of the image as the machine cycles. The machine will be built from readily available materials, and though the intention is for it to reliably produce a preconceived curve, the tolerancing and refinement will be crude at best. The importance here is the proofing of simulation and analysis as opposed to production value of the output curves.